Parallel Ocean Program (POP) Simulation

The Model

    The coupled Arctic Ocean and sea ice model (Maslowski et al., 1999, Zhang et al., 1999) employs the Parallel Ocean Program (POP) (Smith et al., 1992) adopted to the Pan-Arctic region and coupled to a parallel version of the Hibler (1979) dynamic-thermodynamic sea ice model with viscous-plastic rheology and a zero-layer thermodynamics approximation. The model grid is configured on a rotated spherical coordinate system and its resolution is 1/6o (~18 km) with 30 levels. The model domain extends from Bering Strait through the Central Arctic, Nordic and Barents Seas into the sub-polar North Atlantic (to ~45oN) and it includes the Canadian Archipelago. No mass flux is allowed through the lateral boundaries, but 30-day restoring to monthly mean temperature and salinity climatology is used there. Surface temperature and salinity are restored toward monthly climatology on time scale of 365 and 120 days, respectively. Daily-averaged operational atmospheric fields from the European Centre for Medium-range Weather (ECMWF) for 1994-98 are used in addition to the 1979-93 reanalyzed data. An annual cycle of daily-averaged runoff data is used to account for fresh water input from rivers. It is important to note here that the only interannual forcing in the model comes from the prescribed atmospheric fields. The model has been integrated initially for 200 years forced with 1990-94 atmospheric fields. It was then spun up for 20 years using the repeated 1979 annual cycle, which was followed by an additional 2-decade integration using 1979-1998 atmospheric data.

Arctic Ocean Active River Tracer Experiment

    Fresh water and Atlantic Water tracers are introduced at the beginning of the 20-year spinup with 1979 annual cycle and they are integrated for a total of 40 years. Runoff from all the major Russian Rivers, the Mackenzie River and Bering Strait inflow are marked with the separate "dye" tracer. This approach allows tracking of various water masses to determine their distribution, mixing and export from/into the Arctic Ocean. 
The model includes freshwater inflows from the major Arctic rivers (Mackenzie, Dvina and Pechora, Ob, Yenisey, Kotuy, Lena, Indigirka and Kolyma) and the Bering Strait. No mass is exchanged there, but the river runoff and Bering Strait inflow are used to recalculate the salinity and temperature in their source regions, and thus within the model limitations act as a freshwater source to the model domain. In the Arctic, where precipitation is minimal, these inflows are the dominant sources of meteoric waters (Aagaard and Carmack, 1989). In this experiment, river runoff is daily-averaged across all years for which data is available and then it is interpolated to each model time step. In addition to their contribution to the density calculation, the freshwater inflows are also tracked as separate "dye" tracers. Similarly, any water moving northward across the Greenland-Iceland-Scotland Ridge is marked with an "Atlantic" dye. Together, these tracers allow us to track the main sources of distinct water types in the Arctic: Atlantic and Pacific inflows and indigenous waters formed over the Arctic shelves. The distribution and mixing of these water masses accounts for the observed distribution of conserved tracers in the Arctic Ocean. The freshwater and Atlantic dye tracers are not restored. Although feedbacks on density and circulation are limited by surface restoring, the tracers are still useful to qualitatively indicate trends in the surface salinity in response to atmospheric interannual forcing.

Acknowledgements

    The results presented here have been obtained in collaboration between a group at the Naval Postgraduate School (Wieslaw Maslowski, Douglas C. Marble, Waldemar Walczowski, Yuxia Zhang, Albert Semtner) and Bob Newton and Peter Schlosser at Lamont-Doherty Earth Observatory, Columbia University. Funding for this project has been provided by grants from NSF/ARCSS, DOE/CHAMMP, and Cray Research Inc. / UAF. Computer resources were obtained from the Arctic Region Supercomputing Center of the University of Alaska.

References

Aagaard, K. and E.C. Carmack, 1989, The role of sea ice and other fresh water in the Arctic circulation, J. Geophys. Res., 94(C10), 14,485-14,898.
Hibler, W.D. III, 1979. A dynamic thermodynamic sea ice model, J. Phys. Oceanography, 9, 815-846.
Maslowski, W., B. Newton, P. Schlosser, A. Semtner, and D. Martinson, 1999. Modeling Recent Climate Variability in the Arctic Ocean. Geophys. Res. Letter, submitted.
Smith, M., and T. Boyd, 1998. Retreat of the cold halocline layer in the Arctic Ocean, J. Geophys. Res., 103(C5),10,419-10,435. 
Zhang Y., W. Maslowski, and A.J. Semtner, 1999. Impact of mesoscale ocean currents on sea ice in high-resolution Arctic ice and ocean simulations. J. Geophys. Res., 18,409-18,429. 

For more information about the model, model output, or other animations please check our website at:

http://www.oc.nps.navy.mil/~pips3/

or contact: 

Wieslaw Maslowski

maslowsk@ucar.edu

Department of Oceanography
Naval Postgraduate School
Monterey, CA 93943
Tel.: 831/656-3162

Other publications include:

Modeling Recent Climate Variability in the Arctic Ocean

On Large Scale Shift in the Arctic Ocean and Sea Ice Conditions during 1979-1998

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