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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

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.

Variability in the meteoric water, sea-ice melt, and Pacific water contributions to the central Arctic Ocean, 2000–2014

Alkire, M.B., J. Morison, and R. Andersen, "Variability in the meteoric water, sea-ice melt, and Pacific water contributions to the central Arctic Ocean, 2000–2014," J. Geophys. Res., 120, 1573-1598, doi:10.1002/2014JC010023, 2015.

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12 Mar 2015

Fourteen years (2000–2014) of bottle chemistry data collected during the North Pole Environmental Observatory were compiled to examine variations in the composition of freshwater (meteoric water, net sea-ice meltwater, and Pacific water) over mixed layer of the Central Arctic Ocean. In addition to significant spatial and interannual variability, there was a general decrease in meteoric water (MW) fractions at the majority of stations reoccupied over the duration of the program that was approximately balanced by a concomitant increase in freshwater from sea-ice melt (SIM FW) between 2000 and 2012. Inventories (0–120 m) of MW and SIM FW computed using available data between 2005 and 2012 exhibited similar variations over the study area, allowing for first-order estimates of the mean annual changes in MW (–389±194 km3 yr-1) and SIM FW (292±97 km3 yr-1) for the Central Arctic region. These mean annual changes were attributed to the diversion of Siberian river runoff to the Beaufort Gyre and the overall reduction of sea ice volume across the Arctic, respectively. In addition to this lower-frequency variability, spatial gradients and interannual variations in MW, SIM FW, and Pacific water contributions to specific locations were attributed to shifts in the Transpolar Drift that advects waters of eastern and western Arctic origin through the study area.

Changing Arctic Ocean freshwater pathways

Morison, J., R. Kwok, C. Peralta-Ferriz, M. Alkire, I. Rigor, R. Andersen, and M. Steele, "Changing Arctic Ocean freshwater pathways," Nature, 481, 66-70, doi:10.1038/nature10705, 2012.

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5 Jan 2012

Freshening in the Canada basin of the Arctic Ocean began in the 1990s and continued to at least the end of 2008. By then, the Arctic Ocean might have gained four times as much fresh water as comprised the Great Salinity Anomaly of the 1970s, raising the spectre of slowing global ocean circulation. Freshening has been attributed to increased sea ice melting and contributions from runoff, but a leading explanation has been a strengthening of the Beaufort High — a characteristic peak in sea level atmospheric pressure — which tends to accelerate an anticyclonic (clockwise) wind pattern causing convergence of fresh surface water. Limited observations have made this explanation difficult to verify, and observations of increasing freshwater content under a weakened Beaufort High suggest that other factors must be affecting freshwater content.

Here we use observations to show that during a time of record reductions in ice extent from 2005 to 2008, the dominant freshwater content changes were an increase in the Canada basin balanced by a decrease in the Eurasian basin. Observations are drawn from satellite data (sea surface height and ocean-bottom pressure) and in situ data. The freshwater changes were due to a cyclonic (anticlockwise) shift in the ocean pathway of Eurasian runoff forced by strengthening of the west-to-east Northern Hemisphere atmospheric circulation characterized by an increased Arctic Oscillation index. Our results confirm that runoff is an important influence on the Arctic Ocean and establish that the spatial and temporal manifestations of the runoff pathways are modulated by the Arctic Oscillation, rather than the strength of the wind-driven Beaufort Gyre circulation.

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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