Open water in sea ice, such as leads and polynyas, plays a crucial
role in determining the formation of deep- and bottom-water, as well
as their long-term global properties and circulation. Ocean general
circulation models (GCMs) designed for studies of the long-term
thermohaline circulation have typically coarse resolution, making it
inevitable to parameterize subgrid-scale features such as leads and
convective plumes. In this study, a hierarchy of higher-resolution
sea-ice models is developed to reduce uncertainties due to coarse
resolution, while keeping the ocean component at coarse resolution to
maintain the efficiency of the GCM to study the long-term deep-ocean
properties and circulation. The higher-resolved sea-ice component is restricted to the Southern Ocean. Compared with the coarse sea-ice
model, the intermediate, higher-resolution version yields more
detailed coastal polynyas, a realistically sharp ice edge, and an
overall enhanced lead fraction. The latter gives enhanced rates of
Antarctic Bottom Water formation through enhanced near-boundary
convection. Sensitivity experiments revealed coastal katabatic winds
accounted for in the higher resolution version, are the main reason
for producing such an effect. For a more realistic coastline,
satellite passive-microwave data for fine-grid land/ice-shelf â seaice/
ocean boundary were used.
With a further enhancement of the resolution of the Southern OceanâÂÂs
sea-ice component, a grid spacing of 22 km is reached. This is about
the size of the pixel resolution of satellite-passive microwave data
from which ice concentration is retrieved. This product is used in
this study to validate the sea-ice component of the global ocean GCM.
The overall performance of the high-resolution sea-ice component is
encouraging, particularly the representation of the crucial coastal polynyas. Enhancing the resolution of the convection parameterization
reduces spurious coarse-grid polynyas. Constraining the upper-ocean
temperature and modifying the plume velocity removes unrealistic
small-scale convection within the ice pack. The observed highfrequency
variability along the ice edge is to some extent captured
by exposing the ice pack to upper-ocean currents that mimic tidal
variability. While these measures improve several characteristics of
the Southern Ocean sea-ice pack, they deteriorate the global deepocean
properties and circulation, calling for further refinements and
tuning to arrive at presently observed conditions.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/5746 |
| Date | 17 September 2007 |
| Creators | Kim, Joong Tae |
| Contributors | Stoessel, Achim |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 4691465 bytes, electronic, application/pdf, born digital |
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