Land–Boundary Layer–Sea Interactions in the Middle East

Abstract

Understanding the land–boundary layer–sea interactions is a primary target both in the context of low-level jet (LLJ) development and landscape alterations. This thesis attempts to address and study these interactions in the Middle East. The thesis investigates the summertime LLJ over the Persian Gulf, known as the Shamal. Terrain height, land-sea and novel mountain slope sensitivity experiments were conducted and compared with a control run. It was found that the Weather Research and Forecasting (WRF) model accurately simulates the LLJ’s vertical structure, nocturnal features and strong diurnal oscillation of the wind, and that orography, mountain slope and land/sea breezes determine the Shamal diurnal variation of wind speed and wind direction. The Iranian mountain range not only channels the northwesterly winds but also provides a barrier for the easterly monsoon airflow. The steep slopes cause increased wind speeds; however, the shallow slopes reveal a stronger diurnally varying wind direction due to larger diurnal heating of the sloping terrain. The land breeze and the lower friction over the sea increase the intensity of the nocturnal jet over the Gulf. To determine the effects of the Nile Delta man-induced greening on local climate, the WRF model was used to compare control simulations, which employ the present-day Nile Delta landscape, with desertification experiments in which the Nile Delta is replaced by desert. It was found that the low surface albedo of the present-day agricultural Nile Delta increases net radiation, which in turn raises potential evapotranspiration (PET). This suggests that agricultural use increases the water demand by enhancing PET. Non-local effects were also examined. It was found that a frontal system over the eastern Mediterranean Sea, associated with a storm event, is shifted farther away from the coast. This shift is attributed to a stronger land breeze in the present-day land-cover.