Abstract
An analysis is presented of the wind-induced thermocline oscillations of Lake Tanganyika, East Africa. The region undergoes a four month dry season and the wet season for the rest of the year. The dry season is characterised by nearly constant high southeasterly winds, while for the rest of the year mild wind blows generally from the northeast. Observations show that the dry season high winds cause tilting of the thermocline, being higher/lower than normal at the southern/northern ends of the lake. The thermocline tries to restabilise itself after the cessation of dry season winds and oscillates for the rest of the year. A non-linear reduced-gravity model is used to study the thermocline oscillations of the lake. The numerical simulations satisfactorily represent the oscillations, their period and amplitude. Different forcing conditions (thermocline depth, wind stress and stability) are used in the model and their effect on the period and amplitude of the oscillations are studied. The amplitude of oscillations ranges from 15 to 45 m, while their period varies from 3 to 4 weeks according to the variation in the model parameters. Wavelet transform is used to study the evolution of periods of oscillations with depth in the time series of observations and along the length of the lake using model simulations. Wavelet spectra presents several dominant modes including the semidiurnal, diurnal, synoptic, intraseasonal variability, besides the modes representing the wind-induced thermocline oscillations.
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References
Coulter, G.W. and Spigel, R.H.: 1991, In: G.W. Coulter (ed.), Lake Tanganyika and its Life, pp. 49-75,Oxford University Press, London.
Wu, J.: 1975, Wind-induced drift currents, J. Fluid Mech.,68, 49-70.
Plisnier, P.-D. and Coenen, E.G.: 2001, Pulsed and dampened annual limnological fluctuations in Lake Tanganyika, M. Munawar and R.E. Hecky (eds.), The Great Lakes of theWorld, pp. 83-96, Backhuys Publishers, The Netherlands.
Wetzel, R.G.: 2001, Limnology-Lake and River Ecosystems, third edition, Academic Press.
Plisnier, P.-D.: 1998, Lake Tanganyika: Recent climate changes and teleconnections with ENSO, In:G. Demarée, J. Alexandre and M. De Dapper (eds.), Proceedings of International Conference of Tropical Climatology, Meteorology and Hydrology 2000, pp. 228-250.
Plisnier, P.-D., Serneels, S. and Lambin, E.F.: 2000, Impact of ENSO on East Africa ecosystems: a multivariate analysis based on climate and remote sensing data, Glob. Ecol. Biogeogr. 9, 481-497.
Talling, J.F.: 1966, The annual cycle of stratification and phytoplankton growth in Lake victoria (East africa), Intern. Rev. Gesampt. Hydrobiol. Hydrogr. 51, 545-621.
Eccles, D.H.: 1974, An outline of the physical limnology of Lake Malawi (Lake Nyasa), Limnol. Oceanogr. 19, 730-742.
Newell, B.S.: 1960, The hydrology of Lake victoria. Hydrobiologia 15, 363-383.
Meyers, S.D., Kelley, B.G. and O'Brien, J.J.: 1993, An introduction to wavelet analysis in oceanography and meteorology: With application to the dispersion of yanai waves, Mon. Wea. Rev. 121, 2858-2866.
Busalacchi, A.J. and O'Brien, J.J.: 1980, The seasonal variability in a model of the tropic Pacific, J. Phys. Oceanogr. 10, 1929-1951.
Busalacchi, A.J. and O'Brien, J.J.: 1981, Interannual variability of the equatorial Pacific in the 1960's,J. Geophys. Res.86, 10,901-10,907.
Luthar, M. and O'Brien, J.J.: 1985, A model of the seasonal circulation in the Arabian Sea forced by observed winds, Progr. Oceanogr. 14, 353-385.
Woodberry, K.E., Luthar, M.E. and O'Brien, J.J.: 1989, The wind-driven seasonal circulation in the southern tropical Indian Ocean,J. Geophys. Res.94, 17,985-18,002.
Young, B. De, Otterson, T. and Greatbatch, R.J.: 1993, The local and nonlocal response of Conception Bay to wind forcing, J. Phys. Oceanogr. 23, 2636-2649.
Inoue, M. and Welsh, S.E.: 1993, Modelling seasonal variability in the wind-driven upper-layer circulation in the Indo-Pacific region, J. Phys. Oceanogr. 23, 1411-1436.
Handoh, I.C. and Bigg, G.R.: 2001, Use of a reduced-gravity model to evaluate present and past primary productivity in the tropical open ocean, Limnol. Oceanogr. 46, 1632-1641.
Balzano, A.: 1998, Evaluation of methods for numerical simulation of wetting and drying in shallow water flow models, Coast. Engin. 34, 83-107.
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Naithani, J., Deleersnijder, E. & Plisnier, PD. Analysis of Wind-Induced Thermocline Oscillations of Lake Tanganyika. Environmental Fluid Mechanics 3, 23–39 (2003). https://doi.org/10.1023/A:1021116727232
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DOI: https://doi.org/10.1023/A:1021116727232