The isotopic composition of water vapor and the concurrent atmospheric circulations around July-1st Glacier in the northeast part of the Tibetan Plateau
(1) Research Institute for Humanity and Nature
(2) Graduate School of Environmental Earth Science,Hokkaido University
The stable isotopic ratio of water vapor (¦Ä18O and ¦ÄD) was measured near July-1st (Qiyi) Glacier (39.25N, 97.75E, 4250 m) in Northwest China. From 11 to 17 August 2003, we collected and then analyzed atmospheric samples at July-1st Glacier and a base camp (BC), that was 4km from Qiyi. Then the temporal change of the isotopic composition was compared with the atmospheric circulation fields using and European Centre for Medium-range Weather Forecasts (ECMWF) objective analysis dataset.
After a snowfall in the early afternoon of the 14th, a strong northerly wind was observed in the evening. The isotopic analysis revealed a clear difference in the evening of 14th, which showed heavier¦ÄD (and¦Ä18O ) and much higher d-excess compared with those of the previous period. The snowfall and the strong northerly wind that followed were identified with the passing of a deep trough with a cold front that was observed at 500 hPa and dry air from the northwest. A back trajectory analysis revealed that the dry air from the northwest came from the upper troposphere/lower stratosphere.
We also found a diurnal change in the isotopic composition. As the day progressed from noon to late evening, the values of ¦ÄD (and¦Ä18O ) became smaller (lighter) and the values of d-excess became higher. These changes occurred during a northerly valley wind. We suggest here that these changes were observed because BC and Qiyi were located an atmospheric region where the Tibetan Plateau air mass mixes with that from the northerly arid regions. Air from the Tibetan Plateau has relatively high¦Ä18O and ¦ÄD values (relatively heavy water) and relatively low d-excess values. As the air from the northern desert has relatively small ¦Ä18O, relatively small ¦ÄD values and relatively high d-excess values, the valley wind that prevails in afternoon through evening must be bringing air from the northern desert to our site.
Submittal Information
Name :
Date :
Akiyo Yatagai
01-Aug-04-10:31:42
Organization :
Theme :
Research Institute for Humanity and Nature
Theme 5
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Presentation :
335 Takashima-cho, Kammigyo-ku, Kyoto 602-0878, Japan