Polar Jet Associated Circulation Triggered a Saharan Cyclone and Derived the Poleward Transport of the African Dust Generated by the Cyclone

Francis, Diana; Eayrs, Clare; Chaboureau, Jean‐Pierre; Mote, Thomas L.; Holland, David M.

doi:10.1029/2018jd029095

Cited by 40 publications

(43 citation statements)

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“…Other effective mechanisms for dust emission and transport over long range distances have been highlighted over other arid areas. Of relevance to our study, two important mechanisms, namely Cyclogenesis [23][24][25] and density currents fed by evaporationally cooled air, are related to deep moist convection over deserts [26][27][28][29][30]. Both mechanisms can produce quite dramatic dust storms.…”

Section: Introductionmentioning

confidence: 92%

“…During the formation of a cut-off low, air of polar origin is cut off from the main subpolar belt of low pressure and cold air, the normal track of depressions. It usually begins as a trough in the upper-air flow, becomes a closed circulation with a cold core nearly stationary for days and then extends down to the surface during the last stage of its life cycle (e.g., [25,33,56]). A cut-off low is an unstable baroclinic system that slopes to the west with height and is usually associated with very unstable weather in the atmosphere below it [33].…”

Section: The Synoptic Situation Prior To Cyclogenesismentioning

confidence: 99%

“…For instance, over North Africa, cyclones can generate heavy dust storms [31,32] with dust loads estimated at 8 Tg per episode (e.g., [23]). The development of these depressions, mostly to the southeast of the Atlas Mountains, is favored by the strengthening of the meridional temperature gradient over northern Africa during spring time (e.g., [23]) and they are triggered by the intrusion of an upper level trough from high-latitudes [25,33]. About 25% of the total dust emissions in spring over North Africa is due to the occurrence of Saharan cyclones (e.g., [24]).…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2019

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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.

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Section: Introductionmentioning

confidence: 92%

Section: The Synoptic Situation Prior To Cyclogenesismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2019

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“…The model run used a convective mass-flux scheme (Bechtold et al, 2001), a mixed-phase bulk microphysical scheme (Pinty & Jabouille, 1998), a subgrid cloud cover and condensate content scheme (Chaboureau & Bechtold, 2002, a turbulence parameterization (Cuxart et al, 2000), a Rapid Radiative Transfer Model parameterization (Mlawer et al, 1997) that takes into account the radiative effect of dust, and a dust scheme (Grini et al, 2006). The later includes the Dust Entrainment and Deposition (DEAD) scheme (Zender et al, 2003) that calculates dust fluxes from wind friction speeds and the ORganic and Inorganic Log-normal Aerosols Model (ORILAM; Tulet et al, 2005), in which transport, dry and wet deposition, and the radiative properties of three dust particle sizes are parameterized (Bou Karam et al, 2017;Chaboureau et al, 2016;Francis et al, 2018).…”

Section: Model Simulationsmentioning

confidence: 99%

The Role of the Intertropical Discontinuity Region and the Heat Low in Dust Emission and Transport Over the Thar Desert, India: A Premonsoon Case Study

et al. 2019

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Key Points Satellite observations and Meso‐NH model simulations are used to investigate an intense dust storm over north India in June 2018 Dust is mostly confined below 2 km in the monsoon flow over the Thar desert, northwest India and at ~3 km along the Ganges Valley The dust was accumulated in an arc‐shaped cloud in the convergence zone between the southwesterlies and the northwesterlies: the ITD

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“…While several atmospheric phenomena can be at the origin of strong surface winds, inward spiraling winds generated by synoptic-scale cyclones are so powerful and cyclones of different types and categories are considered to be the most powerful atmospheric features around the globe (e.g., Orlanski, 1975;Rudeva & Gulev, 2007) given their significant impacts on the environment on a synoptic scale as a result of the extremely high energy they carry (e.g., Bou Karam et al, 2010;Francis et al, 2018). This is particularly true in polar areas, where polar cyclones are intense and their impact on the surface is believed to be considerable (Kolstad, 2011;Rasmussen & Turner, 2003;Simmonds et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Polar Cyclones at the Origin of the Reoccurrence of the Maud Rise Polynya in Austral Winter 2017

et al. 2019

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This study examines the role of atmospheric forcings in the occurrence of open‐ocean polynyas by investigating the case of the austral winter 2017's polynya located in the Lazarev Sea sector to the east of the Weddell Sea, known as the Maud Rise polynya or the Weddell Polynya. The ice‐free zone appeared in mid‐September 2017 and grew to as large as 80,000 km2 by the end of October 2017 before merging with the open ocean after the sea ice started to retreat at the beginning of the austral summer. Using a combination of satellite observations and reanalysis data at high spatiotemporal resolution, we found that severe cyclones, occurring over the ice pack, have a deterministic role in creating strong divergence in the sea ice field through strong cyclonic surface winds leading to the opening of the polynya. The occurrence of intense and frequent cyclones over the ice pack during austral winter 2017 was unusual, and it occurred under an enhanced strong positive meridional transport of heat flux and moisture toward Antarctica associated with an amplification of the atmospheric zonal wave 3 and a strong positive Southern Annular Mode index. We found that the opening of the polynya was not primarily due to direct ice melt by thermodynamic effects but rather to strong dynamical forcing by the winds on the sea ice, as in the case of coastal polynyas. Indeed, the meridional transport of heat toward Antarctica occurred over the Weddell Sea sector (i.e., to the east of the Lazarev Sea sector where the polynya is located) whereas the Lazarev Sea sector was under the influence of equatorward transport of cold air masses at that time. Our results show that the supply of warm and moist air coming from the west side of the South Atlantic Ocean into the Weddell Sea significantly increased the potential for cyclone formation as measured by the Eady growth rate leading to intense and frequent cyclogenesis over the ice pack, far south from the ice edge. After cyclogenesis in the Weddell Sea, these cyclones intensified as they moved eastward spinning over the Lazarev Sea with intensity comparable to category 11—violent storms—in the Beaufort scale. The cyclonic winds generated sea ice divergence by pushing the ice away from the cyclone center: To the east, north of it and to the west, south of it, which led to the reoccurrence of the Maud Rise polynya in mid‐September 2017.

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Polar Jet Associated Circulation Triggered a Saharan Cyclone and Derived the Poleward Transport of the African Dust Generated by the Cyclone

Cited by 40 publications

References 93 publications

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

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

The Role of the Intertropical Discontinuity Region and the Heat Low in Dust Emission and Transport Over the Thar Desert, India: A Premonsoon Case Study

Polar Cyclones at the Origin of the Reoccurrence of the Maud Rise Polynya in Austral Winter 2017

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