In the north, winds blow anticlockwise into a low pressure system' In the south, they blow clockwise - PowerPoint PPT Presentation

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In the north, winds blow anticlockwise into a low pressure system' In the south, they blow clockwise

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Title: In the north, winds blow anticlockwise into a low pressure system' In the south, they blow clockwise


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CORIOLIS 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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HIGH 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.

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LOW-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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