In recent years, most of the planetary boundary layer research is directed towards the understanding of turbulent fluxes in inhomogeneous conditions, either in time or space. However, only a few studies have reported turbulent flux measurements during temporal transitions The understanding of their behavior in these conditions is very important for obtaining a more realistic description of the surface-atmosphere interaction, something that would improve the description of boundary layer dynamics.

The first hours after sunrise are ideal for the observation of temperature and moisture convergence next to the surface. This is a consequence of the rapid evolution of the convective layer height and the fact that the shallow mixing layer determines relatively large variations of these properties in the period.

The main aim of the present study is to use na alternative approach to estimating surface temperature and moisture fluxes, using simple measurements from tethered balloon soundings. The data was collected as a part of LBA (Large-Scale Biosphere-Atmosphere Experiment in Amazon) project, at the pasture flux tower site, in Santarém, PA (S 03º 01’ 11.4” – W 54º 53’ 39.3´´). The site is located at a farm, at the km 77 of the Santarém-Cuiabá highway. Tethered balloon soundings were made at that location in the months of july and october, 2001.

The surface fluxes are estimated from soundings obtained at eight different mornings and then compared to the tower direct measurements of turbulence. The flux estimation is based on the temperature and humidity convergence during the first hours in the morning. Data from two subsequent soundings are used to determine the height at which the potential temperature and specific humidity coincide. Assuming zero fluxes at the mixing layer top, the integration of the temporal variation of temperature and humidity at the layer provides the surface fluxes.

There is a good comparison between the fluxes estimated from the soundings to those directly measured by eddy correlation, showing that the method is a good approach for estimating the surface fluxes from simple data.