Tropical Plumes over Eastern North Africa as a Source of Rain in the Middle East

Abstract

Tropical plumes (TPs) reflect tropical–extratropical interaction associated with the transport of moisture from the Tropics to extratropical latitudes. They are observed in satellite images as continuous narrow cloud bands ahead of upper-level subtropical troughs at times when the subtropical jet is highly perturbed. Rainstorms usually develop in the exit regions of TPs, so their presence over northern Africa has an impact on the precipitation regime in the southeastern Mediterranean. Based on satellite images and rainfall measurements from Israel, 10 TPs over eastern North Africa between 1988 and 2005 in which considerable rain was recorded were selected. Using the NCEP–NCAR reanalysis data, the structure and evolution of these TPs were characterized and their regional canonical features were identified. A typical TP that occurred in March 1991 is described in detail. The main canonical characteristics are as follows: the TP development is preceded by an incubation period, expressed either as a stationary upper-level trough, persisting 2–6 days, or as two consecutive TP pulses; the preferred location for TP origin is 5°–15°N, 5°W–15°E; the TP is separated from the underlying dry Saharan PBL; the subtropical trough undergoes a phase locking with the lower tropical trough; the cloudiness in the TP-induced rainstorm is mostly stratified with continuous moderate rain, originating from midlevel moisture; and the TP tends to be followed by a midlatitude cyclogenesis over the eastern Mediterranean. This analysis proposes several explanations for the efficiency of the TPs in transporting moisture over a 2000-km distance.

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

“…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). Important gradients have been reported also for the climatology of extreme rainfall.…”

“…This limits our analysis of rain gauge data to durations shorter than 4 h. When possible, rain gauge data have been aggregated into hourly blocks to be as consistent as possible with the remote sensing datasets. Stationarity of the records has been tested at 0.1 significance level (Phillips and Perron, 1988). The selected rain gauges belong to different climatic regions with five, four, and two rain gauges available for Mediterranean, semiarid, and arid climates, respectively (Fig.…”

“…It is described by the location, scale, and shape parameters, representing mean, dispersion and skewness of the distribution, respectively. The GEV distribution has been shown to fit the AMS better than other distributions, such as the Pearson type III or the generalized logistic (Alila, 1999;Kysely and Picek, 2007;Perica et al, 2013;Schaefer, 1990). It is being widely used for rainfall frequency analyses based on remote sensing data (El-dardiry et al, 2015;Marra and Morin, 2015;Overeem et al, 2009;Paixao et al, 2015;Panziera et al, 2016;Peleg et al, 2017b), owing to its ability to include all the three asymptotic extreme value types (Gumbel, Fréchet and Weibull) into one (Katz et al, 2002).…”

Winter synoptic-scale variability over the Mediterranean Basin under future climate conditions as simulated by the ECHAM5

“…These include the Red-Sea trough (Dayan et al 2001), the North African Sharav cyclones (Alpert and Ziv 1989), and tropical plumes (Ziv 2001;Knippertz 2005). Tropical plumes are mainly active in the winter season (Rubin et al 2007). Moreover, there are indications of a possible influence of El Niño Southern Oscillation (ENSO) on the MB (Price et al 1998;Brönnimann 2007), which is, however, still under debate.…”

Review Article: Atmospheric conditions inducing extreme precipitation over the eastern and western Mediterranean

“…The east African band, affecting mainly the eastern MR, was not studied in depth. Observations of the rainfall associated with the tropical cloud development related to such jet streams extending from the tropics into the subtropics, analyzed by Tubi and Dayan (2014) as well as in previous studies in this region (e.g., Dayan and Abramski 1983;Ziv, 2001;Rubin et al, 2007), indicate that their contribution to the water budget in the Middle East, particularly in arid and semiarid locations, is important. Dayan and Abramski (1983) described a major and fatal flooding event caused by very heavy showers that yielded a daily rain amount of 52 mm (a value equivalent to 160 % of the annual average) in Eilat, at the southern tip of Israel, as part of the torrential rain event that occurred over most of the southeastern parts of the MR.…”