PIV- and LDV-measurements of baroclinic wave interactions in a thermally driven rotating annulus

Abstract

We present results of experiments in a rotating, baroclinic annulus of fluid. The apparatus is a differentially heated cylindrical gap with a flat bottom topography and a free surface, rotated around its vertical axis of symmetry, cooled from within, and filled with de-ionised water as working fluid. We used multivariate statistical techniques to understand better the variability of the heated rotating flow $(a)$ in the transition region between regular waves of different zonal wave number, and $(b)$ in the transition region to the quasi-chaotic regime. The former regime is studied by applying the Complex Empirical Orthogonal Function (CEOF) method to Particle-Image-Velocimetry (PIV) data, the latter by applying the Multi-Channel Singular Spectrum Analysis (M-SSA) to Laser-Doppler-Velocimetry (LDV) data. In the annulus, interactions between the dominant mode and so called weaker modes can lead to low-frequency amplitude and wave structure vacillations. Our results complement previous observations recovered primarily by thermocouple arrangements.