Spatial and temporal variability of oceanic heat flux to the Arctic ice pack
Krishfield, Richard A.
Perovich, Donald K.
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In order to simulate the large-scale structure and temporal variability of oceanic heat flux (F w) to the Arctic perennial ice pack, observations of heat in the mixed layer and ice dynamics are compared with parameterizations and climatologies. Long-term drifting platform observations of seawater temperature and salinity (primarily from automated buoys) are used to describe the annual cycle of temperature above freezing (ΔT f) in the mixed layer beneath the ice pack, which are modulated by ice-ocean friction velocities (u*) determined from the platform drifts to produce estimates of F w between 1975 and 1998. On average, ΔT f is not negligible in winter, especially in the Transpolar Drift, which implies a positive F w to the ice pack by means other than solar heating. A parameterization based solely on the solar zenith angle (with a 1 month lag) is found to largely describe the observed ΔT f (with root mean square error of 0.03°C), despite the lack of an albedo or open water term. A reconstruction of F w from 1979 to 2002 is produced by modulating parameterized ΔT f with u* on the basis of daily ice drift estimates from a composite satellite and in situ data set. The reconstructed estimates are corrected for regional variations and are compared to independent estimates of F w from ice mass balance measurements, indicating annual F w averages between 3 and 4 W m−2 depending on the selection of under-ice roughness length in the ice-ocean stress calculations. Although the interannual variations in ΔT f are fixed by the parameterization in the derived reconstruction, the dynamics indicate an overall positive trend (0.2 W m−2 decade−1) in Arctic F w, with the largest variations found in the southern Beaufort Gyre.
Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 110 (2005): C07021, doi:10.1029/2004JC002293.
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