Abstract
Middle East surface air temperature (ME-SAT), during boreal summer (June to August: JJA), shows robust multidecadal variations for the period 1948−2016. Here, using observational and reanalysis datasets, as well as coupled atmosphere–ocean model simulations, we linked the observed summer ME-SAT variability to the multidecadal variability of sea surface temperature (SST) in the North Atlantic Ocean (AMV). This Atlantic−ME connection during summer involves ocean–atmosphere interactions through multiple ocean basins, with an influence from the Indian Ocean and the Arabian Sea. The downstream response to Atlantic SST is a weakening of the subtropical westerly jet stream that impacts summer ME-SAT variability through a wave-like pattern in the upper tropospheric levels. The Atlantic SST response is further characterized by positive geopotential height anomalies in the upper levels over the Eurasian region and a dipole-like pressure distribution over the ME in lower levels. For positive Atlantic SST anomalies this pressure gradient initiates anomalous low-level southerly flow, which transports moisture from the neighboring water bodies toward the extremely hot and dry ME landmass. The increase in atmospheric moisture reduces the longwave radiation damping of the SAT anomaly, increasing further ME-SAT. A suite of Atlantic Pacemaker experiments skillfully reproduces the North Atlantic–ME teleconnection. Our findings reveal that in observations and models the Atlantic Ocean acts as a critical pacemaker for summer ME-SAT multidecadal variability and that a positive AMV can lead to enhanced summer warming over the Middle East.
Highlights
The Middle East (Supplementary Fig. 1a) climate exhibits variability on a wide range of timescales
The current research presents observational evidence and numerical simulations indicating that Atlantic multidecadal variability could have a remote influence on the decadal variability of ME summer SAT
● The leading mode of summer Middle East surface air temperature (ME-SAT) is characterized by positive anomalies all over the region and explains a substantial fraction (42.5%) of the total variability; the associated time series shows significant multidecadal variations
Summary
The Middle East (Supplementary Fig. 1a) climate exhibits variability on a wide range of timescales. The observational analysis provides us with compelling evidence that the Atlantic Ocean is a key driver of decadal variability in the Middle East Mediterranean region This is further supported by the regression of filtered AMO index (smoothed by 11 year running mean) on eddy stream function, lower level winds, precipitable water, downward longwave radiation flux, and surface air temperature (Supplementary Fig. 5). Previous idealized modeling experiments using the SPEEDY AGCM (see the models and experiments) showed that large and persistent Atlantic SST anomalies force low-level convergent flow, bringing moist air during the African and Indian summer monsoon and modulating the summer climate over these regions.[44,45,46] This motivates us to examine further the suggested mechanism for the ME-SAT variability using the SPEEDY AGCM. Focusing on the meridional wind velocity at 200 hPa (Fig. 5a: contours), the anomalous signal suggests a wave train-like response linking the North Atlantic Ocean to the Eurasian continent, in line with previous results,[29] while the zonal component of the wind anomaly exhibits a weakening of the ME jet stream (Fig. 5a: shaded), highlighted by
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