Geology Reference
In-Depth Information
10.7. Ice moTIon
35
Elson Lagoon
Beaufort Sea
MEMLS model
Outdoor ice experiment
The motion of floating ice can be mapped using
sequential remote sensing imagery data. The maps offer a
record of recent ice motion from which a forecast of
motion can be generated by extrapolation. The satellite
data product can be used also to verify motion forecast-
ing produced from ice dynamics models. In fact, motion
field derived from remote sensing data can be assimilated
to improve the model's results. Information on ice motion
is required for marine navigation, offshore engineering
structure, and climate studies. Marine vessels can be
damaged as a result of collision with moving ice floes.
Navigational routes are planned based on informa-
tion not only about the size and thickness of ice floes
but also on their motion. This is particularly true for
hazardous ice types such as thick FY ice or MY ice. The
design of offshore marine structures located in areas
where ice motion is likely to happen should take into
account the ice loads. An example was the design of the
13 km Confederation Bridge across the ice‐covered
Northumberland Strait between Prince Edward Island
and New Brunswick across the Gulf of St. Lawrence in
eastern Canada [
Brown et al.
, 2001]. Moreover, informa-
tion on ice motion is also required by climatologists to
quantify the ice flux between regions of ice export and
import. Ice motion is also required for determining ice
mass balance, lead formation, ridge deformation, and
maintenance of polynyas.
Howell et al.
[2013a] used the
Canadian Ice Service's Automated Sea Ice Tracking
System (CIS‐ASITS), which derives ice motion from a
sequence of Radarsat images, to study the exchange of
sea ice between the Arctic Ocean and the Canadian
Arctic Archipelago. Using the ice velocity component
u
i
,
in direction
i
, the sea ice flux
F
through a distance Δ
x
can be calculated if the ice concentration
c
is known:
30
25
20
15
10
5
-.035
-.030
-.025
-.020
GR
19V37V
-.015 .010
-.005
000
Figure 10.44
Snow depth plotted against microwave gradient
ratio GR
37
V
19
V
. Data are obtained from (1) transects in the Elson
Lagoon and the Beaufort Sea averaged for 200 m running
mean, (2) MEMLS model results using data from each transect,
and (3) microwave emission measurements from snow‐covered
simulated sea ice in an outdoor facility. The AMSR‐E regression
line for snow depth retrievals (solid line) and the regression
line adjusted for a 3.5 cm bias (dashed line) are also plotted
[adapted from
Powell et al
., 2006].
become less negative. Therefore, although these two pro-
cesses tend to cancel each other's effect, they still can
affect the accuracy of snow depth retrievals. Figure 10.44
shows variation of snow depth with GR
37
V
19
V
for three sets
of data presented in
Powell et al
. [2006]: the Elson Lagoon
and the Beaufort Sea data from transects using the 200 m
running mean as well as the MEMLS results. There is a
fourth set from experimental data obtained from an out-
door experiment on simulated sea ice (described briefly in
section 8.2). The AMSR‐E regression line used for snow
depth retrievals is plotted (solid line) along with the same
line after adjusting for the 3.5 cm bias (dashed line). This
bias is established by
Markus and Cavalieri
[1998] using
Antarctic data as mentioned above. It can be seen that the
simulated GR
37
V
19
V
agree with the in situ measurement,
but the scattering of the data from the regression line is
also noticeable. This is a manifestation of the effects of
the snow parameters mentioned above on the observed
radiation, which reduces the accuracy of the snow depth
model. More accurate snow thickness estimation could be
obtained using theoretical emissivity modeling and a ther-
modynamic snow/ice model in combination with the radi-
ometer data.
F ux
i
(10.107)
i
Ice motion is triggered by three major and two minor
forces. The major forces are wind stress, water stress (due
to ocean current), and internal ice resistance. The minor
forces are Coriolis force and sea surface tilt. Each force is
described briefly in the following.
Wind stress transfers momentum to the ice, but it also
drives the ocean surface and therefore adds another force
to move the ice. Ice moves faster in response to the wind
if the surface is rough. As a rule of thumb the speed of ice
motion is nearly 2% of the wind speed when ice moves
freely. The direction of motion has been nearly estab-
lished to be at 20°-40° to the right of the wind direction
in the Northern Hemisphere and to the left in the
Southern Hemisphere. Sea ice across large regions in the
Arctic is stimulated by two wind‐driven oceanic systems:
