2017METEOROLOGY EVENT

TRAINING MANUAL

Prepared August 2016by

Mark A. Van HeckeEast China, Michigan

Copyright 2016National Science Olympiad

All Rights Reserved.

INTRODUCTIONOf all the topics that people talk about, the weather often serves as a springboard from which to talk about everything else. We often make plans- or change them based upon what happens with the weather. In recent years, there is also growing concern that changing climate patterns will have ad-verse effects on our quality of life. Thus a knowledge of meteorology will if nothing else improve our scientifi c literacy as we make decisions because of and often in spite of daily weather and long term changes in climate.

The Meteorology Event rotation in the Science Olympiad Earth Science event catalog provides mid-dle school (Division B) students with a robust curriculum from which to acquire a broad knowledge base of meteorological terms and concepts. In Year One, students will study the concepts of ‘Every-day Weather.’ These concepts are further developed with a more specifi c focus on ‘Severe Storms’ in Year Two. The sequence concludes in Year Three with a study of world and regional climate patterns. Concepts learned in one year are interchangable with those learned in the other two years. In 2017, Science Olympiad students will study severe storms and weather patterns.

This Event Handbook is not an attempt to provide you with all of the intricate details of the event top-ics listed in the 2017 Division B Event Rules. Rather, it is an attempt to provide coaches and students with a basic understanding of the 2017 key event topics as well as resources for further study and activities to introduce and develop what you have learned about. You will also fi nd an event Online Library of selected resources for the Key Event Topics that you can point-and-click. All of these web-sites have been reviewed for grade-level compatibility and content quality to ensure ease of use and content-deep learning. An Event Supervisor Guide is also included on the CD for planning of Meteo-rology events at Regional, state and national Tournaments.

To use this handbook, read each section and use the websites listed under ‘Want to Learn More?’ to further develop your knowledge base. You may use the ‘Featured Activity’ for each section to intro-duce students to what you have learned or to further develop them. In some sections, ‘Excursion’ ac-tivities are also provided to further develop concepts learned or to provide more challenging activities.

We in the Science Olympiad Earth/space Science Event Committee wish you a successful and pro-ductive 2016-2017 school year in your event preparations.

Mark A. VanHecke Co-Chair Earth/Space Science Event Committee

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SEVERE STORMS

Weather is a subject that intrigues students everywhere and affects all of us in our daily lives. Most days are planned with the expectation that the weather is going to do certain things, and our plans often change when the weather does.

The 2017 Science Olympiad Division B Meteorology event will focus on ‘Severe Storms.’ The term ‘Severe Storms as it is described in the 2017 rules parameters focuses on the mechanics of Earth’s atmosphere and how it creates severe weather events.

More specifi cally, the term may include the following topics:

• Air masses, fronts, cyclones, and anticyclones, weather maps, weather stations, global circulation patterns, semi-permanent highs and lows, and scales of atmospheric motion. Regional variability in severe storm weather type (e.g., tornadoes on the Great Plains, direct and indirect hurricane impacts along coasts and inland, etc.)• Mid-latitude cyclones: life cycles, characteristics, structure, and hazards; surface weather maps • All types of thunderstorms, including air mass, multicell, supercell thunderstorms and dryline storms; life cycles, characteristics, and structure, and hazards associated with thunderstorms• Squall lines & mesoscale convective complexes, dry line thunderstorms • Straight line winds, downdrafts, downbursts, gust fronts, micro and macrobursts, derechos, & dust storms • Electrifi cation of clouds, all types of lightning strokes, sprites and jets, & lightning direction fi nders/systems• Tornadoes: life cycles, characteristics, structure, and hazards, and Fujita & E-Fujita Scales• Severe winter storms: blizzards, nor’easters, lake effect snowstorms, characteristics and hazards• Observation technologies, including high-resolution surface-based station networks (e.g., Oklahoma Mesonet), aircraft, satellite (particularly IR) imagery, Doppler Radar, Stationary Radar, interpretation of severe storms including bow echo front, tornadic vortex signature (TVS), hook echo, and debris ball• Identify and interpret cloud types associated with severe storms • Hurricanes, Typhoons and Cyclones: life cycles, including Arctic hurricanes, characteristics, structure, hazards, origin/distribution, & Saffi r-Simpson Scale• Weather safety (hail, fl ooding, winds, storm surges, etc.), NOAA warnings and watches, dependable sources of weather information for preparedness and during a severe weather event or outbreak• Precipitation from severe storms: snow, rain, hail, blizzard, freezing rain, ice pellets & rain, etc.• Severe Storm hazards: Flash fl ood, debris fl ow, mudslide, avalanche, storm surges, river fl ooding, fl ash fl ooding, atmospheric river, winds, etc.• SPECIAL TOPICS for 2017: Hurricane Patricia - October 2015, Eastern U.S. Blizzard - January 2016, Colorado Floods – September 2013, February 23-24, 2016 Tornado Outbreak.

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Origin of the Earth’s Atmosphere

Most of the time, Earth’s atmosphere- the en-velope of gases that surround its surface is a quiescent blue blanket that protects us from harsh solar radiation and the unimaginable cold of space. Thermal energy emitted by the Earth is trapped by the atmosphere, warming its lower layers. Precipitation falls over a broad expanse of the planet’s surface that helps to support a wide variety of plant and animal life. How did Earth’s atmosphere originate?

The origin of Earth’s atmosphere is still subject to lots of debate. One thing we can be fairly certain of is that when the Earth was formed some fi ve billion years ago, it was probably too hot to re-tain any of the gases that it had in its primordial atmosphere. Earth’s fi rst atmosphere most likely consisted of helium, hydrogen, ammonia and methane.

What likely happened over a period of thou-sands of years is that volcanoes emitted copious amounts of water vapor, carbon dioxide and nitro-gen- the same gases emitted by volcanoes today. This expulsion of gases from Earth’s interior is a process known as outgassing.

The water vapor expelled by the hot, volcanic Earth in turn created clouds, which produced rain. Over time, the rainwater would accumulate in basins as rivers, lakes and oceans. These basins in turn acted as sinks for accumulated carbon di-oxide, which later became locked into deposits of limestone and other sedimentary rocks. Nitrogen, which is not chemically active, accumulated in the atmosphere.

Signifi cant amounts of oxygen probably did not exist in Earth’s early atmosphere. Only when anaerobic bacteria dwelling in Earth’s oceans developed the ability to split water molecules apart using the energy of sunlight could signifi -cant amounts of oxygen accumulate in the atmo-sphere. It was the sequential and simultaneous interaction of these processes that appears to have produced the modern atmospheric composi-tion of 78% nitrogen and 21% oxygen.

While atmospheric scientists strive to understand the processes that govern the atmosphere, it is the ability to forecast extreme and severe weath-er that pose the most urgent challenges. Severe weather delivers damage to property and loss of human life unexpectantly and with fi erce intensity.

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STRUCTURE OF EARTH’S ATMOSPHERE

Think of the Earth’s atmosphere as being just like one of those multi-layered Jell-O deserts that you had at your last family reunion. It’s interesting to note that 99% of matter in the atmosphere is found within 20 miles of Earth’s surface. The layered structure of Earth’s atmosphere is defi ned by six prop-erties. These six properties include:

• Air temperature• Air pressure• Wind• Humidity• Clouds• Precipitation• Visibility

We’ll use these six properties to help us understand and describe each of the fi ve layers of the atmo-sphere. Then we’ll use what we have learned to create generalizations that can be used to explain at-mospheric processes and the formation of severe weather systems.

Troposphere

The troposphere is the atmospheric layer closest to Earth’s surface and moving upwards to about 10 miles above. Over 75% of atmospheric mass is found in the troposphere and air pressure is greater here than in any other atmospheric re-gion. The troposphere is where all the weather action takes place. It is a region of rising and fall-ing packets of air moving vertically. Note the thin buffer zone that is found between the troposphere and the next atmospheric layer- the stratosphere.

Stratosphere

Beyond the troposphere and extending upward 20 miles is the stratosphere. The stratosphere rep-resents about 24% of the total mass of earth’s atmosphere. The stratosphere has a very high con-centration of ozone- a reactive form of oxygen. You’ve probably fl own up into the lower levels of the stratosphere above the clouds on an airplane. The skies are always clear in the stratosphere because you are ‘above the clouds’ and there is nothing blocking the Sun’s light. The atmosphere is less mo-lecularly dense in the stratosphere and temperatures are extremely cold- often below -50°F. Unlike the troposphere, airfl ow in the stratosphere is mostly horizontal.

The stratosphere is primarily responsible for absorption of ultraviolet radiation from the Sun. Only when oxygen is produced in the atmosphere can an ozone layer form, preventing an intense fl ux of ultraviolet radiation from reaching the Earth’s surface, where it is hazardous to living things.

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The Mesosphere, Ionosphere and Exosphere

Extending another 20 miles above the stratosphere is the mesosphere. In the mesosphere, tempera-tures drop with increasing altitude to about -100°C- colder than Antarctica’s lowest recorded tempera-ture. The mesosphere is also the layer in which most meteors burn up as they enter Earth’s atmo-sphere. Ice clouds or noctilucent clouds (NLC) formed in the mesosphere can been seen at sunset when the Sun is from 4° to 16° below the horizon.

