サガワ ヒデオ   SAGAWA HIDEO
  佐川 英夫
   所属   京都産業大学  理学部 宇宙物理・気象学科
   職種   教授
言語種別 英語
発行・発表の年月 2015/11
形態種別 研究論文
査読 査読あり
標題 Seasonal variation of the HDO/H2O ratio in the atmosphere of Mars at the middle of northern spring and beginning of northern summer
執筆形態 その他
掲載誌名 Icarus
出版社・発行元 ACADEMIC PRESS INC ELSEVIER SCIENCE
巻・号・頁 260,pp.7-22
著者・共著者 Aoki, S,Nakagawa, H,Sagawa, H,Giuranna, M,Sindoni, G,Aronica, A,Kasaba, Y
概要 We present the seasonal variation of the HDO/H2O ratio caused by sublimation-condensation processes in a global view of the martian water cycle. The HDO/H2O ratio was retrieved from ground-based observations using high-dispersion echelle spectroscopy of the Infrared Camera and Spectrograph (IRCS) of the Subaru telescope. Coordinated joint observations were made by the Planetary Fourier Spectrometer (PFS) onboard Mars Express (MEX). The observations were performed during the middle of northern spring (Ls = 52 degrees) and at the beginning of summer (Ls = 96 degrees) in Mars Year 31. The retrieved latitudinal mean HDO/H2O ratios are 4.1 +/- 1.4 (Ls = 52 degrees) and 4.4 +/- 1.0 (Ls = 96 degrees) times larger than the terrestrial Vienna Standard Mean Ocean Water (VSMOW). The HDO/H2O ratio shows a large seasonal variation at high latitudes. The HDO/H2O ratio significantly increases from 2.4 +/- 0.6 wrt VSMOW at Ls = 52 degrees to 5.5 +/- 1.1 wit VSMOW at Ls = 96 degrees over the latitude range between 70 degrees N and 80 degrees N. This can be explained by preferential condensation of HDO vapor during the northern fall, winter, and spring and sublimation of the seasonal polar cap in the northern summer. In addition, we investigated the geographical distribution of the HDO/H2O ratio over low latitudes at the northern spring in the longitudinal range between 220 degrees W and 360 degrees W, including different local times from 10 h to 17 h. We found the HDO/H2O ratio has no significant variation (5.1 +/- 1.2 wit VSMOW) over the entire range. Our observations suggest that the HDO/H2O distribution in the northern spring and summer seasons is mainly controlled by condensation-induced fractionation between the seasonal northern polar cap and the atmosphere. (C) 2015 Elsevier Inc. All rights reserved.
DOI 10.1016/j.icarus.2015.06.021
ISSN 0019-1035/1090-2643