Vertical Inhomogeneities of Profiles
Several inversions of temperature and salinity and intrusion inhomogeneities (due
to the isopycnal advection) were recorded in the upper part of the section. Stepwise
structures (due to the vertical structure forming processes) of various scales from a
few to several tens of meters are the characteristic features of the vertical structure
of the thermohaline field below the upper high-gradient thermo-halocline and down
to approximately 500 m, which is the transition region to the intermediate salinity
minimum.
The steps consist of thin high-gradient layers (“sheets”) separated by thick
low-gradient layers. The vertical gradients in high-gradient layers exceed 10–100
times and greater the corresponding mean gradients. Such fine structures are clearly
pronounced on the vertical profiles at the southern station 2698. These steps are
clearly seen both in the temperature and salinity fields, but owing to the fact that
they compensate each other they are less manifested in the density field (Fig. 3).
From south to north, the number of steps decreases and the vertical size (the
thickness of well-mixed layers) increases while the salinity (and temperature)
gradients decrease.
Similar structures are also seen on the vertical profiles of velocity but here they
are smoother. The latter can be related to a lower depth resolution of the velocity
profile compared with the temperature and salinity profiles (the vertical steps of the
profiles are 10 and 2 m, respectively). Well-correlated vertical structure of both
thermohaline parameters and velocity is typical for the sections across the EUC,
which was already noticed in the early publications.
The existence of intense stepwise structures on the profiles provides the first
preliminary evidence about intense processes of mixing in the stratified water
column. Below we will address a question of the reality of the significant contribution of convective mixing below the EUC core.
Thermohaline Stratification and Vertical Stability
In this paragraph, we consider the criteria of the types of stratification and vertical
stability and then present and discuss the computed profiles of the density ratio R ρ
and vertical stability parameter E θ, S , computed from the CTD casts. We focus here
on the joint analysis of the thermohaline field structure and the computed parameters with the purpose of detecting conditions, favorable for the development of
double diffusion and salt fingering.
Depending on the background stratification, the effects of double-diffusion
instability are manifested in the modes of salt fingers and interleaving (or diffusion)
convections. Salt fingers occur in steadily stratified layers when both temperature
and salinity decrease with depth. When T and S, on the contrary, increase downwards, the convection in the mode of interleaving occurs [7, 8, 20].
436
T. A. Demidova
Several inversions of temperature and salinity and intrusion inhomogeneities (due
to the isopycnal advection) were recorded in the upper part of the section. Stepwise
structures (due to the vertical structure forming processes) of various scales from a
few to several tens of meters are the characteristic features of the vertical structure
of the thermohaline field below the upper high-gradient thermo-halocline and down
to approximately 500 m, which is the transition region to the intermediate salinity
minimum.
The steps consist of thin high-gradient layers (“sheets”) separated by thick
low-gradient layers. The vertical gradients in high-gradient layers exceed 10–100
times and greater the corresponding mean gradients. Such fine structures are clearly
pronounced on the vertical profiles at the southern station 2698. These steps are
clearly seen both in the temperature and salinity fields, but owing to the fact that
they compensate each other they are less manifested in the density field (Fig. 3).
From south to north, the number of steps decreases and the vertical size (the
thickness of well-mixed layers) increases while the salinity (and temperature)
gradients decrease.
Similar structures are also seen on the vertical profiles of velocity but here they
are smoother. The latter can be related to a lower depth resolution of the velocity
profile compared with the temperature and salinity profiles (the vertical steps of the
profiles are 10 and 2 m, respectively). Well-correlated vertical structure of both
thermohaline parameters and velocity is typical for the sections across the EUC,
which was already noticed in the early publications.
The existence of intense stepwise structures on the profiles provides the first
preliminary evidence about intense processes of mixing in the stratified water
column. Below we will address a question of the reality of the significant contribution of convective mixing below the EUC core.
Thermohaline Stratification and Vertical Stability
In this paragraph, we consider the criteria of the types of stratification and vertical
stability and then present and discuss the computed profiles of the density ratio R ρ
and vertical stability parameter E θ, S , computed from the CTD casts. We focus here
on the joint analysis of the thermohaline field structure and the computed parameters with the purpose of detecting conditions, favorable for the development of
double diffusion and salt fingering.
Depending on the background stratification, the effects of double-diffusion
instability are manifested in the modes of salt fingers and interleaving (or diffusion)
convections. Salt fingers occur in steadily stratified layers when both temperature
and salinity decrease with depth. When T and S, on the contrary, increase downwards, the convection in the mode of interleaving occurs [7, 8, 20].
436
T. A. Demidova