Chapter 2:

Weather and Climate

Victoria Alapo, Instructor

Geog 1010

Introduction to GeographyPeople, Places, and Environment, 4e

Edward F. BergmanWilliam H. Renwick

Weather and Climate

Weather Day-to-day variations in temperature and precipitation.

Examples: temporary storms, temperature changes.

Climate Statistical summary of weather conditions over several

decades or more, but usually 30 yrs.

Thirty years was chosen as a period long enough to eliminate year-to-year variations.

Source: http://www.metoffice.gov.uk/climate/uk/averages/

Intensity of Solar Radiation (Insolation)

Affected by: Angle of incidence –

more vertical at the equator. Oblique towards the poles.

Also, axial tilt = 23.5 degrees.

Latitude Summer Solstice – June 20 or 21

Longer days In the northern hemisphere Winter Solstice – December 20 or 21

Longer nights in the northern hemisphere But in the southern hemisphere, the opposite is

occurring on both days! (June & Dec) Equinoxes

(equal day/night) – see next slide. Vernal/Spring Equinox – March 20 or 21 Autumnal Equinox – Sept. 20 or 21

Greenhouse Effect

Explain the “Greenhouse Effect” Greenhouse gases

Water vapor, carbon dioxide, ozone, methane

Increased greenhouse gases = increased global warming

Relative Humidity

Water content of air; it measures the “wetness of air”.

It’s also the percent (%) of water air could hold at a given temperature (as seen on TV).

Precipitation: 3 Types (ways it forms)

(1) Convectional precipitation Warm, humid air rises, and cools Saturation point is reached Clouds form

Leads to convectional storms

(2) Orographic Precipitation

Wind forces air up and over mountains Rain on windward side Desert on leeward side: Rain shadow Examples

The Rockies and Sierra Nevada. Also, see picture on pg 55, and caption.

(3) Frontal Precipitation

This happens when air is forced up the boundary between cold and warm air masses (called a front).

Cold front When cold air mass moves towards warm air mass

Warm front When warm air mass moves towards cooler air

mass See animation

Circulation Patterns

Air mass = 14.7 lbs per square inch. Air has weight! Think of a cylinder of propane/oxygen.

Atmospheric pressure Varies with altitude

Higher altitude = less atmospheric pressure That’s why your ear ‘pops’ as the pressure

increases on descent in an airplane. Barometer – instrument for measuring

pressure.

Pressure and Winds

Coriolis Effect An apparent deflection of any freely moving object from its

expected (straight) path, caused by the Earth’s rotation. The earth rotates from west to east.

Causes winds to move in an indirect, curving path, including hurricanes, and ocean currents, see next slide. If the earth did not move (rotate), winds would just move in a straight line from high pressure to low pressure.

Happens to planes too, esp. when traveling in a straight line from the north pole to the equator. That’s why pilots fly in a curve. Otherwise, they’ll land to the west of their intended destination. See animation.

Ocean Circulation Patterns

Gyres is the special name ocean currents are called. These are wind-driven circular flows.

Coriolis Effect

Global Circulation

Global Circulation Only 3 of these zones will be discussed:

A) Inter-tropical convergence zone (ITCZ) This is where the N/E & S/E winds converge. See

previous slide. These converging winds are also called “Trade Winds”, because they were important to sailing ships.

B) Subtropical high-pressure zones These are areas of dry, bright sunshine, and little

precipitation. They cause deserts. It is an area of warm dry air found about 30 degrees N & S latitudes. See next slide.

Subtropical Highs

Responsible for the world’s greatest deserts.

Dry conditions caused by no uplift of air due to high pressure.

Global Circulation

C) Polar high-pressure zones The intense cold causes dense air because coldness

causes contraction, and so there is little molecular space, therefore air can’t lift. This causes high pressure.

As a result, the air stays close to the ground and there is little precipitation, leading to “polar deserts”. Polar deserts are typically drier than hot deserts – see climograph of McMurdo, Antarctica.

Storms

Cyclones These are low-pressure systems There are 2 types:

A) Hurricanes (N/America) and Typhoons (Pacific) Also known as tropical cyclones

B) Midlatitude cyclones – tornadoes, Box on pg 66.

Storms

Hurricanes/ Typhoons: Need warm, moist air

Most powerful over oceans (occur more during summer).

Once the winds reach 74 miles/hr they are called hurricanes/typhoons.

They cause storm surges This is when there is an elevated sea level in the

center of the storm. i.e. high waves crashing inland (e.g. Katrina). 90% of people die from this.

2 primary measures of climate are: Temperature & Precipitation

World Precipitation

Classifying Climate The Köppen System

It is the most widely used system and was developed by Wladimir Köppen in 1918.

He used the distribution of plants to help draw boundaries btw climate regions (because vegetation types tend to closely follow precipitation and hence temperature in area). So these 3 are interrelated.

Köppen identified 5 basic climate types, and subdivided them further to reveal important distinctions. See page 74 & 75 of text and next slide. An American Professor added the H Climate (Mountains)

These classifications allows analysis and planning by geographers, govts, etc.

Climate Regions

As the map shows, these regions are horizontal bands based on latitude. Read about each climatic region (A to E) on your own. Pages 76 to 86.

Sometimes climatologists use climographs to show temp and precipitation for every month of the year. Every climatic region and every city in the world has one. Draw a simple one for the test.

The one on next slide is for Lanzhou, China (pg 79).

Also see website for Omaha climograph: http://www.hprcc.unl.edu/stations/index.php?

action=metadata&network_station_id=256255

Omaha – Eppley Station Data:

http://www.hprcc.unl.edu/stations/index.php?action=metadata&network_station_id=256255

Climate Change The earth has alternated btw warm & cold periods over

time.3 hypotheses – reasons given for climate change: Astronomical

Sunspots – relatively cool regions on the surface of the sun, which varies in #, in a cycle lasting 11 yrs.

Geologic Volcanic eruptions – large amts of dust & gases can be ejected

to reduce solar radiation, and cool the earth. E.g. Krakatau, Indonesia.

Human Atmosphere – increase in CO2 in the atmosphere since the start

of the industrial revolution in the 18th century. CO2 is a greenhouse gas.

Vegetation – clearing