Synoptic and thermodynamic patterns of atmospheric rivers associated to heavy precipitation in the cold period of Iran

The atmospheric river is an almost emerging phenomenon in the modern scientific literature of the world that has been studied due to its association with weather extreme events, especially heavy rainfall and floods.In this study, the integrated vertical vapor transport data were used to identify atmospheric rivers, and the criteria were determined for its separation from daily fluxes. The 90th percentile of daily precipitation was then considered as the criterion for heavy precipitation across the country. Dates associated with heavy precipitation in the presence of atmospheric rivers were obtained, and its patterns were extracted by factor analysis after preparation of a 107×1190 matrix from 1000 level Geopotential height. The results showed that the first three factors account for nearly about 70% of the total variance. Overall, Sudan's low-pressure system has an undeniable role in the formation of atmospheric rivers and heavy precipitation. In Sudan's low-pressure and the Mediterranean combination pattern, the most effect was on south-west and west of the country. Sudan's low-pressure and Eastern Europe cyclone combination patterns encompass the wider parts of the country. The influence of such systems on the country was more than other patterns. In the low-pressure combination pattern of Sudan and the migratory cyclone, the rivers and heavy precipitation zones did not much extend to the northern latitudes. In terms of formation, in all patterns, the Sudan low-pressure and the Siberian High Pressure were played a major role in the gradient generation and moisture transfer to the atmospheric rivers, in the low levels of the troposphere. The sources of moisture in these layers were the Oman-Arabian Sea.