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Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr-21-07 (1 of 13) Further Reading: Chapter 10 of the text book Outline - wet tropical climate - coastal trade wind climate - wet-dry and monsoon climate - dry tropical climate Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr-21-07 (2 of 13) 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 Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr-21-07 (3 of 13) Introduction – The circulation in the region is dominated by the Hadley Cell • ITCZ and tropical low-pressures • Subtropical Highs – Wet Equatorial Regime • Easterly trades – Coastal Trade-wind Regime – Low variability in temperature • High temperatures: near equator – Wet-Dry and Monsoon Regime • Low seasonality: near equator – Dry Tropical Regime – 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 Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr-21-07 (4 of 13) Wet Equatorial Climate-1 – Located under the ITCZ from 10N-10S – Two characteristic air masses (warm and moist) • mT • mE ITCZ Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr-21-07 (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 Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr-21-07 (6 of 13) 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 Subtropical High Subtropical High ITCZ ITCZ Subtropical High Subtropical High Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr-21-07 (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 Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr-21-07 (8 of 13) 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 H L H L Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr-21-07 (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 Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr-21-07 (10 of 13) Wet-Dry and Monsoon Climates-3 Dominant vegetation type is savanna, open grassland Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University – – – Myneni L24: Low Latitude Climates Apr-21-07 (11 of 13) Located poleward of the wet-dry region (15-25N) Dry Tropical Climate-1 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 Subtropical High Subtropical High Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr-21-07 (12 of 13) Dry Tropical Climate-2 – Moderate range in temperature due to changes in declination – Persistently low precipitation – Dominant vegetation type is shrubland 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 Myneni L24: Low Latitude Climates Apr-21-07 (13 of 13)