Introduction to Geography
People, Places, and Environment, 4e
Edward F. Bergman
William H. Renwick
Chapter 2:
Weather and Climate
Victoria Alapo, Instructor
Geog 1010
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.
World Precipitation
2 primary measures of climate are: Temperature & 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=metad
ata&network_station_id=256255

Omaha – Eppley
Station Data:
http://www.hprcc.un
l.edu/stations/index.
php?action=metada
ta&network_station
_id=256255
Climate Change
The earth has alternated btw warm & cold periods over
time.
3 hypotheses – reasons given for climate change:
 Astronomical



Geologic


Sunspots – relatively cool regions on the surface of the sun,
which varies in #, in a cycle lasting 11 yrs.
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