عنوان مقاله [English]
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In the present study the total atmospheric ozone distributions over Iran area for different seasons have been studied using data of OMI satellite and the ground station of the Institute of Geophysics, University of Tehran for 2007-2008. The mean daily ozone satellite data are available that are used for 10 points, representing the stations of main province centers around Iran. The data of ground station for Tehran is also used in order to check the satellite data that shows the difference between the two is less than 3 percent.
The mean regional value of total ozone concentration for 2007 was 291 DU, while the maximum and minimum mean monthly values were respectively found for March, 328.2 DU and for October, 267 DU. The annual range of mean ozone variations over the area is 248-360.5 DU. The analyses also showed that the seasonal maximum for summer and autumn was for Rasht area and its minimum was observed for Shiraz.
Investigations of the correlation coeffiecients between total ozone of selected stations show maximum correlation coeffiecients between Tehran and Gorgan stations with a value of 0.97 and 0.98 between Tabriz and Urmia stations that are nearer to each others.
During 2007 the regional monthly mean variations of ozone over this area was between 5 to 27 percent, from which the maximum and minimum variations were respectively for cold and warm seasons. This was so for the daily variations that also increased with latitude. One of the important factors in total column ozone variations in cold season is the increase in synoptic activities which needs further investigations.
Among the selected stations of the region, the highest variations of seasonal total ozone is for Rasht station with 55% and the lowest variations is for Bandar Abbas station with 32.8%.
The most noticeable daily variations of total ozone occur in February and March especially for the stations of Tabriz, Orumieh and Rasht. While the least of variations take place for July to August especially for Shiraz and Zahedan. The range of the monthly mean variations of total ozone for all selected stations was also found to be between 1% to 8%.
For the seasonal spatial distributions of total ozone in the region we prepared contour maps for the years 2007-2008 from the total ozone of about 48 points scattered over the area. These maps show that the total ozone contour for winter and spring were almost zonal, with its value increasing with latitude. This pattern was quite different for summer and autumn, with minimum value over the mountains (especially over Zagros range that have implications for UV radiation increase over the mountains) and maximum over the low land areas of coastal regions. Also in these warm seasons there is a gradual increase of total ozone from west (from the Zagros peak range) to east that appears to be due to the reduction of topographic height in this direction.
In summer as the high pressure belt of 30° moves to the area prevailing a very calm condition the troposphere and stratosphere thicknesses are influenced (thinned slightly) by mountain ranges. This factor may be responsible for ozone reduction over the mountain ranges. In the summer time the spacial gradient of total ozone is largest in the western part of Zagros range and also in the northern part of Alborz Range and the coastal area of Caspian Sea.