May 22 - July 28
Connecting African Easterly Wave Development and Offshore Precipitation
Patrick Thornton, Shun-Nan Wu, and Naoko Sakaeda
What is already known:
- African Easterly Waves (AEWs) have a large effect on weather in Cabo Verde, including the island of Sal
- Climatological precipitation around West Africa maximizes just offshore Guinea
- Mesoscale Convective Systems associated with AEWs bring heavy rains with them
What this study adds:
- Northerly winds on Sal due to approaching AEWs are associated with higher rainfall amounts closer to the Intertropical Convergence Zone (ITCZ)
- Southerly winds on Sal due to leaving AEWs are associated with higher rainfall amounts right along the coast of West Africa
- While AEWs shift the location of rainfall, the amount of rainfall in each region is only weakly explained by the strength of AEWs.
Abstract:
Meridional wind data from radiosondes launched from the island of Sal, Cabo Verde is used to connect African Easterly Wave development and precipitation near coastal West Africa. We utilize the direction of meridional wind to identify the relative position of the waves to Sal. We find that on days with northerly winds, rainfall is enhanced to the south and west, near the inter-tropical convergence zone. On days with southerly winds, precipitation is enhanced in the coastal region and sparse to the southwest. Based on these results, we define two regions, one right on the West African coast, and a second further south and west, towards the Intertropical Convergence Zone to compare the amount of precipitation in these regions with the meridional wind magnitude associated with the AEWs at the Sal Island. We find that there is little relationship between meridional wind strength and precipitation amounts, although there is a slight tendency for more coastal precipitation when southerly winds are stronger on Sal, and more Intertropical Convergence Zone precipitation when northerly winds are stronger on Sal. These findings emphasize the importance of the location of AEWs when forecasting, especially considering how precipitation distribution is dependent on it.