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

2. Introduction Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr-21-07 (2 of 13) 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

3. Introduction Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr-21-07 (3 of 13) –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. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr-21-07 (4 of 13) ITCZ Wet Equatorial Climate-1 –Located under the ITCZ from 10N-10S –Two characteristic air masses (warm and moist) mT mE

5. 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

6. 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 Trade Winds –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

7. 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

8. 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 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 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

9. 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)

10. 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

11. Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr-21-07 (11 of 13) Dry Tropical Climate-1 –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

12. 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

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