Outline

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Myneni L24 Low Latitude Climates Apr-21-07 (1
of 13)
Natural Environments The Atmosphere GE 101
Spring 2007 Boston University
Further Reading Chapter 10 of the text book
Outline
- wet tropical climate
- coastal trade wind climate
- wet-dry and monsoon climate
- dry tropical climate
2
Myneni L24 Low Latitude Climates Apr-21-07 (2
of 13)
Natural Environments The Atmosphere GE 101
Spring 2007 Boston University
Introduction

• Continuing,
• We want to look at low-latitude climates
• Lie between the tropics of Cancer and Capricorn
  (about 23S to 23N)
• Tends to be uniformly warm
• Principally differentiated by variations in
  precipitation

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Myneni L24 Low Latitude Climates Apr-21-07 (3
of 13)
Natural Environments The Atmosphere GE 101
Spring 2007 Boston University
Introduction

• The circulation in the region is dominated by the
  Hadley Cell
• ITCZ and tropical low-pressures
• Subtropical Highs
• 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

4
Myneni L24 Low Latitude Climates Apr-21-07 (4
of 13)
Natural Environments The Atmosphere GE 101
Spring 2007 Boston University
Wet Equatorial Climate-1

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

ITCZ
5
Myneni L24 Low Latitude Climates Apr-21-07 (5
of 13)
Natural Environments The Atmosphere GE 101
Spring 2007 Boston University
Wet Equatorial Climate-2

• Dominated by uniform temperature and
  precipitation
• Precipitation is supplied by tropical convection
  (gt250 cm/yr)
• High temperature due to proximity to equator
• Predominant vegetation type is rainforests

6
Myneni L24 Low Latitude Climates Apr-21-07 (6
of 13)
Natural Environments The Atmosphere GE 101
Spring 2007 Boston University
Coastal Trade Wind Climate-1

• 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

Trade Winds
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Myneni L24 Low Latitude Climates Apr-21-07 (7
of 13)
Natural Environments The Atmosphere GE 101
Spring 2007 Boston University
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

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Myneni L24 Low Latitude Climates Apr-21-07 (8
of 13)
Natural Environments The Atmosphere GE 101
Spring 2007 Boston University
Wet-Dry and Monsoon Climates-1

• 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 masses
• 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

L
H
H
L
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Myneni L24 Low Latitude Climates Apr-21-07 (9
of 13)
Natural Environments The Atmosphere GE 101
Spring 2007 Boston University
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)

10
Myneni L24 Low Latitude Climates Apr-21-07 (10
of 13)
Natural Environments The Atmosphere GE 101
Spring 2007 Boston University
Wet-Dry and Monsoon Climates-3
Dominant vegetation type is savanna, open
grassland
11
Myneni L24 Low Latitude Climates Apr-21-07 (11
of 13)
Natural Environments The Atmosphere GE 101
Spring 2007 Boston University

• 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 -gt very dry
• Semi-Arid - transition between dry tropical and
  wet-dry tropics
• Very short rainy season which sometimes doesnt
  come for years

Dry Tropical Climate-1
12
Myneni L24 Low Latitude Climates Apr-21-07 (12
of 13)
Natural Environments The Atmosphere GE 101
Spring 2007 Boston University
Dry Tropical Climate-2

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

13
Myneni L24 Low Latitude Climates Apr-21-07 (13
of 13)
Natural Environments The Atmosphere GE 101
Spring 2007 Boston University
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