青藏高原上空甲烷的时空分布特征及其夏季高值形成机制分析

Characteristics of Spatial and Temporal Distributions of Methane over the Tibetan Plateau and Mechanism Analysis for High Methane Concentration in Summer

利用搭载在美国Aqua卫星上的大气红外探测仪(AIRS)观测资料反演的全球甲烷(CH_4)产品和NCEP再分析资料,分析了2003~2014年青藏高原上空CH_4的时空变化特征,探讨了夏季CH_4高值变化与季风的关系。研究结果表明:就青藏高原整体而言,CH_4浓度随高度增加递减;对流层中高层CH_4含量季节变化较为明显,其平均浓度在7~9月处于高值,6月、10月次之,其余月份处于低值。2003~2014年CH_4含量呈逐年上升趋势,年增长率约为4.66ppb(10-9)。高原上空CH_4空间分布分析显示,高原北部CH_4浓度高于南部地区。夏季风期间,随着高原上的强对流输送和上空南亚高压的阻塞,对流层中高层CH_4浓度明显增加并不断积累,在8月底至9月初出现最大值。在分析季风指数的基础上发现,夏季季风影响下的强对流输送是高原对流层中高层CH_4高值形成的主要原因之一,对流层中高层CH_4浓度最大值出现时间较季风指数的峰值滞后约半至一个月,随着夏季风的撤退,CH_4浓度高值迅速降低。

Observations of global methane inversion （CH_4） products measured middle-upper by the Atmospheric Infrared Sounder （AIRS） on the Aqua satellite and the NCEP reanalysis data are used to investigate characteristic changes in CH_4 over the Tibetan Plateau from 2003 to 2014. The relationship between the CH_4 change and the monsoon is explored. The results indicate that, taking the Tibetan Plateau as whole, the concentration of CH_4 decreases with the increase in altitude. The seasonal variation of CH_4 in the middle-upper troposphere is significant. Monthly average concentration of CH_4 is the highest from July to September, followed by that in June and October, and the value is low in other months. The concentration of CH_4 increased year by year during 2003-2014, showing an overall increasing trend with an annual growth rate of about 4.66ppb （10-9）. Based on analysis of the spatial distribution of CH_4 over the plateau, the concentration of CH_4 is higher in the north than in the south of the plateau. During the summer monsoon period, CH_4 concentration in the mid-upper troposphere significantly increases and continues to accumulate due to strong convective transport and influences of South Asia high blocking over the plateau. The maximum CH_4 concentration appears at the end of August to early September. Analysis of the monsoon index suggests that strong convection under the influence of summer monsoon is one of the major factors contributing to the high value of CH_4 over the Tibetan Plateau. The maximum CH_4 concentration appears about one month later than the Monsoon Index. With the decline of the monsoon, the high value of CH_4 also quickly decreases.