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Traditional terminology Arabic word mausim meansseason Loose definition: a wind/precipitation pattern that shifts seasonally Classical criteria (Ramage.

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Presentation on theme: "Traditional terminology Arabic word mausim meansseason Loose definition: a wind/precipitation pattern that shifts seasonally Classical criteria (Ramage."— Presentation transcript:

1 Traditional terminology Arabic word mausim meansseason 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% Speed of mean wind exceeds 3 m/s Pressure patterns satisfy a steadiness criterion Classical Example: Indian Monsoon

2 Other Examples North American West African African Winter (Indian Summer) East Asian N.W. Australian N. H. Summer N. H. Winter

3 Surface temperature range that results in the monsoon Kump et al. text (2004) Sea surface temperature variations are much smaller than land surface temperature variations. (Mainly the seasonal cycle) Tibetan plateau: range of 60°C Ocean: range of 3 to 5°C

4 Monsoon schematic Wallace and Hobbs textbook (1977)

5 Combined Monsoon System (Webster et. al. 1988)

6 Orography (Webster et. al. 1988)

7 Upper Tropospheric Temperature JJA DJF

8 Upper Tropospheric Temperature Seasonal Variation July 30 N 90 E 110 W Dec Jan 90 E

9 250 mb Zonal Wind (JJA) Wind Upper Trop Temp

10 250 mb Zonal Wind (DJF) Wind Upper Trop Temp

11 Vertical Motions (Webster et. al. 1988)

12 Meridional Circulation, 90E (Yanai et. al.)

13 June-August winds Dec-Feb winds (SW monsoon) (NW monsoon) SW monsoon winds Trade winds NE monsoon winds

14 Meridional Wind Jan July 5N 925 mb 5N 5N

15 Zonal Wind (JJA) Wind up to 100 mb (0-120 E) (0-40 E)

16 3-d View (Webster et. al. 1988)

17 Outgoing Longwave Radiaton DJF SON JJA SON DJF MAM

18 Indian Monsoon - Rainfall 1963, 71

19 Indian Monsoon - Interannual Variability -1

20 Indian Monsoon - Interannual Variability -2

21 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 days (*) Apparently anti-correlated with El Nino

22 MJO-mature

23 (material from second Webster chapter not included here)

24 North American Monsoon -1

25 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 atmosphere" (Late June - Early September)

26 Burst and Break Burst 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 Late June - Early September

27 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.

28 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.

29 North American Monsoon - rainfall

30 July 500 mb height High Anticyclonic circulation around High involves flow from Gulfs of California and Mexico into Northwest Mexico and Southwest US

31 500 mb heights: May, August, October May August October High

32 North American Monsoon - setup and decay


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