Intense rains in Israel associated with the train effect

Abstract

The "train effect"is defined as a cloud system in which several convective cells pass over the same place in a short time. Trains produce a large amount of rainfall, frequently leading to flash floods, reported mainly over North America during spring and summer. Thirty train events were identified using radar images calibrated by rain gauges for four winters, all associated with Cyprus lows (CLs). The dynamic factors responsible for their formation in Israel were examined, utilizing the ECMWF Integrated Forecast System with 0.1° resolution. Seventeen out of the 30 events share common features. Each one was found within the cold sector in the southern periphery of a CL at its occluded stage and located in the left flank of a maximum wind belt, where cyclonic shear vorticity exists. The trains cross the Israeli coast near 32.2° N, with a mean length of 35 km; last 2-3 h; and yield a total of 30-50 mm of rainfall. The maximum wind belts to the right of the trains were found to delineate the limit of the precipitative region of the CLs. Unlike classical trains, activated by thermal or frontal forcing, the eastern Mediterranean trains that develop in a cold air mass can be referred to as "cold trains"rather than the classical "warm trains".