Understanding South Asian Monsoons and Climate Patterns

Monsoons

A seasonal reversal of winds that bring either wetter or drier conditions.

ITCZ and Siberian High

Migration typically affecting south Asian monsoons.

Siberian High

In the winter, it causes air flow to occur at high clockwise, causing northeast winds to occur over South Asia.

Effect of Siberian High on South Asian Monsoons

When strong, it causes a drier winter; when weak, it allows for wetter seasons in South Asia.

ITCZ

During the summer, it extends northward, creating a thermal low, which is the Tibetan low.

Effect of ITCZ on South Asian Monsoons

As it shifts, it brings in rising air and abundant rainfall, allowing for monsoonal activity.

Tibetan Low

It acts as a heat source, allowing for circulation and moisture transfer, destabilizing the atmosphere.

Effect of Tibetan Low on South Asian Monsoons

It allows abundant moisture near coastal areas due to frequent cyclogenesis.

Himalayas and Western Ghats

They block cold air from the north, allowing for warmer air and producing orographic rain.

Indian Ocean Dipole

A climate pattern in the Indian Ocean where the difference in sea surface temperatures between eastern and western regions fluctuates.

Negative mode of Indian Ocean Dipole

Southwesterly winds break down, causing South Asia to be drier than usual, observed during an El Nino event.

Positive (normal) IOD mode

Brings humid air into Asia during the southwest monsoon; western Indian Ocean becomes warmer than normal.

El Nino year and positive IOD

Can strengthen monsoon winds and increase moisture.

La Nina years and positive IOD

Opposite occurs, weakening monsoon conditions.

Winter climate in India

Cool and dry due to high pressure and northeast winds, blocked by the Himalayas.

Mid-latitude cyclones in winter

A weak front created by the southern branch of westerly jets allows humidity from the Arabian Sea.

Winter maximum precipitation in mountainous areas

Due to orographic effects as mountains force moist air to rise and cool.

Spring climate in India

Details not provided in the notes.

Western polar front

A meteorological phenomenon causing hot and dry conditions due to its northward movement.

Thermal lows

Areas of low pressure near the southern tip of India that can cause convection but do not produce rain.

Summer climate in India

Hot and wet due to the shifting winds from the Siberian High and the movement of the polar front jet stream.

Summer maximum precipitation areas in India

Southern and Western sides of the peninsulas due to moisture from southwesterly countertrades.

Precipitation methods in India during summer

Includes air surges from the south, orographic effect, and monsoon lows caused by easterly waves and tropical cyclones.

Autumn precipitation causes in India

Mainly due to tropical cyclones as monsoon effects weaken with the retreat of the ITCZ.

Climate type in peninsular India

Aw, tropical Wet-dry.

Drying trend in northern India

Becomes drier from east to west due to southwest monsoon humid air cutting back over the Bay of Bengal.

Drying trend in southern India

Becomes drier from west to east due to humid Indian Ocean air moving southwest to northeast.

Central India dryness reason

Caused by the rain shadow of the Ghats and limited direct humid air.

Wettest areas in India

Southwest and northeast regions.

Major ocean currents causing gyres

Canary current, Benguela current, Agulhas current, Somali current, North Equatorial Current, South equatorial current, and equatorial countercurrents.

Canary current

Flows clockwise around the Bermuda-Azores High, creating a cold current that stabilizes the atmosphere.

Benguela current

Flows counterclockwise around the South Atlantic High, creating a cold current that leads to stable atmosphere and foggy conditions.

Agulhas current

Flows counterclockwise in the Southern Hemisphere, creating a warm ocean current.

Somali current

Flows northward along the coast of the Horn of Africa, creating a warm current.

North Equatorial Current

A significant ocean current affecting climate and weather patterns in the region.

South Equatorial Current

Flows east to west as part of southern hemisphere gyres, warm but not warmer than the rest of the water at those latitudes.

Equatorial Counter-Current

Flows from west to east and can slip in between the north and south equatorial currents.

Main Climate Type in Central Africa

'A', specifically Af, Am, and some Aw mainly in the northern and southern parts of the central regions.

