Cloudy and clear‐sky relative humidity in the upper troposphere observed by the A‐train
Cloudy and clear‐sky relative humidity in the upper troposphere observed by the A‐train
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DOI：
10.1029/2009jd011738
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发表时间：
2009-02
影响因子：
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通讯作者：
B. Kahn;A. Gettelman;E. Fetzer;A. Eldering;Calvin K. Liang
中科院分区：
文献类型：
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作者：
B. Kahn;A. Gettelman;E. Fetzer;A. Eldering;Calvin K. Liang
[1]云层和晴空相对湿度与冰（RHI）的分布是从大气红外探测仪和CloudSat和云-气溶胶激光雷达和红外探路者卫星观测卫星的云廓线得出的。在晴朗的天空中，RHI的峰值频率为10-20%，在CloudSat检测到的云层中增加到75-95%。值的范围取决于季节、海拔、纬度、云的类型和冰水含量。RHI的全球分布揭示了在晴朗和多云的热带对流层上部和对流层下部极地地区持续的过饱和，在多云的中纬度风暴路径中大但可变的RHI，以及在晴朗的副热带地区小但可变的RHI。以前的研究使用卫星和现场观测表明，在南半球（SH）中纬度过饱和的频率更高。季节性和年际变化的RHI也表现出较大的频率一般存在于冬季半球的过饱和。提出了一种分析方法，定量分析了平均温度（T）和温度方差（sT）对RHI分布特征的影响。北方半球RHI的季节变化主要受sT的季节变化的调节，而在南半球，T和sT都调节RHI的变化。然而，T和ST的变化并不能解释SH中稍大的过饱和频率的存在，这表明人为气溶胶和冰云过程之间的联系。
[1] Cloudy and clear-sky distributions of relative humidity with respect to ice (RHI) are derived from the Atmospheric Infrared Sounder and cloud profiles from CloudSat and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation satellites. A peak frequency in RHI of 10–20% exists for clear sky, increasing to 75–95% within clouds detected by CloudSat. The range of values depends on the season, altitude, latitude, cloud type, and ice water content. Global distributions of RHI reveal persistent supersaturation in the clear and cloudy tropical upper troposphere and lower tropospheric polar regions, large but variable RHI in the cloudy midlatitude storm tracks, and small yet variable RHI in the clear-sky subtropics. Previous studies using satellite and in situ observations have shown a greater frequency of midlatitude supersaturation in the Southern Hemisphere (SH). Seasonal and interannual variations in RHI are also demonstrated with larger frequencies of supersaturation generally present in the winter hemisphere. An analytical method quantifies the impacts of mean temperature (T) and temperature variance (sT) on the distribution characteristics of RHI. The seasonal variation of RHI in the Northern Hemisphere is primarily modulated by seasonal changes in sT, whereas in the SH, both T and sT modulate variations in RHI. However, variations in T and sT do not explain the presence of slightly greater supersaturation frequency in the SH, suggesting a link between anthropogenic aerosol and ice cloud processes.