Abstracts for the 5th International GAME Conf.

3-5 October 2001

Aichi Trade Center

Nagoya Japan

Variability of surface fluxes depending on wind direction over a glass field in Eastern Siberia

Nakako KOBAYASHI (1), Tetsuya HIYAMA (2), Yoshiyuki ISHII (3), Hironori YABUKI (4), Yoshihiro FUKUSHIMA (5)

There are patch scale grass fields, so called alas, as well as boreal forests of larch, pine and birch in eastern Siberia. Alas is formed as a result of land-atmosphere interactions including permafrost ecosystem change. Because the surface of alas is covered with grass and pasture (partly with pond), and not with forest, the warming and cooling effects of the surface soil is stronger than the forest floor. We had measured the surface heat fluxes (radiation, sensible heat, latent heat and soil heat), canopy CO2 absorption by the eddy correlation method and other meteorological elements on an alas from snowmelt season to mid summer in 2000. There was a surface heterogeneity in conjunction with soil water contents and vegetation due to the existence of a pond at the center, so that the stationary conditions required for flux measurements was not satisfied. In this study, in order to understand the effect of the heterogeneity, we estimated the transpiration ratio in the measured latent heat because it may present the amount of vegetation in the upwind of the measurement point. The analysis is limited only for foliated season in mid summer and then grass of the field had grown up to about 60cm height and the permafrost table was more than 1.2 m in depth in maximum. Although the CO2 flux was slightly positive (source of CO2) after snowmelt, by this period it had changed to negative (sink of CO2) up to –0.8mgCO2m-2s-1 in daytime. Nearly linear relationship between CO2 absorption rate and Absorbed Photosynthetically Active Radiation (APAR) was used for prediction of canopy conductance. And also it was combined with the semi-empirical model of stomatal conductance related to humidity and CO2 concentration over the leaf surface. The derived canopy conductance was used to estimate the transpiration rate. Thus the total evapotranspiration (calculated from latent heat flux) was possible to separate to evaporation and transpiration. It was derived that the evaporation contribution in the latent heat flux was higher in case the wind came from the open water direction and dry grass field with less dense vegetation than in case the wind was from the relatively wet dense grass field near the pond. The characteristics of the region within the fetch estimated by a footprint analysis could explain this tendency. Therefore the land surface heterogeneity seems to be important for the consideration of the seasonal change of regional-scale flux if we measure it on inhomogeneous surfaces.

Submittal Information

Name : Date :
    Nakako Kobayashi
    29-May-01-16:04:00
Organization : Theme :
    Hydrospheric Atmospheric Research Center, Nagoya University
    Theme 2
Address : Presentation :
    Furo-cho, Chikusa-ku, Nagoya, 464-8601
    Poster or oral
Country : Abstract ID :
    Japan
    T2NK29May01160400
Phone : Fax :
    052-789-3474
    052-789-3436
E-mail :
    nakako@ihas.nagoya-u.ac.jp