THE NEAR-SURFACE LAYER OF THE OCEAN
mixing regime below the air-sea interface strongly depends on
meteorological, radiation, and surface wave conditions. Instead in this
monograph the near-surface layer of the ocean is considered as an integral
part of the ocean-atmosphere system. There are in fact some processes that
are unique to the upper few meters (e.g., wave breaking) or even for the
upper few millimeters (e.g., molecular transport) of the ocean. Other
processes may be confined to the upper few meters of the ocean under
certain conditions (e.g., large diurnal warming events) but for different
environmental conditions will have depth scales of tens of meters. There are
also processes that originate at the air-sea interface but extend to the overall
depth of the upper ocean mixed layer (e.g., Langmuir circulations and
nighttime convection).
The variety of forcing factors, in combination with nonlinear feedbacks,
result in different near-surface regimes. Fedorov and Ginzburg (1988)
consider five regimes in the near-surface layer of the ocean:
1) Intensive wind-wave mixing (wind speed at 10 m height above the
ocean surface U 10 > 8-10 m s
-1 );
2) Intensive convection (nighttime, winter, or atmospheric cold fronts);
3) Langmuir circulations (U 10 from 3 to 10 m s
-1 );
4) Intensive solar heating under low wind and calm weather conditions
(U 10 from 0 to 3-5 m s
-1 );
5) Near-surface freshening due to rain.
This classification is still valid in general and is useful for many
practical applications. At this point, however, it requires comment.
The near-surface ocean under regime 1 is usually well mixed. However,
surface molecular sublayers, which are not included in this classification,
may develop even under conditions of intensive wind-wave mixing though
only between wave breaking events (see Chapter 2).
The Langmuir circulations, which are considered as a separate regime
(regime 3) by Fedorov and Ginzburg, is a type of spatially coherent
organized motions in the upper ocean. There are also other types of
organized structures in the upper ocean, that are not included in the Fedorov
and Ginzburg classification but which are widely observed in the nearsurface ocean (see Chapter 5). These are ramp-like structures, largeamplitude internal waves (developing on a shallow diurnal thermocline or
rain-formed halocline), sharp frontal interfaces, and penetrative convection.
Now, it is becoming clear that conditions of very high wind speeds (U 10 >
25-30 m s
-1 ) should be considered as a separate near-surface regime. In these
extreme conditions a two-phase environment with gradual transition from
bubble-filled water to spray-filled air is formed (Chapter 6).
Before proceeding to the main subject of this book, the near-surface layer
of the ocean, in Chapter 1 we provide a general discussion of the governing
2
mixing regime below the air-sea interface strongly depends on
meteorological, radiation, and surface wave conditions. Instead in this
monograph the near-surface layer of the ocean is considered as an integral
part of the ocean-atmosphere system. There are in fact some processes that
are unique to the upper few meters (e.g., wave breaking) or even for the
upper few millimeters (e.g., molecular transport) of the ocean. Other
processes may be confined to the upper few meters of the ocean under
certain conditions (e.g., large diurnal warming events) but for different
environmental conditions will have depth scales of tens of meters. There are
also processes that originate at the air-sea interface but extend to the overall
depth of the upper ocean mixed layer (e.g., Langmuir circulations and
nighttime convection).
The variety of forcing factors, in combination with nonlinear feedbacks,
result in different near-surface regimes. Fedorov and Ginzburg (1988)
consider five regimes in the near-surface layer of the ocean:
1) Intensive wind-wave mixing (wind speed at 10 m height above the
ocean surface U 10 > 8-10 m s
-1 );
2) Intensive convection (nighttime, winter, or atmospheric cold fronts);
3) Langmuir circulations (U 10 from 3 to 10 m s
-1 );
4) Intensive solar heating under low wind and calm weather conditions
(U 10 from 0 to 3-5 m s
-1 );
5) Near-surface freshening due to rain.
This classification is still valid in general and is useful for many
practical applications. At this point, however, it requires comment.
The near-surface ocean under regime 1 is usually well mixed. However,
surface molecular sublayers, which are not included in this classification,
may develop even under conditions of intensive wind-wave mixing though
only between wave breaking events (see Chapter 2).
The Langmuir circulations, which are considered as a separate regime
(regime 3) by Fedorov and Ginzburg, is a type of spatially coherent
organized motions in the upper ocean. There are also other types of
organized structures in the upper ocean, that are not included in the Fedorov
and Ginzburg classification but which are widely observed in the nearsurface ocean (see Chapter 5). These are ramp-like structures, largeamplitude internal waves (developing on a shallow diurnal thermocline or
rain-formed halocline), sharp frontal interfaces, and penetrative convection.
Now, it is becoming clear that conditions of very high wind speeds (U 10 >
25-30 m s
-1 ) should be considered as a separate near-surface regime. In these
extreme conditions a two-phase environment with gradual transition from
bubble-filled water to spray-filled air is formed (Chapter 6).
Before proceeding to the main subject of this book, the near-surface layer
of the ocean, in Chapter 1 we provide a general discussion of the governing
2