青藏高原和北美夏季臭氧谷垂直结构和形成机制的比较

Comparison of vertical structure and formation mechanism of summer ozone valley over the Tibetan Plateau and North America

摘要:

利用MLS卫星资料和ERA-Interim再分析资料，比较了青藏高原和北美夏季臭氧谷的垂直结构和形成机制。结果如下：青藏高原夏季臭氧谷在垂直方向上存在两个低值中心，一个中心位于对流层顶附近，强度约为-15 DU，形成原因主要为水平幅散，另一个中心位于上平流层，强度约为-1 DU，形成原因可能为光化学反应参与的氯自由基的催化损耗。北美夏季臭氧谷仅存在一个低值中心，位于对流层顶附近，该中心强度约为-5 DU，其形成的主要原因是水平辐散。

Abstract:

Since ozone hole in the polar region has been found, ozone depletion aroused extensive concern all over the world.The ozone valley over the Tibetan Plateau(OVTP) and over North America(OVNA) are seasonal ozone lows out of the polar region.They occurred both in middle latitudes and in summer half year.In order to compare their vertical structure and formation mechanism, we calculated ozone zonal deviation rate to show vertical structure of ozone valley over the Tibetan Plateau(OVTP) and North America, using MLS(Microwave Limb Sounder) data from 2005 to 2013, where ozone zonal deviation rate is ratio of ozone zonal deviation to ozone zonal mean, and ozone zonal deviation equals to ozone concentration minus ozone zonal mean.The ozone zonal deviation rate indicates that there are two centers of OVTP and one center of OVNA.One center of OVTP is located in the upper troposphere and lower stratosphere(UTLS) with peak ozone zonal deviation rate of -0.3, the other center is located in the upper stratosphere with peak ozone zonal deviation rate of -0.01.The center of OVNA is also located in the UTLS region with peak value of -0.18.The integration of zonal deviation shows that the UTLS center of OVTP with -15 DU is the strongest, the UTLS center of OVNA with -5 DU is in the middle and the upper center of OVTP with -1 DU is the weakest.Therefore, the vertical structure of ozone valley is clear.Then we analyzed the dynamic and chemical mechanism of the ozone valley.Summer circulation calculated from ERA-interim reanalysis data and summer ozone flux divergence calculated from ERA-interim data show that anticyclones are located over Tibetan Plateau and North America in the UTLS region.The anticyclone domain over the Tibetan Plateau is larger than that over North America.Moreover, corresponding ozone flux divergence over the Tibetan Plateau(1×10^-12 kg·kg^-1·s^-1) is more robust than that over North America(5×10^-13 kg·kg^-1·s^-1), which is the main reason why UTLS center of OVTP is stronger than that of OVNA.UTLS center of OVTP, UTLS center and the only center of OVNA are mainly caused by dynamic processes.However, the MLS data implies chemical reaction may play a role in the upper center of OVTP.Zonal deviation of chlorine monoxide and hydrogen chloride are negative while zonal deviation of nitrogen dioxide is positive at 10 hPa over the Tibetan Plateau, which means chlorine monoxide and hydrogen chloride concentration are higher over the Tibetan Plateau than that in the same latitudes.Besides, nitrogen dioxide concentration are lower over the Tibetan Plateau than that in the same latitudes.Higher chlorine monoxide and hydrogen chloride concentration imply that chlorine catalytic reactions make ozone loss stronger over the Tibetan Plateau.The lower nitrogen dioxide concentrations may slow the reaction which deactivates reactive chlorine into nonreactive chlorine and may strengthen the chlorine catalytic reactions.Consequently, chemical processes may have an effect on the upper center of OVTP.To sum up, there are two centers of OVTP and only one center of OVNA.UTLS center of OVTP with -15 DU is the strongest, the UTLS center of OVNA with -5 DU is in the middle and the center of OVTP in the upper stratosphere with -1 DU is the weakest.UTLS center of OVTP, UTLS center and the only center of OVNA are mainly caused by dynamic processes.However, chemical processes may have an effect on the upper center of OVTP.