Identification of Tropical–Extratropical Interactions and Extreme Precipitation Events in the Middle East Based on Stratospheric Potential Vorticity Intrusions and Poleward Moisture Transport

Extreme precipitation events in the otherwise arid Middle East can cause flooding with dramatic socioeconomic impacts. Most events are associated with tropical-extratropical interactions, whereby a stratospheric potential vorticity (PV) intrusion reaches deep into the subtropics and forces an incursion of high vertically integrated water vapor transport (IVT) into the Middle East. This study presents an object-based identification method for extreme precipitation events based on the combination of these two larger-scale meteorological features. The underlying motivation for this approach is that precipitation is often poorly represented in relatively coarse model simulations, whereas the synoptic-scale circulation is much better represented. The algorithm is applied to ERA-Interim reanalysis data (1979-2015) and detects 90% (83%) of the 99^th (97.5^th) percentile of extreme precipitation days in the region of interest. Our results show that stratospheric PV intrusions and IVT structures are intimately connected to extreme precipitation intensity and seasonality. The farther south a stratospheric PV intrusion reaches, and the larger the IVT magnitude, the more extreme the precipitation. Our algorithm detects a substantial fraction of the climatological rainfall amounts (40-70%), and a large number of the heavy precipitation days (50-80%) and the top 10 extreme precipitation days (60-90%) at many sites in southern Israel and the northern and western parts of Saudi Arabia. This identification method provides a new tool for future work to disentangle teleconnections, assess medium-range predictability and improve understanding of climatic changes of extreme precipitation in the Middle East and elsewhere.