In situ observations of dehydrated air parcels advected horizontally in the Tropical Tropopause Layer of the western Pacific

[摘要] Water vapor observations by chilled-mirror hygrometers were conductedat Bandung, Indonesia (6.90° S, 107.60° E) andTarawa, Kiribati (1.35° N, 172.91° E) in December 2003to examine the efficiency of dehydration during horizontal advectionin the tropical tropopause layer (TTL).Trajectory analyses based on bundles of isentropic trajectories suggest thatthe modification of air parcels' identity due to irreversible mixingby the branching-out and merging-in of nearby trajectories is foundto be an important factor,in addition to the routes air parcels follow,for interpreting the water vapor concentrations observed bychilled-mirror frostpoint hygrometers in the TTL.Clear correspondence between the observed water vapor concentrationand the estimated temperature history of air parcels is foundshowing that drier air parcels were exposed to lower temperaturesthan were more humid ones during advection.Although the number of observations is quite limited,the water content in the observed air parcels on many occasionswas more than that expected from the minimum saturation mixing ratioduring horizontal advection prior to sonde observations.

[学科分类] 大气科学