Climatology of the spring Red Sea Trough

Abstract

The spring Sudan low and its Red Sea Trough (RST) were detected objectively using sea level pressure data obtained from a National Center for Environmental Prediction/National Center for Atmospheric Research reanalysis dataset spanning the period from 1955 to 2014. The climatology of the detected lows suggested that the Sudan low was active for approximately 69.5% of the spring and that approximately 56.2% of this time the Sudan low developed into the RST. Furthermore, three main genesis regions of the RST, which generated 95.25% of the RST, were identified over Sudan, South Sudan and the Red Sea, approximately 61.76% of which was over South Sudan. In addition, three main outermost areas of the RST, which received 94.1% of the RST, were specified to the west, east and north of the Red Sea, approximately 54.88% of which was in the eastern region. Synoptically, the orientations of the detected RST around the Red Sea are strongly influenced by the Siberian and Azores high systems. The RST is directed along the western side of the Red Sea if the Siberian high extends westward and the Azores high shrinks westward, whereas the RST is oriented to the east if the Siberian high shrinks eastward and the Azores high extends eastward. The RST extends directly northward if the Siberian and Azores high systems withdraw eastward and westward, respectively. These results also demonstrate that the core position and strength of the upper maximum winds play an important role in the generation of RST. The selected case studies have confirmed the synoptic climate results and indicate that the Sudan low will not develop into RST when the northern region has been affected by a high-pressure system and the core of the upper maximum wind is located over the northern Arabian Peninsula.

The variability of the Siberian high ridge over the Middle East

“…In summary, although the SH appeared as a shallow system with upper levels that were not deep, in which the surface Siberian high region occupied the upper levels, 850 and 700 hPa, by cyclonic area, the distribution of the static stability from 1,000 to 500 hPa followed the stability distribution of surface pressure systems. Additionally, when the active SH over the Middle East connected with the Azores High, a high‐pressure belt formed over the northern Mediterranean region and prevented the RST from extending northward beyond 30°N, as observed for the winter, spring and autumn RSTs (Awad and Almazroui, 2016; Awad and Mashat, 2018; Baseer et al ., 2019). Further, in the upper levels (850 and 700 hPa), the interaction between the northern cyclone trough and the Arabian anticyclone (De Vries et al ., 2016) or Arabian‐Iran ridge (Kaskaoutis et al ., 2017) formed a geopotential gradient, which developed a strong northerly (shamal) wind that generated dust over the region (Najafi et al ., 2017; Rashki et al ., 2019).…”

“…Synoptically, the SH ridges that terminated over the Levant and Turkey were already imbedded with the synoptic features of the westward extension of the SH. Therefore, the synoptic characteristics of the SH extending southward (O‐SA) and over the Red Sea (O‐RA) were selected to describe the other main extensions, which play a major role in the creation of dust (Saaroni et al ., 1998; Hamidi et al ., 2013; Awad et al ., 2015) and the northward shift and intensification of the RST (Saaroni et al ., 1996; 1998; De Vries et al ., 2013; Baseer et al ., 2019). The number of days with SH extensions terminating in the O‐RA region was 28 (or 112 composite times); the SLPs accompanying the detected times are significant (at the 95% confidence level) over the Middle East, Red Sea and eastern Africa.…”

“…The detected SH from this step was employed to represent the SH used in the following analysis. Identify the new center through the ridge line in the box containing 20 fine grid points surrounding the current local high value. From this step forward, the search for the ridge line points will be referred to as open detection, which means that the new local high value will belong to the ridge line if it is larger than the values in at least 5 of its neighbouring grid points, similar to the procedure used for the detection of RSTs (Awad and Almazroui, 2016; Awad and Mashat, 2018; Baseer et al ., 2019). The previous step is repeated until no centers are identified or the search extends westward beyond 30°E (which may be confused with the Azores High) or southward beyond 10°N (which may be inside the tropical region).…”

“…Therefore, acquiring a better understanding of the atmospheric characteristics accompanying the variability of the SH provides additional knowledge regarding the development of the main atmospheric systems that influence the Middle East, such as dust storms (Awad and Mashat, 2014; Hamidi et al ., 2014; Yu et al ., 2016), the development of the RST (Baseer et al ., 2019), precipitation over the AP and the routes of Saharan/Mediterranean cyclones (Alpert et al ., 1990).…”

ESD Reviews: Extreme Weather and Societal Impacts in the Eastern Mediterranean

“…1 d and Fig. 2 c, d;Krichak et al, 1997a;de Vries et al, 2013;Armon et al, 2018;Baseer et al, 2019). Precipitation typically occurs in the form of numerous localized thunderstorms and mesoscale convective systems (Krichak et al, 1997b;Dayan et al, 2001;Belachsen et al, 2017;Marra and Morin, 2018).…”