Investigating the effect of PV streamer on the activity of the Red Sea trough using the WRF model (case study)

The Middle East region, especially the eastern part of the Mediterranean Sea, is subject to rave events of heavy rains that lead to financial and human losses. These heavy rains can have various causes, one of which is the activation of the Red Sea Trough (RST). The Red Sea trough is an inverted low-pressure trough in the lower troposphere over Northeast Africa and the Red Sea. The main goal of the current research is to investigate the activity of the potential vorticity (PV) streamer caused by the Rossby-wave activity in the upper troposphere, its interaction with the circulation in the lower troposphere and the consequent effect on the activation of the RST and the occurrence of extreme precipitation events (EPE) in the region. The selection of these events is based on the information of the relevant websites and the results of valid researches. In the following, due to the important effect of the eastern Mediterranean Sea trough on the activity of the RST, the investigation of the PV streamer as an effective factor in wave breaking, receiving the moisture of the lower surfaces and the activity of RST will be carried out. This research uses ERA-Interim data and the WRF model to remove the PV anomaly in the upper and middle troposphere levels and investigate the meteorological quantities with and without the presence of the PV anomaly.   In this way, the effect of the PV streamer and the eastern Mediterranean trough is discussed in the activation of RST in several extreme precipitation events in the region. In this study, two categories of EPE, which were caused by the activity of the Red Sea trough (ARST) or by factors other than ARST, were investigated. The results indicate that in most of the EPEs caused by ARST, the southward extension of the upper trough in the eastern Mediterranean Sea along with the PV streamer and the cold advection at the upper levels are present as the main conditions for the formation of EPE. However, there are also rare cases where the aforementioned trough extended southward in the middle level, but it was not accompanied by the Rossby wave breaking and the PV streamer at the upper level; the environmental conditions for the EPEs were provided only by the cold advection to the region at the lower levels by, for example, the westward exptension of the Siberian high pressure. However, in the systems in which RST was not active, the lower-level effects were dominant, and the role of the upper level was only in modifying the amount of moisture transfer to the region.