Comparing spectra and cospectra in nearly flat terrain with those in the roughness sublayer above the Amazon forest

Spectra and cospectra of turbulent velocities and temperature are calculated for three micrometeorological towers of the LBA-ECO. The towers are located at the Amazon basin in a deforested area and at sites in the primary forest near the Tapajós River (3.0120°S, 54.5370°W). The deforested area was planted first in rice and then in soybeans. The tower is located nearly flat terrain on a gentle slope. A 3D anemometer sonic located 10 m above the ground has been collecting data since September 2000. The two forest towers are 60 m tall and sonic anemometers located at different heights permits study of the properties of in-canopy turbulence and that in the roughness layer above. Cases are separated according to the wind speed and stability parameter. Observations of the spectral and of the co-spectral peak permit to infer the most energetic eddy responsible by the turbulent heat and momentum fluxes and the inertial sub-range can be used to estimate the energy dissipation rate. In this study we show that the spectra of the turbulent vertical velocity has a defined peak for all wind and stability conditions that obey the Kolmogorov law in the inertial sub-range. However the spectral behavior of the horizontal velocity components is not as well defined as the behavior of the vertical velocity. In the inertial subrange, spectral power falls off less steeply that does the familiar –5/3 law, at least for low wind speeds. Under this same conditions the spectral maxima are observed at lower frequencies indicating that the signal may include mesoscale motions. Comparison among the vertical velocity spectra showed that in stable conditions it is more sharply peaked than in convective conditions. We present results to test whether water vapor, heat and momentum flux product cospectra follow the peaked form that Sakai et al. (2001) hypothesized or the more familiar Kaimal forms.