The ionosphere (sometimes called the thermosphere) extends 350 miles above the mesosphere where many atoms have become ionized- gaining or losing electrons so they have a net electrical charge. The process of ionization also releases tremendous amounts of thermal energy making this atmospheric region extremely hot. Although it is large in extent, the ionosphere represents only 0.1% of the total mass of Earth’s atmosphere. The structure of the ionosphere is very thin, and strongly in-fl uenced by the solar wind- a charge particle wind emitted from the surface of the Sun by solar activity.

The ionosphere is where the aurora takes place. Charged particles from the solar wind are attracted to the Earth’s magnetic fi eld, which is strongest at the poles and where the subsequent layers of the atmosphere are thinnest. Energy from the solar wind is converted into light forming beautiful arcs, glows, bands and veils. Auroras are usually associated with high latitude regions in both the Northern and Southern Hemispheres.

Auroras that occur in the Northern Hemisphere are commonly referred to as Aurora Borealis and those occurring in the Southern Hemisphere are referred to as Aurora Australis. During periods of in-tense solar activity, auroras may also be seen in northern Europe, and the northern continental United States. Different regions of the ionosphere refl ect radio waves back to Earth making long distance communication possible.

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Beyond the thermosphere, the exosphere extends approximately 6,200 miles from Earth’s surface and 40,000 miles from the ionosphere. It is a very thin layer composed chiefl y of hydrogen and helium, which are present only in extremely low densities. When I was growing up in the 1960s at the height of the Space Race, the exosphere was thought of as a quiet, serene place where not much went on. Yet since then, scientists have learned that the exosphere serves as a transition zone between plan-etary weather and space weather as it forms our fi rst line of defense against deadly cosmic radiation, meteors and asteroid impacts. The low atmospheric density and molecular friction characteristic of the exosphere also makes it an ideal platform for satellite orbits. Air temperatures in the exosphere also vary drastically with readings on the daytime side of the Earth exceeding 1000°F, while those on the side of the Earth facing away from the Sun are only a few degrees above Absolute Zero (-459.67°F).

From what you have read, can you answer these questions?

1. What happens to air temperature as you move upward from the troposphere to the stratosphere? What explains this?2. What happens to air temperature as you move upward from the mesosphere into the ionosphere? What explains this?3. What happens to atmospheric density as you move upwards from the surface of the Earth? How does this upward movement affect air pressure?4. In what atmospheric layers would we expect to encounter the movement of air (wind)? Could we assume that wind exists in all of the atmospheric layers? What evidence would support this?

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FEATURED ACTIVITYMM ATMOSPHERIC COMPOSITION

WANT TO LEARN MORE?

http://www.nasa.gov/pdf/288978main_Meteorology_Guide.pdfLink to a NASA PDF Meteorology: An Educator’s Resource for Inquiry-Based Learning for Grades 5-9. An excellent resource for all three strands of the Meteorology Event Cycle.

http://www.esrl.noaa.gov/gmd/outreach/lesson_plans/An excellent NOAA resource page that includes many lessons related to climate change and other key event topics of the Meteorology and Dynamic Planet Events.

http://teachertech.rice.edu/Participants/louviere/atmos.htmlA nice, simple webpage describing how the atmosphere formed, its composition and structure. The site also incudes some problem solving activities.

Use this tasty activity from the Learning With Boys Homeschool Blog to teach atmospheric composi-tion. In the left image the M&Ms are proportioned to Earth’s atmopsheric composition. The right image compares Earth’s atmospheric composition with that of Venus and Mars. Get complete instrictions for the activity http://learningwithboys.com/2014/08/21/atmospheric-science-part-1/#comment-986

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THE EARTH’S ENERGY BUDGET

A family’s budget or plan for spending money is derived from the amount of money coming in from paychecks, dividends, investments, etc. and the amount of money that is going out for expenses such as utilities, loan payments, food, etc. If the amount of incoming funds is equal to the amount of ex-penses, the family’s budget is said to be in equilibrium.

Likewise, the Earth’s Energy Budget is determined by the amount of incoming energy and the losses of outgoing energy. Nearly all of Earth’s incoming energy (99.98%) is derived from solar radiation. About .013% comes from geothermal energy that is created by stored heat energy and the radioac-tive decay of Earth’s core. About .002% of Earth’s incoming energy comes from the action of tides caused by the gravitational interaction of Earth with the Sun and Moon. Waste heat energy from fossil fuel consumption accounts for approximately .007% of Earth’s Energy Budget.

In measuring outgoing energy, the Earth has an average albedo (refl ectivity) of about 30% of incom-ing solar radiation is radiated back into space before it ever reaches Earth. Of what is left, the atmo-sphere absorbs 19% and 51% is absorbed by the Earth’s surface.

About 70% of solar energy that is absorbed by the Earth and things on it is reradiated as infrared en-ergy. In this scenario, the Earth’s Energy Budget- like the family’s fi nancial budget is in equilibrium as the amount of incoming energy is balanced by the same amount of outgoing energy.

Heat retention in the atmosphere also explains seasonal changes in weather in the Northern and Southern Hemispheres. In the Northern Hemisphere, between late July and late August, the amount of heat retained by the atmosphere each day and the amount that is lost is in equilibrium.

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As the amount of daylight and the intensity of solar radiation continue to decrease after the Summer Solstice, the atmosphere retains less solar energy by late August than is received. This trend con-tinues through late January- even after the Winter Solstice in late December. The declination of the Northern Hemisphere away from the Sun is still too great to allow the atmosphere to begin to retain suffi cient heat energy. Snow and ice on the Earth’s surface during the winter months increase the amount of albedo, as solar radiation is refl ected away from Earth’s surface before it can be absorbed. In the northern states, this is why the weather usually stays cold after the fi rst accumulating snowfall.

By late January however, the atmosphere again reaches a state of equilibrium, as the amount of insolation- the amount of heat energy retained by the atmosphere once again equals the amount that is lost. This is caused by the increased amount of daylight and increased intensity of solar radiation reaching the Northern Hemisphere.

By late February, the atmosphere in the Northern Hemisphere begins to retain more heat energy each day than is lost to irradiation. This trend will continue until late July when after the Summer Solstice, the amount of heat irradiated each day is equivalent to the amount retained creating a state of equilib-rium.

This sequential heating and cooling of the Earth’s atmosphere and surface in its Northern and South-ern Hemispheres is responsible for seasonal weather patterns that affect different regions of the world in different ways.

RADIATION BUDGET

The term radiation budget is used to refer to the balance between incoming radiation from the Sun and the outgoing thermal, or longwave and refl ected shortwave energy from Earth. On a global scale, the budget is balanced as the amount of energy coming in is ‘spent’ as solar radiation is transformed into latent heat, or even into kinetic energy. Energy transfers in the oceans as well as the atmosphere balance the radiation budget.

Locally, this scenario is not balanced, as tropical regions retain more insolation, while less is retained in higher latitudes. As we will learn, this accounts for differences in the temperature and pressure of air masses that originate in both regions affecting weather throughout the planet.

Here’s a few concepts that will help you understand how radiation works:

1. All things that have a temperature above Absolute Zero (-459.67°F) emit electromagnetic radiation. At Absolute Zero there is no molecular movement of electrons-so there are no emissions of electromagnetic radiation.2. The wavelengths of electromagnetic radiation emitted by an object depend primarily on the temperature of the object. The higher the temperature of the object, the shorter the wavelengths of radiation emitted by the object.3. Objects that have a high temperature emit electromagnetic radiation at a greater rate of intensity than objects having a lower temperature.

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ENERGY BUDGETS AND THE DEVELOPMENT OF SEVERE WEATHER SYSTEMS

In the {illustration} {shown}, note that the atmosphere does not immediately absorb radiation with wavelengths between 0.3µm and 1.0µm- the region in which the Sun emits most of its energy. Thus

on a clear day, solar energy passes through the atmosphere with little effect on air temperature. In-stead, this solar radiation reaches the Earth’s surface and warms it.

These warmed air molecules then bounce upwards from the surface in much the same way as popped kernels of corn on a hot pan do. Remember that the air near the surface is denser than that of upper layers of the atmosphere, so these warmed molecules travel only a short distance before they collide with other molecules. Air temperature rises because the rapidly moving molecules inter-act with the slower moving molecules to raise temperatures. As molecular movement of the electrons increases, so does temperature.

As the surface warms, the air that covers it becomes less dense than the air directly above it. This helps to create a convective movement in the air in which the warm air closest to the surface rises, while the cooler air above the surface begins to sink towards the ground. These zones or free convec-tion cells that are created by the movement of air between the atmosphere and the surface are the foundation of air masses or fronts which we will learn about later.

If this rising air is laden with moisture, the water vapor will condense into cloud droplets as it cools. This will release latent heat from within the moisture that will warm the air even more. Are you starting to get some idea of why thunderstorms form on hot, humid days?

