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Roger Andersen

Principal Mathematician

Email

roger@apl.washington.edu

Phone

206-543-1258

Biosketch

Roger Andersen has made 35 trips to the polar regions for scientific research since joining the Polar Science Center in 1975, when it was the Arctic Ice Dynamics Joint Experiment. His current projects include the North Pole Environmental Observatory and the Freshwater Switchyard of the Arctic Ocean.

Department Affiliation

Polar Science Center

Education

B.A. Mathematics, Washington State University, 1970

M.S. Atmospheric Science, University of Washington, 1973

Publications

2000-present and while at APL-UW

The cyclonic mode of Arctic Ocean circulation

Morison, J., R. Kwok, S. Dickinson, R. Andersen, C. Peralta-Ferriz, D. Morison, I. Rigor, S. Dewey, and J. Guthrie, "The cyclonic mode of Arctic Ocean circulation," J. Phys. Oceanogr., EOR, doi:10.1175/JPO-D-20-0190.1, 2021.

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20 Jan 2021

Arctic Ocean surface circulation change should not be viewed as the strength of the anticyclonic Beaufort Gyre. While the Beaufort Gyre is a dominant feature of average Arctic Ocean surface circulation, empirical orthogonal function analysis of dynamic height (1950–1989) and satellite altimetry-derived dynamic ocean topography (2004–-2019) show the primary pattern of variability in its cyclonic mode is dominated by a depression of the sea surface and cyclonic surface circulation on the Russian side of the Arctic Ocean. Changes in surface circulation after AO maxima in 1989 and 2007–08 and after an AO minimum in 2010, indicate the cyclonic mode is forced by the Arctic Oscillation (AO) with a lag of about one year. Associated with a one standard deviation increase in the average AO starting in the early 1990s, Arctic Ocean surface circulation underwent a cyclonic shift evidenced by increased spatial-average vorticity. Under increased AO, the cyclonic mode complex also includes increased export of sea ice and near-surface freshwater, a changed path of Eurasian runoff, a freshened Beaufort Sea, and weakened cold halocline layer that insulates sea ice from Atlantic water heat, an impact compounded by increased Atlantic Water inflow and cyclonic circulation at depth. The cyclonic mode's connection with the AO is important because the AO is a major global scale climate index predicted to increase with global warming. Given the present bias in concentration of in situ measurements in the Beaufort Gyre and Transpolar Drift, a coordinated effort should be made to better observe the cyclonic mode.

Sea state bias of ICESat in the subarctic seas

Morison, J., R. Kwok, S. Dickinson, D. Morison, C. Peralta-Ferriz, and R. Andersen, "Sea state bias of ICESat in the subarctic seas," IEEE Geosci. Remote Sens. Lett., 15, 1144-1148, doi:10.1109/LGRS.2018.2834362, 2018.

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1 Aug 2018

The fine spatial resolution of laser altimeters makes them potentially valuable to oceanography studying features at mesoscale, close to land, and in the marginal ice zone. To fulfill this promise, we must understand laser sea state bias (SSB). SSB occurs in the measurement of sea surface height in the presence of waves when the altimeter observations are preferentially influenced by particular parts (e.g., wave troughs) of the wave-covered surface. Radar altimeters have received considerable attention relating radar SSB to wave properties and wind speed. Comparatively, little attention has been devoted to the SSB of laser altimeters, and the studies of laser SSB which have been done have led to indeterminate or ambiguous results even as to sign. Here, we find that to make changes in satellite dynamic ocean topography (DOT) from the Ice, Clouds, and Land Elevation Satellite (ICESat) period, 2004–2009, to the CryoSat-2 period, 2011–2015, consistent with hydrography plus ocean bottom pressure in the subarctic Greenland and Norwegian seas, we need to correct the ICESat DOT for SSB. On average, ICESat SSB is –18% of significant wave height in excess of 1.7 m.

Arctic ice–ocean coupling and gyre equilibration observed with remote sensing

Dewey, S., J. Morison, R. Kwok, S. Dickinson, D. Morison, and R. Andersen, "Arctic ice–ocean coupling and gyre equilibration observed with remote sensing," Geophys. Res. Lett., 45, 1499-1508, doi:10.1002/2017GL076229, 2018.

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16 Feb 2018

Model and observational evidence has shown that ocean current speeds in the Beaufort Gyre have increased and recently stabilized. Because these currents rival ice drift speeds, we examine the potential for the Beaufort Gyre's shift from a system in which the wind drives the ice and the ice drives a passive ocean to one in which the ocean often, in the absence of high winds, drives the ice. The resultant stress exerted on the ocean by the ice and the resultant Ekman pumping are reversed, without any change in average wind stress curl. Through these curl reversals, the ice‐ocean stress provides a key feedback in Beaufort Gyre stabilization. This manuscript constitutes one of the first observational studies of ice‐ocean stress inclusive of geostrophic ocean currents, by making use of recently available remote sensing data.

More Publications

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center
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