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136. Currents

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Currents

The main cause of currents during the ice free period is the wind. Depending on changes of the wind velocities, wind (drift) currents intensify in May, subside in June-August and again intensify in autumn reaching its maximum in December. Wind-induced currents take place during strong winds, when the surface waters are transferred, thus causing the water level decrease by 10 cm. In summer and autumn, the negative water setout lasts approximately 40 h, and in winter about 35 h, whereas the wind setup continues 44 and 40 h, respectively. Average negative water setout height (decrease of the level near the windward shore) is 9-11 cm, and that of wind setup (increase of the level near leeward shore) is 7-8 cm. Moreover, geostrophic currents are formed at Lake Baikal, which are stationary currents retaining their main characteristics (location, direction and velocity) for a long period of time. They are induced by the difference in temperature (density) of coastal and lacustrine waters, deflecting force of the Earth’s rotation and other factors. These currents covering both the entire Lake Baikal and separate basins are observed throughout the whole year.

Water is transferred counter-clockwise (cyclonic circulation) under the deflecting force of the Earth’s rotation (Coriolis force). Secondary cyclonic circulations are observed in separate basins. The water at the interface of neighbouring cyclonic circulations is transferred across the lake (in Listvennichny Bay, the Selenga delta, Academichesky Ridge and Cape Kotelnikovsky). The same direction of water transfer is also observed in deep water layers of the lake.

The highest current velocities are recorded in the upper lake layers – in the epilimnion and sometimes below the thermocline. Their average velocities are up to tens of centimetres per second intensifying from summer to autumn. Maximal velocity registered near the surface can be over 1 m/sec. In winter, when the whole lake is covered with ice, the vertical structure of the velocity field is usually the same, although because of the ice cover the currents attenuate significantly. Their average velocity in the upper layers (up to 40-50 m) can be 2 cm/s and lower during “calm” periods. However, it can increase up to 3-5 cm/s and even to 10 cm/s during atmospheric pressure drop in case of atmospheric fronts. General character of water mass transfer corresponds to cyclonic circulation (Fig. 2.33) in the water column.

In the 1960-s, V. Sokolnikov [1964], working on the lake ice, discovered the effect of current intensification in the near-bottom layer at large depths of the lake, which was later observed in other seasons of the year. The studies of this phenomenon carried out by V. Verbolov [1996] and A. Zhdanov [2006] showed that the velocities in the near-bottom layer are seasonal. In winter, they episodically exceed 10 cm/s and in summer (July-early August) they are 4-8 cm/s during weak winds. In spring (May) and autumn (October-November) they become an order of magnitude at seasonal increase of the wind with the values corresponding to those in the upper 200-m layer (up to tens of centimetres per second). Usually current velocities decrease in the near-bottom layer with the distance from the foot of the underwater slope, their highest values being recorded at the bottom.

 

References

Ainbund. M. M. (1988). Currents and internal water exchange in Lake Baikal. Leningrad: Hydrometeoizdat. p 248.

Verbolov, V. I. (1996). Currents and water exchange in Lake Baikal. Water Resources, 23(4). P 413-423.

Zhdanov, A. A. (2006). Horizontal transfer and macroturbulent water exchange in Lake Baikal (Abstract of Ph.D. Thesis). Irkutsk. p 22.

Shimaraev, M. N. (2012). Horizontal currents. In Baikal Studies. Novosibirsk: Nauka. p 166-170.

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