| Filtered deviations from equilibrium of surface level allow to study the internal motions. The
method resulting from the consideration that internal oscillations are accompanied by
oscillations at lake surface level, typically 1/1000 smaller in amplitude, was initially
proposed by Mortimer (1963) and later used by different authors, i.e. Caloi et al.,
1986, Sirkes, 1987 and Lemin et al., 2005. Forcat et al. (2011) applied the method
to numerical results obtained by the Princeton Ocean Model for a Mediterranean
reservoir and it was found that the results adequately reproduce all the significant
modes observed and showed the importance of rotational modes. In the present work
the structure of internal waves at the Eastern basin of the Large Aral at the end of
September 2006 is presented based also on numerical simulations with POM. Initial
stratification was that measured in situ and the system was forced by reanalysis wind
data. The sub-daily modes which have been identified are close to the main peaks
observed on the spectral analysis of the water surface level which was measured
during a couple of days at the shore of the Sea and correspond to a combination of
first and second vertical and horizontal modes with no rotational behavior. Modes
with longer periods, which are the most energetic, are however found to rotate
clockwise.
Acknowledgement: Data and facilities for this work were provided within the frame of
the CLIMSEAS project (FP7-IRSES-2009-247512). |