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Climate
Climate versus Weather
Weather is the short-term daily characteristics of the atmosphere in a
given region. It includes wind, humidity, cloud cover, visibility,
temperature, precipitation, and air pressure. Climate is the long term
characteristics of the atmosphere in a region. Climate is like the
average seasonal weather for a given region.
Climatic Controls
Climatic Controls are the major and minor things that help to produce
the climate of a region.
Latitude
Generally the higher latitude a land region is, the cooler it will be
because the sunlight at higher latitudes is spread out over a larger
area which makes the sunlight per given area less which means that
less warming will occur.
Altitude
The greater the altitude, the lower the temperature and pressure. On
average, air temperature drops by 6.4o C for every 1000 m increase in
altitude. This is called the environmental lapse rate. Since the
atmosphere is less dense at higher altitudes, it can not store as much
heat and does not heat up as much.
Mountains
Mountains can act as barriers to air masses, blocking warm humid air
from moving farther inland. Air that rises up a mountain expands,
becomes less dense and cools. Dry air cools 10o C per 1000 m of
vertical rise. This is called the dry adiabatic lapse rate.
Orographic Precipitation
Air rising up a mountain loses its ability to hold water and eventually reaches
its condensation point (dew point) where it form dew, clouds, rain or snow.
If the air continues to rise and cool it does so at the wet adiabatic lapse rate
of 3o C per 1000 m because condensing water releases heat so it doesn’t cool
as quickly. Orographic precipitation is when moist air is lifted up a mountain
range releasing rain on the windward side and sinking as dry, warmer air on
the leeward side, here referred to as a chinook or foehn wind.
Pressure and Wind Systems
Climates at various places are affected by the major wind and pressure
systems on earth. See video, Atmospheric Circulation on you tube.
Seasonal Movement of Pressure Bands and Winds
In the Northern Hemisphere’s Summer, the Pressure bands move
northward as the hemisphere receives more radiation and in winter,
the Northern Hemisphere’s pressure bands migrate southward.
Ocean Currents
Ocean currents generally follow atmospheric winds in their circulation
pattern. The Gulf stream has a major warming effect on Europe and
Northeastern Russia. Regions where ocean currents flow counter to
winds are often stormy regions (like the waters off Labrador and Cape
Horn South America.
The Pattern of Water Bodies and Continents 1
Land locations near large water bodies generally experience wetter
climates unless the water is a cold current, the land is at a high
latitude (with cooler air - unable to hold water), or the land has
offshore winds for much of the year.
The Pattern of Water Bodies and Continents 2
Land near large water bodies generally have cooler Summer temperatures and
warmer Winter temperatures. This is because water has a much higher capacity to
store heat (1 cal/gCo ) from the sun than land (.2 cal/gCo ). An amount of land will
rise in temperature 5X more quickly and cool 5X as quickly as than the same amount
of water. Thus in Summer, water remains cooler than land and heat moves from
land to the adjacent water. In Winter, water drops its temperature less than land
whose temperature is cooler so heat moves from the water to the adjacent land. In
addition, water absorbs heat from the sun to great depths while land only absorbs
heat for a few cm of its surface.
The Pattern of Water Bodies and Continents 3
Inland continental regions warm up faster in summer, which causes air
expansion, rising currents and low pressure regions. Surface winds blow
towards these low pressure regions. In winter, inland regions of continents
cool more and accumulate cool, dense air masses of high pressure over
them. These high pressure regions tend to have more sunny days and also
cause winds to flow outward from them.
The Land Mass of Asia
Asia is the largest land mass so it develops the lowest pressures in the
Summer and the highest pressures in the winter. The winds flowing
into the Asian continent in Summer from the Indian ocean bring
Monsoon rains while winds flowing out from the Asian Continent in
Winter bring a dry season and Monsoon rains to Northern Australia.
Local Factors Affecting Climate: Aspect
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Local Factors Affecting Climate: Incline
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Inclined land that has a south-facing aspect will receive more sunlight.
This is important for some crops like grapes which produce more sugar
and mature faster when they are on a south-facing slope. In the
Cowichan Valley, south-facing slopes are warmer.
Local Features Affecting Climate: Land/Sea or On/Offshore Breezes
For land near a lake or ocean, in the morning the land heats up more
which causes air over it to rise and cool air from the water moves in to
replace the rising air. This produces a offshore breeze. At night the
land cools more quickly and heavier cool air moves from land to the
water while warmer air over the water moves up over the land,
cooling and dropping.
Local Features Affecting Climate: Katabatic and Anabatic Winds
On mountains at night, air at higher altitudes cools causing katabatic
breezes down the mountain slope. On mountains during the day,
warmer air from valleys, lakes or oceans rises up the mountain slopes,
creating up-flowing breezes called anabatic breezes.
Local Features Affecting Climate: Urban Areas
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