Aleutian Passes. In the context of the Bering Sea large-scale dynamics, accurate
MDOT appears to be especially important since the processes of the ventilation of
the deep and shallow parts of the BS occurs through the few relatively narrow
Aleutian Passes. These ventilation processes are one of the key mechanisms controlling the BS ecosystem and, therefore, should be reconstructed with increased
accuracy.
In relation to ecosystem dynamics, the vast shelf of the Eastern Bering Sea
(EBS) represents the major hub located on the crossroads of the pathways between
the Pacific and Arctic Oceans. Extreme complexity of the advective and mixing
processes in the shallow waters of EBS shape the seasonal ecosystem parameters
and require accurate treatment in terms of observational and dynamical consistency.
Eastern Bering Sea: Regional Ocean in Motion
The Eastern Bering Sea (EBS) plays an important role in United States’ fisheries,
dynamics of the immense populations of marine birds and mammals, and subsistence activities of native communities. Therefore, this region has been permanently
studied in the last decades. The most comprehensive studies were conducted in
2007–2010 in the framework of the Bering Sea Integrated Ecosystem Research
Program (BSIERP). Typically, 2–3 hydrophysical (CTD) surveys per year were
conducted and 3 mooring arrays were supported during 2007–2010 (Fig. 5). Note,
however, that each CTD survey usually lasts for 2–3 weeks, providing only a
“snapshot” of a limited area of the EBS, while during the rest of the year, there is no
reliable information about the hydrophysical state. At the same time, moorings
provide continuous time series in a few locations lacking adequate spatial coverage.
Obviously, these data cannot adequately describe the circulation in the entire EBS,
if considered, without additional dynamical constraints. The 4dVar DA provides a
good guide on how to combine observations from different sources for reconstructing the non-stationary state of the ocean in motion.
Nested 4dVar system. The BSIERP observations and other sources of data provide
an excellent opportunity to improve our understanding of changes in the physical
forcing of the Bering ecosystem in its response to the climate change. But due to ice
coverage in the winter, a relatively large regions of the EBS including the key
passages through the Anadyr and Bering Straits were not covered by these studies.
In view of the necessity to adequately resolve the Bering and Anadyr Straits, a
nested SIOM 4dVar DA system was developed. The nested DA system utilized as a
first guess, the momentum, heat and salt fluxes from Bering Ecosystem Study Ice
Ocean Modeling and Assimilation System (BESTMAS) [10, 36].
The nested models were configured in the domains shown in Fig. 5 with a resolution of 7 km for the fine model grid, ω, embedded into a coarser (15–20 km) grid,
Ω (Fig. 1). In the vertical, the coarse (fine) resolution model had 35(15) unevenly
spaced levels with 5 (2.5) m near-surface spacing, which increased to 500(25) m at
The Bering Sea Regional Data Assimilation System …
509
MDOT appears to be especially important since the processes of the ventilation of
the deep and shallow parts of the BS occurs through the few relatively narrow
Aleutian Passes. These ventilation processes are one of the key mechanisms controlling the BS ecosystem and, therefore, should be reconstructed with increased
accuracy.
In relation to ecosystem dynamics, the vast shelf of the Eastern Bering Sea
(EBS) represents the major hub located on the crossroads of the pathways between
the Pacific and Arctic Oceans. Extreme complexity of the advective and mixing
processes in the shallow waters of EBS shape the seasonal ecosystem parameters
and require accurate treatment in terms of observational and dynamical consistency.
Eastern Bering Sea: Regional Ocean in Motion
The Eastern Bering Sea (EBS) plays an important role in United States’ fisheries,
dynamics of the immense populations of marine birds and mammals, and subsistence activities of native communities. Therefore, this region has been permanently
studied in the last decades. The most comprehensive studies were conducted in
2007–2010 in the framework of the Bering Sea Integrated Ecosystem Research
Program (BSIERP). Typically, 2–3 hydrophysical (CTD) surveys per year were
conducted and 3 mooring arrays were supported during 2007–2010 (Fig. 5). Note,
however, that each CTD survey usually lasts for 2–3 weeks, providing only a
“snapshot” of a limited area of the EBS, while during the rest of the year, there is no
reliable information about the hydrophysical state. At the same time, moorings
provide continuous time series in a few locations lacking adequate spatial coverage.
Obviously, these data cannot adequately describe the circulation in the entire EBS,
if considered, without additional dynamical constraints. The 4dVar DA provides a
good guide on how to combine observations from different sources for reconstructing the non-stationary state of the ocean in motion.
Nested 4dVar system. The BSIERP observations and other sources of data provide
an excellent opportunity to improve our understanding of changes in the physical
forcing of the Bering ecosystem in its response to the climate change. But due to ice
coverage in the winter, a relatively large regions of the EBS including the key
passages through the Anadyr and Bering Straits were not covered by these studies.
In view of the necessity to adequately resolve the Bering and Anadyr Straits, a
nested SIOM 4dVar DA system was developed. The nested DA system utilized as a
first guess, the momentum, heat and salt fluxes from Bering Ecosystem Study Ice
Ocean Modeling and Assimilation System (BESTMAS) [10, 36].
The nested models were configured in the domains shown in Fig. 5 with a resolution of 7 km for the fine model grid, ω, embedded into a coarser (15–20 km) grid,
Ω (Fig. 1). In the vertical, the coarse (fine) resolution model had 35(15) unevenly
spaced levels with 5 (2.5) m near-surface spacing, which increased to 500(25) m at
The Bering Sea Regional Data Assimilation System …
509