Evidence of nocturnal horizontal transport of CO2 at an Amazon pasture/agricultural site
Otávio
C
Acevedo, UFSM, otavio@smail.ufsm.br
(Presenting)
Osvaldo
Luiz Leal de
Moraes, UFSM, moraes@mail1.ufsm.br
Rodrigo
da
Silva, UFSM, rodrigo@asrc.cestm.albany.edu
David
Roy
Fitzjarrald, SUNY, fitz@asrc.cestm.albany.edu
Ricardo
K
Sakai, SUNY, sakai@asrc.cestm.albany.edu
Matthew
J.
Czikowsky, SUNY, matt@asrc.cestm.albany.edu
The difficulty in correctly determining nighttime surface CO2 emissions has been a major problem for the closure of carbon budgets of different ecosystems.
Frequently, data from calm nights, for which not enough turbulent activity exists, are neglected and the analysis is restricted to windier conditions. In many cases the use of such technique leads to the removal of an appreciable portion of the datasets. If calm conditions are the predominant state of the lower atmosphere at night, the determination of surface CO2 fluxes from this method becomes seriously questionable.
At deforested regions at the Amazon, such as the LBA-ECO pasture/agricultural site, surface radiative cooling leads to a strong temperature inversion that suppresses turbulent mixing at almost all the time. Alternative techniques are necessary to estimate surface nocturnal fluxes at these locations.
In previous and companion studies this estimate has been done from the profile of CO2 accumulation observed respectively at the site micrometeorological tower and by a tethered balloon system that went up to 300 m above the surface.
However, the integration of the CO2 accumulation rate at the boundary layer only equals the surface emissions if no net horizontal transport exists at the region.
In the present study, it is shown observational evidence that drainage flows exist at the pasture site and that they affect the local CO2 accumulation rate. The magnitude of the horizontal transport is estimated. Finally, the previous estimates of the nocturnal surface fluxes from the vertical profiles are corrected considering the horizontal transport terms and the impact of this correction to the carbon budget is determined.
Submetido por Otávio C Acevedo em 18-MAR-2004
Tema Científico do LBA: CD (Armazenamento e Trocas de Carbono)