Parametrizing turbulent exchange over summer sea ice and the marginal ice zone

Abstract

The surface of the Arctic Ocean in summer is a mix of sea ice and water in both leads and melt ponds. Here we use data collected at multiple sites during the year-long experiment to study the Surface Heat Budget of the Arctic Ocean (SHEBA) to develop a bulk turbulent flux algorithm for predicting the surface fluxes of momentum and sensible and latent heat over the Arctic Ocean during summer from readily measured or modelled quantities. The distinctive aerodynamic feature of summer sea ice is that the leads and melt ponds create vertical ice faces that the wind can push against; momentum transfer to the surface is thus enhanced through form drag. In effect, summer sea ice behaves aerodynamically like the marginal ice zone, which is another surface that consists of sea ice and water. In our bulk flux algorithm, we therefore combine our SHEBA measurements of the neutral-stability drag coefficient at a reference height of 10 m, C DN10 , with similar measurements from marginal ice zones that have been reported in the literature to create a unified parametrization for C DN10 for summer sea ice and for any marginal ice zone. This parametrization predicts C DN10 from a second-order polynomial in ice concentration. Our bulk flux algorithm also includes expressions for the roughness lengths for temperature and humidity, introduces new profile stratification corrections for stable stratification, and effectively eliminates the singularities that often occur in iterative flux algorithms for very light winds. In summary, this new algorithm seems capable of estimating the friction velocity u

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

“…For winter conditions, Andreas et al (2010a) propose a constant z 0 for a large range of friction velocities, and argue that the former stronger dependence on friction velocity found by Brunke et al (2006) might have occurred due to a fictitious self-correlation. Andreas et al (2010b) addressed the Arctic summer, when open water is present due to melt ponds and leads, and proposed C D10N with a dependence on the sea ice concentration. Lüp-kes et al (2012a) revised this dependence by including a drag partitioning concept distinguishing between skin drag over sea ice and open water in melt ponds and leads and form drag caused by the edges of ponds and leads.…”

Estimating the Bowen ratio over the open and ice‐covered ocean

“…Thus, the typical uncertainty in any individual measurement of the Bowen ratio is 640%. But when either flux is smallwhich they almost always are over sea ice Andreas et al, 2004Andreas et al, , 2010aAndreas et al, , 2010b]-uncertainties in individual values can approach 6100%.…”

“…Over a saturated surface with a given surface temperature (and, thus, a given surface specific humidity), a wide variety of air temperatures and specific humidities yield convergent solutions for the similarity equations [e.g., Andreas et al, 2008Andreas et al, , 2010aAndreas et al, , 2010b.…”

“…[71] We say ''crude'' because estimating the sensible heat flux and thus correcting C Er in (4b) for stratification effects [see Andreas et al, 2008Andreas et al, , 2010aAndreas et al, , 2010bFairall et al, 1996Fairall et al, , 2003] have been troublesome because no satellite measurements have been found for the near-surface air temperature  r or for the temperature gradient  s À  r . Often, the sensible heat flux is thus ignored for open ocean applications.…”

“…[7] In bulk flux algorithms (also known as the bulk aerodynamic method), the turbulent surface heat fluxes are usually parameterized as [e.g., Fairall et al, 1996Fairall et al, , 2003Andreas et al, 2008Andreas et al, , 2010aAndreas et al, , 2010b …”