Status of GAME Tropics at the end of 1900's

Overview

As a part of GEWEX/GAME, the objective of GAME-Tropics (GAME-T) is the quantitative monitoring of vapor flux, precipitation, evapotranspiration, radiative flux, and their seasonal, intra-seasonal, and interannual variation in the south-east Asia. In order to accomplish these objectives, various field observations and data collections were planned and implemented. The year 1998 was the Intensive Observation Period (IOP) of GAME and organized field observations and data collections were carried out in the target region. The observations during IOP were generally successful and valuable data were obtained. The data were examined and a comprehensive dataset is now under construction. Following to the IOP year, additional observations were planned and mostly completed.

GAME-T Observations in 1999

Unlike other field experiments under GAME, GAME-T is still keeping the field observation systems almost as same as that were held in the IOP year, 1998. Most of these observations are summarized in the diagram.

Flux Measurements

There are three groups measuring the fluxes between atmosphere and land surface. They are: Basically, all of these groups had/will have campaigns of enhanced flux measurements using eddy correlation instruments etc. in May, August, November 1999, and March 2000. The group of Prof. Suzuki is also contributing to the raingauge network in the MaeChaem River Basin. They have another flux measurements in the forest in Sarawak Island, Malaysia. The group of Prof. Aoki had/will have short-term observations in various vegetation types as he did in 1998. The target in 1999 will be teak forest.

Rawinsonde and GPS

Due to the extensive resource consumption, there was no enhanced observation by rawinsonde at TMD operational stations in 1999. Instead there will be an enhanced observation for two weeks at NongKhai in January 2000. The target of the observation is to obtain the diurnal cycle of the vertical structure in dry season at NongKhai. Mainly for the measurements of the boundary layer of the lower atmosphere, intensive observations were carried out at EGAT Tower station during February 15th through March 3rd, 1999 by the group of Prof. Sugita. Eighty rawinsonde were released mainly during daytime and synchronized with NOAA/AVHRR, TRMM, and LANDSAT observations. GPS observation will continue long-term at Bangkok and SiSamrong by the group of Prof. Kato.

Radar

Data recording and frequent monitoring of precipitation by TMD operational Radar was done at ChiangMai in August 1999. The Omkoi radar of BRRAA has been operated under their project named Applied Atmospheric Resources Research Program (AARRP). It will finish in the year 1999 and it will be operated under the dam operation project 2000-2005. The new project has arose 1999-2005 for the rain making research in the Northeastern region of Thailand. The new radar system has been installed at Pi Mai and similar observation, more than 10 times 3D volume scan per hour for 24 hours associated with air craft in-situ measurements, will be done. The raingauge network as well as disdrometer observation may be relocated to the Pi Mai radar range.

Radiometer and Lider

The observation by the precise radiometer and lider at SiSamrong by Prof. Nakajima and Prof. Takeuchi is continuing in long range. The 11 radiometers installed all over Thailand, managed by Prof. Aoki and the Agromet division of TMD, was/will be maintained in June and December 1999. They have the target of long term monitoring, as well.

Future Perspective

Prof. T. Koike introduced the following project after the current GAME project. The proposed project is called Coordinated Enhanced Observational Period(CEOP). The idea should be described in another article, but the major points are: In the discussion at the GAME-T Workshop in Kanchanaburi in March 1999, the proposal was warmly accepted and many positive comments were given. CEOP is planned to start in the year 2001 and should be discussed more in detail in the planned GAME-T workshop in Thailand near Bangkok in March 2000.

Quick Research Report

Application of SiB2 to GAME-Tropics IOP98 Data
by
Takashi ARAI, Wonsik KIM, Taikan OKI, Katumi MUSIAKE
Institute of Industrial Science, University of Tokyo
4-6-1, Komaba, Meguro-ku, Tokyo 153-8505, Japan
Tel +81 3-5452-6381, 6382
Fax +81 3-5452-6383

SiB2 (Sellers et al., 1996) is one of the latest Land Surface Model, and the source code of the one-dimensional version of SiB2 is opened to the public. Compared with the original SiB, the new version is incorporated with a realistic canopy photosynthesis-conductance model in order to describe the simultaneous transfer of CO2 and water vapor into and out from the vegetation.

In this study, SiB2 was applied to the observational data at a tropical paddy field. These data was collected by micrometeorological observational system over paddy field in Sukhothai, Thailand during GAME-T IOP. Flux data were calculated by the Bowen-Ratio Method using net radiation, soil heat flux, water heat storage and temperature and water vapor at two height.

Comparison of simulated heat flux and observed values on 21st and 22nd October in 1998 (LAI=5) is shown in Fig1. Latent heat flux (LE) and sensible heat flux (H) were well simulated, and simulated ground heat flux (G) is almost equal to the sum of observed G and water heat storage (W). In this case, daily variation of heat flux was well simulated by SiB2.

Comparison of simulated heat flux and observed values on 21st and 22nd August in 1998 (LAI=1) is shown in Fig2. LE is underestimated and H is overestimated, and simulated G is also larger than the sum of observed G and W. In the case of small LAI, exchange of energy and water is conducted mainly at water surface under canopy layers. Therefore evaporation from water surface is large. On the contrary, in SiB2, capacity of surface water storage is too small to store enough water realistically. As a result, soil surface becomes dry quickly, evaporation from surface is suppressed, and LE is underestimated.

In order to make up for these defects, SiB2-Pad in which water body is taken into account was developed. Surface water storage is for puddle storage in original SiB2, but in SiB-Pad, is corresponded to paddy field to prevent soil surface from being dry and to simulate water depth and evaluate water heat storage. Further, water temperature is made independent from ground temperature and then heat balance equations is revised for representing realistic water heat storage and heat flux from water surface.

In the test run of SiB2-Pad, variation of water depth was well simulated by adjusting soil conductivity. Water temperature was a little underestimated during night time, but was much closer to observed value compared with ground surface temperature by original SiB2.

Comparison of heat flux simulated by SiB2-Pad and observed values on 21st and 22nd August in 1998 (LAI=1) is shown in Fig3. Latent heat flux (LE) and sensible heat flux (H) were well simulated. As the result, heat flux is also well simulated under small LAI by SiB2-Pad, and estimation of heat flux over paddy field all of the year has become possible. Since the paddy field is popular in the South East Asia, such a modification to a land surface model should be relevant for the various scales of modelling study in the region. The developed SiB2-Pad is now under coupling with a GCM and a regional climate model for further investigations of the energy and water cycles.

Acknowledgments

The authors would like to extend their best thanks to Prof. M. Aoki for his efforts to collect the energy and water flux data at Sukhothai paddy field used in this note.

References

Figure 1:
Comparison of heat flux simulated by original SiB2 and Observation in Sukhothai paddy field (LAI=5) October 1998. Rn:net radiation, LE: latent heat, H:sensible heat, G:ground heat flux, W:water heat storage.

Figure 2:
Same as Figure 1 but for August 1998, LAI=1.


Figure 3:
Same as Figure 2 but simulation by SiB2-Pad.



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(Last updated at Sunday, 21-Nov-1999 16:21:58 JST, by Taikan Oki [HOME] )