Extreme precipitation events in the Middle East: Dynamics of the Active Red Sea Trough

Abstract

[1] The Active Red Sea Trough (ARST) is an infrequent weather phenomenon that is associated with extreme precipitation, flash floods, and severe societal impacts in the Middle East (ME). Using reanalysis (ERA-Interim) and observational precipitation (Aphrodite and stations) data, we investigate its underlying dynamics, geographical extent, and seasonality. Twelve ARST events affecting the Levant have the same dynamical characteristics as those associated with a major flood in Jeddah (Saudi Arabia) on 25 November 2009. Hence, the Jeddah flooding was caused by an ARST, which implies that ARSTs can affect a much larger part of the ME than previously assumed. We present an ARST concept involving six dynamical factors: (1) a low-level trough; the Red Sea Trough (RST), (2) an anticyclone over the Arabian Peninsula; the Arabian Anticyclone (AA), (3) a transient midlatitude upper trough, (4) an intensified subtropical jet stream, (5) moisture transport pathways, and (6) strong ascent resulting from tropospheric instability and the synoptic-scale dynamical forcing. We explain the ARST as the interaction of a persistent stationary wave in the tropical easterlies (i.e., the RST) with a superimposed amplifying Rossby wave, resulting in northward propagating moist air masses over the Red Sea. Our findings emphasize the relevance of the AA, causing moisture transport from the Arabian and Red Seas. The particular topography in the Red Sea region and associated low-level circulation makes the ARST unique among tropical-extratropical interactions. The ARST seasonality is explained by the large-scale circulation and in particular the seasonal cycle of the semipermanent quasi-stationary RST and AA.

Revealing the meteorological drivers of the September 2015 severe dust event in the Eastern Mediterranean

“…The streak is situated exactly upstream of the mesoscale convective system (MCS) development region. As suggested in previous studies (Krichak et al, 2012;Vries et al, 2013), this marked jet could provide significant moisture transport for the MCS from the Red Sea and Africa in the form of an atmospheric river with high values of atmospheric humidity. At upper-tropospheric levels above 400 hPa a shortwave trough exists in the region above Syria.…”

“…In combination with the orographic lifting by the Zagros mountain range, the position of the slowly eastward-moving trough enables the development of mesoscale organized convection and determines its position throughout the event. The combination of a low-level RST extending northward and upper-tropospheric troughs extending southward into the EM has been termed an active RST in previous studies due to its high potential for severe weather (Krichak et al, 2012;Vries et al, 2013). The timing of the active RST synoptic situation is exceptional, as the RST usually starts to occur only by late September or early October (Alpert et al, 2004;Tsvieli and Zangvil, 2005), although events have been documented in August and September (Osetinsky, 2006).…”

“…The timing of the active RST synoptic situation is exceptional, as the RST usually starts to occur only by late September or early October (Alpert et al, 2004;Tsvieli and Zangvil, 2005), although events have been documented in August and September (Osetinsky, 2006). The active RST has been linked to severe weather phenomena in the EM and the Arabian peninsula in connection with atmospheric rivers transporting large quantities of precipitable water from eastern Africa, although the specific moisture sources are still debated (Vries et al, 2013, and references therein). The clustering of convectively active days with mesoscale convective organization is often observed during active RST situations (Krichak et al, 2012;Vries et al, 2013).…”

Forcings and feedbacks on convection in the 2010 Pakistan flood: Modeling extreme precipitation with interactive large‐scale ascent

“…Globally, a large number of the most intense precipitation events occur in the subtropical belt during summer [Zipser et al, 2006;Cecil and Blankenship, 2012], likely results of interactions between extratropical dynamics with sufficient moisture supply from the tropics. Applying the CQG method of this study to events in other regions, e.g., Texas [e.g., Simon Wang et al, 2015] or the Middle East [e.g., de Vries et al, 2013], may be useful in identifying the most important physical factors leading to extreme precipitation events in these different regions.…”

Intensity–duration–frequency curves from remote sensing rainfall estimates: comparing satellite and weather radar over the eastern Mediterranean

“…The summer is dry, with almost no rain from June to August. Rainfall over the Mediterranean areas is generally brought by cold fronts and post-frontal systems, associated with mid-latitude cyclones (Goldreich, 2003;Peleg and Morin, 2012), and by Syrian low and active Red Sea Trough, occasionally correlated with flash floods, in the semiarid and arid climates (Dayan et al, 2001;Dayan and Morin, 2006;Kahana et al, 2002;de Vries et al, 2013). On rare occasions the subtropical jet, or tropical plume, brings widespread rainfall over the whole region (Dayan and Morin, 2006;Kahana et al, 2002;Rubin et al, 2007;Tubi and Dayan, 2014;Dayan et al, 2015).…”