o level - weather & climate - factors affecting air pressure and wind

Weather & Climate

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

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

Barometer

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)

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

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

Anemometer & Wind Vane

PitStop 4Q1 & 2

Local Winds: Sea Breeze

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.

Local Winds: Land Breeze

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?

Monsoon Winds

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.

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

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

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


► 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.

Southwest Monsoon

SW, SE Monsoon winds

N

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.


► 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.

Northeast Monsoon


N

PitStop 4Q3 to 5Geography Insights Pg. 94

o level - weather & climate - factors affecting air pressure and wind

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