General aspects of the rebio-jaru Amazon forest micrometeorological tower LBA wet season campaign and preliminary results

A description of the 60m height micrometeorological tower built at the Amazonian Forest Rebio-Jaru Reserve (10 04' S; 61 56' W) during the LBA (Large Scale Biosphere Atmosphere Experiment in Amazonia) wet season campaign (January to March 1999), in the Brazilian State of Rondonia, is presented. Also, some of the preliminary results obtained during the campaign are presented. The Amazonian forest canopy has a mean height of 35m; however, some of the higher tree branches have heights up to 45m. So, to start the turbulent exchange process studies in this site, it is important to admit that there is a thermodynamic canopy height of about 35m, and another aerodynamic of about 45m. These facts were considered to decide the appropriate height at which the instruments were placed on the tower. Fast response instruments (3D sonic-anemometers, thermometers and hygrometers), with a sampling rate of 16 Hz (except during three days, when the sampling rate was 60Hz), were installed. Also, slow response instruments, operated at a sampling rate of 0.1Hz, provided vertical profiles of the following meteorological variables: wind velocity, temperature, specific humidity, incoming solar radiation, net radiation and photosynthetically active radiation (PAR). One of the goals of this investigation was to analyse the dependence of the vertical eddy fluxes on the cutoff time scale, as well as on the flux averaging time scale. In this sense, graphs of composite averaged fluxes and their changes with increasing cutoff scale, for several hours in a typical convective day in Amazonia are presented. They are similar to the ones presented by Sun et al (1). The results show that the flux averaging scale needed to stabilize the flux calculation changes along the day, and reaches a value greater than 20min around noon time. Some typical patterns of the diurnal variability of the measured micrometeorological variables above and inside the forest canopy are also presented. These results explain some of the physical aspects of the time variability patterns in the Amazonian Forest on a wet day.

(1) Sun, J.; Howell, J.F.; Esbensen, S.K.; Mahrt, L.; Greb, C.M.; Grossman, R.; LeMone, M.A., Journal of the Atmospheric Sciences, v.53, no21, p.: 2997-3012, 1 nov. 1996.