1. African Monsoon Wassila M. Thiaw NOAA/ Climate Prediction Center 21 February 2012 CPC International Desks Training Lecture Series

2. Outline Forcing of the annual cycle –Sea Surface Temperature (SST) –Sea Level Pressure (SLP) –Wind –Precipitation Convergence Zones African Monsoon

3. SST: Major Features Atlantic Warm Pool Pacific Warm PoolEquatorial Cold Tongues

4. SST: Extremes in the Annual Cycle Equatorial SSTs are warmest in April Equatorial cold tongues are strongest in Jul.-Oct.

5. SST: Seasonal Cycle

6. Sea Level Pressure Largest annual cycle over the Northern Hemisphere Southern Hemisphere displays weaker annual cycle

7. Annual Range in SLP (hPa) Large annual range: Mongolia/China Aleutian Islands Iceland Southern Africa Australia South America

8. SLP: Major NH Features H H H H H L L H HHH L L H High pressure dominates continental areas (Asia, North America, Europe) during the NH winter, while low pressure is observed over the North Pacific (near the Aleutian Islands) and North Atlantic (near Iceland). Low pressure dominates continental areas (Asia and Africa) during the NH summer, while high pressure is observed over the eastern North Pacific and central North Atlantic.

9. H H H H H L L H HHH L L H SLP: Major SH Features High pressure dominates continental areas (South America and Africa) during the SH summer, while low pressure is observed over the subtropical and lower mid-latitude oceanic areas. High pressure dominates continental and oceanic regions in the subtropics and lower-mid-latitudes during the SH winter.

10. Global precipitation analyses based on station data and satellite-derived estimates Greatest precipitation over warm surfaces where ample moisture is available, and in areas of mid-latitude storm activity –Tropical land masses –Intertropical Convergence Zones (ITCZs) –South Pacific Convergence Zone (SPCZ) –South Atlantic Convergence Zone (SACZ) –Mid-latitude winter storm tracks Precipitation: Major Features

11. Least precipitation in regions lacking moisture or featuring pronounced subsidence, and in colder regions –Equatorial cold tongues –Deserts –Subtropical high pressure systems –High latitudes

12. Precipitation: Major Features IOCZ SPCZ ITCZ SACZ Storm Tracks

13. Precipitation: July

14. Monsoons Seasonally varying winds Typical monsoon regions include: –Asia –Africa –South America –Central America/ North America

15. CDAS Low level, 850 hPa geopotential heights DJF 1979-2008 Atmospheric Circulation

16. Subtropical highs CDAS Low level, 850 hPa geopotential heights DJF 1979-2008

17. Thermal lows CDAS Low level, 850 hPa geopotential heights DJF 1979-2008

18. Low level, 850 hPa geop. heights & winds DJF 1979-2008

19. Is this dynamics similar to anywhere else? South America is the closest analog …

20. Low level, 850 hPa geop. heights & winds DJF 1979-2008

21. What is the relationship between the large- scale circulation and the precipitation climatology?

22. Precipitation Climatology DJF 1981-2010 PREC/L CMAP SACZ) SICZ

23. Boreal summer: June-July-August

24. Latitude-Height Cross Section (V;W) 5E 1979- 2010 Northward low-level flow onto Guinean coast extends well into 20N Southward flow Divergence center over continental thermal low (Saharan High) Meridional divergence associated with southward velocity near 15N Eastward Coriolis force generates African Easterly Jet (AEJ) near 600 hPa Southward outflow over Region of deep convection near 5N extends Tropical Easterly Jet (TEJ) near 200 hPa TEJ AEJ Shading indicates meridional wind speed Thick white line indicates zero meridional velocity contour Deep Convective System

25. Longitude-Height Cross Section (U;W) Eq. 1979- 2010 Shading indicates vertical wind speed Thick white line denotes zero vertical velocity contour Rising motion in association with Congo rain forest Subsidence over the Gulf of Guinea

26. Indian Monsoon West African Monsoon Somali Jet Reanalysis 1 Low level, 925 hPa geop. heights & winds, JAS 1979-2008 Somali Jet Likely the strongest and most Sustained low-level wind patterns in the world Accounts for 65% of global cross equatorial mass flux Links African and Asian rainfall systems

27. Is there an analog for this system? Maybe South America again? No …

28. Low level, 925 hPa geop. heights & winds, JAS 1979-2008

29. Somali Jet Characteristics Also called the East African Jet (EAJ) or Findlater Jet Likely the strongest and most sustained low-level wind patterns in the world (mean maximum wind speeds of 25 m/s – observed up to 50 m/s) Low-level wind speed maximum at 1.5 km msl Accounts for 65% of global cross equatorial mass flux Links African and Asian rainfall systems

30. Mid level, 600 hPa geop. heights & winds, JAS 1979-2008 Saharan high African Easterly jet

31. Indian monsoon upper-level high Tropical Easterly Jet Upper level heights and winds 200 hPa JAS

32. Precipitation Climatology JAS 1981-2010 PREC/L CMAP Dry Summer in East Africa

33. The transition (equinox) seasons bring most rainfall to East Africa Long rains in spring Short rains in fall

34. East Africa Annual Cycle Precipitation & 850 hPa Wind1981-2010

35. East Africa Annual Cycle Precipitation & 850 hPa Wind1981-2010

36. African Monsoon: Prominent features and Evolution West African Monsoon – NH Summer –Extension of the Asian low –Continental thermal low –Low level southwesterly flow –African Easterly Jet –Tropical Easterly Jet Southern Africa –Angola low –Interactions between mid-latitude and tropical systems East Africa –ITCZ –Transitional equinox spring and autumn seasons –Long rains in MAM –Short rains in OND