120
L.M. Mitnik and V.A. Dubina
homogenization of the oceanic characteristics in the area southeast of Krilion Cape
(Danchenkov et al., 2003) where cold waters are located (Fig. 7.5b). The band 1 is
close to the boundary dividing warm and cold waters (as the position of the current
shift zone may be different from the thermal boundary). A first eddy-like structure A
is located to the southeast of Rock of Danger. The eddy is better distinguished in the
AVHRR thermal image. A second eddy B, consisting of a cold core, of about 8 km in
size, and two spiral “tails” are apparent in both images. The dark features cover the
eddy’s core from the north/south and increase its radar contrast. They are very likely
due to damping of the small-scale sea surface roughness by the surfactant films. The
distance between “tails” is ∼15 km and can be considered as the eddy’s size. The
third eddy C also has a cold central area with SST of about 5 ◦ C. The coldest waters
(4 ◦ C) are in a band to the southeast of the eddy’s centre. The cold waters in the third
eddy’s area are characterized by a decreased backscatter level.
The current shift zone is visible north of the eddy, where SST is around 6.5 ◦ C and
rather uniform. The eddies are located at a distance of ∼25 km from the coastline,
while the distance between their centers is ∼37 km, in close agreement with the
results of model experiments (Ohshima and Wakatsuchi, 1990) and coastal radar
observations (Ebuchi, 2006).
7.3.2 Ice Eddies
In the winter season, pack ice visualizes the features of surface circulation with
weak winds and sea ice concentration of less than ∼70%. An increased viscosity of the ice-water surface layer influences the interaction of an eddy with the
surrounding waters. Figures 7.6a, c show a complex surface circulation pattern
in the partly ice-covered Southern Okhotsk Sea, imaged by ASAR on 8 February
2003. The images cover the high ice concentration area, the Marginal Ice Zone
with ice bands and eddies, and ice-free waters, with brightness variations caused
by surface wind variations accompanying cellular convection in the atmospheric
boundary layer (Fig. 7.6a) and high winds (area 1). The most interesting objects
are eddies I and II. Eddy I (size of ∼90 km) is formed by two spirals consisting of 5–7 elliptical eddies (size of ∼7–10 km). These small-scale eddies, at the
periphery of the large ones, are manifestation of the increased viscosity of the icewater surface layer influencing the interaction of an eddy with the surrounding
waters.
The large, elliptical eddy II, located to the southeast from eddy I, was formed by
two bands of grease ice (a soupy layer of frazil crystals clumped together, which
makes the ocean surface resemble an oil slick). It looks dark on the images since
grease ice damps the small-scale waves. The brightness variations in the ice-free
area 1 surrounded by the ice bands are also caused by mesoscale convection in the
atmosphere.
These ice eddies were observed again by ASAR in approximately 11 hours
(Fig. 7.6c). The ice concentration in the central area of eddy I decreased sharply
due to strong winds. Several small-scale spiral elliptical eddies in the western part
L.M. Mitnik and V.A. Dubina
homogenization of the oceanic characteristics in the area southeast of Krilion Cape
(Danchenkov et al., 2003) where cold waters are located (Fig. 7.5b). The band 1 is
close to the boundary dividing warm and cold waters (as the position of the current
shift zone may be different from the thermal boundary). A first eddy-like structure A
is located to the southeast of Rock of Danger. The eddy is better distinguished in the
AVHRR thermal image. A second eddy B, consisting of a cold core, of about 8 km in
size, and two spiral “tails” are apparent in both images. The dark features cover the
eddy’s core from the north/south and increase its radar contrast. They are very likely
due to damping of the small-scale sea surface roughness by the surfactant films. The
distance between “tails” is ∼15 km and can be considered as the eddy’s size. The
third eddy C also has a cold central area with SST of about 5 ◦ C. The coldest waters
(4 ◦ C) are in a band to the southeast of the eddy’s centre. The cold waters in the third
eddy’s area are characterized by a decreased backscatter level.
The current shift zone is visible north of the eddy, where SST is around 6.5 ◦ C and
rather uniform. The eddies are located at a distance of ∼25 km from the coastline,
while the distance between their centers is ∼37 km, in close agreement with the
results of model experiments (Ohshima and Wakatsuchi, 1990) and coastal radar
observations (Ebuchi, 2006).
7.3.2 Ice Eddies
In the winter season, pack ice visualizes the features of surface circulation with
weak winds and sea ice concentration of less than ∼70%. An increased viscosity of the ice-water surface layer influences the interaction of an eddy with the
surrounding waters. Figures 7.6a, c show a complex surface circulation pattern
in the partly ice-covered Southern Okhotsk Sea, imaged by ASAR on 8 February
2003. The images cover the high ice concentration area, the Marginal Ice Zone
with ice bands and eddies, and ice-free waters, with brightness variations caused
by surface wind variations accompanying cellular convection in the atmospheric
boundary layer (Fig. 7.6a) and high winds (area 1). The most interesting objects
are eddies I and II. Eddy I (size of ∼90 km) is formed by two spirals consisting of 5–7 elliptical eddies (size of ∼7–10 km). These small-scale eddies, at the
periphery of the large ones, are manifestation of the increased viscosity of the icewater surface layer influencing the interaction of an eddy with the surrounding
waters.
The large, elliptical eddy II, located to the southeast from eddy I, was formed by
two bands of grease ice (a soupy layer of frazil crystals clumped together, which
makes the ocean surface resemble an oil slick). It looks dark on the images since
grease ice damps the small-scale waves. The brightness variations in the ice-free
area 1 surrounded by the ice bands are also caused by mesoscale convection in the
atmosphere.
These ice eddies were observed again by ASAR in approximately 11 hours
(Fig. 7.6c). The ice concentration in the central area of eddy I decreased sharply
due to strong winds. Several small-scale spiral elliptical eddies in the western part