Characteristic Parameters Of Fluxes In A Tropical Seasonal Rainforest Of Xishuangbanna, SW China

Based on the eddy covariance method and by using a open-path CO2 analyzer placed on a tower in a tropical seasonal rain forest in Xishuangbanna (ChinaFlux), we got the data at 10 Hz of six microclimate factors (three dimensional direction wind speed (u, v, w), CO2 concentration, H2O concentration and air temperature) above the canopy. we adopted several clear day's data selected from four typical months (January, April, July and October) and divided one day into five parts to calculate the power spectrum and cospectrum for each variable to vertical velocity(w). Our aim is to analyze the high-low responsivity by employing the previous figures we calculated. We adopted several clear day's data selected from 12 months in 2008, then take the averaging period of 30 mins flux data to calculate footprint in the afternoon.The results showed that:1. Under the condition of clear weather and good turbulence above the canopy in the tropical seasonal rain forest, the power spectras slopes for six velocity components and scalars followed the expected -2/3 power law in the inertial subrange, and their cospectral slopes were closed to -4/3 power law in the inertial subrange. This explains the contribution of large-scale motions to matter and energy transference above the canopy can totally satisfy the requirement of responsivity in high and middle frequency signal areas, not cery good in low frequency. We could infer that our sampling frequency of flux observation is reasonable and our data getting from the complex topographical condition in clear days are valid and could be used as the actual flux figures in the further study. 2. We got flux information from two Open-Path Eddy Covariances (OPEC).One sensors installed at the top level of the tower(70.0m), and the other at the up level, at 48.8m above the canopy. For the same period of one day in each month, when the atmospheric stabilities are similitude, all the information came from a settled aera. wind speed change is the main incentive for deviation of individual months, but not because of the seasons. In the same atmospheric conditions, with the increased of the observation height, the source area of footprint will be larger, and extend along the wind direction. This result confirmed that our flux data adequately revealed the characteristics of the area where we have long-time observation(Permanent observation plots), and not too much influence by the local terrain conditions, can be used in the study of Bio-climatology and carbon flux.