Meteorology group, Sciences and Researches branch, Islamic Azad University (IAU), Tehran, Iran.
Environ Monit Assess. 2010 Sep;168(1-4):429-39. doi: 10.1007/s10661-009-1124-1. Epub 2009 Aug 14.
Understanding the exchange mechanism between stratosphere and troposphere is one of the most important concerns of meteorologists and climatologists for decades. Different methods are being adopted to study those mechanisms. One of those methods is the study upon the tropospheric concentration of conserve or passive entities with stratospheric origin. One of those passive entities is (7)Be that is produced upon the incident of cosmic rays on light atmospheric nuclei in the stratosphere. The availability of 5 years observations of (7)Be concentration in surface air in Tehran (35 degrees 41(') N, 51 degrees 18(') E) encouraged us to investigate meteorological condition effect on the surface concentration of (7)Be. Also, the intention was to see if there was any intrusion of stratospheric air into the troposphere at the time of high surface concentration of (7)Be and scavenging mechanism when the concentration was low. During the course of this study, it has been found that (7)Be concentration is high whenever there is a jet stream over Tehran. Since high-level jet streams normally form near tropopause folding, it could be interpreted as a sign of the intrusion of stratospheric air into the troposphere. It was also found that high concentration of (7)Be in the Tehran surface air in summer is associated with an upper ridge on 500 hPa surface located east of the city, and low concentration in winter is associated with an upper trough. The latter normally is seen whenever there is precipitation that suggests wet scavenging could be the reason for that observed low concentration.
了解平流层和对流层之间的交换机制是几十年来气象学家和气候学家最关心的问题之一。为了研究这些机制，人们采用了不同的方法。其中一种方法是研究具有平流层来源的保守或被动物质在对流层中的浓度。这些被动物质之一是（7）Be，它是在平流层中宇宙射线撞击轻大气核时产生的。在德黑兰（北纬 35 度 41'，东经 51 度 18'）进行了 5 年的（7）Be 浓度在地表空气中的观测，这一观测结果促使我们研究气象条件对（7）Be 表面浓度的影响。此外，我们还想观察在（7）Be 表面浓度较高时是否有平流层空气进入对流层，以及在浓度较低时的清除机制。在这项研究中，人们发现每当德黑兰上空有急流时，（7）Be 浓度就会升高。由于高空急流通常在对流层顶附近形成折叠，因此可以将其解释为平流层空气进入对流层的迹象。人们还发现，德黑兰夏季地表空气中（7）Be 浓度较高与城市东部 500 hPa 地表的一个高空脊有关，冬季浓度较低与高空槽有关。后者通常在有降水时出现，这表明湿清除可能是导致观测到的低浓度的原因。
