Effect of drag coefficient formula choice on wind stress climatology in the North Atlantic and the European Arctic

Abstract

Summary: Interactions between the atmosphere and the ocean determine boundary conditions for physical and biogeochemical processes in adjacent boundary layers, and the ocean surface is a complex interface where all air-sea fluxes take place and is a crucial valuable for ocean circulation and the ecosystem. We have chosen to study the differences between the relevant or most commonly used parameterizations for drag coefficient (CD) for the momentum transfer values, especially in the North Atlantic (NA) and the European Arctic (EA), using them together with realistic wind field. We studied monthly mean values of air-sea momentum flux resulting from the choice of different drag coefficient parameterizations, adapted them to momentum flux (wind stress) calculations using wind fields, sea-ice masks, as well as integrating procedures. We compared the resulting spreads in momentum flux to global values and values in the tropics, an area of prevailing low winds. We found that the spread of results stemming from the choice of drag coefficient parameterization was 14% in the Arctic, the NA and globally, but it was higher (19%) in the tropics. On monthly time scales, the differences were larger at up to 29% in the NA and 36% in the EA (in months of low winds) and even 50% locally (the area west of Spitsbergen). Comparing the values of drag coefficient from chosen parameterizations, it showed that momentum fluxes were largest for all months, in both regions with low and high winds, when the CD values increased linearly with wind speed. Keywords: Drag coefficient, European Arctic, North Atlantic, Parameterizations