Observations of surface momentum exchange over the marginal ice zone and recommendations for its parametrisation

Abstract

Abstract. Comprehensive aircraft observations are used to characterise surface roughness over the Arctic marginal ice zone (MIZ) and consequently make recommendations for the parametrisation of surface momentum exchange in the MIZ. These observations were gathered in the Barents Sea and Fram Strait from two aircraft as part of the Aerosol-Cloud Coupling And Climate Interactions in the Arctic (ACCA-CIA) project. They represent a doubling of the total number of such aircraft observations currently available over the Arctic MIZ. The eddy covariance method is used to derive estimates of the 10 m neutral drag coefficient (C DN10 ) from turbulent wind velocity measurements, and a novel method using albedo and surface temperature is employed to derive ice fraction. Peak surface roughness is found at ice fractions in the range 0.6 to 0.8 (with a mean interquartile range in C DN10 of 1.25 to 2.85 × 10 −3 ). C DN10 as a function of ice fraction is found to be well approximated by the negatively skewed distribution provided by a leading parametrisation scheme (Lüpkes et al., 2012) tailored for sea-ice drag over the MIZ in which the two constituent components of drag -skin and form drag -are separately quantified. Current parametrisation schemes used in the weather and climate models are compared with our results and the majority are found to be physically unjustified and unrepresentative. The Lüpkes et al. (2012) scheme is recommended in a computationally simple form, with adjusted parameter settings. A good agreement holds for subsets of the data from different locations, despite differences in sea-ice conditions. Ice conditions in the Barents Sea, characterised by small, unconsolidated ice floes, are found to be associated with higher C DN10 values -especially at the higher ice fractions -than those of Fram Strait, where typically larger, smoother floes are observed. Consequently, the important influence of sea-ice morphology and floe size on surface roughness is recognised, and improvement in the representation of this in parametrisation schemes is suggested for future study.

Atmospheric Conditions during the Arctic Clouds in Summer Experiment (ACSE): Contrasting Open Water and Sea Ice Surfaces during Melt and Freeze-Up Seasons

“…However, it appears on average higher over ice than over open water. Sea ice has greater roughness than open water (e.g., Elvidge et al 2016); this difference is more pronounced in melt than in freeze-up, consistent with a larger fraction of new and smoother ice forming in the latter season. Seasonal differences in sensible heat flux (Figs.…”

Retrieving Sea Ice Drag Coefficients and Turning Angles From In Situ and Satellite Observations Using an Inverse Modeling Framework

“…Petty et al (2017) used the same parameterization with airborne observations of sea ice conditions to produce Arctic maps and time series of C A . Elvidge et al (2016) performed extensive validation for the Lüpkes et al (2012) parameterization from airborne observations of eddy-covariance-derived neutral atmospheric drag. Renfrew et al (2019) tested the atmospheric sensitivity of the Lüpkes et al parameterization in a fully coupled model.…”

Atmospheric form drag coefficients over Arctic sea ice using remotely sensed ice topography data, spring 2009–2015

“…Observational estimates of the atmospheric drag coefficient have been based on data collected predominantly within the Marginal Ice Zone (MIZ) [e.g., Andreas et al , ; Elvidge et al , , and references therein]. In the Fram Strait MIZ, the impact on from pressure ridges was shown to be small [ Mai et al , ] and is instead thought to be driven by variability in ice concentration and the resultant variability in exposed floe edges.…”