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 (1 of 13) - wet-dry and monsoon climate

Introduction Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr (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

Introduction Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr (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

Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr (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 Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr (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 (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

Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr (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 (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

Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr (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 (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 (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

Natural Environments: The Atmosphere GE 101 – Spring 2007 Boston University Myneni L24: Low Latitude Climates Apr (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 Myneni L24: Low Latitude Climates Apr (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