تازه های تحقیق
عنوان مقاله [English]
Flood phenomenon is one of the atmospheric hazards whose frecuncy is remarkable in the northwest of Iran and every year, there are a lot of Casualties and financial losses on different parts of the study area. The aim of this study was the feasibility of using the new Doppler radar technology to predict the short term flood phenomenon and send timely warning to the relevant organizations and residents of the flood prone areas. To this end, Tabriz Radar products, which can be expanded in a three dimentional structure based on the direction and speed of movement and water content of cloudes in the event of flood of the gallezar village, were selected and carefully monitored. The resuls showed that due to the ability of the radar to penetrate into the clouds and its appropriate spatial and temporal resolution, depending on the formation location and the speed of development of super cells, flood phenomena can be detected several hours before the occurrence. In case of coordination with the crisis organization and prompt warning, it can decrease its damages.
In recent years, Doppler weather radar is one of the new remote sensing technologies that can give valuable information about cloud and type of precipitation. The new technology of meteorology radar can be fruitful in the identification, monitoring, and early warning, and, eventually, reducing damage inflicted to the environment. Therefore, this study aimed to evaluate the efficiency of the products of Doppler radar in monitoring the cells of showery severe rain-producing clouds. The aim of this study was also to evaluate the performance and functional advantages of radars in monitoring and analyzing the characteristics of flash flooding covective cells in the northwest of Iran. For this aim, the production or incoming , direction of motion, and attenuation of floodable convective cells in the study area were monitored by 15-minute time steps by three main radar products including maximum display (MAX), surface rainfall intensity (SRI), and precitipation accumulation. The obtained results can be applied in establishing scientific information and missions in establishing rapid meteorological warning system and, hence, making required decisions in reducing casualties brought about by flood.
The area under study is part of the northwest of Iran that is located in the effective range of Tabriz radar. According to the power of the radar waves, its effective range can be used up to 250 km radius. For analytical studies, like this study, it is applicable to the whole range of the northwest of the country. A variety of radar products produced by the radar reaches to more than fifty products. Each product has different output specifications and performance with graphics, charts, and meteorological signs. Of these products, about 20 products are generated and stored by Tabriz radar. Some of the applied products in this study will be briefly discussed. The maximum product of the exhibition is displayed on a graphical screen after processing. It contains information which displays the maximum height and interior density of the cloud. Surface rainfall intensity product showed the intensity of precipitation at a specific level. For this purpose, a surface close to the ground was determined and by the equation between Z-R, the value of z reflection was transformed to the intensity of the rainfall. To achieve the objectives of the study, Azarshahr flood event, which occurred in 2017, was selected using the currently reported weather codes in synoptic stations in the studied area. In sampling, there was an atempt to place cases in different geographical distances and directions with respect to the radar. For the close monitoring of the showers, from the early days of the reported barrage above, the radar products were examined with 15-minute intervals. On the basis of these images, time and place, route, time and peak locations of the activities, and the death of rainfall cell were monitored.
Result and Discussion
In this study, floodable convective cloud cells producing heavy rain showers grew within a few hours from small cumulus clouds (type one without rainfall), into cumulonimbus flood-causing clouds, along with heavy rainfall and hail. The 4 April 2017 flood event convective rainfalls, which created heavy rains in small area was selected. Naturally, in the selected case, the rest of the stations had meager amount of rainfall that was not possible to recognize these convective cells with satellite images or by synoptic maps. Doppler radars had tremendous role in detecting, routing, and monitoring of the maps. Indeeed, with proper management and timely warning, a significant amount of the casualties caused by the phenomenon can be decreased. Cooperation with the crisis organization and prompt warning can also decrease its damages.
Doppler radars have great potential to improve the quality of the rainfall data because of the ability of producing data with a spatial resolution of less than 500 m and 15-minute temporal resolution and its wide coverage. The results showed that the flood event which occurred on April 4th, 2017 was a local rainfall. It was formed in a short time and at a relatively small scale and was invisible by meteorological observations and satellite images. Primary cloud cell (cumulonimbus) of an intense shower rain was formed in the early hours of the morning and gradually was grown and reached the strongest form in the afternoon and early evening and created an intense flood in the form of a shower rain. After intense rainfall event, the cloud cells became weak and collapsed. In some cases, the peak of its convective clouds got to 10 km.