Aircraft‐based observations of air–sea fluxes over Denmark Strait and the Irminger Sea during high wind speed conditions

Abstract

AbstractDuring the Greenland Flow Distortion experiment (GFDex), aircraft‐based observations of air–sea fluxes were obtained over Denmark Strait and the Irminger Sea. High‐frequency observations of velocity, temperature and water vapour have been used to calculate turbulent fluxes of momentum, heat and moisture using the eddy covariance method. These are the first direct air–sea flux observations in this region, and add to the relatively small collection of direct air–sea flux observations made in high wind speed conditions. The aircraft‐based turbulence legs were flown at remarkably low levels, only 30–50 m above the sea‐surface and so within the atmospheric surface layer. Results are presented for 145 flux runs, each of 2 min (approximately 12 km), 131 over open water and 14 over sea ice and the marginal ice zone. The flux data were obtained in 10 m neutral wind speeds of up to 25 m s−1, with 80% of the flux data in the range 15–19 m s−1.Over open water, the wind stress varied from 0.2 to 1.9 N m−2 and the surface sensible and latent heat fluxes from 50 to 300 W m−2, resulting in total surface heat fluxes of up to 600 W m−2. The exchange coefficients are at the upper end of those previously observed. Mean values for the 15–19 m s−1 range are CDN = 2.04 × 10−3, CHN = 1.63 × 10−3 and CEN = 1.57 × 10−3 for momentum, heat and moisture, respectively. The value of the momentum exchange coefficient is in line with previous studies; however, both the heat and moisture exchange coefficients are higher than in previous studies. Values of CDN over sea ice and the marginal ice zone were in the range 1.67–6.29 × 10−3 and were, for these conditions, generally higher than CDN over adjacent open water areas. No significant spatial patterns in the exchange coefficients over open water have been detected, although there is some suggestion of higher exchange coefficients immediately downwind of the sea ice. Copyright © 2009 Royal Meteorological Society