(Keynote) A hybrid ice model

The viscous-plastic sea-ice model is widely used in climate models to
simulate large-scale sea ice dynamics, usually on grids of several
kilometers (>10 km). Recently, there has been increasing interest in
modeling small-scale processes that have the potential to affect
large-scale dynamics, such as sea-ice-iceberg interactions associated
with ice mélange or fast ice. Small scale sea-ice iceberg interactions
could not be resolved in climate models because numerically efficient
realizations did not exist. This motivates the development of a
prototypical dynamic hybrid ice model presented in this talk.

In the first part of the talk, the hybrid ice model is derived. In this
approach, icebergs, modeled as particles, are included as thick and
compact pieces of sea ice in a continuum sea-ice formulation. The latter
is based on the viscous-plastic sea ice rheology. Starting from the
continuum mechanical formulation, we modify the rheology such that
icebergs are held together by a modified tensile strength in the
material law.

The second part of the talk discusses the numerical discretization of
the model. Due to the particle approach, we do not need high-resolution
spatial grids to represent small icebergs (<500 m). Instead, icebergs
can be tracked at a sub-grid level while maintaining the typical sea-ice
model resolution (>10 km).

The talk concludes with a discussion of idealized test cases. These
setups demonstrate that the proposed changes in the material law allow a
realistic representation of icebergs within the viscous-plastic sea-ice
rheology. Furthermore, we show that sub-grid dynamics, such as the
formation of polynyas by grounded icebergs, can be represented by the
hybrid model. Overall, the proposed extension of the viscous-plastic
sea-ice model is a promising way to integrate small-scale interactions
between sea ice and icebergs into climate models.