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

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

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

SST: Seasonal Cycle

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

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

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.

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.

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

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

Precipitation: Major Features IOCZ SPCZ ITCZ SACZ Storm Tracks

Precipitation: July

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

CDAS Low level, 850 hPa geopotential heights DJF Atmospheric Circulation

Subtropical highs CDAS Low level, 850 hPa geopotential heights DJF

Thermal lows CDAS Low level, 850 hPa geopotential heights DJF

Low level, 850 hPa geop. heights & winds DJF

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

Low level, 850 hPa geop. heights & winds DJF

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

Precipitation Climatology DJF PREC/L CMAP SACZ) SICZ

Boreal summer: June-July-August

Latitude-Height Cross Section (V;W) 5E 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

Longitude-Height Cross Section (U;W) Eq 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

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

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

Low level, 925 hPa geop. heights & winds, JAS

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

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

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

Precipitation Climatology JAS PREC/L CMAP Dry Summer in East Africa

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

East Africa Annual Cycle Precipitation & 850 hPa Wind

East Africa Annual Cycle Precipitation & 850 hPa Wind

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