Journal Article Balloon-borne observations of lower stratospheric water vapor at Syowa Station, Antarctica in 2013

9 ( 4 )  , pp.345 - 353 , 2015-12
Balloon-borne observations of lower stratospheric water vapor were conducted with the Cryogenic Frostpoint Hygrometer (CFH) in July, September, and November 2013 at Syowa Station (69.0oS, 39.6oE) in the Antarctic. High-precision and high vertical resolution data of water vapor concentration up to an altitude of about 28 km were obtained successfully except for a contamination in the observation of July 2013. A comparison between the CFH and coincident satellite (i.e., Aura/MLS) observations showed a good agreement within their uncertainty. A position of Syowa Station relative to the stratospheric polar vortex edge varied depending on both the observation date and altitude. Temperature and pressure histories of the observed air parcels were examined by 10-day backward trajectories. These analyses clearly demonstrated that most air parcels observed in the lower stratosphere above Syowa Station experienced final dehydration inside the polar vortex. On the other hand, a clear signature of rehydration or incomplete dehydration was also observed around a 25 hPa pressure level in the observation of July 2013.
2013年7月、9月、11月に南極昭和基地(南緯69.0度、東経39.6度)において水蒸気ゾンデ観測を実施し、高度28 km付近までの水蒸気濃度を高精度・高鉛直分解能で測定することに成功した。水蒸気ゾンデ観測と昭和基地近傍の衛星観測で得られた水蒸気濃度はそれぞれの誤差の範囲内でほぼ一致した。昭和基地の成層圏の極渦境界に対する位置は日時・高度によって変化していた。観測された空気塊の10日間の後方粒跡線を調べたところ、昭和基地上空の下部成層圏で観測された低水蒸気濃度の空気塊は大部分が過去10日間のうちに脱水されていたことがわかった。一方で、2013年7月の観測では、再蒸発または不十分な脱水を受けたと考えられる空気塊が25 hPa付近で捉えられていた。

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