African easterly waves (AEWs) are areas of low air pressure that move westward across North Africa and into the Atlantic Ocean. AEWs can cause intense thunderstorms, and, once over the warm waters of the Atlantic Ocean, they may become tropical cyclones that might affect the Caribbean and North America. In summer, many AEWs form in, or move through, the West African Monsoon (WAM), a seasonal shift in winds and rain that causes most of the rainfall in the region. AEWs change intensity during the summer season (called “intraseasonal cycles”), and these changes are important for farming in Africa and for tropical cyclones in the Atlantic Ocean. Most intraseasonal cycles in the tropics are associated with the Madden-Julian oscillation (MJO), a pulse of winds, clouds and rainfall that moves eastward around the world near the equator every 30 to 60 days. It was believed that the MJO controlled intraseasonal cycles of the WAM, including AEWs. The authors used a new technique in the Weather Research and Forecasting (WRF) Model to block the MJO and its impacts from reaching Africa.
Satellite imagery showing thunderstorms that form with AEWs (circled) moving westward across Africa into the Atlantic Ocean.
- The MJO is not necessary for intraseasonal cycles of the WAM, including AEWs.
- Even though the MJO is not necessary for these intraseasonal cycles, it is important for the pacing of AEW activity.
You can read the paper at http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0750.1.