Estimating Sensible and Latent Heat Fluxes Using the Integral Method from in situ Aircraft Measurements

Abstract

n September 2009, several Aerosonde unmanned aerial vehicles (UAVs) were flown from McMurdo Station to Terra Nova Bay, Antarctica, with the purpose of collecting three-dimensional measurements of the atmospheric boundary layer (ABL) overlying a polynya. Temperature, pressure, wind speed, and relative humidity measurements collected by the UAVs were used to calculate sensible and latent heat fluxes (SHF and LHF, respectively) during three flights. Fluxes were calculated over the depth of the ABL using the integral method, in which only measurements of the mean atmospheric state (no transfer coefficients) were used. The initial flux estimates assumed that the observations were Lagrangian. Subsequent fluxes were estimated using a robust and innovative methodology that included modifications to incorporate adiabatic and non-Lagrangian processes as well as the heat content below flight level. The SHF ranged from 12 to 485 W m?2, while the LHF ranged from 56 to 152 W m?2. The importance of properly measuring the variables used to calculate the adiabatic and non-Lagrangian processes is discussed. Uncertainty in the flux estimates is assessed both by varying the calculation methodology and by accounting for observational errors. The SHF proved to be most sensitive to the temperature measurements, while the LHF was most sensitive to relative humidity. All of the flux estimates are sensitive to the depth of the boundary layer over which the values are calculated. This manuscript highlights these sensitivities for future field campaigns to demonstrate the measurements most important for accurate flux estimates.