In situ observations of dehydrated air parcels advected horizontally in the Tropical Tropopause Layer of the western Pacific F. Hasebe1, M. Fujiwara1, N. Nishi2, M. Shiotani3, H. Vömel4, S. Oltmans5, H. Takashima3, S. Saraspriya6, N. Komala6, and Y. Inai7 1Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Japan 2Geophysical Institute, Kyoto University, Kyoto, Japan 3Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Japan 4CRES, University of Colorado, Boulder, CO, USA 5Climate Monitoring and Diagnostics Laboratory, NOAA, Boulder, CO, USA 6Lembaga Penerbangan dan Antariksa Nasional, Bandung, Indonesia 7Graduate School of Environmental Science, Hokkaido University, Sapporo, Japan
Abstract. Water vapor observations by chilled-mirror hygrometers were conducted
at Bandung, Indonesia (6.90° S, 107.60° E) and
Tarawa, Kiribati (1.35° N, 172.91° E) in December 2003
to examine the efficiency of dehydration during horizontal advection
in the tropical tropopause layer (TTL).
Trajectory analyses based on bundles of isentropic trajectories suggest that
the modification of air parcels' identity due to irreversible mixing
by the branching-out and merging-in of nearby trajectories is found
to be an important factor,
in addition to the routes air parcels follow,
for interpreting the water vapor concentrations observed by
chilled-mirror frostpoint hygrometers in the TTL.
Clear correspondence between the observed water vapor concentration
and the estimated temperature history of air parcels is found
showing that drier air parcels were exposed to lower temperatures
than were more humid ones during advection.
Although the number of observations is quite limited,
the water content in the observed air parcels on many occasions
was more than that expected from the minimum saturation mixing ratio
during horizontal advection prior to sonde observations.
Citation: Hasebe, F., Fujiwara, M., Nishi, N., Shiotani, M., Vömel, H., Oltmans, S., Takashima, H., Saraspriya, S., Komala, N., and Inai, Y.: In situ observations of dehydrated air parcels advected horizontally in the Tropical Tropopause Layer of the western Pacific, Atmos. Chem. Phys., 7, 803-813, doi:10.5194/acp-7-803-2007, 2007.