بررسي افت‌وخيزهاي زمستاني ازن كلي جوّ مربوط به امواج مقياس همديدي در منطقه ايران

Study of atmospheric total ozone variations due to winter synoptic scale disturbances over Iran

در اين تحقيق، پريشيدگي‌هاي ازن كلي ايجاد شده از امواج وردسپهر بالايي زمستاني در منطقه ايران براي سال‌هاي 2005 تا 2013 بررسي شده است. حضور ناوه‌‌ها و پشته‌‌هاي وردسپهر بالايي زمستاني در منطقه مي‌‌تواند باعث افزايش و كاهش مقدار روزانه ازن كلي در منطقه شود. اين الگوهاي توزيع ازن كلي از نقشه‌‌هاي ارتفاع ژيوپتانسيلي در سطح hPa 300 تبعيت مي‌‌كنند. افزايش روز‌به‌روز ازن در اثر ناوه ممكن است تا مقدار DU 140 و كاهش روز‌به‌روز ازن در اثر پشته ممكن است تا مقدار DU 75 برسد. اغلب اين افزايش‌‌ها و كاهش‌‌هاي ازني، كل منطقه ايران را تحت‌تاثير قرار مي‌‌دهد ولي بيشينه آنها بيشتر در محدوده عرض‌هاي 30-35 درجه شمالي و 50-60 درجه شرقي رخ مي‌‌دهد. اين بيشينه‌‌هاي افزايش روز‌به‌روز ازن يا در محدوده بيشينه روزانه ازن و يا در نزديكي گراديان شديد پربندهاي ازني روزانه تشكيل مي‌‌شوند. موقعيت بيشينه افزايش و كاهش روزانه ازن به‌‌ترتيب در نزديك محور ناوه‌‌ها و پشته‌‌ها و همچنين در سرعت‌‌هاي كم جريان جتي جنب‌‌حاره‌‌اي قرار دارد. در مناطق گراديان افقي شديد ازني در محدوده محور ناوه و در راستاي نصف‌النهاري، مقدار افزايش ازن بر كاهش ارتفاع ژيوپتانسيلي براي الگوهاي گوناگون بين DU/gpm 2/0 تا 8/0و به‌طور متوسط DU/gpm 5/0 است. در اغلب الگوهاي به‌دست آمده، بيشينه سرعت نزولي هوا بيش از Pa/s 2/0 و نمونه بيشينه سرعت نصف‌النهاري باد بيش از m/s 30 و نشان‌‌دهنده فعاليت موج قابل‌‌ ملاحظه‌‌اي است. اين فعاليت موج مي‌‌تواند هواي با غلظت زياد ازن وردسپهر فوقاني را كه از منطقه شكست امواج سياره‌‌اي راسبي در پوشن‌سپهر (stratosphere) عرض‌هاي بالا منشا مي‌گيرد، به عرض‌هاي كمتر در اين منطقه بياورد.

Ozone is an important chemical constituent of the atmosphere, and stratosphere it protects the Earth surface from harmful UV radiations, such that it is known as “good ozone” while, in the lower troposphere it is a highly oxidizing pollutant and known as “bad ozone”. It is also a greenhoure gas that can affect the climate. Hence, the study of spatial and temporal variations of ozone is important in the atmosphere. Large scale atmospheric flows, specially large scale wave activities can contribute to stratosphere-troposphere interaction, leading to the vertical exchange of ozone. Specially transfer of good ozone to the troposphere where it can chemically react fast, through which regionally changes the total atmospheric ozone. These large-scale synoptic systems often occur in winter when the condition of baroclinic conversion of the potential energy to the kinetic energy in the middle latitudes is the largest. The wave activities at this time are also greatest, leading to meridional and vertical transfer of air. In this work the total atmospheric ozone variations over Iran due to upper tropospheric wave activities in winter for the period of 2005-2013 have been investigated. The data are acquired from the Ozone Monitoring Instrument (OMI) satellite, while the ground ozone data are from the Geophysics Station (51?23’E 35?44’N and 1419 m above sea level), University of Tehran. The OMI data has a resolution of 1 degree and have been acquired from TOMS site The synoptic data have also been obtained from NOAA. Results show that large-scale synoptic troughs and ridges are associated with the daily variations of increase (up to 140 DU) and decrease (down to 75 DU) of total ozone, respectively. The pattern of total ozone distributions over this area are well correlated with the 300hpa geopotentail maps. The variations of total ozone cover most of the Iranian Plateau, particularly 30-35°N and 50-60°E. Regions with the maximum variations of total ozone are also found in areas with the largest gradients of ozone concentrations. The areas with the largest decrease or increase of total ozone are found at the axes of troughs and ridges, respectively where large vertical motions are expected, and the westerly component of the subtropical jet stream has the least intensity. It is also found that at the axes of troughs, the gradient of ozone with respect to the geopotentail height is between 0.2 and 0.8 DU/gpm, with an average of 0.5 DU/gpm. In the dominant synoptic patterns associated with variations of total ozone, the vertical motions of 0.2 Pa/s and typical meridional velocity of 30 m.s-1 are found, indicating large wave activities in the region. Also, regions of maximum ozone appear as bands with their axes often being in the northeast-southwest direction, corresponding to the final stage of the development of large-scale mid-latitude baroclinic disturbances. These regions with such activities also cover the whole area of Iran usually from the Persian Gulf to the Caspian Sea.