Moisture transport by tropical plumes over the Middle East: a 30‐year climatology

Abstract

This study conducts a 30‐year climatological analysis of tropical plumes (TPs) observed over the Middle East (ME). These moisture bursts, conveying water vapour from tropical Africa to the arid ME at mid‐ to upper tropospheric levels, were identified and analysed using multiple data sources and empirical tools, including satellite images, reanalysis data, backward trajectories, and calculation of moisture profiles, water vapour transport and moisture flux convergence. The analysis of the 140 days in which TPs were identified focused on three main elements: (i) TP seasonal distribution and contribution to rainfall regime, (ii) TP moisture pathways, and (iii) the mechanisms leading to TP‐induced precipitation. TPs over the ME are found to be most frequent in the winter season, with the second highest frequency observed during the spring. The estimation of TPs' contribution to the rainfall regime over the ME, the first of its kind, shows that such contribution is limited. However, extreme events may have a significant effect on the overall annual precipitation amount. Two moisture pathways are identified, exhibiting very limited mixing, if any, with the dry air mass at shallow tropospheric levels. The first, originating in tropical West Africa, is associated with the penetration of an intensified subtropical jet stream towards lower latitudes. The second, emanating from East to Central African sources, is closely associated with an anomalous anticyclonic flow over southern Arabia. Moisture conveyed by the latter pathway is supplied from sources that are closer to the target area, transported at lower atmospheric levels, and exhibits more pronounced vertical dispersion. Compared to TPs that did not lead to precipitation, precipitative TPs feature enhanced moisture transport and stronger convergence of moisture flux. Similarly, the belt of moisture flux convergence stretching from the Tropics to the ME is interrupted when non‐precipitative TPs occur but uninterrupted during precipitative events.

Radar-based characterisation of heavy precipitation in the eastern Mediterranean and its representation in a convection-permitting model

“…These values are comparable to previously reported observations (e.g. Ciach and Krajewski, 2006;Morin et al, 2003;Peleg and Morin, 2012;Villarini et al, 2008) and are somewhat larger than the reported values for the south-eastern part of the area by Marra and Morin (2018). However, it should be noted that Marra and Morin (2018) examined 1 min rainfall fields versus the 10 min fields examined here.…”

“…Heavy precipitation events (HPEs) cause natural hazards such as flash, riverine, and urban floods as well as landslides and debris flows; they also serve as a resource for recharging groundwater and surface water reservoirs (e.g. Bogaard and Greco, 2016;Borga and Morin, 2014;Doswell et al, 1996;Nasta et al, 2018;Raveh-Rubin and Wernli, 2015;Samuels et al, 2009;Taylor et al, 2013;UN-Habitat, 2011). Diverse rainfall patterns during HPEs cause different hydrological responses; thus, an accurate representation of rainfall patterns during these events is crucial for detecting and predicting climate-change-induced precipitation changes (Maraun et al, 2010;Trenberth et al, 2003).…”

Radiokrypton unveils dual moisture sources of a deep desert aquifer

“…4B). Because they are isolated from the planetary boundary layer beneath them, TPs can transport tropical moisture to North Africa and the Levant over the dry Sahara (43,44). A combined study of the air-mass trajectory and δD-δ 18 O in the Negev reported that low D-excess values in precipitation (+10.36, +10.37, and −5.77‰ observed for three rainfall events) tend to be associated with air masses from the southwest (45).…”

Characterising patterns of heavy precipitation events in the eastern Mediterranean using a weather radar and convection-permitting WRF simulations

“…While MCs move inland and towards the desert, a substantial amount of the moisture is lost, and rainfall occurrence and amounts are greatly reduced (Enzel et al, 2008). In this arid region HPEs are associated not only to MCs (Armon et al, 2018;Kahana et al, 2002), but also to the Active Red Sea Trough (ARST) (Ashbel, 1938;Krichak et al, 1997;De Vries et al, 2013) and, more rarely, to Tropical Plumes (Armon et al, 2018;Rubin et al, 2007;Tubi et al, 2017). Commonly, rainfall during ARSTs is of spotty nature, could reach far into the desert, and could have very high intensities (Armon et al, 2018;Sharon, 1972).…”

“…Similarly, we classified a HPE as an ARST if (1) the majority of its days were classified as ARST according to Alpert et al (2004), or (2) one of its days was an ARST and none of them was a MC. The abovementioned TP synoptic pattern (Rubin et al, 2007;Tubi et al, 2017) is not a part of our classification because of the low frequency and because they do not appear in a near sea level pressure meteorological fields. Specifically, one HPE (#41; Table S1) was characterised, during its 5-day duration, first by the prevalence of TP (Armon et al, 2018) and then by MC; it was classified here as a MC.…”