Outline

Further Reading: Chapter 10 of the text book

- wet tropical climate

- coastal trade wind climate

- dry tropical climate

Natural Environments: The AtmosphereGG 101 – Spring 2005

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MyneniL25: Low Latitude Climates

Apr-04-05(1 of 13)

- wet-dry and monsoon climate

Introduction

Natural Environments: The AtmosphereGG 101 – Spring 2005

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MyneniL25: Low Latitude Climates

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• Continuing,

– We want to look at low-latitude climates– Lie between the tropics of Cancer and Capricorn – Tend to be uniformly warm– Principally differentiated by variations in precipitation

Introduction

Natural Environments: The AtmosphereGG 101 – Spring 2005

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MyneniL25: Low Latitude Climates

Apr-04-05(3 of 13)

– The circulation in the region is dominated by the Hadley Cell• ITCZ and tropical low-pressures• Subtropical High• Easterly trades

– Low variability in temperature• High temperatures: near equator• Low seasonality: near equator

– High variability in precipitation• Humid: ITCZ• Desert/Arid: Subtropical high• Strong seasonality between the two as the ITCZ shifts north and south

– Creates 4 main climate regimes

– Wet Equatorial Regime– Coastal Trade-wind Regime– Wet-Dry and Monsoon Regime– Dry Tropical Regime

Natural Environments: The AtmosphereGG 101 – Spring 2005

Boston University

MyneniL25: Low Latitude Climates

Apr-04-05(4 of 13)

ITCZ

Wet Equatorial Climate-1

– Located under the ITCZ from 10N-10S– Two characteristic air masses (warm and moist)

• mT• mE

Natural Environments: The AtmosphereGG 101 – Spring 2005

Boston University

MyneniL25: Low Latitude Climates

Apr-04-05(5 of 13)

Wet Equatorial Climate-2

– Dominated by uniform temperature and precipitation– Precipitation is supplied by tropical convection (>250 cm/yr)

– High temperature due to proximity to equator– Predominant vegetation type is rainforests

Natural Environments: The AtmosphereGG 101 – Spring 2005

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MyneniL25: Low Latitude Climates

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Coastal Trade Wind Climate-1

Trade WindsSubtropical High

Subtropical High

ITCZSubtropical High

Subtropical High

ITCZ

– Located along narrow belts on the coasts (5-25N)– Persistent precipitation supplied by orographic lifting as easterlies flow over

the coasts– In addition these regions are strongly influenced by the presence of tropical

cyclones

Natural Environments: The AtmosphereGG 101 – Spring 2005

Boston University

MyneniL25: Low Latitude Climates

Apr-04-05(7 of 13)

Coastal Trade Wind Climate-2

– Precipitation influenced by trade-winds– Temperature is persistently warm, although there is summer seasonality due to changes

in insolation– Also note that there is a break in the precipitation due to the southerly movement of

the subtropical high– Predominant vegetation type is also rainforests

Natural Environments: The AtmosphereGG 101 – Spring 2005

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MyneniL25: Low Latitude Climates

Apr-04-05(8 of 13)

Wet-Dry and Monsoon Climates-1

HL

LH

– Located between equatorial and subtropics– 5° to 20° N and S in Africa and the Americas, and at 10° to 30° N in Asia – Strongly influenced by the movement of the ITCZ

• Summer: ITCZ moves north and the weather is dominated by convective precipitation and mT,mE air

• Winter: ITCZ moves south and the weather is dominated by the sub-tropical high, cT air– Technically, ‘wet-dry’ region is in the continental interior while ‘monsoon’ region is closer to the

coasts

Natural Environments: The AtmosphereGG 101 – Spring 2005

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MyneniL25: Low Latitude Climates

Apr-04-05(9 of 13)

Wet-Dry and Monsoon Climates-2

– Temperature is persistently warm, although there is summer seasonality due to changes in insolation

– Note the strong seasonality in precipitation• Wet-dry region dominated by precipitation associated with the ITCZ• Monsoon region dominated by precipitation associated with winds coming off the

ocean (hence the relation to coastal wind regime)

Natural Environments: The AtmosphereGG 101 – Spring 2005

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MyneniL25: Low Latitude Climates

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Wet-Dry and Monsoon Climates-3

Dominant vegetation type is savanna, open grassland

Natural Environments: The AtmosphereGG 101 – Spring 2005

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MyneniL25: Low Latitude Climates

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Dry Tropical Climate-1

Subtropical High

Subtropical High

– Located poleward of the wet-dry region (15-25N)– Strongly influenced by the subtropical high

• Associated with the descending limb of the Hadley circulation• Produces clear sky, warm stable air

– Two subtypes• Western litteral - west coasts of Africa and S. America where cold-air reinforces the atmospheric stability

-> very dry• Semi-Arid - transition between dry tropical and wet-dry tropics

– Very short rainy season which sometimes doesn’t come for years

Natural Environments: The AtmosphereGG 101 – Spring 2005

Boston University

MyneniL25: Low Latitude Climates

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Dry Tropical Climate-2

– Moderate range in temperature due to changes in declination– Persistently low precipitation– Dominant vegetation type is shrubland

Natural Environments: The AtmosphereGG 101 – Spring 2005

Boston University

MyneniL25: Low Latitude Climates

Apr-04-05(13 of 13)

Summary

• Overall there is a fairly simple set of controls– Temperature is controlled by distance from equator

• Generally warm everywhere• Higher seasonality as one moves away from the equator

– Precipitation is dominated by 4 factors• ITCZ - wet equatorial regime• Sub-tropical high - Dry tropical regime• Easterly trade winds - trade wind regime• Seasonal shift in ITCZ - wet-dry and monsoon regime

– Could also define by variability in precipitation• Low variability - wet equatorial and trade-wind regime• Moderate variability - wet-dry and monsoon regime• High variability - dry tropical regime