METEOROLOGY

GEL-1370

Grading Scheme

• Assignment – 30 points

• Exam – 1 – 30 points

• Exam – 2 – 30 points

• Final Exam – 40 points

Lowest one unit of 30 points will be dropped

Turning-in Assignment is a MUST!! – If not, one of the tests will not be counted towards the final course grade

Pop Quizzes as a bonus will be periodically given

Historical Developments - Meteorology

• ‘Meteorology’ comes from the Greek Word ‘Meteoros’ meaning ‘high in the air’

• STUDY OF THE ATMOSPHERE AND ITS PHENOMENA

• Greek Philosopher Aristotle (340 BC) wrote a book on natural philosophy entitled “Meteorologica” – first attempt to explain atmospheric phenomena in a philosophical and speculative manner

• Aristotle’s student, Theophrastus, compiled a book on weather forecasting – ‘Book of Signs”

Historical Developments – contd.

• Meteorological Parameters: Air temperature, pressure, humidity, wind speed and direction

• During 1500s, Italian Physicist and Astronomer, Galileo: Invented a cruse water thermometer

• 1643: Evangelista Torricelli, student of Galileo, invented Hg barometer to measure air pressure

• A few years later, Blaise Pascal and Rene Descartes (French): Atmospheric pressure decreases with increasing altitude

• 1667: Robert Hooks (British): Invented a Plate Anemometer for measuring wind speed

Historical Developments – contd.• 1719: Gabriel Fahrenheit (German), developed a temperature

scale• 1742: Anders Celsius (Swedish), developed centigrade scale• 1780: Horace deSaussure (Swiss), invented hair hygrometer to

measure humidity• 1787: Jacques Charles (French), discovered the relationship

between temperature and volume of air• 1835: Gaspard Coriolis (French) demonstrated the effect that the

earth’s rotation has on atmospheric motion• 1840s: Ideas about winds and storms were partially understood• 1843: Invention of Telegraph• 1869: Isobars (lines of equal pressure) were placed on weather

maps• Ca. 1920: Concepts of air masses and weather fronts were

formulated in Norway.

Historical Developments – contd.

• 1940s: Upper-air balloon observations of T, P, Humidity yielded 3-D view of the atmosphere and military aircrafts discovered existence of jet streams

• 1950s: High-speed computers to solve mathematical equations to describe the atmospheric behavior

• 1960: First weather satellite, Tiros I was launched – Space Age Meteorology

• Princeton, NJ (Geophysical Fluid Dynamics Program): Numerical methods to predict weather

• Mid-1990s: Conventional radars were replaced by Doppler radars to peer into severe thunderstorms and unveil their winds

•

Chapter One Chapter One

The Earth’s AtmosphereThe Earth’s Atmosphere

Grading

• Assignment – 30 points

• Exam – 1 – 30 points

• Exam – 2 – 30 points

• Final Exam – 40 points

Lowest one unit of 30 points will be dropped

Turning-in Assignment is a MUST!! – If not, one of the tests will not be counted towards the final course grade

Pop Quizzes as a bonus will be periodically given

Some Basic Questions – Why Meteorology??

• If we approach near a fire place, we feel hotter – if we move to a hill resort (towards the sun) why we feel cooler (not hotter)?

• What is the role of atmosphere in ‘Greenhouse Effect’ and ‘acid rain’

• Why hurricanes is confined to certain regions – lessons from (St.) Andrew?

• Why thunderstorm in the Gulf Coast is much stronger than the Midwest?

• What would happen to this planet if there were no atmosphere??

How Weather Affects our Lives?• Our lives center around the weather – type of clothing we wear,

plants we grow, our comforts in the form of heating/cooling our homes, etc.

• Wind chill makes us feel lot colder than what it is• Health is affected – Arthritis pain is likely to occur when rising

humidity with falling pressure; our mood swings (hot, dry wind vs cool breeze); incidence of heart attacks shows statistical peak after the passage of warm fronts when rain and wind are common

• Cold summer of 1992 – saved billions of $ to people• Bitter cold winter of 1986-1987 in Europe: several hundred

people died• Huge Ice storm in Jan 1998 in Northern New England and

Canada – millions of people without power

How weather affects our lives – contd.