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For a more advanced treatment of temperature and radiation, visit NASA’s Climate Science Investigations Temperature and Radiation webpage. It explains mathematical equations such as the Stefan-Boltzmann and Wein’s law as tools in understanding heat transfer. Visit the site by clicking http://www.ces.fau.edu/nasa/module-2/correlation-between-temperature-and-radiation.php

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FEATURED ACTIVITYPOPCORN HEAT/CONVECTION

WANT TO LEARN MORE?

http://earthobservatory.nasa.gov/Features/SORCE/sorce_04.phpNASA Earth Observatory discussion of the Sun’s effect on global climate. This is a good place to start discussion of this key event topic area.

http://www.physicalgeography.net/fundamentals/7y.htmlPhysical Geography page discussing causes of climate change, the Milankovitch Cycle, and many other variables affecting climate.

http://www.physicalgeography.net/fundamentals/6i.htmlPhysical Geography page describing insolation and Sun-Earth relationships.

https://www.youtube.com/watch?v=20carbgO45IA brief description of solar insolation. It also describes the difference between insolation and insula-tion.

http://www.physicalgeography.net/fundamentals/7t.htmlPhysical Geography webpage describing the formation of thunderstorms and tornadoes.

http://www.indiana.edu/~geol105/images/gaia_chapter_4/weather_phenomena.htmUniversity of Indiana discussion of thunderstorm and other severe storm formation.

It’s important to remember that temperature and heat are not the same thing. Temperature refers to the average motion of heat and molecules while heat is energy that fl ows due to differences in tem-perature as heat is transferred from warmer to cooler substances. This PDF uses popcorn as a model for atmospheric heating including conduction, convection and radiation. The Reading Convection PDF at the end of this Handbook explains the procedures.

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WATER IN THE ATMOSPHERE

The atmosphere of our planet, like most every place on the planet is laden with water. In temperate and tropical regions of earth, water exists primarily in liquid form. In the poles and higher latitudes, much of Earth’s water exists as solid ice locked away in alpine or continental glaciers. The physical composition of Earth’s atmosphere consists primarily of water vapor.

Humidity refers to the amount of water vapor that is in the air. This water vapor exists in a gaseous state. The process in which water changes from a liquid into a gaseous state is evaporation. Each water molecule that becomes water vapor also takes with it a parcel of heat energy from the surface it evaporates from. This process is known as evaporative cooling. Evaporative cooling explains why you may feel a chill after swimming as water evaporates off the surface of your skin, taking with it heat energy from your body.

During the spring months when the amount of daylight is increasing and the declination of the hemi-sphere is tilting towards the Sun, the intensity of solar radiation increases causing ice crystals in the upper troposphere to melt and fall to the Earth as rain. As the water is exposed to increased solar radiation it evaporates and returns to the atmosphere in a gaseous state- as water vapor.

The humidity of the atmosphere increases as spring turns into summer. Measurement of the vapor content of air is made through an instrument known as a hygrometer. Measurements of humidity are often expressed as a percentage, which is termed relative humidity. Complete saturation of the air (100% relative humidity) occurs when the amount of water vapor in the air is equal to the amount of water vapor that the air can hold. If the relative humidity is less than 100%, this means that the amount of water vapor in the air is not equal to the amount that it could hold.

AEROSOLS

Aerosols are tiny solid particles such as ice crystals, smoke, sea salt crystals, dust and volcanic emis-sions that are suspended in the air. Aerosols may also include tiny droplets of liquid water that form fog. Aerosols are sometimes referred to as particulates.

Aerosols interact directly and indirectly with Earth’s radiation budget. Aerosols directly affect weather and climate by scattering sunlight directly into space. Indirectly, aerosols in the lower troposphere can modify the size of cloud particles and the ways in which clouds refl ect and absorb sunlight, as we will learn later.

Volcanic aerosols signifi cantly affect Earth’s weather and climate as the sulfur dioxide gas spewed forth by active volcanoes as they erupt converts to droplets of sulfuric acid in the stratosphere within a week to several months following an eruption. Once formed, these aerosols will stay in the atmo-sphere for about two years refl ecting sunlight and reducing the amount of energy that reaches Earth’s lower atmosphere and surface.

Major volcanic eruptions can signifi cantly affect weather patterns over a short period of time. The eruption of Mt. Pinatubo in the Philippines in 1991 produced an aerosol cloud that covered much of the Northern Hemisphere within a year after the eruption signifi cantly reducing temperatures and increasing rainfall amounts the following summer.

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Intense dust storms over desert regions of Africa and Asia may also have a signifi cant effect on weather and climate as sand and dust is carried to altitudes as high as 15,000 feet. Sand and dust absorb solar radiation as well as refl ect it. The warmer air created by higher concentrations of dust and sand- without the enhanced ability of the air to hold more water vapor is believed to suppress the formation of rain-carrying storm clouds. This probably explains the phenomenon of desertifi cation- the expansion of deserts into adjacent non-desert regions.

The third type of aerosols is derived from human activities such as the burning of fossil fuels, and deforestation. Sulfate aerosols produced by such human activities increase the concentration of aero-sols, especially in the Northern Hemisphere, where industrial activities are more concentrated. Higher concentrations of sulfate aerosols refl ect sunlight back into space and cause clouds to produce small-er size droplets.

CLOUD FORMATION

Clouds are really nothing more than small droplets of water and ice crystals that clump together within the atmosphere. They then may produce precipitation in the form of liquid water and/or ice crystals that fall to the Earth’s surface.

Rising air is an important process in the formation of clouds. Let’s imagine a block of air rising upward through the atmosphere. If you recall from our discussion of the troposphere, the movement of air in this layer tends to be vertical.

As the air rises, it expands causing it to lose heat energy and hence the temperature of the air de-creases. The water vapor molecules that are in the air also increase the humidity of the air until it is saturated (100% relative humidity). Excess water vapor condenses- changing from a gas into a liquid on large aerosol particles in the atmosphere if the relative humidity is not in excess of 100% (see how this is all starting to come together). When the at-mosphere cools, it will reach the point at which the air is saturated with water vapor and can precipi-tate. The dew point is defi ned as the temperature to which a particle of air would need to be cooled in order to reach this point of saturation. The air’s capacity to hold water vapor is temperature depen-dent. Warmer air tends to hold more moisture, while cooler air holds less.

The dew point and relative humidity can be measured using a psychrometer, a weather measurement tool consisting of two identical thermometers mounted side by side. One of the thermometers- the dry bulb measures air temperature. The other thermometer- the wet bulb- has a damp wick wrapped around it allowing it to measure any decrease in temperature. This indicates the maximum amount of cooling that can result from evaporation.

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Cloud formation is closely related to the cooling of humid air masses. As water vapor expands- it cools in temperature. Likewise, when air is compressed- it heats up.

This change in temperature caused by the expansion or contraction of gases is known as adiabatic tem-perature change . This is a cooling or warming of the air caused by expansion or contraction and not by the increase or irradiation of heat.

The effects of adiabatic temperature change in Earth’s atmosphere can be dramatic. Air sinking down from higher latitudes is warmed by an increase in atmospheric pressure as it contracts. Likewise, warm air that climbs in altitude is under less pressure and cools as it expands. When this air is enriched in water vapor and cooled down to its dew point, con-densation and cloud formation can then take place.

TYPES OF CLOUDS

While clouds may appear to be chaotic masses of puffed air moving through the skies, clouds do have s high level of organization that enables us to study and classify them into different categories. I will describe the basic categories of clouds that you will need to review with students for the 2017 Meteorology competition.

Cirrus Clouds

Cirrus clouds are found at high altitudes (greater than 6,00 meters) and appear as thin and often wispy sheets with a feathery appearance. Cirrus clouds are usually composed of ice crystals that originate from the freezing of super cooled water droplets. Cirrus clouds are usually fair weather clouds and point in the direction of air movement at their elevation.

Cirrostratus Clouds

Cirrostratus clouds are sheet-like, high level clouds that are also composed of ice crystals. Cirrostratus clouds can cover the entire sky and be up to sev-eral thousand feet thick, but they are also relatively transparent as the Sun and Moon can easily be seen through them.

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Altocumulus Clouds

Altocumulus clouds appear as parallel bands or per-haps as rounded masses found at medium altitudes of 2,000-6,000 meters. Altocumulus clouds have a white, fl uffy appearance and are commonly nicknamed ‘sheep-back’ clouds because of their wooly appear-ance.

Fair weather cumulus clouds develop vertically at alti-tudes of 500 meters or above. These clouds have the appearance of fl oating cotton and often have a lifetime of around 5-40 minutes. Fair-weather cumulus clouds may occur as individual or isolated groups of clouds.

Fair weather cumulus clouds are fueled by thermals- buoyant bubbles of air that rise upward from the Earth’s surface. As they rise, the water vapor within these air parcels cools and condenses. Evapora-tion along the cloud edges cools the air around it making it heavier and producing a sinking motion or subsidence outside of the cloud. The North Carolina State University drawing below illustrates this process very well.

