Purpose. The paper is aimed at studying the thermocline response to slow (during a few days) and fast (up to two days) change of the current velocity, and also the process of changing in depth of the upper mixed layer lower boundary depending on the current velocity (at that the process is accompanied by the thickness and temperature gradient alteration in the thermocline).

Methods and Results. The thermocline responses were analyzed using the data on the upper layer temperature derived from the drifter experiment in 2012‒2014. The drifters equipped with the thermal chains made it possible to measure temperature in the upper layer up to 80 m. The data covering the cold period (December – March) and obtained in five sub-regions in the Rim Current zone in the western and eastern parts of the sea were analyzed. The sub-regions were chosen proceeding from absence of the synoptic and mesoscale eddies in them. In each sub-region, the drifter position was estimated relative to the core of the Rim Current. Based on the mean daily sea temperature, the thermocline profiles were constructed, the thermocline boundaries, depth of the upper mixed layer lower boundary, the thermocline thickness and the temperature gradient in it were determined. The analysis showed that in case of a slow increase (decrease) in the current velocity, in all the sub-regions, there were a deepening (rise) of the upper mixed layer lower boundary, a decrease (increase) in the thermocline thickness and an increase (decrease) of the temperature gradient in it. This process is explained by possible propagation of the internal waves induced by the Rim Current velocity varying in the thermocline.

Conclusions. The results obtained showed that the fluctuation of the Rim Current velocity increased (decreased) the depth of the upper mixed layer lower boundary, the change of which was associated with an increase (decrease) in the thermocline thickness and in the temperature gradient in it. The drifters' data are significantly "noisy" due to the spatial inhomogeneities of the temperature field in the sea upper layer. Therefore, to obtain more accurate estimates of the processes, a study at the anchored measuring platforms installed in the zone of the Rim Current action is required.

upper mixed layer, thermocline, geostrophic velocity, surface velocity, Rim Current, drifter.

The investigation was carried out within the framework of the state task on theme No. 0555-2021-0002 “Fundamental studies of interaction processes in the ocean-atmosphere system conditioning regional spatial-temporal variability of natural environment and climate”.

Original Russian Text © А. A. Sizov, T. M. Bayankina, N. E. Lebedev, 2022,
published in MORSKOY GIDROFIZICHESKIY ZHURNAL, Vol. 38, Iss. 1, pp. 73-88 (2022)

Sizov, A.A., Bayankina, T.M. and Lebedev, N.E., 2022. Thermocline Dynamics in the Zone of the Rim Current Action in Winter Period (Based on to the Drifter Experiment Data). Physical Oceanography, [e-journal] 29(1), pp. 67-82. doi:10.22449/1573-160X-2022-1-67-82

10.22449/1573-160X-2022-1-67-82

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