Obesrvational Study of the Horizontal Wind Momentum Components at Central Amazon

The maintenance of the Amazon rainforest, as well as any other biome across the planet, are dependent on the influx and outflux of moisture, heat, and momentum. These in- out- fluxes may have vertical and horizontal components, but most of the scientific community's attention has been focused on the vertical transport, especially after the implementation of surface flux stations which make use of eddy-covariance systems. The reason for such tendency may reside on the fact that, ultimately, only the turbulent fluxes, which seems to be most important for the vertical transport, connects the surface to the atmosphere. However, the horizontal wind is the agent responsible for the horizontal transport (advection) of moisture, aerosols, heat, and momentum across wide regions, where there are gradients of water vapor, temperature, and wind velocity. These horizontal transports cause these quantities to be supplied or removed from the overlying atmosphere, which in the end establish the differences or gradients between surface (biome) and atmosphere. So, the aim of the study is to understand how the horizontal wind, inside the atmospheric boundary layer (ABL), is controlled by the components horizontal momentum budget. For the study we use data from more than hundred surface weather stations across north Brazil, from the 2010 year to nowadays, to determine the local wind tendency (time variation of the local horizontal wind vector), pressure gradient force (PGF), and Coriolis force (Fc). The preliminary results show that the wind, in the region, is dominated by easterly winds. The average wind has a distinct pattern increasing during the course of the morning and afternoon hours to decrease by the end afternoon and night. This behavior suggests that the convection of the ABL, during the daytime, may mix down horizontal momentum from layers above to the surface, while the lack of strong mix during the nighttime, when ABL is stable, diminish this vertical transport of momentum. The local tendency of the horizontal wind may seem partially controlled by the PGF during the convective ABL and not related to it in the morning hours. Another conclusion, as expected, is that the FC is very small, around one order of magnitude smaller than PGF. The future task includes the analysis of the fast response wind data from the Amazon Tall Tower Observatory (ATTO), which we expect to show the daily wind behavior for higher layers and to determine a characteristic or seasonal value for the vertical divergence of horizontal momentum, another term of the momentum budget.