Abstract
In this study, the Sudan low and the Red Sea trough (RST) are objectively detected using the mean sea level pressure data from the NCEP/NCAR reanalysis data set. The results show that the RST exists for 37.45% of winter and that approximately 64% of RSTs are classified as long RSTs. Most of these long RSTs are generated at night and decrease in abundance from December to February; thus, the generation timing is affected by high water-land temperature contrasts. Additionally, this study demonstrates that the Sudan low predominantly forms over the South Sudan region (70.59%) and to a lesser extent over the Sudan region (26.06%). The empirical orthogonal function (EOF) statistical analysis of long RST events indicates that the first ten modes represent 82% of the cases and that the first four modes represent 57.86% of the cases. For simplicity, this synoptic study focuses on the first four modes because they reliably represent the long RST modes. The synoptic study of the four modes demonstrates that as the mode percentage increases, the main dominant synoptic regimes that are associated with the modes and that affect the Red Sea region decrease in number and intensify in strength. Thus, the highest percentage modes are those with the lowest numbers, and strong atmospheric systems are distributed over large areas of the northern Red Sea. Furthermore, this study shows that the relative positions of the main synoptic components consisting of the northern European low-pressure system/Azores high-pressure system or the Siberian high-pressure system cause the long RSTs to be oriented east of or over the Red Sea, respectively. In addition, the study shows that the maximum wind core area expands eastward under strong mode conditions and shrinks westward from the Red Sea under weak mode conditions.