10.3 Aircraft-based observations of air-sea fluxes over Denmark Strait and the Irminger Sea during high wind speed conditions (2009

10.3

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

G. N. Petersen, University of East Anglia, Norwich, Norfolk, United Kingdom; and I. A. Renfrew

During 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 content 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 minutes (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

ms-1, with 80% of the flux data in the range 15-19 ms-1.

The observed range of air-sea turbulent fluxes was large. Over open water, the wind stress varied from 0.2 to 1.9 Nm-2 and

the surface sensible and latent heat fluxes from 50 to 300 Wm-2 - resulting in total surface heat fluxes of up to 600 Wm-2.

The exchange coefficients are at the upper end of those previously observed. Mean values for the 15-19 ms-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 the bin-median coefficients suggested by previous work. Values of CDN over sea ice and the marginal ice zone

ranged from 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.