Abstracts for the 5th International GAME Conf.
3-5 October 2001
Aichi Trade Center
Nagoya Japan
Seasonal characteristics of diurnal variation of precipitable water in Thailand
NAKAEGAWA Tosiyuki (1), KATO Teruyuki (2), SATOMURA Mikio (3)
(1) Meteorological Research Institute
(2) Earthquake Research Institute, University of Tokyo
(3) Faculty of Science, Shizuoka Unviersity
This study explores the diurnal variation of precipitable water
vapor estimated from GPS data (GPS-PWV) with high time resolution at
Bangkok and Chiang Mai during the GAME-Tropics Intensive Observation
Period (IOP) of 1998.
GPS$-$PWV at one$-$hour interval are calculated
from the total zenith atmospheric delay
with the surface temperature and pressure.
There exist diurnal variations of GPS$-$PWV at both sites
in the premonsoon period from mid April to early May,
but GPS$-$PWV at Bangkok reaches the maximum vales at around
early morning while that at Chiang Mai reaches that
at around evening. Such a reverse phase may be due to the
geographical location. PWV may affect the see-breeze induced
water vapor fluxes at Bangkok and
the mountain-valley induced local circulation at Chiang Mai.
Diurnal variations of the specific humidity at the surface level
do not shows apparent consistency with those of GPS$-$PWV.
The amplitude of GPS$-$PWV during the onset period from mid May to mid June,
reduced about a half of that during the premonsoon period
at both sites. GPS$-$PWV at both sites has a maximum amplitude
in the morning and in the evening. Such a double peak are
also found in the deep convection over seas such as ITCZ and SPCZ.
Hence the double peak suggests the the peak of the other convection
such as the shallow one at the different hour.
The decrease of GPS$-$PWV in the evening is consistent with
the precipitation events and it could be considered
as the conversion of water vapor to the cloud through the convection
and finally to the precipitation.
Rainy days and no rainy days are decomposited and the diurnal variations
are also examined.
The double peak appear in both composite figures but the amplitude
of rainy days is larger than that of the no rainy days.
This results suggest the double peak occurs
irrespective of the precipitation events, and therefore
the double PWV peak might link with the double peak of the
convection.
In the late monsoon period, the basic feature of the diurnal variation
at both points are similar to those in the early monsoon period.
No unique characteristics is found in this period, which
suggests that the effect of the land surface on the diurnal variation
differ so much in the two periods.
The present study reveals the characteristics of
the diurnal variation of PWV at Bangkok and Chiang Mai, and they
have different phases in premonsoon period while they are the same
in early and mature monsoon seasons.
Valley-induced local circulation might contribute to this phenomena
but it is not so much significant because the diurnal variation of
wind vectors is not consistent with it. Further an intensive observation
and a numerical experiment is needed to clarify the mechanism
responsible for it.
Submittal Information
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Meteorological Research Institute | |
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1-1 Nagamine, Tsukuba city Ibaraki | |
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