A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Evidence of non-existence of a "spectral-gap" in turbulent datameasured above Rondonia, Brazil. Part I: Amazonian ForestMargarete O. Domingues 1,* , Gannabathula S.S.D. Prasad 1 , Leonardo D. A. Sá 1 , Celso vonRandow 1 , Antônio O. Manzi 1 , Bart Kruijt 31. Laboratório Associado de Meteorologia e Oceanografia, Centro de Previsão deTempo e Estudos Climáticos, Instituto Nacional de Pesquisas Espaciais, CP 515,12201-970, São José dos Campos, Brazil2. Alterra, P.O. Box 47,Wageningen, NetherlandsAbstract:Wavelet and Fourier analyses are used to identify the spectral characteristics of windvelocity (u, v, w components), temperature, humudity and CO 2 concentration data sets,obtained during dry and wet seasons above Amazonian forest. The data were measured inAugust-September (dry-season) and in December (wet-season), year of 2000, as a part ofthe Brazil/European Union LBA Tower Consortium, in southwestern part of Amazonianregion. Measurements are made at micrometeorological tower located in the BiologicalReserve of Jaru (10 o 04´ S, 61 o 56´ W) above a 32 m height forest canopy. The fastresponse wind speed and temperature measurements, sampled at 10.42 Hz rate, were madeusing a three-dimensional sonic anemometer (Solent A1012R, Gill Instruments), at aheight of 62.7 m. Analyses are performed over a wide frequency range, from the inertialsubrange domain up to one day time-scale. Data are studied for a five day only spectrumand for one day mean spectra and cospectra. Results showed that is not possible to identifyspectra gap in any of the investigated variables. This has important consequence in thatseparating the turbulence flow into mean and fluctuation components may not be valid.This also makes it difficult to determine a cutoff frequency for filtering the data. Thisabsence of a spectral gap is probably due to the non-stationary characteristics of turbulentfields above Amazonian forest. Some physical phenomena in tropical meteorology areproposed to explain the findings.__________________* Corresponding author.E-mail address: margaret@cptec.inpe.br