Continuous wavelet transform; Lake Tanganyika; Morlet wavelets; Reduced-gravity model; Thermocline oscillations; lake; thermal analysis; wavelet analysis; wind; lake dynamics; thermocline; wind forcing; Africa
Abstract :
[en] 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.
Disciplines :
Aquatic sciences & oceanology
Author, co-author :
Naithani, J.; Universite catholique de Louvain, Inst.d'astronomie et de geophysique, Louvain-La-Neuve B-1348, Belgium
Deleersnijder, Eric ; Université de Liège - ULiège > Département ArGEnCo > Hydraulics in Environmental and Civil Engineering ; Universite catholique de Louvain, Inst.d'astronomie et de geophysique, Louvain-La-Neuve B-1348, Belgium
Plisnier, Pierre-Denis ; Université de Liège - ULiège > Département d'astrophysique, géophysique et océanographie (AGO) > Chemical Oceanography Unit (COU) ; Royal Museum for Central Africa, Geology and Mineralogy Department, Leuvensesteenweg 13, Tervuren B-3080, Belgium, Facultes Univ.Notre-Dame de Paix, Lab. d'Ecologie des Eaux Douces, Rue de Bruxelles 61, Namur B-5000, Belgium
Language :
English
Title :
Analysis of wind-induced thermocline oscillations of Lake Tanganyika
Publication date :
2003
Journal title :
Environmental Fluid Mechanics
ISSN :
1567-7419
eISSN :
1573-1510
Publisher :
Kluwer Academic Publishers, Nl
Volume :
3
Issue :
1
Pages :
23 - 39
Peer reviewed :
Peer Reviewed verified by ORBi
Funding text :
This work was carried out for the project, ‘Climate Variability as Recorded by Lake Tanganyika’ (CLIMLAKE), which is funded by the Belgian program of Sustainable Development (Federal Office for Scientific, Technical and Cultural Affairs (OSTC), Prime Minister’s Office). We thank the FAO/FINNIDA project GCP/RAF/ 271/FIN for the data used in this study. Eric Deleersnijder is a Research Associate with the Belgian National Fund for Scientific Research (FNRS).
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