The effects of Atmospheric Rivers on Iran climate

Document Type : Full length article


1 M.A. in Synoptic Climatology, Kharazmi University, Tehran, Iran

2 Associate Professor of Climatology, Kharazmi University, Tehran, Iran


Water vapor can spread in molecular, unstable and erratic phase and can also transfer by convection and advection process. This transfer happens from the earth and ocean surfaces to the atmosphere in hot air. This type of transfer is considered as the main pattern. In the studies of the atmosphere, one of the prominent factors to be considered is the complexity of water vapor and its cycle. Water structure is different above the surface of the earth and the oceans. The study on water structure was initially conducted in 1960, in which a great deal of information gathered by the meteoric satellites and many researches were carried out about this phenomenon. One of the water structures is the atmospheric river, which is recently considered as a separate factor. The definition of the atmospheric river as the Tropospheric River was initially introduced by Riginald Newell in 1992. Given the fact that Middle East, especially Iran, is facing an overwhelming trend of drought, it is necessary to provide programs and plans to prevent this phenomenon. Moreover, the vast and small water sources and the moisture entries have to be identified.
Materials and Methods 
In this research the specific humidity maps were reanalyzed in three years (2011, 12, 13), as provided by NOAA administration. About 1000 maps from different surfaces were drawn in this period. After the days with the occurrence of Atmospheric River were identified, jet stream maps were produced. For the jet stream maps two types of winds were used: UWND and VWND. They are derived from the NOAA administration. The maps were designed by the GRADS program by the use of 300 hPa of the defined day. Then, we studied the relation between the atmospheric river and jet stream of 300 hPa for the defined day. These relations with zonal wind were calculated in SPSS program by using the Pearson correlation coefficient.
Results and Discussion
The average occurrence of ARS phenomenon in Iran is 13. These are entering to the country from different directions. In 2012, the highest amount of atmospheric river was reported. Approximately, 27 percent of the rivers were from the West, and the southeast, southwest and south with 8, 46 and 19 percent, respectively. West ARS happened mostly in February, 80 percent in the winter. The other 20 percent happened in the late autumn in December. The ARS are considered in 400hPa height, with 90 percent of them at this height level. East south ARS occurrence rate is the least with just 8 percent. Based on the seasons, these Atmospheric Rivers happen more in August and July. Their movement level is 600 hPa, which is in a lower level compared with the western ARS. West south ARS are considered as the main entries, due to the fact that 46 percent of the ARS are from this direction. These rivers are in lower levels, 600 and 700 hPa. About 60 percent of these rivers happened in the autumn, as the winter has the second rate. The other direction of the rivers is the southern part, which is considered as the most unregulated AR and can happen during all seasons except the winter. This direction is on the third stage according to the occurrence, and includes only 19 percent of the rivers. It enters Iran at the level of 700hPa, and is rarely reported by other levels.
The occurrence of Massive flood in the southern regions in the one hand, and reduction of the average total rainfall in the country on the other hand are influencing Iran from the destructive and climate events and phenomena. To predict flooding and accordance of economic activities related to water, it is necessary to recognize their sources and the transport of moisture factors in different levels of the atmosphere. In this study, we have studied transportation of water vapor through distinct phenomena on synoptic atmospheric rivers (ARS). In the beginning of the research re-processed data of specific humidity, were taken for a period of three years (2011-2013) from the NOAA. Then, the maps were prepared by Software GRADS. The results show that about 12 atmospheric rivers were observed during the study period on average annually and have been classified so-called western, southwestern, southern and southeastern Atmospheric Rivers. The studies show that River Winds have created the phenomena. Moisture in the river is about 6 times of surroundings on the average. Atmospheric rivers feed atmospheric spring head along the way. Southern and southwestern Atmospheric Rivers have the highest amount of moisture. Rainfall maps also showed the rainfall of Southern Atmospheric Rivers that lead to the flood and water logging passages in the southern cities. Pearson correlation coefficients indicated the relationship between atmospheric rivers with orbital indexes, respectively. The southern, southwestern and western ARS have correlation values of 28, 53, and 85 percent.


Main Subjects

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Volume 48, Issue 2
July 2016
Pages 247-264
  • Receive Date: 21 September 2015
  • Revise Date: 17 November 2015
  • Accept Date: 02 January 2016
  • First Publish Date: 21 June 2016