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Investigation of the Spring Thermal Regime in Lake Ladoga Using Field and Satellite Data

Joakim Malm, Dmitrii Mironov, Arkadii Terzhevik and Lennart Jonsson
Limnology and Oceanography
Vol. 39, No. 6 (Sep., 1994), pp. 1333-1348
Stable URL: http://www.jstor.org/stable/2838136
Page Count: 16
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Investigation of the Spring Thermal Regime in Lake Ladoga Using Field and Satellite Data
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Abstract

We use a combination of field and satellite data to investigate the thermal regime in Lake Ladoga in spring 1992. The analysis concentrates mainly on the temperature structure in the convectively mixed region and the dynamics of a special thermo-dydrodynamic phenomenon called "thermal bar" (a zone of descending water with the temperature of maximum density equal to $\thicksim4^circC)$. A theoretical model of the temperature distribution in the convectively mixed region (temperatures $<4^\circC)$ and the thermal bar progression is also applied and compared with satellite data. The study shows that the temperature offshore the $4^\circC$ istotherm in the convectively mixed region of the lake is almost depht-constant because of strong covective mixing and that the horizontal heat flux seems to be of minor importance in this region. The comparision between predictions from the simple theoretical model describing the temperature in this region. The comparison between predictions from the simple theoretical model describing the temperature evolution and movement of the thermal bar with observations showed a fairly good agreement. However, calculations of the change of heat content in water columns along sections indicate heat transport from the nearshore, stably stratified region toward the $4^\circC$ isotherm which will affect the movement of the thermal bar. This effect has been incorporated in an improved model of the thermal bar progression. A better agreement between predictions and observations was also obtained with this model.

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