A parametrization, based on sea ice morphology, of the neutral atmospheric drag coefficients for weather prediction and climate models

Abstract

Abstract.A hierarchy of parametrizations of the neutral 10 m drag coefficients over polar sea ice with different morphology regimes is derived on the basis of a partitioning concept that splits the total surface drag into contributions of skin drag and form drag. The new derivation, which provides drag coefficients as a function of sea ice concentration and characteristic length scales of roughness elements, needs fewer assumptions than previous similar approaches. It is shown that form drag variability can explain the variability of surface drag in the marginal sea ice zone (MIZ) and in the summertime inner Arctic regions. In the MIZ, form drag is generated by floe edges;in the inner Arctic, by edges at melt ponds and leads due to the elevation of the ice surface relative to the open water surface. It is shown that an earlier fit of observed neutral drag coefficients is obtained as a special case within the new concept when specific simplifications are made which concern the floe and melt pond geometry. Due to the different surface morphologies in the MIZ and summertime Arctic, different functional dependencies of the drag coefficients on the sea ice concentration result. These differences cause only minor differences between the MIZ and summertime drag coefficients in average conditions, but they might be locally important for atmospheric momentum transport to sea ice. The new parametrization formulae can be used for present conditions but also for future climate scenarios with changing sea ice conditions.

Advances in understanding and parameterization of small-scale physical processes in the marine Arctic climate system: a review

“…stand-alone atmosphere or coupled ocean-sea-ice-atmosphere model). Compared to pre-IPY results, the role of melt ponds in the parameterizations by Andreas et al (2010) and Lüpkes et al (2012a) is a new aspect. Lüpkes et al (2013) showed on the basis of sea ice concentration and melt pond fraction data obtained by MODIS (Rösel et al, 2012) that the inclusion of the melt pond effect on roughness has a significant impact on the drag coefficients to be used in climate models.…”

“…In addition to the skin friction over smooth ice/snow surface, the aerodynamic roughness of sea ice is affected by factors generating form drag: ridges, floe edges, and sastrugi (Andreas et al, 2010a, b;Andreas, 2011;Lüpkes et al, 2012aLüpkes et al, , 2013. This generates a challenge for operational modelling: the above-mentioned characteristics of sea ice surface vary rapidly in time and often over small spatial scales, but they are difficult to observe by remote sensing.…”

“…The observational values include a large scatter, and a major question is how to parameterize the role of form drag due to flow edges and keels. In the atmosphere, the new parameterizations for z 0 have dealt with the same issue: the role of ridges, flow edges, melt pond edges, and sastrugi in the generation of form drag (Andreas et al, 2010a, b;Andreas, 2011;Lüpkes et al, 2012aLüpkes et al, , 2013. The z 0 values applied in large-scale atmospheric models, however, sometimes strongly differ from the results of field experiments, because z 0 is used as a tuning parameter.…”

neXtSIM: a new Lagrangian sea ice model

“…Tremblay and Mysak, 1997;Hopkins, 2004;Schreyer et al, 2006;Wilchinsky and Feltham, 2006;Sulsky et al, 2007;Girard et al, 2011;Tsamados et al, 2013;Herman, 2016;Rabatel et al, 2015;Dansereau et al, 2016), and wind and/or ocean drag parameterisations (e.g. Lu et al, 2011;Lüpkes et al, 2012;Tsamados et al, 2014). These developments still need to be further evaluated regarding their contribution to better reproduce the complexity of sea ice dynamics mentioned earlier, in realistic set-ups.…”

Processes controlling surface, bottom and lateral melt of Arctic sea ice in a state of the art sea ice model

“…Wave-ice interaction fractures the ice and leads to smaller floes in the marginal ice zone. The average floe size typically varies with the ice concentration and was parametrized in the marginal ice zone by Lüpkes et al [42] to be:…”