大气红外探测器(AIRS)资料在塔克拉玛干沙漠的适用性检验与评估

Applicability validation and evaluation of AIRS retrievals in the Taklimakan Desert

由于沙漠恶劣的环境,观测站点稀少,塔克拉玛干沙漠地区的温度、湿度时空分布很难仅仅依靠少量的常规观测资料分析得到,高分辨率的大气红外探测器(AIRS)资料可有效弥补这个空缺。地形和地表发射率是影响AIRS反演温湿度廓线产品进度的两大要素,在塔里木盆地的塔克拉玛干沙漠地区使用AIRS温湿度产品必须首先对其质量进行检验。本研究主要对2016年7月1~15日晴空背景下AIRS反演的温度、位势高度、水汽数据在塔克拉玛干沙漠及周边绿洲地区在早晨和傍晚的可信度作了详细的对比分析。结果表明:(1) AIRS卫星资料集里的温度资料与探空数据有很好的吻合度。温度资料在沙漠腹地尚有较小偏差,在周边绿洲地区尤其是其中高层一致性较高。AIRS反演温度在沙漠腹地的塔中站在早晨各层的偏差明显大于傍晚,其余各站早晨和傍晚反演偏差不大。(2) AIRS卫星测得的位势高度资料几乎与探空资料的完全一致,是本对比研究中观测质量最好的要素,但AIRS探测层次能达到1 hPa,探测高度优于探空。(3)反演的湿度廓线与探空偏差较大。AIRS资料的混合比在300 hPa上的高层与探空吻合,在中层偏干,低层偏湿,低层水汽探测误差可能与盆地地形和沙漠下垫面有关。(4)早晨沙漠腹地的塔中站AIRS反演气温平均偏差在各层均比其余7个绿洲站明显偏大,在500 hPa以下的低层明显偏冷,在其上明显偏暖,偏暖幅度随高度的升高而增大。早晨绿洲AIRS反演温度在所有气压层上温度偏差绝对值均在1℃以内,均方根误差小于2℃,傍晚偏差绝对值在3℃以内,均方根误差在700 hPa以下的低层较高层大,700 hPa以上在3℃以内。绝对误差在早晨和傍晚均随高度的升高而减小,在100 hPa以上又有逆转,这种逆转在塔中站尤为明显。

The temporal and spatial distribution features of air temperatures and humidity in Taklimakan Desert, south Xinjiang, China, could hardly be learned by the seven sounding sites there, while the high resolution atmospheric infrared sounder （AIRS） data can effectively make up for the vacancy. However, the quality of AIRS retrievals suffers from complex topographic condition and land-surface emissivity, it is necessary to do the quality validation before applying them in this desert region. This study mainly focused on quality validation of AIRS retrieved air temperature, geopotential height as well as water vapor mixing ratio by comparing them with the field experimental soundings in both Taklimakan Desert and other seven traditional sounding sites over oasis region at nightfall and in the morning respectively. It is showed that, Firstly, the temperature data in the AIRS satellite data set are in good agreement with the radiosonde observation （RAOB）. The temperature data are relatively small in the hinterland of the desert, and higher in the surrounding oasis regions, especially in the upper level. The AIRS inversion of temperature in the tower of the desert hinterland, the deviation of each layer in the morning is obviously greater than that at nightfall, and the other stations have little deviation in the morning and nightfall. Secondly, the geopotential height data measured by AIRS satellite is almost the same as RAOB, which is the best factor in the comparative study. The detection level of AIRS can reach 1 hPa,which is much higher than that of RAOB. Thirdly, mixing ratio of AIRS data coincides with the upper RAOB of 300 hPa, and smaller in the middle layers, higher in the lower layers. Finally, the statistical results showed that in the morning, the AIRS inversion temperature deviation over Tazhong sounding station in each layer were higher than that over the other 7 oasis stations ,warmer above 500 hPa and cooler below, and the higher the warmer. While the AIRS inversion temperature over the remaining 7 oasis sounding station is generally higher than soundings above 500 hPa and lower below. The RMSE of the AIRS inversion temperature over the selected seven oasis sounding sites is decreased with the height being increased. The RMSE of the AIRS inversion temperature over desert sites is acceptably small, but presents a comparatively larger bias in the morning possibly due to the great emissivity there and its location in the center of the Tarim Basin.