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Monsoon ClimatePart1W4930
Earth’s oceans and atmosphere
03/24/05Chie Ihara
• What is monsoon?• Where can we see monsoons?• Why are monsoons important?• What is the physical mechanism of monsoon?• Examples: Asian monsoon, North American monsoon, West African monsoon • Can we predict monsoons?
‘A name for a wind system that changes in speed and direction with season.’ (derived from an Arab word)
What is monsoon?
Surface Wind: January
July
Where?
•Asian monsoon
•Australian monsoon
•North American monsoon
•African monsoon
Asian-Australian monsoon
Cold season: Dry winds blow from land to ocean
Warm season: Wet winds blow from ocean to land transport moisture large rainfall
Why are monsoon rainfalls important? water management, disaster mitigation, agricultural efficiency
e.g.) Asian monsoonsAbout 60% of the world’s population depends on monsoon
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e.g.) Asian monsoons (India)•8.2 % economic growth in the year ending 2004 March with the help of the good monsoon •5.5-6.5% in this year’s growth because of the late onset of monsoon last summer. (Asian Development Bank)•Onset, extent and overall amount of monsoon rainfall play a key role
Relationship between Indian rice production and Indian monsoon rainfall
(Webster et al. 1998)
Mechanisms of monsoon1. Difference in heat capacity of land and ocean
Mechanisms of monsoon
Temperatures over oceans do not change as much as over lands January Surface Air Temperature
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July Surface Air Temperature
Large differences occur over the continents and smaller ones over the oceans- an indication of the heat capacity of the surface
Difference between the January and July surface temperature
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Mechanisms of monsoon
July SLP
Mechanisms of monsoon
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January SLP
Mechanisms of monsoon
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July
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SLP
Wind
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Surface Wind: JanuaryQuickTime™ and aTIFF (Uncompressed) decompressor
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SLP
Wind
Ocean Land
H L
Warm season
~ Gigantic land-sea breeze ~
HL
cold warm
wet
Chen et al. 2002
Cold season
Ocean Land
HL
H L
warm cold
dry
Chen et al. 2002
Examples of monsoons
1. Asian monsoon : the largest monsoonIndia, Sri Lanka, Bangladesh, Indonesia and etc
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SW monsoon
NE monsoon
The Current system of the Indian Ocean
From:Tomczak, Matthias & J Stuart Godfrey: Regional Oceanography:
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History of Indian summer monsoon rainfall prediction
Motivated by the Great Indian Drought of 1877, the India Meteorological Department is established in 1875 for the seasonal forecast of Indian monsoon rainfall. In the early part of the 20th century, Sir Gilbert Walker studied the global teleconnections of monsoon for the monsoon rainfall prediction, which led him to the discovery of Southern Oscillation. .
From:http://www.met.rdg.ac.uk/cag/MOL/Introduction/frameindex.html
The factors influencing interannual variability Indian summer monsoon rainfall
• Himalayan snow cover more snow higher albedo less ∆T weaker monsoon• Soil moisture more moisture less ∆T weaker monsoon• ENSO• ?• ?
2. North American monsoon ~ Southwest United States monsoon ~ Mexican monsoon ~ Arizona monsoon
Increase in rainfall during summer over the dry regions about 35% of Arizona's annual precipitation about 45% of New Mexico's annual precipitation, about 60% of northern Mexico’s annual precipitation
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Seasonal distribution of precipitation across southwesternNorth America. Note that northwestern Mexico shows thestrongest monsoon signal, which diminishes through Arizona,New Mexico, and Nevada. Northeastern Mexico and Texasdisplay early summer–late fall precipitation peaks, while the WestCoast has a dry summer Mediterranean distribution (vertical axisof all graphs represents 180 mm with 20 mm increments). Areassouth of the broken line receive greater than 50% of their annualrainfall in July, August, and September (after Douglas et al. 1993).
Mid-to late summer rainfall max following extremely dry condition
Vertical cross sectionWarm season
Predictability
Monsoon rainfall :
Important water resources
Hazards(storms)
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USA today 06/25/2004The North American Monsoon Experiment, announced Friday, is getting underway this month to help better understand the weather in northwest Mexico and the southwestern United States…
Monsoon influenced thunderstorm
3. West African monsoon
Precipitation SST
JuneAugust
Interannual variability of African monsoon
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Wet 50-60s,
Dry 70-90s
Warmer SST Weaker monsoon
Global warming Dryer ??