Study on the dehydration processes in the tropical tropopause layer by measurements of minor constituents and numerical modeling

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The purpose of the present study is to better understand the dehydrationprocesses in the TropicalTropopause Layer and to monitor the water vapor trend in the tropical lower stratosphere by conducting radiosonde observations using frostpoint hygrometers in the western for the water tropical Pacific. Uniqueness of this project lies in the coordinated observation strategy for the water vapor "match", that is, to operate a network of stations to catch the same air parcels twice or more toquantify the dehydrated amount for the specific air observed. The main findings so far obtained from the accumulated data are: There are close relationships between the water amount of the observed air parcel and the saturation water mixing ratio along the trajectories of the corresponding air parcel reflecting the meteorological conditions such as the location of the stations, isentropic levels, season and ENSOstatus. Specific features of the sonde profiles such as a jump in the relative humidity could be traced as a difference in the origin of the air parcel on an individual sounding basis. This fact provides us some confidence in identifying the "match" pairs in spite of the difficulties in such an attempt. Comparisons of the water profiles with cirrus distributions observed by lidars show interesting results on the condensation and super saturation for the air. Some of these results have been presented in international conferences and published in the literature. Unfortunately, the collaborative observations with TC4 did not take place due to the budget problem in US. However, our data have contributed to the validation of satellite observations. Finally it will be worth mentioning that we have conducted some test flights with Lyman alpha hygrometer and are preparing some assimilation runs by incorporating observed data for the future extension of the current study.