Cyclogenesis and Density Currents in the Middle East and the Associated Dust Activity in September 2015

Abstract

The first 10 days of September 2015 were marked by intense dust activity over the Middle East and the Arabian Peninsula. This study examines the atmospheric conditions at the origin of the large dust storms during this period. We particularly investigate the atmospheric dynamics leading to the development of a large dry cyclone over Iraq on 31 August 2015 which in turn generated an intense dust storm that affected most of the countries around the Arabian Gulf and lasted for 5 days. We found that the cyclone developed over Northwest Iraq as a transfer to low levels of a cut-off low which had formed two days earlier at upper levels over Turkey. Large dust loads exceeding 250 tons were emitted and moved southeast in a cyclonic shape toward the Arabian sea. The second large dust storm on 6-8 September 2015 occurred over Syria and affected all the coastal countries on the eastern side of the Mediterranean Sea. It was associated with the occurrence of a series of density currents over northeast Syria emanating from deep convection over the mountainous border between Syria and Turkey. The unusual development of deep convection over this area was associated with a blocking high and interaction with orography. Both the cut-off high and the cut-off low occurred during a period characterized by a meandering polar jet and an enhanced subtropical jet causing unstable weather over mid-latitudes which in turn led to highly polluted atmosphere by natural dust in the affected countries.

Atmospheric Dynamics from Synoptic to Local Scale During an Intense Frontal Dust Storm over the Sistan Basin in Winter 2019

“…Meso-NH is a non-hydrostatic mesoscale model coupled with an online dust emission and transport module [70]. The model has been extensively validated against ground-based, airborne, and satellite datasets [41,[71][72][73] and is very capable of simulating the atmospheric dynamics for dust mobilization, dust emission, and transport pathways as previous studies over Sahara have shown [30,37,[74][75][76]. In this study, the model was run during four days [from 4 February 2019 at 00:00 UTC (Universal Time Coordinated) to 8 February 2019 at 00:00 UTC] over the domain 45…”

“…Cut-off cold lows in the middle and upper troposphere are usually developed over the subtropics and mid-latitudes associated with penetrating deep troughs from high latitudes [30,87,88]. They usually begin as a trough, as was shown on 5 February, and progressively become a closed circulation with a cold core, which may be stationary for days and be extended down to the surface forming a baroclinic system with unstable weather conditions [30,89,90]. The cut-off low in our case was transferred to low levels when it reached central Afghanistan on 6 February and it caused the development of deep convection facilitated by orographic blocking.…”

“…The cut-off low in our case was transferred to low levels when it reached central Afghanistan on 6 February and it caused the development of deep convection facilitated by orographic blocking. The development of deep convection over Afghanistan was accompanied by the generation of cold downdrafts enhanced by evaporational cooling over the desert areas [30,39]. This generated a mesoscale density current-like flow in the dry desert detected at the surface as a cold front and caused additional dust emissions [91].…”

“…Ground-based measurements at meteorological/atmospheric stations provide useful information about dust-aerosol characteristics via sun photometers and lidar systems (e.g., [25,26]), as well as visibility observations (e.g., [27][28][29]). Apart from the Sahara, the Middle East and southwest Asia emit large quantities of dust mainly in summer [30], while some rare but intense dust storms may also occur during winter (e.g., [31,32]). Dust storms in the Middle East and southwest Asia are usually associated with enhanced pressure gradients initiating intense northerly winds able to emit and transport dust plumes hundreds of kilometers downwind [33][34][35][36].…”

“…Furthermore, mountains in arid areas can trigger deep convection under certain conditions. The convectively-generated density currents that emanate from the developing clouds can then trigger dust emissions [30,40,41]. These phenomena are not well studied over Sistan due to the lack of sufficient observational network and lack of high-resolution modeling studies [42,43].…”