Title: In the north, winds blow anticlockwise into a low pressure system' In the south, they blow clockwise
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13CORIOLIS FORCE
High
- Pressure gradient wind blows from high presure
towards low pressure. - The earths rotation diverts this wind direction
laterally. This force is called the CORIOLIS
FORCE. - The Coriolis force diverts wind the the right in
the northern hemisphere to the left in the
south. - The effect is stronger at high altitude where
ground level friction is less significant.
Theoretical wind which would result solely from
pressure gradient
Actual wind which blows, as diverted by Coriolis
Force
Low
LOW
In the north, winds blow anti-clockwise into a
low pressure system. In the south, they blow
clockwise.
In the north, winds blow clockwise out from a
high pressure. (In the south, they blow
anti-clockwise).
HIGH
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16HIGH PRESSURE
High Pressure means that air tends to sink.
Sinking air is compressed, warms up as a result
and its relative humidity falls below saturation.
Any clouds evaporate. Rainfall is unlikely, apart
from occasional short, intense convectional
storms due to insolation with lack of clouds in
daytime.
- In Britain, high pressure systems have clear
skies, little or no wind, little rainfall and
tend to be stable and slow moving. - Visibility is intially good, but rapidly
deteriorates as dust is trapped by sinking air
and is not washed out by rainfall. - Cloud cover is slight, resulting in a high
diurnal ranges of temperature (hot days, cold
nights). Due to the trapped dust particles and
cold nights, dew, frost, fog or smog are common. - Air quality is low as all forms of pollution are
retained in the lower atmosphere.
17LOW-LATITUDE LOW PRESSURE SYSTEMS
Low pressure systems involve air that tends to
rise, thus causing clouds and precipitation.
Those near the equator tend to be high energy due
to strong ground heating (convectional). Low
pressure systems may develop tornadoes and
sometimes develop into hurricanes, fuelled by
warm, very humid air evaporated from tropical
oceans in summer. They tend to be fast moving,
with plenty of cloud cover that reduces diurnal
temperature range, strong winds and high rainfall.
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