RESEARCH HIGHLIGHT

Studying the currents of the Bering Sea using the variational data-assimilation technique: possibilities for forecasts and hindcasts of local circulation

G. Panteleev, D. Nechaev, V. Luchin, P. Stabeno, N. Nezlin, M. Ikeda

February 15, 2006

A more detailed version of this highlight may be found here.

The Bering Sea off the west coast of Alaska controls the heat and freshwater exchange between the North Pacific Ocean and the Arctic Ocean. This exchange is important to the balance of the world’s ocean circulation, which affects weather across the globe.

Weather systems drive circulation currents back and forth through four passes in the Aleutian Islands and the continuation of the Aleutian arc toward Russia—Kamchatka Strait, Near Strait, Amchitka Pass and Amukta Pass. Moorings in Bering Strait off Alaska’s Seward Peninsula monitor the current there, but some researchers have relied on dynamical methods to estimate the currents through the Aleutian arc. A 2005 velocity measurement taken by Stabeno in Amutka Pass revealed an inflow of North Pacific water to the Bering Sea that is four times larger than dynamical-method estimates.

Such direct velocity measurements are expensive given the cost of reaching the remote straits and passes in the Aleutian arc. Here, we have combined historical mooring measurements, surface drifter measurements, and meteorological measurements with historical temperature and salinity data to come up with an estimate of Bering Sea circulation.

Into an ocean general circulation model, we input more than 40,000 temperature and salinity profiles gathered by U.S., Japanese and Russian scientists from 1932 to 2004; 500 satellite-tracked floating drifters deployed by NOAA; transport estimates from the work of Woodgate et al. in 2005; NCEP/NCAR wind stress and surface heat/salt flux data; and  sea surface height provided by AVISO project.

We used a data-assimilation technique to find the optimal solution of the model. We used a similar primitive equation model to reconstruct the evolution of summer climatological circulation in the Barents Sea. Nechaev et al. (2005) also used it for the hindcast of the circulation in the Tsushima Strait.

Our results suggest that the current knowledge of water balance in the Bering Strait should be re-examined. Our results also allowed us to derive a new estimate of mean summer transport through Kamchatka Strait.

These preliminary results of circulation estimation in the Bering Sea show advantages to using the data-assimilation approach, and a possibility of using this method for issuing reliable forecasts and hindcasts of current activity in the region.

Figure.   Hindcast and forecast in the Bering Sea through the assimilation of the SSH data.  Blue arrows – model results. Black arrows – surface drifters velocities.