Physical Oceanography, Vol. 14, No. 6, 2004
ANALYSIS OF OBSERVATIONS AND METHODS FOR CALCULATING
HYDROPHYSICAL FIELDS IN THE OCEAN
FORMATION OF THERMOCLINE IN THE EQUATORIAL ZONE
OF THE OCEANS
Boguslavskii, and I.
We study the formation of the vertical distribution of temperature in the upper layer of the oceans
at low latitudes
by using the nonlinear dependence of the vertical heat
flow on the vertical temperature gradient with regard for the influence of the bulk absorption of
solar radiation and heat sink on the temperature of water. The thermocline is formed under the
condition that the modulus of temperature gradient attains values for which their subsequent in-
crease leads either to insignificant variations of the heat flow or even to its decrease. We consi-
der the possibility of solution of inverse problems for the evaluation of the heat-exchange coeffi-
cient and the parameter of the heat sink. For the Equatorial Atlantic considered as an example,
we compare the theoretical results with the data of instrumental measurements.
Thermocline is a global phenomenon in the World Ocean. It covers practically the entire water area of the
oceans and seas. At high and middle latitudes, the period of spring–summer heating of waters is characterized
by the formation of the seasonal thermocline. At the end of the period of winter cooling of waters, this thermo-
cline disappears. At the same time, in the tropical zone occupying a significant part of the surface of the World
Ocean, we observe the quasistationary thermocline. The variations of its characteristics in the annual cycle de-
crease from the tropics of Cancer and Capricorn to the equatorial zone.
There are numerous works devoted to the theory of thermocline in the oceans. In our opinion, the source
differential equation whose solution determines the temperature field in the upper layer of the ocean is not well
justified in the major part of these works. Thus, in particular, the dependence of the vertical heat flow q on the
vertical temperature gradient T
= dT dz and the direct influence of the bulk absorption of solar radiation on
the temperature of water are not taken into account in this equation.
To determine the thermocline, we study specific features of the mechanism of vertical heat transfer in a
stratified medium. If the heat-conduction coefficient is constant, then the temperature field in the analyzed me-
dium is described by a linear heat-conduction equation deduced for the case of a linear dependence of the heat
flow on the temperature gradient. However, this equation does not characterize the process of formation of the
temperature fields of water basins for high temperature gradients, when the influence of the temperature gradient
on the density stratification is noticeable. In this case, the turbulence energy is spent not only for the dissipa-
tion but also to overcome the buoyancy force. Under these conditions, the vertical heat flow is a complex func-
tion of the temperature gradient T
. In , on the basis of the data of in-situ experiments in the Black Sea and
Sea of Japan, it is demonstrated that the vertical heat flow in the sea is satisfactorily described by the formula
Marine Hydrophysical Institute, Ukrainian Academy of Sciences, Sevastopol. Translated from Morskoi Gidrofizicheskii Zhurnal,
10–16, November–December, 2004. Original article submitted April 4, 2003.
328 0928-5105/04/1406–0328 © 2005 Springer Science+Business Media, Inc.