The Persian Gulf summertime low‐level jet over sloping terrain

Abstract

There are few observational and numerical studies of the summertime low-level jet (LLJ) over the Persian Gulf, known as the shamal. In this study, the Weather Research and Forecasting (WRF) model accurately simulates the LLJ's vertical structure, nocturnal features and strong diurnal variation of the wind. The casestudy period is divided into a period during which the shamal is spatially extended (strong winds over the Gulf and Iraq) and a period during which it is less spatially extended (strong flow only over the Gulf). Orography, mountain slope and land/sea breeze are found to be key factors for the shamal diurnal variation of wind speed and wind direction; the Blackadar mechanism appears to be secondary to the heating in forcing the shamal. The Zagros Mountains not only channel the northwesterly winds but also provide a barrier for the easterly monsoon airflow, which maximizes the wind speed. Only during the less extensive period does the Zagros Mountains slope significantly affect the shamal wind intensity and direction. Both shallow and steep mountain slope sensitivity studies feature a jet-like flow over the Persian Gulf. The steep slopes cause larger wind speeds; however, the shallow slopes reveal a stronger diurnally varying wind direction due to larger heating and cooling of the sloping terrain. It is also shown that, during the less extensive period, the land breeze and the lower friction over the sea increase the intensity of the nocturnal jet over the Gulf. Copyright c 2011 Royal Meteorological SocietyKey Words: blocking; inertial oscillation; land/sea breeze; shamal

Climatology of nocturnal low‐level jets over North Africa and implications for modeling mineral dust emission

“…Low‐level jets (LLJs) are wind speed maxima in the lower troposphere, as defined in the meteorological terminology data base METEOTERM run by the World Meteorological Organization (http://wmo.multicorpora.net/METEOTERM). Most previous studies focus on LLJs in specific parts of the world, e.g., north‐east Australia [ May , ], the Nares Strait channel near Greenland [ Samelson and Barbour , ], the USA [ Bonner , ; Hoxit , ; Whiteman et al , ; Banta et al , ], Cabauw in the Netherlands [e.g., Baas et al , ], the Persian Gulf [ Giannakopoulou and Toumi , ], the Bodélé Depression in Chad [ Washington and Todd , ; Washington et al , ], and the Sahara [ Schepanski et al , ]. Some work has been done on compiling a global distribution of LLJs.…”

“…Other NLLJ generating conditions include compensating air flows for low‐level baroclinicity in regions of differential heating and cooling. Evidence from the Arabian Peninsula shows that baroclinicity can be a more important forming mechanism for LLJs than the inertial oscillation [ Giannakopoulou and Toumi , ]. In contrast to the concept of an inertial oscillation, LLJ formation due to baroclinic condition can occur during day and night.…”

Satellite retrievals of dust aerosol over the Red Sea and the Persian Gulf (2005–2015)

“…The Persian Gulf, also known as the Arabian Gulf, is subject to atmospheric flows and dust storms emanating from Iraq (e.g. Giannakopoulou and Toumi, 2011;Smirnov et al, 2002) and Saudi Arabia and occasionally also from Iran. Closer to the active source areas, the Gulf is often affected by Middle Eastern dust storms earlier during their life cycle than is the Red Sea.…”

“…This is less intense than in the southern Red Sea in summer, but is a more prolonged feature, and has a more homogeneous spatial pattern within its basin. Due to its closer geographical proximity to the northern Syrian and Iraqi dust sources which flow directly into it, and due to the wind patterns in this region (Giannakopoulou and Toumi, 2011), the Gulf is more heavily influenced by the springtime dust events from the Middle East than the Red Sea.…”

Climatology of summer Shamal wind in the Middle East

“…The low pressure over Iran, Pakistan, and Afghanistan is considered a “heat low,” caused by intense surface heating during summer [ Bollasina and Nigam , ]. The summer Shamal is enhanced by the Zagros Mountains in southwest Iran, which intensify the pressure gradient by daytime heating over elevated regions and channel the northwesterly wind [ Walters and Sjoberg , ; Zarrin et al ., ; Giannakopoulou and Touni , ]. The winter Shamal usually occurs in 2–5 days episodes with wind speed up to 15–20 m s −1 near the surface over the Persian Gulf, associated with cold frontal passages from the Mediterranean Sea during November to March [ Perrone , ; Rao et al ., ; Thoppil and Hogan , ].…”