Document Type : Research Paper
Authors
1
physical geography,geography faculty,university of tehran
2
Associate Professor of Climatology, Faculty of Geographical sciences, Tehran University, Tehran, Iran
3
Associate Professor of Climatology, Faculty of Geosciences, Shahid Beheshti University
4
geography faculty, university of tehran, tehran, iran
Abstract
This study purposes to identify and analyze the synoptic-dynamic patterns of the inclusive summer super-heavy rainfalls in the southeast of Iran. To do so, the rainfall data of 14 synoptic stations and 126 raingauge stations were investigated over a 26-years period of time between 1989 and 2014.The criteria, considered in this paper, for the inclusive summer super-heavy rainfalls, is the rainfall for which the Standard Score during 24 hours is “99th” percentile and more than that and also it covers at least 50 percent of the area under study. Using this criteria, heavy rainfall for 22 days was identified. In order to extract the effective synoptic patterns in the super-heavy rainfalls, for every rainy day the 0.75*0.75-degree data including sea level pressure, geopotential heights of 850, 700, 500, and 200 hPa, and zonal and meridian components of the wind flow at the levels of 850, 700, 500, and 200 hPa as well as the specific humidity of 1000, 850, 700, and 500 hPa were received from the European Centre for Medium-Range Weather Forecasts and plotted in the GrADS environment. Analyzing different synoptic maps at different levels demonstrates that three patterns of trough, low-pressure Monsoon , and high-altitude have the main role in occurrence of the summer super-heavy rainfalls in the area. One important point about the identified patterns relates to the amount of their specific humidity which ranges from 10 to 20 g / kg at sea level and 850 hpa; This means in the presence of ascent, thermal or dynamic, the summer super-heavy rainfall can be expected.
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