Causal drivers of eastern Mediterranean tropospheric circulation during boreal summer

During boreal summer, large scale subsidence and a persistent northerly flow, known as the Etesians, characterize the tropospheric circulation over the eastern Mediterranean, respectively bringing clear skies and mitigating the emergence of heat waves. Atmospheric drivers over both South Asia and the North Atlantic have been proposed to influence the intraseasonal variability of subsidence and Etesians over the eastern Mediterranean. Here, we employ Causal Effect Networks, obtained by applying the Peter and Clark Momentary Conditional Independence (PCMCI) causal discovery algorithm, to identify causal precursors of subsidence and Etesians in a set of atmospheric fields. We find that both wave train activity over the North Atlantic/North American region and convective activity over the northern Indian Ocean are causally related to the 3-day average 850 hPa meridional wind variations over the eastern Mediterranean at a lag of 3-to-6 days. For 3-day average 500 hPa vertical wind velocity, causal precursors over the Middle East and Arabian Sea similar to those identified for the Etesian are found. We further explore in detail the different nature of the causal precursors to the Etesians and subsidence over the eastern Mediterranean by applying varying averaging in the variables representing the involved phenomena.