Circulation Aspects Associated With Heatwave Events Over Iraq

Abstract

Heatwaves are responsible for increased mortality, heightened energy demands, economic challenges and other societal impacts. Whilst heatwave events are a global concern, Middle Eastern heatwaves have received relatively little attention. This study offers a comprehensive analysis of summertime heatwave events over Southern Iraq during 1980–2022 based on ERA5 re-analysis data. We show that heatwaves typically exhibit a gradual intensification over the week preceding the central day, followed by a more rapid decrease in strength. On the central day, the warming tends to extend from the Arabian Peninsula northward across Iraq and into southwestern Russia. We find these heatwaves to be generally associated with a pronounced weakening of the prevailing north-westerly low-level jet (the so-called Shamal winds), i.e., a strong reduction of the cooling effect of these winds. These Shamal winds result from the climatologically existing low-level pressure gradient over the northern Arabian Peninsula, consisting of a thermal low over the Zagros mountains and a high over the Eastern Mediterranean. It is the weakening of this pressure gradient that ultimately results in the heatwave events. We find that for the majority of heatwave events, this weakening results from a quasi-stationary anticyclonic high to the northeast of Iraq, embedded in a Rossby wave train propagating along the North Atlantic jet and then further along the North African–Asian jet. The circulation associated with the high-pressure system further appears to cause downslope (Foehn-like) winds on the leeward side of the Zagros Mountains that create additional heating. A subset of the heatwave events is not preceded by Rossby wave activity and instead seems to be associated with alternative mechanisms that weaken the low-level pressure gradient. We speculate that the interaction of the Sudanese low-pressure system with the Red Sea Trough, which could be modulated by the position of the inter-tropical convergence zone, may be contributing to the weakening of the low-level pressure gradient and thereby the occurrence of heatwaves.