CLIMATE

CLIMATE

The average weather in an area.

Major Factors: Precipitation and Temperature

Earth’s Topography: why distribution?

Earth’s Living Things: why distribution?

Climate Concepts: rise or sink

• Warm air rises


• Warm air rises– Open the oven, you feel the heat

on your face



on your face• Cold air sinks



on your face• Cold air sinks

– Open the freezer, you feel the cold at your feet


• When air rises, it cools– Top of Mt.

Lemmon is cooler

• When air sinks, it warms– Warmer here

than top of Mt. Lemmon

Climate Concepts: warm or cold

• Warm air holds more water; cold air holds less water

Climate Concepts: water in air

• Absolute humidity: the amount of water in the air


• Absolute humidity• Relative humidity: a measurement

(%) of how saturated the air is with water vapor

Depends on temperature and how much water vapor is in the air


• As air rises, it cools• Cooler air holds less water vapor so

the Relative Humidity increases.• So as air cools more and more the

RH increases more and more until it hits 100%.

• If it gets even cooler, then it rains


• The temperature to which the air had to cool to become totally saturated (100% RH) is called:

• Dew point: the temperature at which the relative humidity = 100%


• Example:• Monday, the dew point is 50

degrees.• Tuesday, the dew point is 70

degrees.• What does this tell you?• There was more water vapor in the

air on Tuesday• Thus, the chance of rain was

greater on Tuesday.


• When we experience 3 consecutive days with dew points of 55 degrees F or greater.

• How do we know when the monsoon period begins?

Climate Concepts: Review• Warm air holds (more or less?)

water vapor; cold air holds (more or less?) water vapor.

• As air cools down, the relative humidity increases or decreases?

• As air rises, the relative humidity increases or decreases?

Effects of precipitation and temperature on biomes

Conif erousrainforests

Temperaterainforests

Tropicalrainforests

Polargrasslands

Temperategrasslands

Tropicalgrasslands

Cool deserts Temperatedeserts

Tropicaldeserts

temperature

pre

cip

itati

on

What causes Precipitation?• Rain = moisture + cooled down air

• No Rain = low moisture and/or heated up air

Rain = moisture + cooled down air• Moisture must evaporate into air, then

moist air must move over Tucson.– Winter: moves in from Pacific– Summer Monsoon: moves in from

Gulf of California and Gulf of Mexico• Air must cool.

– Air cools when it rises•It rises three different ways…

TYPES OF PRECIPITATION

1. CONVECTION

2. OROGRAPHIC

3. FRONTAL

Back to the beginning:Biomes

• The two things that determine what kind of a biome exists in any place are– Precipitation: done– Temperature

Climate Concepts: temperature

• What determines what the temperature is on Earth?– 3 things

• 1. Elevation– Temperature is cooler at higher

elevations– Temperature is warmer at lower

elevations


Low elevation

High elevation


• 2. Greenhouse gas concentration in the atmosphere– Gases like carbon dioxide, water

and others are greenhouse gases– They absorb energy, keeping us

warmer at night and cooler during the day


• 3. latitude

equator

Cold Poles: same energy covers more land, and there is more atmosphere to go through which reflects/absorbs energy.


• 3. latitude

equator

Cold Poles: same energy covers more land, and there is more atmosphere to go through which reflects/absorbs energy.

What causes the seasons?

• In other words, why is it warmer in the summer and colder in the winter?

82o

34o

Source: Audubon Society

Why is it warmer in the summer?

• Because the sun is more directly overhead in summer (82o) vs. winter (34o).– The sun’s rays are spread over less area.– The sun’s rays don’t have to pass

through as much atmosphere (which would absorb and reflect energy).

Because Earth is tilted 23.5° relative to Sun and revolves around the sun.

Sun’s raysEquator 23.5°N

23.5°S

Tropic of CancerTropic of Capricorn

23.5°N

23.5°S

Why does the sun’s angle change from season to season?

Season here?

Season here?

http://www.physicalgeography.net/fundamentals/6h.html

http://www.physicalgeography.net/fundamentals/6h.html

How is my shadow going to change during day? Why?

– Swings from west to north to east.

– Longest morning and evening and shortest at noon

West

Long

Sun at low angle

East

Long

Sun at low angle

North

Short

Sun most directly overhead

How is my shadow going to change annually at noon each day?

Gets longer and shorter. When is it long? Short?

Why?

104”8’8”

(=5’10”/tan 34)(=5’10”/tan 82)

longer

shorter

10”

winter

summerwinter

summer

So, why doesn’t it rain much in Tucson?


1. Rainshadow Effect2. Descending Air in Hadley Cells3. Cold Ocean Current4. Distance from source of water.

First 3 reasons have to do with air heating.• as air heats, its capacity to hold water

increases, thus relative humidity decreases, decreasing the chance for rain and increasing potential evaporation (let’s call this sentence “the blurb”).

Orographic Rain this side

this side

Rainshadow Effect: we are downwind of mountain ranges and as air blows down the downwind side, the air heats and the blurb happens.


Descending Air in Hadley Cells: as air in Hadley Cells descends at 30 degrees latitude, it heats and the blurb happens.

Hadley Cells

http://en.wikipedia.org/wiki/Image:AtmosphCircNT.png


Cold Ocean Current: as cold air over ocean moves over warm land, the air heats and the blurb happens.

cold

warm

Warm currentsCold currents


Cold Ocean Current continued


Distance from source of water: All else equal, the farther from a body of water, the less moisture will be in the air.

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