Download WEATHER AND CLIMATE

WEATHER AND CLIMATE
How do they differ?
• Weather - short term - at a given place and
time in the troposphere
– Temperature, pressure, humidity, precipitation,
sunshine, cloud cover, wind direction & speed.
• Climate - long term average – General pattern of atmospheric conditions
– Main factors are temperature and precipitation
Why does weather change?
• Caused by masses of
air - either warm or
cold that are either
high or low pressure
and move across the
land
• Changes as air masses
replace or meet one
another.
• FRONT - where air
masses meet.
Warm front
• Boundary between
approaching warm air
mass and cool air mass
it is replacing.
• Warm air less dense &
rises over cool air
– Moisture
– Thick clouds
– Rainfall common
Cold front
• Cold air meeting
warm air
• More dense so wedges
under warm air
– Thunderheads
– Precipitation
– Surface winds and
thunder storms
• Afterwards, cool temp.
& clear skies
Properties of warm and cold air
• Warm air rises, cold air sinks
• As air rises,cools, releases water at the
equator - radiates heat into space - low
pressure at equator
• Cooler drier air - more dense, sinks - creates
high pressure areas
• Heats again, rises, etc
• Causes different climate patterns and
vegetation.
Pressure
• High pressure air mass - cool, dense air
descends toward earth’s surface and
becomes warmer. Fair weather follows for
as long as mass remains.
• Low pressure air mass - cloudy, sometimes
stormy weather - Less dense warm air
spirals inward toward center, rises, cools,
moisture condenses and rains.
Microclimates
• Topographic features
create local climatic
conditions - differ
from the general
climate of the region.
• Mountains - interrupt
wind patterns and
storm movements
• Moisture is dropped
on the windward side
of mountains and on
the leeward side is the
RAINSHADOW
EFFECT.
• Arid or semiarid
conditions
Causes of Microclimates
• Topography can cause different location to
receive different amounts of sunlight.
• Vegetation also creates microclimates forests are warmer in winter, cooler in
summer, have lower wind speeds and higher
humidity.
• Cities create microclimates- buildings,
asphalt, hold heat, change wind patterns,
etc.
Rainshadow effect
Hadley Cells
Global Circulation of air and
regional climates
• Several factors affect
regional climates:
– Uneven heating of
earth’s surface
• Air is heated much
more at equator than at
poles- sun’s rays hit at
an angle due to tilt
– Seasonal changes in
temperature and
precipitation
– Earth’s rotation on
its axis
• Causes coriolis effect winds are deflected to
the right in the northern
hemisphere and to the
left in the southern
hemisphere
• Results in 6 convection
cells called Hadley
cells - move heat &
water .