While appearing innocent enough, cumulus clouds can very quickly develop into their alter-ego cumu-lonimbus clouds associated with thunderstorms. Cumulonimbus clouds (shown to the right) are fueled by strong convective updrafts sometimes at speeds of over 50 knots.

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The tops of these clouds are quite high often reaching 12,000 meters or higher. Lower levels of cumulonim-bus clouds consist mainly of water droplets, while at higher elevations where temperatures are below 0°C, ice crystals are predominant.

OTHER TYPES OF CLOUDS

Fog occurs when the base of a cloud extends all the way to the ground. Fog often forms with the cooling of warm humid air, the movement of warm humid air over a cool surface- such as snow-cov-ered ground. Other fogs may form on clear, cool nights when the surface cools quickly by radiation causing a layer of air near the surface to drop below the dew point. Fogs may also form when humid air rushes up a mountaintop and cools and condenses rapidly. Heavy fog can reduce ground visibility signifi cantly making it diffi cult to drive or operate watercraft. Most fogs usually burn up within a couple of hours after sunrise.

Billow clouds are created from instability that is asso-ciated with weak thermal stratifi cation. These clouds often appear as a row of horizontal eddies that are aligned within a layer of vertical shear.

Mammatus clouds are pouch-like in their appearance, and although they look threatening, do not indicate that a tornado may form. Mammatus clouds are often seen in the aftermath of thunderstorms.

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Orographic clouds often develop in response to the forced lifting of air such as when air is forced over a mountaintop.

Pileus clouds are smooth clouds that are attached to either a mountaintop, or a growing cumulus tower.

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FEATURED ACTIVITYUSING THE NOAA/NASA SKYWATCHER CHART

The NOAA/NASA Skywatcher Chart is a great way to learn about the different types of clouds and how they are classifi ed with exampls of each of 27 different categories. It also includes a handy table for considering the effect of elevation on cloud observations. You can visit the site at:

http://oceanservice.noaa.gov/education/yos/resource/JetStream/synoptic/clouds_max.htm

Each of the images is clickable and provides information including a brief description, call symbol, large image and multiple views. On the left menu bar is a lesson plan overview with additional re-sources.

WANT TO LEARN MORE?

http://www.srh.noaa.gov/srh/jetstream/clouds/cloudwise/types.htmlNOAA/NWS discussion of the ten basic cloud types.

http://www.windows2universe.org/earth/Atmosphere/clouds/cloud_types.htmlWindows to the Universe discussion of cloud types.

http://scied.ucar.edu/webweather/clouds/cloud-typesUCAR Web Weather for Kids webpage. Check out the cloud gallery link shown in the right menu.

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PRECIPITATION

In the lexicon of meteorology, precipitation is defi ned as any form of water-rain, snow, sleet or hail that falls to the Earth’s sur-face. For precipitation to happen though, a cloud’s water droplets must become large and heavy enough to make it to the ground before they evaporate. Keep in mind that the average size of a cloud’s water drop-lets is seven times smaller than the width of a human hair, so chances are pretty good that most water droplets will never go splat on the Earth’s surface. It would take about two days for a water drop-let of this size to fall through 1km of air.

There are ways of bringing water drop-lets together though. At high altitudes, water droplets can freeze into ice crys-tals that will grow into larger snowfl akes. As the snowfl akes fall to lower elevations, they warm and begin to melt. Clouds at lower altitudes, where temperatures are too warm for ice crystals to form may co

alesce into larger droplets through numer-ous collisions with other water droplets until they are big enough to survive the long fall to Earth without evaporating fi rst. The covalent bonding properties of wa-ter molecules create a tendency for wa-ter to be more attracted to molecules like itself rather than to the surrounding air at all temperatures. The diagram below shows how hydrogen atoms share elec-trons in the process of covalent bonding.

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LIQUID PRECIPITATION

It’s easy to assume that all liquid precipitation that falls to Earth is rain. But as we will see, there are two other categories of liquid precipitation used by meteorologists to describe liquid precipitation.

Mist consists of droplets less than .05mm in diameter. Droplets larger than .05mm, but less than 0.5mm across is considered drizzle. Anything larger than 0.5mm across is termed rain. Most raindrops are not larger than 5mm across because of air drag effects that would tear larger droplets into smaller ones as they descended through the air.

FROZEN PRECIPITATION

Snowfl akes are nothing more than aggregates of ice crystals that collect to each other as they fall towards the Earth’s surface. The diagram at the right shows a temperature profi le of the atmo-sphere that is typical for snow. The red line indi-cates the temperature of the atmosphere at any given altitude. The vertical line in the center indi-cates the freezing line. Temperatures to the left of the line are below freezing, while temperatures to the right are above freezing.

If the air temperature throughout the atmosphere is below freezing as shown in this diagram (note the positioning of the red line on the graph), then the snowfl akes do not pass through a layer of air warm enough to melt them allowing them to fall to the ground as snow.

Snowfl akes fall as ice crystals and have diameters of between 1mm and 2cm. Larger frozen precipitation, with diameters of up to 5mm that fall as soft and mushy ice is termed graupel. Sleet is similar to graupel, but differs in that it is smaller. Sleet is re-ally nothing more than frozen raindrops. Anything larger than 5mm that makes it to the ground as rounded clumps of hard ice is termed hail. Hail is usually associated with thunderstorms as water droplets are continually propelled into the atmosphere by strong winds where they coalesce with other water droplets and freeze into large clumps of ice that become heavy and fall to Earth.

Another variation of icy precipitation is rime- a deposit of ice that freezes out of the air onto a surface that has a temperature below 0°C.

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FREEZING RAIN

Ice storms in which precipitation falls from the sky as rain, but freezes on contact with the surface can be the most devastating of winter weather, often causing power outag-es, automobile accidents and broken bones from slips and falls. My own memories of the ice storm of 1976 that devastated Michi-gan for over two weeks still linger more than 40 years later.

Freezing rain is most commonly found in a narrow band on the cold side of a warm front as shown in the diagram to the right, where temperatures are at or just below freezing. The freezing rain occurs in an area where a warm front of air is lifting over a mass of colder air. This is common during the late winter and early spring months in the Midwest.

Now, let’s use a temperature profi le for freezing rain similar to what we used above to describe snow. The diagram below shows the profi le for freezing rain with the red line indicating the atmosphere’s temperature at any given altitude. The vertical line at the center of the graph indicates the freezing line. Temperatures to the left of the line are below freezing. Temperatures to the right of the line are above freezing.

Freezing rain develops initially as falling snow. The snow encounters a layer of warm air (from the approaching warm front that lifts over colder air at the surface) deep enough to completely melt the snow into rain.

The rain then passes through a thin layer of cold air at the surface below 0°C and cools to a temperature below freezing. Keep in mind that the drops themselves do not freeze before they reach the surface. Rather the drops are super cooled while falling through this layer of cold air-allowing them to remain in a liquid state. When these super cooled raindrops strike the frozen ground- or things on the surface such as power lines and tree branches, they instantly freeze forming a thin fi lm of ice.

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HAIL

Hailstones are chunks of ice that fall from severe thunderstorms. They are highly dam-aging to crops. In the U.S., hail causes over 1 billion dollars in damage to both crops and property on average each year. Hail is formed when ice crystals in a thunderstorm grow as they come into contact with water vapor in the clouds. Strong updrafts in the thunderstorm keep the ice crystals from falling out of the cloud until they grow to a fairly large size and become too heavy to remain aloft. The hailstones may cycle through a storm several times before falling to the ground, resulting in an onion-like layering in the ice as the hail stones move through areas of extremely cold temperatures near the top of the cloud, where water droplets freeze quickly, and warmer areas near the bottom of the cloud where water freezes more slowly. The National Weather Service considers hail to be severe if it has a diameter of one inch or more. However, even smaller hailstones can cause signifi cant damage to crops.

VIRGA

When you watch a weather report, the meteorologist might speak of precipitation that falls from clouds- but never reaches the surface of the Earth. This type of precipitation is termed virga. At high altitudes, precipitation falls mainly as ice crystals before it melts and evaporates before reaching the ground because of compressional heating that occurs as a result of increasing air pressure closer to the ground (remember- air that is compressed becomes warmer). This phenomenon is also common in deserts.

Virga can produce dramatic and beautiful scenes in the sky- especially during red sunsets. Streams of falling precipitation that never reach the ground make the clouds appear to have commas at-tached to them as aloft winds push the bottom ends of the virga into angles. Virga can also be hazardous to pilots as the pockets of extremely cold air descending from the upper atmosphere can create microbursts that make aviation diffi cult.

