waters on the eddy periphery) and vertical (due to upwelling/downwelling motions
of the water at the eddy center) mixing in the ocean.
Observations (photographs in sunglitter areas on the sea surface) of American
space oceanographers from the spacecrafts, especially during shuttle mission 41-G,
US (1984), have shown that submesoscale (D less than R d ) eddies exist throughout
the ocean [23, 29–31]. They have a spiral form, rotate in the cyclonic direction and
are observed in the ocean beyond six degrees north and south latitude [31]. Such
eddies are also found on the radar images in different regions of the ocean/seas (e.g.,
[2, 10, 20]).
It is assumed that submesoscale flows are characterized by a larger Rossby
number (Ro of O(1)) and higher (on order of magnitude) vertical velocity than the
mesoscale, which determines their important role in the vertical exchange between
surface and deeper layers of the ocean/sea [35]. However, to date, information on
the mechanisms of their generation, life history and vertical structure is clearly
insufficient. In-situ measurements in the eddies’ areas are practically absent because
of their small time of life and small spatial sizes. Therefore, the accumulation of
satellite observations of submesoscale vortices in various oceans/seas together with
related information on hydrophysical and meteorological conditions is extremely
important.
In this paper, observations of submesoscale eddies in the Russian seas (the
Black, Caspian, Baltic, and White) are discussed and assumptions are made about
possible mechanisms of their formation.
Manifestation of Eddies on the Sea Surface and Data Used
Submesoscale eddies rarely appear in satellite visible band and infrared (IR) images
acquired by sensors MODIS Aqua/Terra and AVHRR because of the weak thermal
or optical contrasts of the structures relative the surrounding water and insufficient
spatial resolution of the sensors (1 km). However, sometimes they were detected in
satellite optical images with high spatial resolution (meters–tens of meters): for
example, in optical images of the QuickBird sensor (resolution of 0.6–2.44 m) [18]
or the Landsat-5 Thematic Mapper (TM) sensor (resolution of 30 m) [20].
The main source of information on submesoscale eddies are satellite radar
images [10, 11, 13–15, 20, 21]. The advantage of the latter images is the all-weather
survey (independence from time of day, and cloudiness) and high spatial resolution
(10 to 100 m) in a swath from 100 to 500 km. The best conditions for eddies to be
manifested in radar images (RI), wind speed range 2–5 m/s and the presence of
surface films of surface-active substances (oil films, films of biogenic origin during
the phytoplankton bloom), which smooth the sea surface due to the suppression of
small-scale component of sea waves. These films can be found virtually everywhere
on the vast sea surface, mostly in warm seasons, they are very sensitive to surface
currents and typically form the shape of a local circulation pattern. A manifestation
of eddies on the sea surface is due to the involvement of the slick strips in the eddy
398
A. G. Kostianoy et al.
of the water at the eddy center) mixing in the ocean.
Observations (photographs in sunglitter areas on the sea surface) of American
space oceanographers from the spacecrafts, especially during shuttle mission 41-G,
US (1984), have shown that submesoscale (D less than R d ) eddies exist throughout
the ocean [23, 29–31]. They have a spiral form, rotate in the cyclonic direction and
are observed in the ocean beyond six degrees north and south latitude [31]. Such
eddies are also found on the radar images in different regions of the ocean/seas (e.g.,
[2, 10, 20]).
It is assumed that submesoscale flows are characterized by a larger Rossby
number (Ro of O(1)) and higher (on order of magnitude) vertical velocity than the
mesoscale, which determines their important role in the vertical exchange between
surface and deeper layers of the ocean/sea [35]. However, to date, information on
the mechanisms of their generation, life history and vertical structure is clearly
insufficient. In-situ measurements in the eddies’ areas are practically absent because
of their small time of life and small spatial sizes. Therefore, the accumulation of
satellite observations of submesoscale vortices in various oceans/seas together with
related information on hydrophysical and meteorological conditions is extremely
important.
In this paper, observations of submesoscale eddies in the Russian seas (the
Black, Caspian, Baltic, and White) are discussed and assumptions are made about
possible mechanisms of their formation.
Manifestation of Eddies on the Sea Surface and Data Used
Submesoscale eddies rarely appear in satellite visible band and infrared (IR) images
acquired by sensors MODIS Aqua/Terra and AVHRR because of the weak thermal
or optical contrasts of the structures relative the surrounding water and insufficient
spatial resolution of the sensors (1 km). However, sometimes they were detected in
satellite optical images with high spatial resolution (meters–tens of meters): for
example, in optical images of the QuickBird sensor (resolution of 0.6–2.44 m) [18]
or the Landsat-5 Thematic Mapper (TM) sensor (resolution of 30 m) [20].
The main source of information on submesoscale eddies are satellite radar
images [10, 11, 13–15, 20, 21]. The advantage of the latter images is the all-weather
survey (independence from time of day, and cloudiness) and high spatial resolution
(10 to 100 m) in a swath from 100 to 500 km. The best conditions for eddies to be
manifested in radar images (RI), wind speed range 2–5 m/s and the presence of
surface films of surface-active substances (oil films, films of biogenic origin during
the phytoplankton bloom), which smooth the sea surface due to the suppression of
small-scale component of sea waves. These films can be found virtually everywhere
on the vast sea surface, mostly in warm seasons, they are very sensitive to surface
currents and typically form the shape of a local circulation pattern. A manifestation
of eddies on the sea surface is due to the involvement of the slick strips in the eddy
398
A. G. Kostianoy et al.