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African Monsoon

African Monsoon. Wassila M. Thiaw NOAA/ Climate Prediction Center 21 February 2012. CPC International Desks Training Lecture Series. Outline. Forcing of the annual cycle Sea Surface Temperature (SST) Sea Level Pressure (SLP) Wind Precipitation Convergence Zones African Monsoon.

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African Monsoon

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  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 Pool Equatorial 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 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). H L H L H H H 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. H L H L H H H

  9. 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. H L H L H H H High pressure dominates continental and oceanic regions in the subtropics and lower-mid-latitudes during the SH winter. H L H L H H H

  10. Precipitation: Major Features • 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

  11. Precipitation: Major Features • 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 Storm Tracks ITCZ SPCZ SACZ IOCZ

  13. Precipitation: July

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

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

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

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

  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 SICZ SACZ)

  23. Boreal summer: June-July-August

  24. Latitude-Height Cross Section (V;W) 5E 1979-2010 TEJ • Southward outflow over • Region of deep convection • near 5N extends Tropical • Easterly Jet (TEJ) near • 200 hPa Deep Convective System • 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 AEJ Northward low-level flow onto Guinean coast extends well into 20N Southward flow Shading indicates meridional wind speed Thick white line indicates zero meridional velocity contour

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

  26. Low level, 925 hPa geop. heights & winds, JAS 1979-2008 Reanalysis 1 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 Indian Monsoon West African Monsoon Somali Jet

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

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

  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

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