Long term monitoring of surface enrgy fluxes of the Amdo PBL site in the east Tibetan Plateau
Kenji TANAKA (1), Hirohiko ISHIKAWA (2)
(1) Department of CIvil and Environmental Engineering, Kumamoto Univ.
(2) Disaster Prevention Research Institute, Kyoto Univ.
In the Tibetan Plateau, several Automated Weather Stations (AWSs) has been continuously working since GAME/Tibet IOP in 1998. It is one of major goal in GAME/Tibet to evaluate surface energy fluxes in seasonal or (inter-)anuual scale. Therefore, the surface energy fluxes of one of the site, Amdo, is estimated using 14m tower data between 1998 and 2000.
The sensible heat flux is estimated using the bulk transfer coefficient, which is obtained as the function of the bulk Richardson number from the analysis of the observed turbulent fluxes and mast profiles. The latent heat flux is estimated using bowen ratio and the sensible heat flux above, instead of using the bulk transfer coefficient because of the difficulty of estimating the surface specific humidity. The net radiation flux is obtained from 4-component radiation system. The soil heat flux is obtained from the heat plate and temperature profile of near surface soil layer.
The remarkable change of sensible and latent heat fluxes could be seen between pre-monsoon and summer monsoon season, as seen by eddy correlation method in IOP. After the onset of summer monsoon, the latent heat flux increases and sensible heat flux decrease as the surface becomes wet by frequent precipitation. What is more, when such a rapid change begins varied interannually: the middle of June in 1998, and in middle of May in 2000. On interannual variation of surface energy fluxes, a heavy snowfall in late winter and spring season might give a large impact. In these season, the relative humidity of the atmospheric boundary layer is less than 30% in the daytime. And the sensible heat flux is almost same value as the net radiation. Once a heavy snowfall comes, the surface albedo become higher and the net radiation and sensible heat flux become lower raipdly.
On surface energy budget, the budget was well closed under fine condition in winter and spring, but, unexplainable residual energy exists in summer and autumn. Therefore, the authors are making attempt to estimate latent heat flux using other parameters, such as evaporative fraction and so on.
Submittal Information
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Mr. Kenji TANAKA
09-Jun-01-11:17:25
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Department of civil and environment engineering, Kumamoto Univ.
