A climatology of the winter low-level jet over the Red Sea

摘要

This study presents the f irst climatology of the low-level jet (LLJ) over the southern part of the Red Sea during the winter season. ERA-Interim pressure levels with 25 hPa vertical resolution were analysed for a 10-year period from 2006 to 2015. The jet was found to be a relatively frequent phenomenon, occurring on 37% of all 6-hr time steps in all 10 years in the south at 13.5 degrees N and 43 degrees E, decreasing to 15% of the data farther north at 19.5 degrees N and 39 degrees E. The core of the jet was usually close to the ground, with occurrence maximized at the 925 and 950 hPa levels corresponding roughly to 540-800 m above sea level. The study defined three criteria for the jet based on peak wind speeds. The jets that met the weaker criterion were frequent north of the straight of Bab el Mandeb in the far southern part of the Red Sea. The jets that met the two stronger criteria were more frequent further north approximately between 14 degrees-17 degrees N and 39 degrees-42 degrees E. Although the jet was present in the strait of Bab el Mandeb as found in earlier studies, the extension of the jet so much farther north suggests that other processes besides channelling must be acting to produce this jet. It also appears that the jet plays a significant role in moisture advection towards the central Red Sea region, which can contribute towards precipitation there as it was found that the moisture concentration increased in that region when the LLJ was present. It must be noted, however, that the present study relied upon reanalysis data to document the jet. Upper level observations in the region are scarce, so caution should be used in the interpretation of the results.