The Impact of Orography on the African Easterly Wave Stormtrack

TL;DR

This study investigates how elevated terrain influences African easterly waves using numerical simulations, revealing that orography significantly affects AEW intensity and dynamics through thermodynamic and dynamic feedback mechanisms.

Contribution

It provides new insights into the sensitivity of AEWs to specific North African mountain ranges and their impact on wave energetics and structure.

Findings

Southern AEWs are most sensitive to Ethiopian highlands.

Diminished diabatic heating weakens AEWs via baroclinic overturning.

Northern AEWs are affected by Hoggar and Tibesti mountains through vertical shear changes.

Abstract

We examined the sensitivity of African easterly waves (AEWs) to elevated terrain over North Africa using a numerical weather prediction model. We formed five ensembles of simulated AEW activity with orographic features independently reduced in four key regions. The ensemble members consisted of 10 consecutive AEW seasons simulated separately. From the ensembles, the southern AEW stormtrack was most sensitive to the reduction of the Ethiopian highlands. Energy budgets showed that diminished diabatic heating associated with precipitating convection was the likely driver of the weaker AEWs. Baroclinic overturning was the dominant pathway for this response. The northern AEW stormtrack was most sensitive to the reduction of the Hoggar and Tibesti mountains. In this case, a reduction in the vertical shear and diminished baroclinic energy conversions from the background state was associated with weaker AEWs. Through terrain reduction, our results provide a view of thermodynamic and dynamic feedback in AEWs that is complementary to what has been shown in past studies.