Abstracts for the 5th International GAME Conf.
3-5 October 2001
Aichi Trade Center
Nagoya Japan
Structure of intraseasonal oscillations over Indonesia and South-East Asia
Toshiki Okuda (1), Sin-ya Ogino (1), Manabu D. Yamanaka (3), Noriko Okamoto (1), Tien Sribimawati (5)
(1) Graduate School of Science and Technology, Kobe University
(3) Graduate school of Science and Technology, Kobe University, Japan, and Frontier Observation Research System for Global Change, Japan
(5) Agency for the Assessment and Application of Technology, Indonesia
Intraseasonal oscillations of humidity and wind have been analyzed
on the basis of rawinsonde data over Indonesia. The rawinsonde data
were obtained daily at 11 operational stations of Indonesian
Meteorological and Geophysical Agency (BMG) and 22 stations in
South-East Asia and Australia in 1995. Relative humidity data at each
11 stations of BMG averaged vertically for standard pressure levels
between 1000-250 hPa at each sounding have shown good correlations
between all the stations, suggesting existence of intraseasonal
oscillations with a zonal wavelength sufficiently larger than the
extension of the Indonesian maritime continent (about 5000 km). In order
to obtain the three-dimensional structure of such oscillations, at first
the vertically-averaged daily humidity data have been averaged over all
the stations, and the resulting single time series of the mean
tropospheric humidity over Indonesia oscillations has been smoothed by
a band-pass filter with periods of 20-90 days. Centering at each
maximum/minimum of this time series, a composite analysis of humidity
and wind fields has been done.
Upper-tropospheric divergence and lower-tropospheric convergence of
zonal wind have been seen near at the humidity maximum corresponding to
a super cloud cluster propagating eastward. Near the equator, axes of
divergence (convergence) of zonal wind are inclined eastward from upper
troposphere to lower stratosphere, and the divergence region becomes
weaker and thinner in the upper troposphere (around 250 hPa). As they
are propagating eastward, these phase structures are also seen as a
downward progression, which is centered upon the equator. However, such
inclined phase structures are scarcely seen far from the equator in
Southern Hemisphere, and almost vertical phase structures spreading
upward above 500 hPa level are clearly seen in the troposphere in Jawa,
southern Surawesi (south of 5S) and Australia. On the other hand, in
Northern Hemisphere, vertical phase structures are weakened. The
observational results mentioned above show a modification of the
intraseasonal oscillations or super clusters by mountainous topography
of Sumatera, as so far suggested by Nitta et al. (1992). The inclined
phase structures observed over the equator look like an equatorial
Kelvin wave propagating in the lower stratosphere, which is shaded just
in the back of Sumatera Mountains.
Submittal Information
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Graduate School of Science and Technology, Kobe University | |
| Address : | Presentation : |
1-1 Rokkodai-cho Kobe, Hyogo 657-8501, Japan | |
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| E-mail : | |
okuda@shizen.sci.kobe-u.ac.jp | |