Enhancing the resolution of sea ice in long-term global ocean general circulation model (gcm) integrations
Abstract
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.
Citation
Kim, Joong Tae (2003). Enhancing the resolution of sea ice in long-term global ocean general circulation model (gcm) integrations. Doctoral dissertation, Texas A&M University. Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /5746.