o level - weather & climate - factors affecting air pressure and wind
TRANSCRIPT
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Weather & Climate
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Pressure and Winds Explain the formation of land and sea
breezes along the coast
Explain the occurrence of the monsoon season in South East Asia
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Air Pressure
► The force exerted on the Earth’s surface by the weight of air above it.
► Measured in milibars (mb) using a barometer
► Average sea level value of air pressure is 1,013 mb High pressure = above 1,013mb Low pressure = below 1,013mb
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Barometer
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Air Pressure
► Relationship to altitude: Inverse r/s: air
pressure decreases as altitude increases
► Why? (hint: link back to what we learnt about altitude under temperature)
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Air Pressure
► Maps that show air pressure are known as synoptic charts
► Isobars* are lines that join places of equal air pressure together
► Closer isobars = steep pressure gradient = stronger winds
*not to be confused with contour lines
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Wind
► Wind occurs because: Air always flows from high pressure to low
pressure
► Wind speed is measured in km/hr using an anemometer
► Wind direction is measured using a wind vane
► Types of winds: Local winds
Regional winds
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Anemometer & Wind Vane
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PitStop 4Q1 & 2
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Local Winds: Sea Breeze
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Local Winds: Sea Breeze
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Local Winds: Sea Breeze
► During the day, air over the land heats up faster than air over the sea.
► As warm air rises, a low pressure area is formed.
► Air over the sea is cooler as the sea heats up slower.
► The cool air sinks and forms a high pressure area
► As air always moves from a high pressure area to a low pressure area, this causes air to move from the sea towards the land, forming a sea breeze.
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Local Winds: Land Breeze
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Quick Check
► Which time of the day do sea breezes occur?
► Which time of the day do night breezes occur?
► What if the place does not receive any sunlight throughout the day? What type of breeze would be dominant?
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Monsoon Winds
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Local Winds: Land Breeze
► During the night, the land cools down faster than the sea.
► As cool air sinks, a high pressure area is formed.
► Air over the sea is warmer as the sea loses heat slower.
► The warm air rises and forms a low pressure area.
► As air always moves from a high pressure area to a low pressure area, this causes air to move from the land towards the sea, forming a land breeze.
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Monsoon Winds
► Regional wind patterns that reverse direction seasonally. They bring about changes in the
precipitation level over the places that blow over.
► Two types in South East Asia Southwest monsoon: June and Sept Northeast monsoon: October and Feb
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Coriolis Effect
► What? It is the force produced by the Earth
as it rotates on its axis At the Equator, the Earth is moving at
over 1,500 km/hr
► Effect on winds Forces the winds moving from one
point to another to deflect or bend from their original path
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SE, SW Monsoon winds
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SE, SW Monsoon winds
► The Northern hemisphere experiences summer while the Southern hemisphere experiences winter between June and September.
► The land in Central Asia heats up, forcing the air to warm and rise, forming a low pressure region
► At the same time, the air over Australia cools and sinks, creating a high pressure region
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SE, SW Monsoon winds
► The difference in pressure results in winds blowing from Australia, towards Central Asia as the Southeast Monsoon winds.
► At the Equator, the Coriolis effect forces the Southeast Monsoon winds to deflect to the right, becoming the Southwest monsoon.
► The warm air picks up moisture as it travels over the Indian Ocean, bringing heavy rain to India during this period.
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SE, SW Monsoon winds
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Southwest Monsoon
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SW, SE Monsoon winds
N
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NE, NW Monsoon winds
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NE, NW Monsoon winds
► The northern hemisphere experiences winter while the Southern hemisphere experiences summer between December and February.
► The land in Australia heats up and rises, causing a low pressure area.
► However the air over Central Asia cools and sinks, causing a high pressure area.
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NE, NW Monsoon winds
► The difference in pressure results in winds blowing out from Central Asia, towards Australia, forming the Northwest Monsoon winds.
► At the Equator, the Coriolis effect forces the Northwest Monsoon winds to deflect to the right, becoming the Northeast monsoon.
► As it passes over the South China Sea, it picks up moisture, bringing heavy rain to many countries in South East Asia during this period.
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NE, NW Monsoon winds
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Northeast Monsoon
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NE, NW Monsoon winds
N
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PitStop 4Q3 to 5Geography Insights Pg. 94