Introduction - Sea Ice: Physics and Remote Sensing - page 13

extent by the Journal of Geophysical Research (JGR).
Physics of ice in general and details on sea ice, especially
of areas surrounding the continent of Antarctica and
Okhotsk Sea, can be found in a number of articles in
Japanese published by the Institute for Low Temperature
Science, University of Hokkaido, Sapporo, Japan, since
1950s in the Low Temperature Science Series . It should be
mentioned here that the first man‐made snowflakes were
also produced at this institute in Sapporo. On a regular
basis, the International Symposium on Okhotsk Sea &
Sea Ice (ISOSSI) is held in Mombetsu, Hokkaido, Japan.
The Okhotsk Sea & Cold Ocean Research Association
linked with the Sea Ice Research Laboratory, Hokkaido
University, publishes the proceedings volumes of ISOSSI
(articles in both English and Japanese).
The inner structures of any material that cannot be
recognized by human eyes are known as microstructure.
Microstructure‐property (thermal, optical, mechanical,
electrical, etc.) relationships of materials are very com-
plex and depend on their texture and structure. The use
of knowledge about ice microstructure for understanding
and demystifying the behavior of several alloys at high
temperatures was highlighted and pioneered in an early
study by Tabata and Ono [1962]. No doubt, the extremely
high thermal states, in case of sea ice, add even more
complexities in the microstructure‐property relation-
ships. But then, gas turbine engine materials have also
became highly complex over the years [ Sims et al. , 1987].
As pointed out earlier, sea ice floating on its own melt
exists at temperatures of about 5%, or less, than its melting
point. This is significantly more than the maximum tem-
perature allowed for the operation of man‐made nickel‐
base directionally solidified (DS) columnar‐grained (CG)
superalloys, used in blades of modern gas turbine engines
(jet or power‐generating engines) and end casings of rocket
engines. Nickel‐based DS, CG superalloys were introduced
in jet engines during the late 1960s [ Duhl , 1987, in Chapter 7
of Sims et. al. , 1987]. Physicists, ceramicists, and high‐tem-
perature metallurgists, are therefore, interested in applying
lessons learnt from studying structure‐property relationship
of ice directly to complex high‐temperature, titanium‐ and
nickel‐base superalloys [ Sinha , 2009a]. They can perform
experiments under varying conditions of thermal and
mechanical loading, in conjunction with microstructural
analysis at the experimental (high) temperature, and model
thermomechanical behavior of gas turbine engine materi-
als, such as stress relaxation processes and strain rate sen-
sitivity of yield strengths [ Sinha and Sinha , 2011]. Moreover,
the microstructure of sea ice exhibits impurity entrapment
and grain‐ and subgrain‐scale substructure very similar to
high‐temperature metallic alloys and ceramics. These fea-
tures are key factors in determining many properties of sea
ice, including thermal conductivity, microwave emissivity,
dielectric constant, and mechanical strength.

Since ice has an accessible melting temperature, it
could provide a model of how other materials will behave
at very high temperatures near their melting points.
Physicists have applied theories and experimental tech-
niques that describe the behavior of snow and ice around
their melting temperatures to high‐temperature materials
such as ceramics and advanced alloys used inside jet
engines or gas turbine engines (examples include tita-
nium‐based and nickel‐based superalloys). This has been
substantiated by the fact that sea ice is a prime example
of a natural material that exhibits impurity entrapment
and grain‐scale substructure very similar to binary alloys.

1.4.3. Sea Ice in Climatology

Sea ice plays a key role within the climate system and
has long been thought to be a primary indicator of global
warmimg. Climatologists are interested in sea ice because
of a number of reasons, such as (1) its thermal and opti-
cal properties are important input to climate models,
(2) its extent in the polar regions is a strong indicator of
climate change, and (3) its strong influence in the high as
well as midlatitude large‐scale circulations of the atmos-
phere and ocean.
Thermal properties of sea ice determine the thermody-
namic interaction between the cold atmosphere and the
warm underlying ocean. This is demonstrated in two pro-
cesses: the heat exchange between the two media and the
heat of fusion released or acquired when ice freezes or
melts, respectively. The thermal conductivity of sea ice is
relatively low (2.25 W/m · K) compared to thermally con-
ductive metals (205 W/m · K of aluminum or 401 W/m · K
of copper). When covered with snow, the effective con-
ductivity becomes even lower (thermal conductivity of
snow is between 0.1 and 0.25 W/m · K, depending on its
density and wetness). Therefore, the presence of the ice
cover on the ocean surface reduces the ocean‐atmosphere
heat exchange even in the presence of thin ice [ Maykut ,
1978, 1982]. This reduces the moisture transfer from the
ocean to the atmosphere, the momentum transfer from
the atmosphere to the ocean, and the exchange of chemi-
cals constituents between the two media.
The heat of fusion of water (defined as the heat required
for transforming one gram of water at freezing tempera-
ture to ice) is one of the highest of all substances. When
sea water freezes, it releases approximately 80 cal/g of
heat to the atmosphere. This is the energy needed to
establish the hydrogen bonding between the ice molecules.
It is equivalent to energy required to raise the tempera-
ture of one gram of water from 0 to 80 °C. When ice melts
it absorbs the same energy to produce water at the same
temperature. This represents a huge amount of heat
exchange between the ocean and the atmosphere that
affects weather systems and eventually regional climate.