• 1999: Heat waves in US caused 250 deaths• 1995: >500 people died due to high humidity and heat

waves in Illinois• People are killed by Tornadoes• 10 yrs ago, 55 people died due to Andrews in FL (30

billion $ loss)• Fog can affect the visibility• Weather Channel, NOAA Weather Radio Station

CHAPTER – 1

THE EARTH’S ATMOSPHERE*ATMOSPHERE: LIFE-GIVING BLANKET OF AIR

HORIZONTAL LONG-DISTANCE MOVEMENT IS EASY – WE CAN’T DO MORE THAN 8 KM FROM EARTH’S SURFACE - SUFFOCATION

SURVIVING WITHOUT FOOD OR WATER FOR A FEW DAYS POSSIBLE – NOT WITHOUT AIR

IF THERE IS NO ATMOSPHERE, THERE WON’T BE ANY LAKE OR OCEANS

ATMOSPHERE SERVES AS A BUFFER FOR EARTH’S CLIMATE – FROM UNBEARINGLY HOT DURING DAY AND UMIMAGINABLY COLD AT NIGHT

AIR PROTECTS FROM SCORCHING SUN – AIR MOLECULES TRAVEL FROM ONE CONTINENT TO ANOTHER IN LESS THAN A WEEK TIME SCALE

:

Introduction-contd.

• Our planet is driven by the solar energy – a small portion of the outgoing solar radiation is intercepted by the Earth- Sun is at 150 million km away from us (93 million miles)

• Average temp of earth ~15°C (59 °F)

• Temperature fluctuation: -85 °C to 50 °C (-121 °F to 122 °F)

Introduction-contd.• Composition of the Atmosphere (Permanent

Gases)

• Gas Symbol % (volume) dry air– Nitrogen N2 78.08

– Oxygen O2 20.95

– Argon Ar 0.93– Neon Ne 0.0018– Helium He 0.0005

– Hydrogen H2 0.00006

– Xenon Xe 0.000009

Composition of the Atmosphere Near the Earth’s surface-contd.

Gas & particles Symbol % (volume) ppm

Water vapor H2O 0 to 4

Carbon dioxide CO2 0.037 368

Methane CH4 0.00017 1.7

Nitrous Oxide N2O 0.00003 0.3

Ozone O3 0.000004 0.04

Particles (dust, soot, etc) 0.000001 0.01-0.15

Chlorofluorocarbons (CFCs) 0.00000002 0.0002

Atmospheric composition-contd.• 99% of the atmosphere lies within 30 km from surface of

the earth– Atmosphere protects us from

• UV Radiation from Space• Impact of high energy particles from Cosmos• Extreme temperature fluctuations

• Water vapor varies from place to place – up to 4% warm tropical locations to <1% in colder arctic areas

• Condensation (vapor into liquid) and evaporation (liquid becoming vapor)

• Importance of Water vapor in the atmosphere:– Releases large amounts of latent heat (source of atmospheric

energy for thunderstorms and hurricanes)– Water vapor is a ‘greenhouse gas’ (absorbs outgoing energy)

Importance of CO2

• 0.037% • Sources: Burning of fossil fuel, deforestation, volcanic eruption, decay

of vegetation, exhalation of animal life

• Ocean is a huge reservoir – Phytoplankton uptake (source and Sink; Fe expt; atmospheric transport of dust)

• Oceans hold X 50 times the atmospheric CO2

• Before Industrial revolution, CO2 level at 280 ppm and it is now ~370 ppm

(1.5 ppm/yr; ~32% increase) and expected to reach 500 ppm by end of this century [Freight train won’t stop; US consumption of 1/3 vs population of 5%]

• Increase in CO2 will result in global warming – 1 to 3.5°C – Flooding in

certain areas and drought in other regions; global sea level change; global air currents that guide the major storm systems could shift

Measurements of CO2 (ppm) at Mauna Loa Observatory

Other Greenhouse gases

• Methane: Increases by 0.5%/year; Sources include: Paddy fields (breakdown of plant material by certain bacteria), wet oxygen-poor soil, biological activity of termites and biochemical reactions in the stomachs of cow

• Nitrous Oxides: Increases by 0.25%/year; Sources include: release from industrial activity followed by chemical reactions, formation in the soil by microbial activity

• Chloroflurorocarbons (CFCs): Increases with time; Sources include: solvents for cleaning electronic microcircuits; propellants for the blowing of plastic-foam insulation, etc – Play a part in destroying Ozone molecule in the stratosphere - Implications

Ozone (O3)

• The Primary ingradient of photochemical smog (chemical reaction of pollutants in big cities with sunlight)

• ~92% found in stratosphere (11-50 km) – formed when O combines with O2 – abundance < 0.002% by volume

• Shields plants, animals and humans from sun’s harmful UV rays- offers protective shield – CFCs release ozone destroying Cl – Ozone conc. has been decreasing over parts of the Northern and Southern Hemisphere – Ozone hole in Antarctica during September & October

Aerosols

• Smoke from Forest fires, salt particles from sea-water spray, aeolian dust, fine ash particles and gases derived from volcanic eruptions –aerosols– Act as surfaces for nuclei condensation

