Airborne flux measurements and budget estimates of trace species over the Amazon Basin during the GTE/ABLE 2B expedition

Abstract

In situ airborne measurements of turbulent heat, moisture, momentum, ozone, and carbon monoxide fluxes in a convective boundary layer were obtained over a tropical rain forest between 1100 and 1630 LT on May 4, 1987. The aircraft flight path was chosen so as to fly over the tower site at the Ducke Forest Reserve near Manaus, Amazonas, Brazil. Both turbulence statistics and mean quantities were used to study the budgets of heat, water vapor, ozone, and carbon monoxide. Residuals were found in the heat and water vapor budgets and are largely explainable in terms of the bandwidth of the respective sensors used for making flux measurements. The confidence of the findings for the O3 and CO budgets were found to be limited by the error in the determination of the along‐track advective component. The ozone budget study shows an accumulation rate in the boundary layer of 0.3±0.2 ppbv h−1. The surface resistance to ozone during this flight was determined to be 0.06±0.03 s cm−1, while the aerodynamic resistance was 0.14–0.17 s cm−1. Results from the CO budget analysis show a midday accumulation rate of 0.6±0.3 ppbv h−1 in the Amazonian boundary layer. The evidence suggests production of CO in the PBL. A source of CO may exist below the lowest flight level (≈ 150 m), although it was not possible to determine what part of the flux at flight level was due to chemical production and what part may be due to surface emission.