青藏高原大气甲烷浓度时空分布变化特征

Characteristics of Spatial-Temporal Variation of Atmospheric Methane over the Tibetan Plateau

利用瓦里关大气本底站甲烷观测数据对美国Aqua卫星的AIRS观测结果进行对比分析,并分析研究了2003~2012年青藏高原对流层大气甲烷的时空分布特征,结果表明:1)AIRS观测结果与近地面观测资料变化趋势一致,存在显著的正相关关系,突变时间比较一致,可以用于青藏高原区域的甲烷浓度特征分析。2)青藏高原对流层甲烷浓度在空间分布上存在显著的西北—东南走向的低值带及其南北侧存在4个固定的高值中心,分别位于阿里、那曲、山南和玉树。3)青藏高原甲烷浓度呈现显著随高度而降低的趋势,年平均甲烷浓度分别为1.810ppm(1 ppm=10-6)、1.797 ppm和1.781 ppm。在对流层中层和中上层,甲烷浓度基本呈现低值带最低、南北侧均高的山谷型分布特征。在对流层层顶,以低值带为分界线,呈现明显的南高北低特征。4)青藏高原甲烷浓度随时间呈缓慢上升趋势,平均速度为0.0018 ppm/a,夏季上升最快,秋季上升最慢。5)青藏高原甲烷存在明显的单峰型季节变化特征,夏秋季高,冬春季低,与东部地区冬、夏双峰型特征不同,随着高度上升季节变化更为明显。

This paper presents a comparative analysis of retrievals of atmospheric methane （CH4） by the Atmospheric Infrared Sounder （AIRS） on the EOS/Aqua platform and CH4 observations from 2003 to 2012 at Waliguan atmospheric benchmark station. Characteristics of spatiotemporal distribution of tropospheric methane over the Tibetan Plateau （TP） are revealed based on AIRS retrievals. The results are as follows： 1） The AIRS retrievals and the surface observation data at Waliguan show a consistent increasing trend. The time series of AIRS retrievals and surface observations are positively correlated and the correlation is statistically significant. The time of abrupt changes are consistent between the two data series. Therefore it is possible to analyze the characteristics of spatiotemporal distribution of CH4 in the tropospheric over the TP using the AIRS retrievals. 2） A northwest-southeast oriented low concentration zone （LCZ） of CH4 above the central area of TP and four permanent high concentration centers of CH4 to the south and north of LCZ （Ngari, Nagqu, Lhoka, and Yushu） are found based on spatial analysis. 3） With the increase in altitude, an obvious decreasing trend of CH4 concentration is found over the TB. In the middle and upper troposphere, the CH4 concentration is lower in the LCZ but higher on both sides of it. In the top troposphere, CH4 is higher to the south and lower to the north of LCZ. 4） CH4 concentration shows a slowly rising trend with a rate of 0.0018 ppm/a over the TB with the fastest rise in the summer and the slowest in autumn. 5） CH4 over the TB shows a clear seasonal and unimodal variation characteristic. It is higher in the summer and autumn than in winter, which is quite different to the summer-winter bimodal variation characteristic of CH4 in East China. Seasonal variation of CH4 over the TP increases as elevation increases.