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FEATURED ACTIVITYHOW CLOUDS MAKE RAIN

As water droplets and ice continue to accumulate in clouds, they get heavier and heavier. This eventually causes the water in clouds to fall as precipitation. In this Homeschool Mom activity, stu-dents use shaving cream, a jar, water and food coloring to demonstrate how clouds make rain. Find out more by clicking http://thehappyhousewife.com/homeschool/summer-cloud-science/#_a5y_p=2113691

WANT TO LEARN MORE?

https://eo.ucar.edu/basics/wx_2_b.htmlNational Center for Atmopsheric Research introductory level descriptions of precipitation

http://www.physicalgeography.net/fundamentals/8g.htmlPhysical Geography webpage describing the relationship of precipitation to global climate patterns

http://www.srh.noaa.gov/jetstream/global/preciptypes.htmlNOAA/NWS webpage describing forms of precipitation

http://www.nssl.noaa.gov/education/svrwx101/National Severe Storm Laboratory discussion of severe weather precipitation

http://climate.ncsu.edu/edu/k12/.SevereWeatherOutstanding North Carolina State website that discusses severe weather precipitation

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ATM

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UNDER PRESSURE

Atmospheric pressure can be likened to as the weight of the overlying column of air above you. As you increase your altitude above the Earth’s surface, the amount of air pressure decreases, because there is less air mass on top of you. Likewise, as you decrease your altitude above Earth’s surface, the amount of air pressure increases, as there is more air on top of you. Over 80% of the mass of Earth’s atmosphere is within the closest 18km to its surface.

Atmospheric pressure is usually measured in units called millibars (mb). One millibar is equivalent to 1 gram per centimeter squared (1g/cm2). At sea level, the amount of air pressure ranges from 960 to 1,050mb, with an average of around 1,013mb. At the top of Mt. Everest- the highest point on Earth, the air pressure is as low as 300mb. The amount of oxygen in the atmosphere is decreased at higher elevations because of the lower air pressure, as the pressure of gases such as oxygen is related to density. That means there is only about 1/3 as much oxygen on Mt. Everest as there is at sea level. This why many people who attempt to climb Mt. Everest experience shortness of breath as they climb to higher elevations.

Descending air forms high pressure centers or divergence. Polar highs result from the descent of cold air and its movement towards onto the surface. Subtropical highs form as warm air in the 20-30° latitude range in both hemispheres rises and then begins to cool as it falls towards the surface. This air is very dry making surface conditions in these regions very arid. Most of the world’s deserts in both hemispheres are found in this latitude range.

Ascending air forms low-pressure systems or areas of convergence. Tropical lows form as warm air ascends up into the atmosphere. Sub polar lows form as warm air in the 50-60° lati-tude ranges of both hemispheres rises producing abundant precipitation. Low-pressure cells move in a counterclockwise direction as shown on the diagram above.

Air tends to move from areas of high pressure to areas of low pressure. Air is denser and highly concentrated in high-pressure cells, which means that it is drier. Air is less dense in low-pressure cells, which means that it is capable of holding more moisture.

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FEATURED ACTIVITYCRUSHING A PLASTIC BOTTLE

WANT TO LEARN MORE?

https://eo.ucar.edu/kids/sky/images/PressureActivities.pdf23-page PDF with some great activities for teaching air pressure including ‘Not Your Uusal Pop,’ and the “Plunger Pull.’

https://www.youtube.com/watch?v=jmQ8FWnM0fAA nice video which explains the relationship of air pressure to other meteorological phenomena

https://www.teachengineering.org/activities/view/cub_airplanes_lesson01_activity2Teach Engineering webpage describing the role of air pressure in solving engineering peoblems such as aerodynamics. Recommended for more advanced students

http://climate.ncsu.edu/edu/k12/.IsobarIsothermNorth Carolina State website describing how to read isobars

Cold air sinks resulting in areas of ‘high’ pressure, Warm air rises and creates areas of ‘low’ pressure. Check out this great Cool Science Experiments website which describes how to use ice and hot water to demonstrate changes in air pressure. Click http://coolscienceexperimentshq.com/how-to-crush-a-bottle/

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ATMOSPHERIC CIRCULATION

So Far we’ve learned about the structure of the atmosphere, the properties of water as related to meteorology, cloud types and formation, and forms of precipitation. Let’s now take a look at the motion of the atmosphere on a global scale and look at how its is as-sociated with everyday weather.

A non-spinning planet would only experience the infl uence of unequal heating by the Sun, with the most direct sunlight reaching the tropics and the least amount reaching the polar regions. Under these circumstances, a simple convection system would suffi ce with extreme heating in the low latitudes causing warm air to rise. When this rising air mass reaches the tropopause (the very top layer of the troposphere) its upward move-ment is halted and the warm air then begins to move towards the poles as an upper-level wind.

Likewise, cooling air at the Polar Regions en-courages the air to sink downward and fall towards the surface. At the surface, this cold air then begins to fl ow towards the equator as shown in the diagram to the left.

These convection cells transfer heat by the movement of a mass or substance- one for the Northern and one for the Southern Hemisphere. Both transport air from the equator towards the poles and then cycle air near from the surface to the equator.

The cells in turn establish four pressure zones in each hemisphere. Two low-pressure areas are set up in each hemisphere- one in the equatorial region and the other in the sub polar region of the hemisphere. Likewise, two high-pressure areas are established in the subtropi-cal and the polar regions of each hemisphere where air fl ows downward and then outward onto the surface. The diagram below will give you an idea of how these pressure systems are arranged on Earth.

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FEATURED ACTIVITYWAYS OF THE WIND

WANT TO LEARN MORE?

http://www.indiana.edu/~geol105/1425chap4.htmUniversity of Indiana website that discusses global energy transfer as it relates to oceanic and atmo-spheric circulation.

http://www.tulane.edu/~sanelson/Natural_Disasters/oceanatmos.htmA very comprehensive PDF handout from Tulane University that addresses many key event topics of the Meteorology Event. It includes a discussion of atmospheric and oceanic circulation.

http://about.metservice.com/our-company/learning-centre/how-to-read-weather-maps/MET website describing how to read isobars related to wind speed and direction

http://www.physicalgeography.net/fundamentals/7p.htmlPhysical geography webpage describing atmospheric circulation patterns

http://www.physicalgeography.net/fundamentals/7n.htmlPhysical geography website related to forces creating wind

http://www.physicalgeography.net/fundamentals/7o.htmlPhysical geography website related to local and regional wind systems. It also includes tips for read-ing isobars related to wind

In all three of the Meteorology event themes, students should have a through understanding of the role of winds and atmospheric circulation in weather. This very complete lesson package should provide students with the background they need. Click http://teachingboxes.org/jsp/teachingboxes/weatherEssentials/wind/sequence/lesson4_activity1.jsp

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AIR MASSES AND FRONTS

Large bodies of air pass slowly over an extensive area of Earth’s surface, or the oceans, where they take on the characteristics of that region’s temperature and humidity. The area from which the air mass derives its characteristics is its ‘source region.’

Air mass source regions can be large snow covered areas in the poles, arid deserts, tropical oceans among others. Air masses that form over the ocean are termed maritime air masses, while those forming over land are termed continental air masses. Further classifi cation of air mass-es may be based on longitude. Tropical air masses are formed in low latitudes, while polar are formed in high latitudes.

To make things even more interesting, me-teorologists will combine the two classifi ca-tion categories as shown on the previous page into the following descriptions:

The principal air masses that infl uence the United States are shown on the diagram be-low. Polar air masses that form over Canada and Alaska often affect the weather of the United States as they move south and eastward. The Gulf Coast states and the Eastern United States often experience the effects of tropical air masses that migrate northward creating humid subtropical and continental climates. Occasionally, arctic air masses may descend from high latitude regions in the winter months creating bitterly cold weather. Tropical air masses from the Pacifi c may affect California and the Southwestern United States during the winter months. Although it is infl uenced by these major air masses, the United States itself is not a favorable source region for fronts because so many weather disturbances disrupt opportunities for the formation of air masses.

Air masses move from their source region due to the Coriolis Effect where they will meet adjacent air masses with different properties. When these two air masses of different ori-gin meet, the boundary between them is termed a front. Frontal boundaries are very nar-row- often less than 200km wide. In most cases, one air mass is cooler than the other, giving the warmer air a tendency to fl ow up and over the cooler air mass. This cooler and denser air acts as a wedge that allows warmer less dense air to rise over it.

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If the warm air moves in and displaces an area of once cooler air, this frontal bound-ary is called a warm front. The diagram above illustrates a warm front. Warm fronts

are characterized by an increase in tem-perature and the appearance of cirrus clouds. As warm fronts continue to move forward, cirrostratus and then altostratus clouds form. Denser stratus and nimbo-stratus clouds may also appear at the beginning of warm fronts with their asso-ciated rain and snowfall.

Cold fronts are formed when cooler air replaces an area that was once occupied by warmer air as shown in the diagram to the left. Cold fronts are usually associat-ed with more turbulent changes in weath-er than are warm fronts. As a cold front moves in, temperatures drop as warm air is pushed aside vertically and abruptly. Tall, cumulonimbus clouds take shape. An approaching cold front will usually create signifi cant changes in weather-especially during the summer months. Severe weather events are often the result of this movement of air masses.

