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Arabic word “mausim” means“season” “Traditional” terminology Loose definition: a wind/precipitation pattern that shifts seasonally Classical criteria (Ramage 1971) Prevailing wind shifts 120 o between Jan & July Average frequency of prevailing wind > 40%

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traditional terminology

Arabic word “mausim” means“season”

“Traditional” terminology

Loose definition: a wind/precipitation pattern

that shifts seasonally

Classical criteria (Ramage 1971)

Prevailing wind shifts 120o between Jan & July

Average frequency of prevailing wind > 40%

Speed of mean wind exceeds 3 m/s

Pressure patterns satisfy a steadiness criterion

Classical Example: Indian Monsoon

other examples

N. H. Summer

Other Examples

North American

West African

African Winter

(Indian Summer)

East Asian

N.W. Australian

N. H. Winter

surface temperature range that results in the monsoon

Tibetan plateau: range of 60°C

Ocean: range of 3 to 5°C

Surface temperature range that results in the monsoon

Sea surface temperature variations are much smaller than land surface temperature variations. (Mainly the seasonal cycle)

Kump et al. text (2004)

monsoon schematic
Monsoon schematic

Wallace and Hobbs textbook (1977)

250 mb zonal wind jja
250 mbZonal Wind(JJA)





250 mb zonal wind djf
250 mbZonal Wind(DJF)





june august winds dec feb winds sw monsoon nw monsoon

Trade winds

June-August winds Dec-Feb winds(SW monsoon) (NW monsoon)

SW monsoon winds

NE monsoon winds

meridional wind



Meridional Wind

925 mb

5N -

925 -



925 mb

5N -

925 -

zonal wind jja
Zonal Wind(JJA)

Wind up to 100 mb

(0-120 E)

(0-40 E)

outgoing longwave radiaton
Outgoing Longwave Radiaton







madden julian oscillation

(*) Eastward progression of regions of both enhanced

and suppressed tropical rainfall,

mainly over the Indian Ocean and Pacific Ocean.

(*) Anomalous rainfall is usually first evident over

the western Indian Ocean; propagates over

warm western and central tropical Pacific.

(*) Pattern of tropical rainfall weakens/disappears

over the cooler waters of the eastern Pacific;

reappears over the Atlantic and Indian Ocean.

(*) Each cycle lasts approximately 30-60 days

(*) Apparently anti-correlated with El Nino

Madden-Julian Oscillation

north american monsoon description

(Late June - Early September)

North American Monsoon - description

* Summer daytime heating over the Sonoran Desert of Mexico and

Arizona forms large surface low-pressure cell over the region,

* The low draws moist tropical air from the Gulfs of California and Mexico,

triggering thunderstorms as it is lifted by the mountains and solar heating.

* The monsoonal circulation does not produce thunderstorms every day but

rather occurs in a pattern that has "bursts" and "breaks:"

Burst: A movement of a weak trough in the upper level westerly wind

into the southwest U.S. which spreads upper level cold air into the region. In

the lower levels of the atmosphere, strong surface heating and southerly winds

transport moisture into the region, creating unstable conditions and leading

to widespread thunderstorm outbreaks.

"Break: An enhanced ridging of the Pacific subtropical High Pressure

moves inland, effectively cutting off the moisture flow and stabilizing the


burst and break

Late June - Early September

Burst and Break



weak disturbances in the upper atmosphere act to focus thunderstorm activity over the 4 corners

for a period of a few days to more than a week

more on the north american monsoon

More on the North American Monsoon

On a typical Arizona Monsoon day, thunderstorms initially develop I

n the early afternoon over the higher mountains and the Mogollon

Rim. Rain-cooled air from these thunderstorms descends from the

high country and into the desert. Acting like a cold front, this

mesoscale outflow induces the hot desert air to rise, again

producing thunderstorms. Over the higher deserts, they usually

occur during the mid to late afternoon, while over the lower deserts

storm activity is most common during the late afternoon and

evening. Generally, thunderstorm activity ceases around midnight.

north american monsoon more description

North American Monsoon - more description

During the monsoon season, the region receives most of its

annual precipitation, approximately 35 to 45 percent for Arizona

and New Mexico and 60 percent for northern Mexico.

For example, Acapulco rainfall totals 51.8 inches June-October

(more than 9 inches each month except October), while only

3.3 inches falls during the rest of the year.

july 500 mb height
July 500 mb height


Anticyclonic circulation around High involves flow from Gulfs

of California and Mexico into Northwest Mexico and Southwest US