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JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 110,
C10008,
doi:10.1029/2004JC002858,
2005
A numerical study of the western Cosmonaut polynya in a coupled ocean–sea ice model
T. G. Prasad
Department of Oceanography, Naval Postgraduate School, Monterey, California, USA
Julie L. McClean
Department of Oceanography, Naval Postgraduate School, Monterey, California, USA
Elizabeth C. Hunke
Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico, USA
Albert J. Semtner
Department of Oceanography, Naval Postgraduate School, Monterey, California, USA
Detelina Ivanova
Department of Oceanography, Naval Postgraduate School, Monterey, California, USA
Abstract
Employing results from a 0.4°, 40-level fully global, coupled ocean–sea ice model, we investigated the role of physical processes
emanating from atmosphere, ocean, and ice in the initiation, maintenance, and termination of a sensible heat polynya with
a focus on the western Cosmonaut polynya that occurred during May–July 1999. The Cosmonaut polynya first appeared in early
May 1999 in the form of an ice-free embayment, transformed into an enclosed polynya on 5–9 July, and disappeared by late July,
when the ice from the surrounding regions began to encircle the embayment. Except for the differences in ice concentrations,
the time of appearance, size, and shape of the Cosmonaut polynya simulated by the model are in approximate agreement with
the Special Sensor Microwave/Imager (SSM/I) observations. Between May and July 1999 the Cosmonaut Sea experienced two synoptic
storms, both lasting ∼5 days. Followed by the passage of the first storm on 12–19 June, there was a remarkable growth in the
size of the embayment by 21 × 103 km2. Associated with this, the sea surface temperature (SST) rose by 0.15°C, the upward heat flux jumped from 5 to 94 W m−2, and a net freshwater flux into the ocean increased by 2 cm d−1. By running the model simulation with a 20% wind speed increase, it is demonstrated that the twofold increase in SST and
upward heat flux increased the embayment area by 15 × 103 km2 and decreased the ice concentration by approximately 10% from the control run. A similar, but somewhat weaker wind event
that took place on 30 June to 10 July had less influence on the embayment area although the upward heat flux (65 W m−2) was comparable to the first event. By examining the vertical displacement of the −1.6°C isotherm depth prior to, during,
and after these two storms, we demonstrate that the impetus provided by these storms was able to raise the −1.6°C isotherm
depth by 30 m through wind-driven mixing, making sufficient oceanic heat input from beneath the mixed layer available to prevent
freezing and/or delay ice formation while ice in the adjacent regions continued to grow. A sudden shift in the ice drift direction
from southwest to northeast (3 July) followed by the second storm, accompanied by large air-sea temperature differences, caused
the enclosure of the embayment, subsequent formation of the polynya, and its termination.
Received 22
December
2004;
accepted 23
May
2005;
published 8
October
2005.
Keywords: Cosmonaut polynya;
coupled ocean–sea ice model;
Southern Ocean.
Index Terms: 4572 Oceanography: Physical: Upper ocean and mixed layer processes; 4532 Oceanography: Physical: General circulation (1218, 1222); 4504 Oceanography: Physical: Air/sea interactions (0312, 3339); 4255 Oceanography: General: Numerical modeling (0545, 0560); 9310 Geographic Location: Antarctica (4207).
Read Full Article (file size: 2460686 bytes) Cited by
Citation: Prasad, T. G., J. L. McClean, E. C. Hunke, A. J. Semtner, and D. Ivanova
(2005),
A numerical study of the western Cosmonaut polynya in a coupled ocean–sea ice model,
J. Geophys. Res.,
110,
C10008,
doi:10.1029/2004JC002858.
This paper is not subject to U.S. copyright. Published in 2005 by the
American Geophysical Union.
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