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FEATURED ACTIVITYWHEN AIR MASSES COLLIDE

WANT TO LEARN MORE?

https://earth.usc.edu/~stott/Catalina/WeatherPatterns.htmlWell-illustrated description of different types of weather fronts.

https://www.youtube.com/watch?v=zAEEqEF-KZ4Weather Classroom discussion of air masses and fronts. Includes a hands-on activity.

https://www.youtube.com/watch?v=fdSWC5hYI0UAnimated discussion of weather fronts as related to severe weather.

http://www.physicalgeography.net/fundamentals/7r.htmlPhysical geography webpage describing air masses and fronts

http://www.srh.weather.gov/srh/jetstream/synoptic/wxmaps.htmlNOAA/NWS reading surface weather maps

The clash of warm and cold air masses is a classic meteorological confrontation that explains a great deal of what happens during severe weather. In this activity, students will simulate and visualize what happens when masses collide. Click http://www.education.com/science-fair/article/when-air-masses-collide/ to begin!

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SEVE

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THUNDERSTORMS

An understanding of the formation of thunderstorms will help you to understand how many other severe weather systems form. A thunderstorm is really nothing more than a rain shower in which you hear thunder. Because thunder comes from lightning, all thunderstorms have lightning. Now that we’ve stated the obvious, the average thunder-storm is approximately 15 miles in diameter and lasts an average of 30 minutes. At any given time, there are about 2,000 thunderstorms in progress throughout the world, with about 100,000 occurring annually.

Thunderstorms are classifi ed as ‘severe’ when they contain hail measuring ¾” or great-er in diameter; Winds gusting in excess of 50 knots (57.5mph); One or more tornadoes.

Thunderstorms need three things to form: Moisture, rising unstable air, and a lifting mechanism to keep air rising.

In turn, the ‘trigger’ (forcing mechanism) that starts the air moving is related to:

• Unequal heating of the surface• The effects of terrain on the lifting of air• The lifting of air along shallow boundaries of converging surface winds• Diverging upper-level winds coupled with converging surface winds and rising air• Warm air rising along a frontal zone

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As described in the earlier discussion of the Energy Budget, the Sun heats the surface of the Earth, which warms the air above its surface. This warm air may be forced to rise by changes in topography (hills, mountains, etc.) or in areas where warm/cold or wet/dry air collide. This air will continue to rise as long as it weighs less and continues to stay warmer than the air around it.

As the air continues to rise, it will transfer heat from the Earth’s surface to the upper levels of the Troposphere. This process is known as convection. As the water vapor (moisture) begins to cool, heat is released and condensed into a cloud that eventu-ally grows upward into areas of the atmo-sphere where the temperatures are below freezing. Some of this water vapor will turn to ice and some will turn into water drop-lets. Both forms have electrical charges. Ice particles will have positive charges and water droplets usually have negative charges. When enough of these charges build up, they are discharged as lightning, which in turn causes the sound waves we hear as thunder.

More specifi cally, the violent air currents found in thunderstorms move different-sized droplets, ice crystals and dust par-ticles at different speeds. Those of the same size and electrical charge become concentrated in the same parts of a cloud as shown in the diagram to the right. Very high positive charges are found in the upper levels of the cloud where the air is colder, while near the ground the air is negatively charged. This polarity between the ground and upper levels of the cloud creates a powerful voltage that sends lightning through the cloud and between those areas with opposite electrical charges. In an average thunderstorm, the energy released amounts to about 10,000,000 kilowatt-hours (3.6 x 1013 joule), which is equivalent to a 20-kiloton nuclear warhead. A large, severe thun-derstorm might be 10 to 100 times more energetic.

The developing stage of a thunderstorm is marked by cumulus clouds that are pushed upward by a rising column of air known as an updraft. The cumulus cloud takes on the appearance of a tower as this updraft continues to move upward. There is usually little or no rain during the developing stage, but occasional lightning. The developing stage usually lasts for ten minutes or so.

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Thunderstorms enter the mature stage when the updraft continues to feed the storm. But by this time, the air is so laden with moisture that precipitation begins to fall out of the sky and a downdraft or downward movement of air from the cloud begins. This downdraft and rain-cooled air forms a line of gusty winds. The mature stage of a storm is the stage most likely to include hail, heavy rain, tornadoes, frequent lightning and strong damaging winds. The appearance of the sky may be very black or even a dark green in appearance in this stage.

In the dissipating stage, the updraft is fi nally overcome by the downdraft of air. The line of gusty winds moves away from the storm cutting off the moist air that was feeding the storm. While rainfall decreases in intensity, lightning may remain a danger.

SINGLE CELL THUNDERSTORMS

Single-cell thunderstorms are often called ‘scattered’ storms because they are not as-sociated with a signifi cant weather front. Typically, they are less than a half-mile wide and go through a fairly predictable life cycle of developing, mature and dissipating stages.

Single-cell thunderstorms are actually rare as gusts from one thunderstorm add to an already unstable situation by triggering the growth of other thunderstorms. Most single cell storms are not severe. When they are severe, single-cell storms have strong up-drafts and downdrafts and can produce brief microbursts-or rapid downdrafts of cold air that can produce isolated severe damage. Single-cell storms usually only last about 20 minutes or so.

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MULTICELL CLUSTER STORM

Multicell cluster storms are among the most common of thunderstorm types, consisting of a group of storm cells that move together as one unit. Although these storms move together as a single unit, they are all in different stages of the thunderstorm life cycle. Mature cells will usually be in the center of the cluster, while dissipating cells can be found at the ends. Cold downdrafts of air that move downward from the high clouds reach the Earth’s surface and push downwards in all directions. These gusts can be over 1000 feet deep and move at speeds of 10-30mph. As these winds pass, tempera-tures drop sharply, the wind direction shifts and gusts with speeds of over 60mph. The high winds behind these strong gusts are often termed straight-line winds. This name is given to distinguish them from the rotating winds of tornadoes.

Multicell clusters are capable of producing moderate size hail and weak tornadoes. Each of the individual cells lasts only about 20 minutes or so, but because gusts from the different cells often spawn new storms, clusters of such storms may persist for sev-eral hours.

MULTICELL STORM LINE (SQUALL LINE)

Multicell storm lines are more organized versions of the multicell clusters, having a well-developed gust line at the leading edge of the storm line. Such squall lines are capable of producing golf-ball size hail, heavy rainfall and weak tornadoes. Occasionally, strong downbursts will move a portion of a squall line ahead of the rest of the line. This produces what in meteo-rology is known as a bow echo.

Mesoscale Convective Systems are orga-nized thunderstorms that may appear as circular vortices or elongated squall lines. These mesoscale storms are large enough to cover entire states and last for several hours as these systems slowly move unlike other multi-cell storms. Mesoscale systems usually form during the summer months in regions where upper-level winds are weak and found beneath a ridge of high pressure. A weak cold front that stalls beneath the ridge with adequate surface heating and moisture may provide the right conditions for formation of these storms.

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SUPERCELL STORMS AND TORNADOES

Supercells are highly organized lines of thunderstorms having a single updraft of air, unlike cluster storms, which have multiple updrafts. The updrafts of supercell storms are extremely powerful, often reaching speeds of 150-175 miles per hour. This rotating updraft is often called a Mesocy-clone when visible on radar. Giant hail-stones greater than 2 inches in diameter, strong downbursts of 80 miles per hour or more and violent tornadoes are often as-sociated with supercell thunderstorms.

Tornadoes are a form of supercell storms that consist of a rapidly rotating tube of air that whirls around an area of intense low pressure with a circulation capable of reaching the surface. This ground circula-tion of the storm is observed as a funnel-shaped cloud or a swirling cloud of dust and debris with no apparent organization. Most tornadoes have wind speeds of less than 135mph, but some violent tornadoes may have speeds in excess of 250mph.

Many tornadoes do not reach the surface. A funnel cloud is a tornado whose circulation has not reached the ground. Most North American tornadoes rotate counterclockwise at their central core.

Tornadoes evolve through a series of stages similar to the description given below:

1. The warm updraft and cool downdraft of supercell storms interact forming a tube of spinning air (mesocyclone).

2. Part of this tube is pushed into a vertical column under the storm and tilted into two columns of spinning air- one spinning clockwise, the other counterclockwise.

3. The up drafted air stretches the counterclockwise spinning air into a tornado as the two columns of air connect.

Tornadoes occur in many regions of the world, but the United States by far has the most averaging more than 1000 annually.

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Tornadoes have occurred in all fi fty states, but are most prevalent in an area of the Central Plains from North Dakota through Southern Texas known as ‘Tornado Alley.’ This region of the Central Plains is conducive to tornado development. Warm humid surface air from the Gulf of Mexico is frequently overlain by cold drier Canadian air that moves south along the Rocky Mountains. Vertical wind shears produced by low-level jets and the polar jet stream forces surface air upwards increasing the likelihood of supercell storm formation. Tornado frequency is highest during the spring when the surface air begins and continues to warm, and is lowest in the winter when warmer sur-face air is usually absent.