• Pollutants: Derived from automobiles: CO, hydrocarbons, NO2, sulfur-containing fuels (coal and oil) releases SO2 --- lead to acid rain; NO2 reacts with hydrocarbon in the presence of light to produce ozone

Early Atmosphere• Earth’s first atmosphere is believed to contain mainly H

and He (with traces of NH3 and CH4) – Earth’s hot surface led to the escape of these gases

• Later, escaped gases from volcanic eruptions & steam vents, surrounded the Earth – Mostly water vapor and CO2 formed the second atmosphere --- CO2 reached the ocean and eventually got locked in carbonate rocks --- Slowly but steadily, the N2 content of the atmosphere increased

• Energetic cosmic rays split H2O molecule in O and H – escape of H lead to increase in Oxygen – Plant growth led to the increase in Oxygen levels

Vertical Structure of the Atmosphere• Classification based on: Temperature, composition or

electrical properties• Air Density: number of air molecules/volume• Atmospheric Pressure: Force/area of surface • Total weight of air 5,600 trillion tons• Units of pressure: 1 Atmosphere = 1.01325 bars =

1013.25 millibars (mb) = 101326 Pascal = 1013.25 hectopascal = 29.92 in. Hg = 760 mm Hg = 14.7 lb/inch

Air pressure and density decrease with increasing altitude

Atmospheric pressure rapidly decreases with height

Layers of atmosphere• Earth’s surface to 11 km – temp decreases – sunlight warms the

earth’s surface and the surface warms the air above it

• Lapse Rate (LR) = Rate of decrease of temp. with height; in the lower atmosphere, LR ~ 6.5°C/km; colder air leads to higher LR and warmer air to lower LR; LR fluctuates from day to day & season to season;

• Isothermal Zone: At Tropopause, Stratopause and Mesopause, the Lapse Rate is zero

• Temperature Inversion: Occasional increase of temp. with height known as Temp. Inversion;

• Troposphere: From earth’s surface to where the air stops becoming colder with height; up to 11 km from earth’s surface; controls all the weather; the layer is well mixed by ascending/descending air masses

Temperature-based classification of atmosphere

Atmospheric layers – contd.

• Stratosphere: From the top of tropopause to until the temperature remains constant (~50 km);

• Tropopause height varies – higher in the equatorial region & decreases poleward; tropopause is higher in summer and lower in winter at all latitudes;

• In some regions, tropopause breaks, leading to stratosphere-troposphere air mixing (mainly during spring/summer months and in mid latitudes – Stratosphere-Troposphere Exchange; these breaks also mark the position of jet streams (wind speeds >100 knots)

• At ~20 km from earth, air temperature increases with height – Temperature Inversion – This inversion reduces the vertical movement of air masses within the stratosphere (temp at ~30 km from earth is ~-46°C); this reason

Atmospheric layers – contd.• Inversion in the stratosphere is due to heating of

stratosphere from the absorption of UV rays by O3; absence of O3 ---- air would become colder with height

• Mesosphere: Extremely thin air, low pressure and density; average temp. ~-90°C;

• Thermosphere: Hot layer above Mesosphere; very few atoms and molecules in air; Range of an air molecule ~ 1km (compare with < 10-6 cm in earth’s surface)

• At the top of thermosphere (>500 km from earth’s surface), particles can escape to space – Water Loss Possible?? (this region called Exosphere- upper limit of our atmosphere)

Composition-based Atmospheric Layering

Homosphere: A well-mixed layer in terms of composition; below the thermosphere, the composition of air (78% N2 and 21% O2) remains constant by turbulent mixing

Heterosphere: Complete stirring in the thermosphere is not possible due to few atoms/molecules; diffusion is dominant; heavier atoms at the bottom & lighter atoms at the top – heterogeneity in introduced

Ionosphere: Region within the upper atmosphere where large concentrations of ions and free electrons exist

Layers of atmosphere

Ionosphere

Simplified surface weather map

Weather Map

• Weight of air in the column varies and hence atmospheric pressure

• L: Marks the center of the middle-latitude storm• H: Regions of high atmospheric pressure, anticyclones• Coriolis Force: Earth’s rotation causes the wind to

deflect toward the right in the Northern Hemisphere. This deflection causes the winds to blow clockwise and outward from the center of the highs & counterclockwise and inward toward the center of the low

• Front: A boundary that separates the warm and cool air appears as a heavy, dark line on the map.

Weather Map – contd.

• Weather front is to the west of Chicago – when westerty winds push the front eastward, areas in outskirts of Chicago will observe the approaching front as a line of thunderstorms – heavy showers with thunder and lightning and gusty winds are expected