Af Climates

Tropical rain forest with an average temperature of 70-72 degrees F and precipitation year-round but does not extend all the way eastward to the Indian ocean due to the rift zone blocking Indian Ocean moisture from the southeast Trade.

Humidity Source in 'A' Climate Areas

The counterclockwise flow around the southern part of the south Atlantic high produces enough westerly flow to give some humid air advection into Africa.

Walker Circulation

A large-scale atmospheric circulation pattern in the tropics, specifically over the Pacific Ocean, characterized by rising air over the western Pacific and sinking air over the eastern Pacific.

Walker Circulation during El Niño

During El Niño, this circulation weakens.

Walker Circulation during La Niña

During La Niña, this circulation strengthens.

Impact of Walker Circulation on Africa

By weakening the subtropical jets during ENSO impacting the Indian Ocean Dipole.

Walker Circulation and ENSO Events

The Walker Circulation plays a central role in the development and variability of El Niño and La Niña events by driving atmospheric and oceanic conditions across the equatorial Pacific.

Normal Conditions of Walker Circulation

Features strong easterly trade winds that push warm surface waters westward toward the western Pacific, causing upwelling of cooler, nutrient-rich waters in the eastern Pacific.

El Niño Event Effects

During an El Niño event, the Walker Circulation weakens or even reverses, leading to reduced trade winds and a shift of warm waters toward the central and eastern Pacific.

La Niña Event Effects

During a La Niña event, the Walker Circulation intensifies, strengthening trade winds and enhancing upwelling in the eastern Pacific.

Seasonal Rainfall Pattern in the Caribbean

The dry season (typically December to April) can lead to water scarcity and stress on agriculture and water supplies, while the wet season (May to November) brings risks of flooding and landslides, especially in mountainous areas.

Natural Hazards in the Caribbean Islands

Particularly vulnerable to climate and geography-related hazards.

Tropical Cyclones

Hurricanes that can cause devastating wind damage, flooding, and landslides in the Caribbean, particularly between June and November.

El Niño

A climate pattern that can cause droughts in the Caribbean, especially during certain years.

Trade Winds

Winds that bring moisture and influence rainfall patterns in the Caribbean.

Sea Surface Temperatures

Temperatures that impact humidity and precipitation in the Caribbean.

Topography

The physical features of the land that shape local rainfall distribution in the Caribbean islands.

Ocean-Atmosphere Interactions

Interactions, especially ENSO, that can cause droughts or heavy rains in the Caribbean.

Latitude

The geographical position of the Caribbean islands in the tropics, leading to high solar radiation year-round.

Orographic Rainfall

Rainfall that occurs on windward slopes of mountainous interiors, creating microclimates.

Tropical Climate (Aw)

Characterized by high temperatures year-round and distinct wet and dry seasons in the Caribbean islands.

Thermocline

The boundary between the warm surface water and the much colder water beneath it where temperature changes very abruptly in the ocean.

Walker Circulation

A circulation pattern that can cause a reversal of oceanic directions during certain events.

South Pacific Convergence Zone (SPCZ)

A region that is not really a front due to insufficient contrast between air masses.

SPCZ Movement

The SPCZ moves due to ENSO events.

SPCZ Diagonal Path

The SPCZ runs diagonally due to the convergence of Australian high winds and South Pacific High winds.

SPCZ Rainfall

The SPCZ causes more rain to occur near the South Pacific islands.

SPCZ Path

Runs diagonally from Papua New Guinea to New Zealand and fluctuates like a swinging gate.

Climate Associated with SPCZ

A persistent band of cloudiness and storms that moves north and east during ENSO events and south and west during La Niña events.

Antarctic Circumpolar Current (West Wind Drift)

Flows near the surface of the ocean from west to east, preventing warmer water from infiltrating into Antarctica's coastal areas.

Antarctic Bottom Water

A large mass of deep, cold water at the bottom of the Southern Ocean with higher oxygen content due to less oxidation of decaying matter.

Antarctic Deep Water

Moves on top of the bottom water, flowing northward and upwards to eventually reach the North Atlantic deep water.

Tropical Rainforest Climate (Af)

Found in regions like the Amazon Basin, Congo Basin, and Southeast Asia, influenced by ITCZ shifts and Monsoonal effects.