Geology Reference
In-Depth Information
3
Sea Ice Properties: Data and Derivations
This chapter presents a brief account of basic physical
properties of sea ice and snow required for thermodynamic
and radiation modeling of snow‐covered ice and to inter-
pret remote sensing observations. The chapter includes data
most commonly used for ice under different conditions as
well as mathematically derived and empirical equations to
calculate a few parameters. This includes temperature, salin-
ity, density, volume fractions of sea ice constituents (pure
ice, brine, air, and solid salts in side brine pockets), thermal
parameters (conductivity, specific heat, and latent heat), and
dielectric properties (permittivty and loss).
The key physical property that influences practically all
the sea ice characteristics is the ice temperature. This is
triggered, of course, by variations in air temperature. Ice
temperature determines the evolution of brine pockets
within the ice crystallographic structure and, therefore,
together with the brine drainage processes, the bulk ice
salinity, and the brine salinity and geometry. The last two
items influence the thermal and dielectric properties of
sea ice. The dielectric properties are presented in detail
since they are of particular importance to remote sensing,
a central theme of this topic. A two‐phase dielectric mix-
ing model that can apply either to FY ice or MY ice is
presented in section 3.6.2. It is worth mentioning at this
point that calculations of thermal parameters related to
thermodynamic growth of sea ice require information
about a few seawater parameters. A comprehensive pres-
entation of those parameters is included in
Sharqawy
et al.
[2010]. While this chapter addresses physical prop-
erties of sea ice, the radiometric properties are presented
in Chapter 7 (definitions and theoretical background)
and in Chapter 8 (measurements and modeling).
Typical values of key parameters of sea ice, snow, and
seawater are included in Table 3.1. These values are usu-
ally used as first approximations in developing physical,
thermal, forward electromagnetic scattering, and radiative
models of sea ice. Most of these parameters vary with
temperature and salinity of ice (which leads to variations in
the volume fractions of ice constituents and geometric
characteristics of the brine inclusions). Therefore, the table
provides only reference values. A few equations (mostly
empirical) that describe variations of the parameters are
included in Table 3.2. More equations are included in the
subsequent subsections. Note that the average salinity of
sea ice
S
si
is the same as the bulk ice salinity
S
B
, which is
used in a few equations later in this chapter.
Physical properties of sea ice are different for different
ice types. Unless otherwise mentioned, the data and the
equations in this chapter apply mostly to mature FY ice.
This is also the case of the typical data given in Tables 3.1
and the equations in Table 3.2. However, accurate repre-
sentation of sea ice in weather and climate models requires
distinction of ice types with their typical values or ranges
of related parameters. This distinction is possible only in
some cases, notably perennial versus seasonal ice types.
The former is characterized by its low salinity, density, sur-
face and sub-surface temperatures, thermal conductivity,
and dielectric constant. The properties of perennial ice are
almost independent of weather conditions (though the
snow cover is affected by these conditions). On the other
hand it is difficult to assign a set of typical physical proper-
ties to each type within seasonal ice (e.g., new, young, and
first‐year types and their subcategories). That is because
the properties are not a sole function of ice age, but depend
also on the history of ice formation and deformation, and
most importantly on the current atmospheric temperature.
Approximate values of key properties of seasonal and per-
ennial ice types, compiled from different sources, are sum-
marized in Table 3.3. These values can be used as coarse
estimates of the given properties, bearing in mind the wide
range of each parameter under different meteorological,
oceanic, and climatic conditions.
