Meteorological drivers of a winter shamal dust storm over the Middle East

Severe dust storms are frequent throughout the year in the Middle East. While dust events are more active during winter and spring in the north, their maximum activity with the greater intensity occurs in the summer in the southwest of the region. The Middle East is affected by frontal dust storms mainly in winter and “Shamal” dust storms mostly in summer.Surface and satellite observations as well as ERA5 reanalysis data were used to describe the formation and evolution of a winter shamal dust storm that occurred in February 2017. It initiated in central western Iraq and dust was transported southeastward towards the Persian Gulf, impacting all the countries in the region up to the Oman Sea.The SEVIRI Dust RGB product shows dust mobilization at 07 UTC (10 LT) in several point areas west of the Euphrates River and over Mesopotamia, in Iraq. A dense dust plume is then advected between the Zagros Mountains, to the North and East, and the high plains of Saudi Arabia, to the South and West, reaching the Persian Gulf in the first hours of February 18. The next day, dust spreads throughout the Persian Gulf and surrounding countries. It resulted in the widespread reduction of horizontal visibility and impaired air quality, as reported by the region's Synop/METAR surface observations and air quality stations.The large-scale upper-level processes leading to this event started days before with a strong amplification of an anticyclonic Rossby wave break in the Polar Jet over the North East Atlantic, with large penetration poleward of subtropical air up to Scandinavia and cold air advection equatorward over Iberia on February 11. At a late dissipative stage and downstream displacement, the RWB resulted in a closed ridge over southeastern Europe and Turkey and a trough downstream over the study area. A strong pressure gradient was established at low levels between high pressures centered over southeastern Europe and the Black Sea and low pressures over the Persian Gulf with minima over the Arabian Peninsula and over Iran to the north of the Zagros Mountains. Strong northerly winds, imposed by the pressure gradient, accelerated downslope in the lee of the mountains in southern Turkey. The analysis suggests the formation of a low-level jet to the south of the mountains. During the morning hours of February 17 it mixed with the air over the surface, transferring momentum and initiating dust deflation in source areas of northern Iraq and Syria. Dust plumes were transported southeastward at heights below 2 km, as shown by CALIPSO profiles in the first half of February 18, within the PBL. On February 19, the dust plume was mixed all over the Persian Gulf basin.