TORNADO SAFETY

The winds produced by tornadoes are capable of damaging or even destroying many buildings presenting an obvious threat to human life and well-being. As high winds blow over a roof, the air pressure above the roof falls, while the greater air pres-sure inside a building may be enough to lift the roof high enough for the winds to carry it away. This is similar to Bernoulli’s Principle that explains how airplanes fl y. Building explosions during tornadoes may also be caused when low pressure systems associated with tornadoes pass overhead. The momentary drop in pres-sure outside the building may be enough to cause the higher pressure air in the building to move outward causing it to explode.

It was once thought that opening windows during a tornado would cause an equaliza-tion of pressure that would prevent building explosions. In many Caribbean nations, this is a common practice during tropical storms and hurricanes. However, we now know that opening windows during tornadoes may actually increase the likelihood of building collapse as pressure on the opposing walls increases rather than decreases. In most cases, windows are damaged by fl ying debris anyway. The best course of ac-tion then to prevent injury or death caused by building collapse or fl ying debris is to im-mediately seek shelter if a tornado is spotted in your area and/or if you have received an offi cial warning.

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Here are some practical suggestions for seeking shelter during a tornado or severe thunderstorm:

1. Go to the basement if the building you are in has one.2. If the building does not have a basement, go to an interior room or hallway away from windows. Ideally, the room should be small and on the lowest level of the building.3. Wherever possible cover yourself by lying under an overturned sofa or under a bed. You can also remove the cushions or mattress and place them over you.4. If you have a football, motorcycle or bicycle helmet wear it to protect your head from fl ying debris.5. If you are in a mobile home, leave immediately and seek substantial shelter (64% of fatalities during tornadoes occurred in mobile homes in 2007- 45% most other years).6. If you are in school, move to an interior hallway away from windows and cover your head with a hardbound textbook.7. If you are driving, do not attempt to outrun the tornado. Tornadoes often move in erratic paths with overland speeds exceeding 80mph. Instead, stop the car and let the tornado go by or drive in the opposite direction of the tornado.8. Do not attempt to hide under an overpass. If the tornado passes through the overpass, its winds may strengthen as air fl ow is constricted and cause the collapse of the structure over you.9. If no shelter is available, look for a low-lying ditch, streambed or ravine and lie fl at with your head covered until the storm passes.10. Have a cell phone, portable radio, fl ashlight and other emergency devices available.

TORNADO WATCHES AND WARNINGS

The average number of tornadoes in the United States during the decade of the 1950s was 480 tornadoes per year with an average of 148 deaths per year. In the decade of the 2000s, there was an average of over 1,300 tornadoes per year, but the average number of deaths has dropped to approximately 52 per year continuing a downward trend that began in the 1980s. The drop in fatalities is due in large part to improve-ments in forecasting that identify areas of tornado and severe storm formation as well as in communications technologies that can deliver that information to more people in less time.

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This is also in spite of the fact that populations in Tornado Alley states have increased faster than the national average since the 1960s.

A tornado watch is issued by the Storm Prediction Center located in Norman, Oklaho-ma to alert the public that conditions in a region are ideal for the development of torna-does during a certain time period. Many communities have trained volunteer tornado spotters who will look for tornadoes after a watch is issued.

Once a tornado is spotted, a Tornado Warning is issued by the local National Weather Service offi ce. In many communities, a piercing siren is used to alert people of the ap-proaching storm. Radio and television- even cable and satellite networks will interrupt regular programming to alert the public. Once the storm has moved away, watches and warnings are lifted, but may be issued for localities now in the path of the oncoming storm.

THE FUJITA SCALE

In 1971, a scale for classifying tornado damage incurred by a frame house was implemented by Theodore Fujita, a meteo-rologist at the University of Chicago. Initially, the Fujita Scale aroused controversy as tornado winds were estimated on the damage caused by a storm- a very subjective premise to most scientists. It also did not accurately account for the many types of structures that were susceptible to tornado damage besides residential homes. Nevertheless, by the late 1970s, the Fujita Scale became widely used by meteorologists.

In February 2007, a new Enhanced Fujita Scale (EF) was devel-oped to provide a wider range of criteria in estimating a tornado’s wind speed. These indicators included mobile homes, barns, trees and schools. {EF Scale}. The impor-tance of the Fujita and Enhanced Fujita Scales is their attempt to establish benchmarks for the severity of tornadoes. To put the EF scale in perspective, consider that as wind speed doubles in a violent tornado, the force of the wind exerted on an object such as a building increases by a factor of four. Thus a 200mph wind of an E4 tornado exert four times as much force on a building as do the 100mph winds of an EF1 storm. Click http://www.tornadofacts.net/tornado-scale.php to see the original and Enhanced Fujita Scales.

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HURRICANES

Tropical weather systems differ markedly from the mid-latitude systems that character-ize most of the United States and Canada. In the tropics (located between 23.5°N lati-tude and 23.5°S latitude), the noon Sun is always high in the sky, meaning that diurnal and seasonal changes in temperature are small. Instead, most seasonal variations in tropical weather are marked by changes in precipitation rather than in changes in tem-perature. The greatest cloudiness and pre-cipitation most often occur during the high-sun period.

The daily surface heating and high humidity found in most tropical regions favors the development of cumulus clouds and afternoon thunderstorms. Most storms are single-cell and not severe. Winds in the tropics generally blow from the east, northeast or southeast. Troughs of low pressure called tropical or easterly waves form moving from east to west that may form tropical storms or hurricanes.

A hurricane is an intense storm originating in the tropics with sustained winds of over 74mph that form in the Atlantic Ocean north of the Equator or the eastern/north Pa-cifi c Ocean. In the western Pacifi c Ocean, these storms may be called typhoons, in India cyclones and in Australia tropical cyclones. By international agreement, tropical cyclone is the name used to describe all forms of these storms. In this presenta-tion, I will use the familiar American term of hurricane.

Hurricanes that affect the Caribbean and the East Coast of the United States origi-nate from tropical waves that begin in western Africa. Easterly winds blow these nascent storms off the west coast of Af-rica into the war waters of the Atlantic.

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As the storm moves slowly westward, it picks up copious amounts of moisture fi lled with sensible heat and latent heat energy transferred from the ocean. Heat energy is converted into wind energy during the process of condensation. Latent heat is released inside deep convective clouds. For a hurricane to form, a cluster of thunderstorms must become organized around a central area of surface low pressure. Huge amounts of latent heat are released inside clouds during condensation, warming the air aloft and causing the temperature near the thunderstorms to be much higher than the tempera-ture further away.

Gradually, the storms swing poleward if they are caught in subtropical highs. As they move further north, they diminish in strength as they move over colder water. This also happens if a hurricane moves over a landmass. Fair weather is found on the west side of the hurricane as the storm approaches and in the eye of the storm, while heavy rainfall- as much as ten inches per-hour occur as the storm moves through and as it continues eastward.

HURRICANE SAFETY

A good analogy that might be used to compare severe thunderstorms with hurricanes might be that of the common cold and the fl u. Like the discomfort one experiences dur-ing cold, most severe thunderstorms run their course anywhere from a few minutes to a half-hour or so. Hurricanes on the other hand are much more severe just like a bout with the fl u. The effects may be felt for days before the arrival of the storm as well as for days or even weeks afterward.

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Rainfall as high as ten inches per hour will often generate fl ash fl ooding. The high winds of hurricanes also generate waves as high as 30-50 feet that move outward from the storm carrying the storm to coastal areas. The low pressure of the storm itself also allows the level of the ocean to rise, similar to soft drinks that rise up inside a straw as air is withdrawn. Potable water supplies may become contaminated by fl oodwaters and sewage. Roads may be blocked by fl oodwaters, fallen trees or power lines. Many people may be homeless and in need of aid. In 2005, over 1,500 people died either from Hurricane Katrina’s storm surge or from fl ooding. The future trend is for larger and more frequent storms as global mean temperatures continue to increase.

Up until 2005, the annual death toll from hurricanes averaged less than 50 persons per year. While many move to higher ground, many others refuse to leave their homes or have no means of seeking safe shelter. With improvements in forecasting and commu-nications technologies loss of life can be reduced dramatically. Unlike severe thunder-storms and tornadoes which appear suddenly, meteorologists are able to track hurri-canes over a period of several days before they make landfall.

The best advice for hurricane preparation is to leave the affected region and seek safe shelter as soon as possible. If this is not possible, seek shelter in higher ground or in designated shelter areas.

SAFFIR-SIMPSON SCALES

Like the Fujita Scales used to determine the strength of tornadoes, the Saffi r-Simpson Scale is used to gauge the severity of hurricanes. While the Fujita Scales attempt to discern the strength of tornadoes based on the damage they have caused, the Saffi r-Simpson Scale uses meteorological data such as air pressure, wind speed and storm surge to assess the potential damage that may be caused by a storm.

SEVERE WINTER WEATHER

Shortly after World War I, a group of Norwegian scientists including Vilhelm Bjernes, Jakob Halvor Solberg and Tor Bergeron published the widely acclaimed Polar Front Theory to explain mid-latitude cyclone development. Polar Front Theory created a working model of how a mid-latitude cyclone forms, develops and dissipates. Essen-tially, a Polar Front exists where cold polar air is separated from warm subtropical air. Storms thus develop as warm air and cold air along these fronts clash.

