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Publication Date
16 June 2021

Anthropogenic Influences on the African Easterly Jet – African Easterly Wave System

Subtitle
Future climate change increases the number and strength of African easterly waves.
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Count per 150 km box of the May-October 2001-2010 African easterly wave tracks from the (a) ERA5 reanalysis, and the Weather Research and Forecasting tropical channel model (b) historical, (c) late-century, and (d) late-century minus historical.
Science

The African easterly jet (AEJ) and African easterly waves (AEWs) are important features of the summertime atmospheric circulation over North Africa. The AEJ and AEWs can have both local and far-reaching effects on weather. Specifically, AEWs have been shown to serve as precursors to tropical cyclones that develop in the Atlantic Ocean. It is therefore important to understand the effects of climate change on AEWs, as changes to the AEWs will affect tropical cyclone development. This research shows that in the future climate, AEWs will increase in number and in strength.

Impact

Better understanding of the future of AEWs will help our understanding of how climate change may affect tropical cyclone development. Although there are many factors that contribute to the development of tropical cyclones, a change in the frequency and/or intensity of AEWs will alter the favorability for tropical cyclone development. In this study, we found an increase in the number and strength of AEWs in the late 21st century. This suggests potentially more favorable conditions for tropical cyclone development.

Summary

In this study, we examine anthropogenic influences on the AEJ–AEW system using the Weather Research and Forecasting (WRF) model configured as a tropical channel model (TCM). Hindcast simulations for the years 2001–2010 were performed using the WRF TCM, and ten additional years of simulations were performed using the pseudo-global warming method with the initial and boundary conditions of the model modified as if it were the late twenty-first century. A comparison of the simulations from the two climate scenarios indicates robust changes to both the AEJ and AEWs. For the AEJ, the jet is weaker and shifted northwards and upwards in the future climate, in association with an increase in precipitation over the Sahel and a strengthening of the meridional temperature gradient. For the AEWs, there is an increase in the number and strength of the waves in the future climate, in association with an increase in energy conversions.

Point of Contact
Emily Bercos-Hickey
Institution(s)
Lawrence Berkeley National Laboratory
Funding Program Area(s)
Publication