Lec1 monsoon

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

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





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




July SLP




January SLP



July



SLP

Wind



Surface Wind: JanuaryQuickTime™ and aTIFF (Uncompressed) decompressor


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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are needed to see this picture.From:http://snrs.unl.edu/amet351/ogren/monsoons.html

SW monsoon

NE monsoon

The Current system of the Indian Ocean

From:Tomczak, Matthias & J Stuart Godfrey: Regional Oceanography:



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

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)



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



Wet 50-60s,

Dry 70-90s

Warmer SST Weaker monsoon

Global warming Dryer ??

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