Climate Change and Climate Disaster

Investigation variation in atmospheric circulation affecting the time delay of Comprehensive and effective autumn precipitation

Document Type : Original Article

Authors

Zahra Hejazizadeh 1
Mohammad Darand 2
bouhlol alijani 3
mohammad hosean naserzadeh 4
nabi mirzaei 5

1 Kharazmi University Professor

2 Department of Climatology, Faculty of Natural Resources, University of Kurdistan

3 Professor of Climatology, Faculty of Geographical Sciences, Kharazmi University, Tehran, Iran.

4 Associate professor of Climatology, Faculty of Geographical Sciences, Kharazmi University, Tehran, Iran

5 ph-d

Abstract
Westerlies are the main driver of rainfall in Iran, and its spatial variations are an important parameter to identify the spatial and temporal differentiation of rainfall, especially its role in the temporal distribution of autumn rainfall at the same time as the beginning of the water year is very important. Early and late fall rain is a good criterion for starting the cultivation of autumn (rainy) crops. In order to explain the role of variations in atmospheric circulation on the time delay of autumn rains, rainfall data, weather patterns, wave indices, intensity and high pressure level in the subtropical region were used. The results show the weakening of the westerly wind waves due to the spatial variations of Subtropical High Pressure(STHP). The decrease in tides in October has been associated with the time delay of rainfall and the shortening of rainy days. The delay in the high-pressure southerly regression is associated with a 20-day delay and a decrease of 7 mm of monthly rainfall and finally a decrease of 15 mm of autumn rainfall. From a synoptic point of view, the time delay of precipitation is associated with the positive anomaly of geopotential height and high pressure strengthening. The time shift of the effective autumn rainfall (from October to November) is accompanied by an increase in rainfall due to the provision of suitable instability conditions. The time delay of autumn rainfall is associated with the shortening of the rainy season, the reduction of autumn and annual rainfall and finally drought.

Keywords

Synoptic
atmospheric circulation
westerly waves
subtropical high pressure
effective autumn precipitation

Subjects

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