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

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

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

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.

SE, SW Monsoon winds

Southwest Monsoon

SW, SE Monsoon winds

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NE, NW Monsoon winds

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.

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.

NE, NW Monsoon winds

Northeast Monsoon

NE, NW Monsoon winds

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