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 II: Amazonian PastureGannabathula S.S.D. Prasad 1,* , Margarete O. Domingues 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 in a pasture in a deforested area in Amazonian. Thedata were measured in August (dry-season) and in December (wet-season), year of 2000, asa part of the Brazil/European Union LBA Tower Consortium, in southwestern part ofAmazonian region. Measurements are made at micrometeorological tower located in theNossa Senhora Farm (10 o 045.7´ S, 62 o 21.4´ W) county of Ouro Preto D’Oeste. 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 4 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 deforested area. A comparison is made with the turbulent spectra computedabove the Amazon rain forest in Rebio Jaru. Possible physical phenomena in tropicalmeteorology are proposed to explain the findings.__________________* Corresponding author.E-mail address: prasad@cptec.inpe.br