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The Theory of Polar Fronts can be used to explain severe weather systems in mid-lati-tude regions throughout the year, including the development of severe winter weather.

A blizzard is a storm that is characterized by low temperatures, high humidity and strong winds that produces prodigious amounts of snowfall. The National Weather Service classifi es a winter storm as a bliz-zard using the following criteria:

1. Winds of at least 35mph2. Falling or blowing snow that reduces visibility to less than ¼ mile3. Lasts for more than three hours

Blizzards occur in all northern states, but are most common in a band that stretches from eastern Colorado north ward into the Dakotas and the state of Minnesota. Bliz-zards are formed from mid-latitude cyclonic storms that are characterized by areas of deep low-pressure with a southward extending cold front. Northwest of the storm is usually found an area of high pressure associated with extremely cold arctic air that moves into an affected region after the storm exits. The storm forms as warm moist air from the Gulf of Mexico or the eastern Pa-cifi c wraps around a counterclockwise spin-ning low pressure system. Heavy snow falls in the region of this low. Visibility is reduced as the fl uffy snow falls to the cold surface and is picked up by winds.

In severe blizzards, temperatures can drop well below 0°F. Snow can pile up around homes trapping the people inside. Streets and highways can become impassable. Cattle and other livestock can be frozen to death. Frostbite on exposed human skin can occur in minutes as well as hypothermia or rapid loss of body heat.

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LAKE EFFECT SNOW

Living in Michigan, lake effect snow is a fact of life every winter- more so on the west side of the state than on the east if you live in the Lower Peninsula. In the Upper Peninsula, wherever you live there is lots of lake-effect snow. Lake-effect snow is also common in many other regions of the Great Lakes in-cluding Northeastern Ohio, Upstate New York and Northeastern Illinois.

Lake-effect snow is created by the action of cold air rushing over large bodies of water such as the Great Lakes where it picks up prodigious amounts of moisture. As this moisture-laden air makes landfall, it condenses and freezes into snow. It is not uncommon for areas near the shoreline to receive up-wards of 20-inches of snow at rates of 2-3-inches per hour.

Unlike the mid-latitude cyclones associated with blizzards, lake effect snows are much more localized in their coverage. As an example, Lambton County in southwest-ern Ontario, Canada had a lake-effect snowstorm totaling over 60 inches in December 2010. Cold air blowing across Lake Huron created the storm just east of Sarnia, Ontario. But just west of the St. Clair River and only 20 miles south where I live, we only received 3 inches from that same storm.

As you can see, there are many forms of severe weather. An understranding of how severe weather forms will not only help you succeed in the Meteorology Event, but also in your everyday life. Use the Online library, Science Olympiad website and other re-sources to further develop your understanding of the event rules and concepts. Good luck!!

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Conduction, Convection, and Radiation: Popcorn Lesson (Three Methods of Heating)(http://aspire.cosmic-ray.org/labs/atmosphere/popcorn.html)

All forms of matter, whether a solid, liquid, or gas, are composed of atoms or molecules inconstant motion. Because of this constant motion, all atoms have thermal (heat) energy. Whenever asubstance is heated, the atoms move faster and faster. When a substance is cooled, the atoms moveslower and slower. The “average motion” of the atoms that we sense is what we call temperature.

Temperature and heat ARE NOT technically the same thing. Temperature is the average motionof atoms and molecules. Heat is the energy that flows due to temperature differences. Heat is alwaystransferred from warmer to cooler substances. (When there is no temperature difference, it is calledthermal equilibrium, and no heat is transferred.)

There are three ways to heat the atmosphere (or anything else, for that matter). These waysinclude conduction, convection, and radiation. How can you remember these? Let’s use an analogy tohelp you figure this out.

There are three ways to cook popcorn:1. Put oil in the bottom of a pan. Cover the bottom of the pan with popcorn kernels. Place the

pan on the stove and turn on the burner to medium heat. Cover the pan with a lid.Periodically shake the pan so the kernels move around in the oil.

2. Obtain a popcorn popper. Place the popcorn kernels in the popper. Plug in/turn on thepopper. Hot air will transfer heat to the kernels, making them expand and pop.

3. Microwave a bag of microwave popcorn.

Each of these methods of cooking popcorn is really an example of the three ways heat can betransferred.

Conduction: This method of heat transfer is most familiar to people. If you have ever burnedyourself on a hot pan because you touched it, you have experienced this first-hand. Conduction is heattransfer through matter. Metals conduct heat well. Air is not as good a conductor of heat. This is adirect contact type of heat transfer. The only air heated by the Earth is the air at the Earth’s surface. Asa means of heat transfer, conduction is the least significant with regard to heating the Earth’satmosphere. Which popcorn example does it relate to? (#1) The heat is transferred by direct contactfrom the pan, to the oil, to the kernels of popcorn.

Convection: Convection is heat transfer by the movement of mass from one place to another.It can take place only in liquids and gases. Heat gained by conduction or radiation from the sun ismoved about the planet by convection. The radiation from the sun heats the air of the atmosphere, butthe heating of the Earth is not even. This is because the amount of sunlight an area receives dependsupon the time of day and the time of year. In general, regions near the equator have hotter air. This hotair rises, allowing cooler air to move in underneath the warm air. In our popcorn example this relatesto #2. The hot air transfers the heat to the cooler kernels, and when enough hot air heats the kernels,they pop.

Radiation is the only way heat is transferred that can move through the relative emptiness ofspace. All other forms of heat transfer require motion of molecules like air or water to move heat. Themajority of our energy arrives in the form of radiation from our Sun. Objects that are good absorbersof radiation are good radiators as well. The atmosphere, which does not absorb certain wavelengths ofsolar radiation, will absorb certain wavelengths of radiation. The particles that reach Earth from the Sunare within a wavelength that the Earth’s atmosphere will absorb. When the Sun heats the Earth, theEarth gets warmer in that location and re-radiates heat into the atmosphere, making it doubly warm. This relates to popcorn example #3. The kernels are heated by the radiation in the microwave, and the

kernels heat up, giving off more heat to the kernels surrounding it and making it “doubly warm.”

Radiation is the primary way that air is heated. Convection currents move that heated air aroundthe earth, and the difference between warm and cold air provide the energy needed to create weather.

How Does Heat Travel?(http://coolcosmos.ipac.caltech.edu/cosmic_classroom/light_lessons/thermal/transfer.html)

Heat can be transferred from one place to another by three methods: conduction in solids,

convection of fluids (liquids or gases), and radiation through anything that will allow radiation to pass. The method used to transfer heat is usually the one that is the most efficient. If there is a temperaturedifference in a system, heat will always move from higher to lower temperatures. CONDUCTION:

Conduction occurs when two objects at different temperatures are in contact with each other.Heat flows from the warmer to the cooler object until they are both at the same temperature.Conduction is the movement of heat through a substance by the collision of molecules. At theplace where the two objects touch, the faster-moving molecules of the warmer object collidewith the slower-moving molecules of the cooler object. As they collide, the faster moleculesgive up some of their energy to the slower molecules. The slower molecules gain more thermalenergy and collide with other molecules in the cooler object. This process continues until heatenergy from the warmer object spreads throughout the cooler object. Some substances conductheat more easily than others. Solids are better conductor than liquids, and liquids are betterconductor than gases. Metals are very good conductors of heat, while air is very poor conductorof heat. You experience heat transfer by conduction whenever you touch something that ishotter or colder than your skin (e.g., when you wash your hands in warm or cold water).

CONVECTION:In liquids and gases, convection is usually the most efficient way to transfer heat. Convectionoccurs when warmer areas of a liquid or gas rise to cooler areas in the liquid or gas. As thishappens, cooler liquid or gas takes the place of the warmer areas which have risen higher. Thiscycle results in a continous circulation pattern, and heat is transfered to cooler areas. You seeconvection when you boil water in a pan. The bubbles of water that rise are the hotter parts ofthe water rising to the cooler area of water at the top of the pan. You have probably heard theexpression “Hot air rises and cool air falls to take its place”– this is a description of convectionin our atmosphere. Heat energy is transfered by the circulation of the air.

RADIATION:Both conduction and convection require matter to transfer heat. Radiation is a method of heattransfer that does not rely upon any contact between the heat source and the heated object. Forexample, we feel heat from the sun even though we are not touching it. Heat can be transmittedthough empty space by thermal radiation. Thermal radiation (often called infrared radiation) isa type electromagnetic radiation (or light). Radiation is a form of energy transport consistingof electromagnetic waves traveling at the speed of light. No mass is exchanged and no mediumis required.

Objects emit radiation when high energy electrons in a higher atomic level fall down to lowerenergy levels. The energy lost is emitted as light or electromagnetic radiation. Energy that isabsorbed by an atom causes its electrons to “jump” up to higher energy levels. All objectsabsorb and emit radiation. When the absorption of energy balances the emission of energy, thetemperature of an object stays constant. If the absorption of energy is greater than the emissionof energy, the temperature of an object rises. If the absorption of energy is less than the emissionof energy, the temperature of an object falls.