Abstracts for the 6th International GAME Conf.

3-5 December 2004

Kyoto Japan

Lower-stratospheric and upper-tropospheric disturbances over Thailand during January 2000

Shin-Ya Ogino (1), Kaoru Sato (2), Manabu D. Yamanaka (3), Akira Watanabe (4)

The radiosonde observations conducted by GAME project provided valuable information not only in the troposphere but also in the lower stratosphere. Although phenomena in the lower stratosphere are not directly related to the GAME objectives, we consider that it is also important to understand the stratosphere-troposphere coupling and exchange in relation to the monsoon circulation. As the first step to approach this issue, disturbances in the lower-stratosphere and the upper-troposphere over Thailand during January 2000 were studied by GAME-T enhanced rawinsonde observations. The temporal sampling interval of the observations was 3 hours. Such high temporal resolution data were used to analyze the wind fluctuations due to lower-stratospheric and upper-tropospheric disturbances with a period shorter than about 10 days. Frequency spectra showed three distinct peaks: a 1-day period above 20 km in height, a near-inertial period at heights around 19 km and 27 km, and a period of 2.5-9 days (or longer) in the height range of 12-17 km. The wave with a 1-day period was interpreted as a diurnal tide. A comparison with the migrating tide in the global scale wave model showed that the observational results had larger amplitude and shorter vertical wavelength than the model. The difference between the observation and the model may be caused by the superimposition of the non-migrating tide. The wave with the near-inertial period was interpreted as an internal inertial gravity wave. A hodograph analysis was performed in order to investigate the wave properties. It was found that the wave which appeared at a height around 19 km (just above the tropopause height) propagated southwestward with a ground-based group velocity of about 1.4 m/s. The longer period disturbances which appeared at 12-17 km had layered structures with the vertical scales of 2-4 km. They were considered to be due to inertial instability, based on the facts that the potential vorticity of the background atmosphere was nearly zero and that their phase structures were consistent with theory. It was shown by a backward trajectory analysis that the air parcel with negative potential vorticity had its origin in equatorial Indonesia. It was also shown by a forward trajectory analysis that the air parcel was transported to the Pacific to the south of Japan. This is consistent with the existence of similar layered disturbances that are shown using rawinsonde data at a station there.

Submittal Information

Name : Date :
    Dr. Shin-Ya Ogino
    09-Aug-04-17:13:02
Organization : Theme :
    Graduate School of Science and Technology, Kobe University
    Theme 3
Address : Presentation :
    Nada-ku, Kobe 657-8501, Japan
    Only poster
Country : Abstract ID :
    Japan
    T3DSO09Aug04171302
Phone : Fax :
    +81 78 803 6558
    +81 78 803 5787
E-mail :
    ogino@ahs.scitec.kobe-u.ac.jp