Abstracts for the 5th International GAME Conf.
3-5 October 2001
Aichi Trade Center
Nagoya Japan
Seasonal and Interannual variations of large circulations over Indonesia
Noriko Okamoto (1), Manabu D. Yamanaka (2), Shin-Ya Ogino (1), Hiroyuki Hashiguchi (4), Noriyuki Nishi (5), Tien Sribimawati (6), Atusi Numaguti (7)
(1) Graduate school of Science and Technology, Kobe University, Japan
(2) Graduate school of Science and Technology, Kobe University, Japan, and Frontier Observation Research System for Global Change, Japan
(4) Radio Science Center for Space and Atmosphere, Kyoto University, Japan
(5) Department of Geophysics Graduate School of Science Kyoto University
(6) Agency for the Assessment and Application of Technology, Indonesia
(7) Graduate school of Environmental Earth Science, Hokkaido University, Japan
Seasonal and interannual variations of wind and temperature in the troposphere
are analyzed based on observational data of operational rawinsondes at 11 stati
ons
over Indonesia for 1991--99.
In the upper troposphere, annual oscillation of meridional wind owing to north--
south
shift of a Hadley-like circulation is clearly found.
The Hadley-like circulation in the Indonesian sector is stronger than the zonal-
mean
Hadley circulation, and is intensified in particular during northern winter.
The intensified Hadley-like circulation induces the lowest temperature near the
tropopause.
Along the boundary of twin Hadley-like cells, the Walker-like circulation exists
and
has easterly (westerly) in the upper (lower) troposphere in the Indonesian regi
on.
The Walker circulation is also shifted from the equator associated with the Hadl
ey-cell
boundary, which may explain a part of seasonal (annual) variations of zonal win
d.
However, a semiannual oscillation which has easterly maxima in January--February
and
July--August is more clearly observed in the upper-tropospheric zonal wind, whi
ch can
be explained by conservation of absolute angular momentum for the upper-troposp
heric
winter-poleward (equatorward) air mass transport associated with the winter-hem
ispheric
Hadley-like cell invading the summer hemisphere across the equator.
Because the invasion is deeper in northern summer than in southern summer, the J
uly--August
maximum of easterly is relatively stronger than the January--February maximum,
which
also contributes to a part of annual variation of the upper-tropospheric zonal
flow.
Interannual variations are strongly affected by ENSO.
Abnormal northern-autumn westerly wind appears in the lower troposphere.
In the following winter, westerly (monsoonal) wind in the lower troposphere is v
ery weak
and tropopause height is slightly (about 0.5 km) higher than seasonal average
in an El Nino year, such as in 1997.
Somewhat similar features also appear in 1994, which is not remarkable El Nino y
ear
under the definition over the whole equatorial Pacific but is associated with s
ituations
similar to El Nino.
As other interannual variations, westerly wind magnitude
observed by BLR (Boundary Layer Radar) at Serpong (6.4 degrees south, 106.7 deg
rees east)
in the lower troposphere increases year by year in spite that easterly wind doe
s not
show such a clear change.
Tropopause height also increases about 1 km for 7 years at almost all stations.
Appearance altitudes or intensity of Hadley-like circulation are considered
as tropospheric (side) factor in tropopause height variation,
but increase of appearance altitudes in southerly with upper Hadley-like branch
was recognized only at northern Kalimantann and the Caroline islands.
Submittal Information
| Name : | Date : |
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| Organization : | Theme : |
Graduate school of Science and Technology, Kobe University, Japan | |
| Address : | Presentation : |
1-1 Rokkodai-cho, 657-8501, Kobe, Hyogo | |
| Country : | Abstract ID : |
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| Phone : | Fax : |
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| E-mail : | |
okamoto@shizen.sci.kobe-u.ac.jp | |