Study on the dehydration in the Tropical Tropopause Layer by observations of minor constituents and analyses of 4-D assimilation field

热带平流层水浓度的长期趋势是通过无线电探空仪的现场观测估计出来的。在热带对流层顶层（TTL）水平平流的卷云中，观测到相对于冰的相对湿度接近80%的过饱和度。通过研究观测到的空气包裹的水混合比及其沿上游轨迹估计的最小饱和混合比，首次在观测上描述了TTL中缓慢上升的空气包裹与水平平流相关的脱水的一般特征。

The long-term trend of the water concentration in the tropical stratosphere has been estimated from in situ observations by radiosondes.Supersaturations close to 80 % in relative humidity with respect to ice have been observed in cirrus clouds advected horizontally in the Tropical Tropopause Layer (TTL). General features of dehydration associated with horizontal advection for the air parcels slowly ascending in the TTL have been observationally described for the first time by investigating the water mixing ratio of the observed air parcels and their minimum saturation mixing ratio estimated along the trajectories upstream.