Synoptic and dynamic analysis of few extreme rainfall events in Iraq

Rainfall is most important factor influencing the atmospheric cycle of the atmosphere, since its spatial and temporal distributions are very complex. Heavy rainfall events may cause flash floods in the arid and semi-arid regions Middle East. The present study investigates the synoptic and dynamics situations of four extreme rainfall events that occurred in Iraq on 04, 15, 24, and 30 of November 2018. Rainfall data were acquired from the Global Precipitation Mission (GPM), and surface and upper meteorological variable were acquired from the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA5). The Rainfall analysis showed that November 2018 was characterized by the most unusual heavy rain events during the past two decades with a maximum of 200 mm/month (an anomaly of about 120 mm/month) near the town of Kut in the east part of the country (with an anomaly of about 120 mm/month). Analysis of surface and upper level charts indicated that during the four events the region was dominated by the Active Red Sea Trough (ARST), a situation when RST at the surface is associated by mid-tropospheric trough. The results also denoted that moisture was transported from equatorial north east Africa and the Red Sea towards north east regions including Iraq. The 850 hPa chart denoted that the warm moist air was advancing towards the cooler areas with a maximum speed of 20 m/s above the axis of the RST. The negative vertical pressure velocity along with high values of relative humidity suggests that cloud continued to develop at that level. 500 hPa charts showed that during all four events there was a positive vorticity advection towards the areas where rain was falling. This advection process contributes to a lifting of the air to upper levels. The 200 hPa composite maps of polar front jet stream and ageostrophic divergence indicated that in all four events there were high air suction from lower levels which enforced upward vertical motion at these levels and deepening low pressure areas at the surface.