NAME =  Dr. Shin-Ya Ogino  
ORGANIZATION =  Graduate School of Science and Technology, Kobe University  
ADDRESS =  Nada-ku, Kobe 657-8501, Japan  
COUNTRY =  Japan  
PHONE =  +81 78 803 6558  
FAX =  +81 78 803 5787  
E-MAIL =  ogino@ahs.scitec.kobe-u.ac.jp  
POSTER_ONLY =  yes  
THEME =  T3  
DATE =  09-Aug-04-17:13:02  
ABSID = T3DSO09Aug04171302 
TITLE = Lower-stratospheric and upper-tropospheric disturbances over Thailand during January 2000 
AUTHOR_1 = Shin-Ya Ogino 
INSTITUTION_1 = Graduate School of Science and Technology, Kobe University 
AUTHOR_2 = Kaoru Sato 
INSTITUTION_2 = Arctic Environment Research Center, National Institute of Polar Research 
AUTHOR_3 = Manabu D. Yamanaka 
INSTITUTION_3 = Frontier Observational Research System for Global
Change (FORSGC), Graduate School of Science and Technology, Kobe University 
AUTHOR_4 = Akira Watanabe 
INSTITUTION_4 = Faculty of Education, Fukushima University 
ABSTRACT =   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.