OceanObs’09
Community White Paper Proposal
Combining satellite altimetry, time-variable gravity, and bottom pressure
observations to understand the Arctic Ocean: A transformative opportunity
R. Kwok, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
(ron.kwok@jpl.nasa.gov)
S. Farrell, NOAA Laboratory for Satellite Altimetry, Silver Spring, MD 20910 (sinead.farrell@noaa.gov)
R. Forsberg, Geodynamics Department, Danish National Space Center, Copenhagen, DK
(rf@space.dtu.dk)
K. Giles, Centre for Polar Observations and Modelling, University College London, London WC1E 6BT, UK
(k.giles@cpom.ucl.ac.uk)
S. Laxon, Centre for Polar Observations and Modelling, University College London, London WC1E 6BT, UK
(swl@cpom.ucl.ac.uk)
D. McAdoo, NOAA Laboratory for Satellite Altimetry, Silver Spring, MD 20910 (dave.mcadoo@noaa.gov)
J. Morison, Polar Science Center, Applied Physics Lab, University of Washington, Seattle, WA 98105, USA
(morison@apl.washington.edu)
L. Padman, Earth & Space Research,, Corvallis, OR 97333 (padman@esr.org)
A. Proshutinsky, Woods Hole Oceanographic Institution, Woods Hole, MA 02543
(aproshutinsky@whoi.edu)
M. Steele, Polar Science Center, Applied Physics Lab, University of Washington, Seattle WA 98105, USA
(mas@apl.washington.edu)
Recent developments in our observational capabilities present an unprecedented opportunity to make
significant progress towards an integrated ability to address scientific issues of both the ocean and ice
components of the Arctic Ocean system.
Sea level and circulation
Although hydrographic observations - and some oceanographic models - indicate substantial changes in
the Arctic Ocean's general circulation since 1980, such observations are sparse. In consequence, the
circulation of the Arctic Ocean is more poorly understood than in the lower latitude oceans. However,
integrated analyses of new data from in-situ hydrographic observations, gravity satellites (GRACE and the
upcoming GOCE), and polar-orbiting altimeters (e.g., Envisat, ICESat, and upcoming CryoSat-2 and
ICESat-2) show promise of redressing our poor understanding of the Arctic Ocean circulation and mass
variations. Satellite altimeters observe the total sea level variation, including the signal caused by
temperature and salinity fluctuations (the steric effect) and non-steric barotropic and mass variations.
Separately, gravity satellites like GRACE measure temporal changes in the Earth’s gravity field caused by
the movement of water masses. Together with an optimally designed bottom pressure array for resolving
shorter time scale processes, the steric and non-steric effects can be separated for quantifying changes in
circulation and variability in Arctic sea level. Sea surface heights from altimetry when differenced with the
mean Arctic satellite geopotential constrain the geostrophic circulation. Morison et al. [2007] demonstrated
a synthesis of hydrographic observations and satellite time-variable gravity for detection of decadal
changes in Arctic Ocean circulation.
Sea ice cover
While Arctic Ocean sea-ice extent has been monitored for ~30 years, there has been a paucity of timevarying ice thickness data available for estimating ice volume changes. With altimetry data from the ERS,
Envisat, and ICESat missions, investigators have demonstrated the potential of extracting fields of sea ice
freeboard and thickness estimates. The upcoming CryoSat-2 and ICESat-2 missions, both with primary
scientific objectives of addressing changes in the Arctic sea ice thickness, will provide extensive coverage
of the Arctic Ocean in the next decade.
Sustained observational network
Potentially, a sustained observational network of repeat hydrographic sampling, sea surface height and sea
ice thickness (from altimeters, upward looking sonars and submarines) and bottom pressure (from gravity
satellites and bottom pressure arrays) will provide the data sets needed to quantify the seasonal,
interannual and decadal basin scale changes of the Arctic Ocean. We suggest that an integrated,
coordinated, interdisciplinary approach, taking advantage of recent developments, is essential to the
advancement of Arctic oceanography in the coming decade.