Cooperative Institute for Research in Environmental Sciences

Estimating sensible and latent heat fluxes using the integral method from in situ aircraft measurements

Shelley L. Knuth and John J. Cassano

2014, Journal of Atmospheric and Oceanic Technology, In press

In 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 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) during three flights. Fluxes were calculated over the depth of the boundary layer using a robust and innovative method in which only measurements of mean atmospheric state (no transfer coefficients) were used. The initial flux estimates assumed that the observations were Lagrangian. Subsequent fluxes were estimated that included modifications to incorporate adiabatic and non-Lagrangian processes, and these estimates were deemed to be the most accurate. The SHF ranged from 11 to 373 Wm-2, while the LHF ranged from 19 to 121 Wm-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.