Outline

1. 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 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 Introduction

3. 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 Located under the ITCZ from 10N-10S Two characteristic air masses (warm and moist) mT mE Wet Equatorial Climate-1 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 (>250 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 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 Coastal Trade Wind Climate-1 Trade Winds

7. 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

8. 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 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 L H H L

9. 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) 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

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. 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 Myneni L24: Low Latitude Climates Apr-21-07 (11 of 13) Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University 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. 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) Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Summary