عنوان مقاله [English]
Synoptic Analysis of Flood Precipitation in North of Iran (Case Study: Heavy and pervasive rainfall 4 to 7 October 2018)
The importance of precipitation as a vital component is clear, but sometimes it becomes a heavy precipitations and flood and causes very damages and sometimes irreparable the flood situated areas. The present research, synoptic investigats the flood water precipitations in Iran North in October 2018, which has caused very damage to life, financial and environment in these areas. The purpose of research is providing a comprehensive research from causes and mechanisms atmospheric of heavy precipitations caused to flood in Iran North in 5 to 7 October 2018.
Materials and method:
For research purposes, two categories of data have been used, the first category is recorded data with earth stations, which includes precipitation data of last 24 hours from the date of 5 October to 8 October 2018 which was received from the National Weather Administration website, the next category is also data the atmosphere upper levels, and the reanalysis data includes sea level pressure, geopotential heights, relative humidity, specific humidity, zonal wind, merridional wind, and omega, which are available from the National Oceanic and Atmospheric Administration website, is being prepared by the National Center for Environmental Prediction. The research was carried with environmental to circulation approach that For the one day before of precipitations start (4 October) and three days of precipitation day (5,6,7 October), maps of the geopotential height, wind direction and velocity, omega and humidit flow in 1000 to 500 hPa levels, jet stream and wind velocity in 500 to 200 hPa levels, total spatial humidity from 1000 to 500 hPa levels, hafmuler diagram of relative humidity of 1000 to 500 hPa levels and sea level pressure have been mapping with the Grads software and analyzed synoptic.
Results and discussion:
On the day before the start of precipitations, the region located between the pressure difference between the high pressure system in western Black Sea and Central Europe. The tabs of this high pressure system reach the center of the Caspian Sea, several high pressure centers in central and western China and Central Asia, the low pressure system of northern Europe and low pressure and Sudanese low pressure contract. with start of precipitations, the high pressure system in western Black Sea moved eastwards, leads to the transfer of humidity from the north to the northeast from the humidity sources of the Black Sea and the Caspian Sea to the region, and on this day, the pressure gradient between this high pressure and Sudanese low pressure tab in addition to the transfer of humidity to the region, has created baroclinic and convulsive atmosphere in the region. On the next day, high pressure system, the eastern movement from the Caspian Sea and the Aral lake, entered the are the humidity flow, with finished precipitations dominant high pressure moved to Central Asia and there are no tabs from it to the region of study .At the atmosphere upper levels at the before day of precipitations, there was a wet, windy wind flowing north to northwest from the Mediterranean and Black Seas to the region, with the start of precipitations, the southeast of the system, like omega blocking in the region, leded to the transfer of wet air from The Mediterranean, Black and Caspian Seas, and the next day, by precipitations reducing, an air convergent flow in the Republic of Azarbaijan leded to humidity transfer of the Caspian and Black Seas, and in addition, the southwest shallow humidity flow also in this day from Mediterranean Sea has entered the region, with the finished of precipitations, the main stream of winds in the western region. In these days, jet streams in the Caspian Sea around have been with indirect effects that created atmosphere baroclinic and convulsive in the area for flood water, wind speeds in the area. In the before and after days of precipitations, the atmospheric spatial humidity total was between 5 to 40 g/kg and relative humidity from 20 to 80 percent, and during precipitations days the humidity content increased and the spatial humidity total from 20 to 45 g/kg and relative humidity varied from 30 to 90 percent. In the before and days of precipitations, the omega negative values in the region, that is representative upward movement and baroclinic atmosphere, but the next day, Negative omega's levels have been receding from the region. The humidity sources in atmosphere upper levels the before and start days of precipitations of the Mediterranean and Black Seas and the precipitation next day from Mediterranean, Black and Caspian Seas, that in day finished of precipitations, humidity flow is slightly observed from the Mediterranean and Caspian Sea to the area, in earth surface near levels, there was humidity flow from the Mediterranean, Black and Caspian Seas, the before and start days of precipitations in the area, and in the second day, the precipitations included the Black, Caspian Seas and the Aral Lake, that with finished of precipitations are not humidity flow to region in this levels.
The results indicate that pressure gradient in region humidity flux from high pressure system and humidity stream flow system is due to the movement of the high pressure system towards low pressure in earth surface, the influx of humid air in atmosphere upper levels, high relative humidity and total spatial humid, indirect effects of atmospheric jet streams in atmosphere upper levels, high wind velocity in upper and lower levels of the earth, with major humidity sources that in atmosphere upper levels, including the Mediterranean, Black and Caspian Seas, in earth surface near levels, includes the Black, Caspian, Mediterranean Seas, and the Aral lake, and in earth surface, including the Black and Caspian Seas and the Aral lake, Conditions necessary to climb of humidity air intranting to area (omega negative) provided and creating destructive and flood water precipitation and has been in the study area.
Heavy precipitation, Synoptic Analysis, North of Iran
Ahmadi, M., and Jaefari, F. 2016, Synoptic analysis of desolater flood in July 2015 in the Iran North, Journal of natural geography, 9(34), pp. 83-104.