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Cold trap dehydration in the Tropical Tropopause Layer characterised by SOWER chilled-mirror hygrometer network data in the Tropical Pacific

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Title: Cold trap dehydration in the Tropical Tropopause Layer characterised by SOWER chilled-mirror hygrometer network data in the Tropical Pacific
Authors: Hasebe, F. Browse this author →KAKEN DB
Inai, Y. Browse this author
Shiotani, M. Browse this author →KAKEN DB
Fujiwara, M. Browse this author
Voemel, H. Browse this author
Nishi, N. Browse this author →KAKEN DB
Ogino, S. -Y. Browse this author →KAKEN DB
Shibata, T. Browse this author →KAKEN DB
Iwasaki, S. Browse this author
Komala, N. Browse this author
Peter, T. Browse this author
Oltmans, S. J. Browse this author
Issue Date: 26-Apr-2013
Publisher: Copernicus Gesellschaft Mbh
Journal Title: Atmospheric Chemistry and Physics
Volume: 13
Issue: 8
Start Page: 4393
End Page: 4411
Publisher DOI: 10.5194/acp-13-4393-2013
Abstract: A network of balloon-borne radiosonde observations employing chilled-mirror hygrometers for water and electrochemical concentration cells for ozone has been operated since the late 1990s in the Tropical Pacific to capture the evolution of dehydration of air parcels advected quasi-horizontally in the Tropical Tropopause Layer (TTL). The analysis of this dataset is made on isentropes taking advantage of the conservative properties of tracers moving adiabatically. The existence of ice particles is diagnosed by lidars simultaneously operated with sonde flights. Characteristics of the TTL dehydration are presented on the basis of individual soundings and statistical features. Supersaturations close to 80% in relative humidity with respect to ice (RHice) have been observed in subvisible cirrus clouds located near the cold point tropopause at extremely low temperatures around 180 K. Although further observational evidence is needed to confirm the credibility of such high values of RHice, the evolution of TTL dehydration is evident from the data in isentropic scatter plots between the sonde-observed mixing ratio (OMR) and the minimum saturation mixing ratio (SMRmin) along the back trajectories associated with the observed air mass. Supersaturation exceeding the critical value of homogeneous ice nucleation (OMR > 1.6 x SMRmin) is frequently observed on the 360 and 365K surfaces indicating that cold trap dehydration is in progress in the TTL. The near correspondence between the two (OMR similar to SMRmin) at 380K on the other hand implies that this surface is not sufficiently cold for the advected air parcels to be dehydrated. Above 380 K, cold trap dehydration would scarcely function while some moistening occurs before the air parcels reach the lowermost stratosphere at around 400K where OMR is generally smaller than SMRmin.
Type: article
Appears in Collections:環境科学院・地球環境科学研究院 (Graduate School of Environmental Science / Faculty of Environmental Earth Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 長谷部 文雄

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