Synoptic pattern of the Red Sea trough associated with spring dust over the northern and western Arabian Peninsula

Abstract

From 1979 to 2006, the Red Sea trough (RST) in spring was objectively detected and classified into three categories (short, moderate and long) depending on its northward extension. The results indicated that most short RSTs appeared during a cold spring (larger by 7% in March than May), while most long RSTs appeared during a warm spring, where reached 71.7% in April and May. The dust events during the study period were identified using a threshold value of the Total Ozone Monitoring Satellite (TOMS) aerosol index (AI). The identified dust cases were used to classify each RST category into two classes, dust RSTs and non-dust RSTs. The synoptic characteristics of the RSTs associated with dust events that influenced the northern and western Arabian Peninsula (AP) were studied using each dust category (i.e., comparing dust and non-dust cases) and were compared between the different categories (i.e., comparing the dust cases among short, moderate and long categories). The synoptic study shows that the condition favorable for transporting dust westward into the AP occurs when an interaction is produced between the low pressure over the southern AP and Sudan low and forms a wavy zonal pressure gradient. When the RST is relatively strong, i.e., the situation has a pronounced wavy zonal and meridional pressure gradient area, it produces conditions favorable for transporting dust around the Red Sea. Commonly, dust RSTs are atmospherically integrated systems with pronounced circulation (downward motion in the eastern AP and upward motion in the western AP), a vertical westward trough tilt, horizontal tropical–extratropical interactions and north–south orientations of pressure/geopotential isolines.