On the sensitivity of the generalised linear Rossby wave theory to uncertainties in the determination of the background mean flow: updated results

Angela Maharaj (Climate Change Research Centre and ARC Centre of Excellence for Climate System Science, Australia)

CoAuthors

Chaehyeon Chelsea Nam (School of Earth and Environmental Sciences, Seoul National University , South Korea); Remi Tailleux (Department of Meteorology, University of Reading, United Kingdom)

Event: 2014 Ocean Surface Topography Science Team Meeting

Session: Science Results from Satellite Altimetry: Finer scale ocean processes (mesoscale and coastal)

Presentation type: Type Poster

It is now well established that both the bathymetry and the background mean flow can significantly affect the propagation of linear Rossby waves, and that both effects are important for correctly interpreting satellite observations of Rossby wave speeds. However, rigorously testing theoretical predictions of Rossby wave propagation against satellite observations is challenging, due to the notorious difficulty of estimating the background mean flow from observations, which introduce significant uncertainty into the problem. We investigate the sensitivity of theoretical dispersion relations for linear Rossby waves in the presence of mean flow to uncertainties in the determination of the background mean flow. These are evaluated against empirical dispersion relations obtained from the spectral analysis of sea surface height data for previously examined regions of the South Pacific Ocean. We also assess to what extent the theoretical dispersion relations in the presence of mean flow based on Killworth and Blundell (JPO,2003,2004)'s theory are affected by the error reported in Tailleux (JPO,2012).

This paper is an update on research presented at OSTST in 2013. Our new results confirm that the error in Killworth and Blundell (2003) theory identified in Tailleux (2012) dramatically affects the nature of the theoretical dispersion relation at high wavenumbers, but on the cases considered, the differences occur in a part of the wavenumber space that is not observable. In the 11 case studies examined, generally neither the time nor the longitudinal variations of the zonal mean velocity appear to affect inferences based on the temporal mean at the central longitude of the domain considered. Additionally, the standard deviation in the region considered appears to be very large compared to the mean zonal velocity, casting doubt on the validity of the linear approximation. In regions dominated by westward propagating eddies,the eddies can also contribute to the definition of the zonal mean velocity, raising the question of the correct theoretical approach to studying linear Rossby waves. This study confirms that for wavelengths below the Rossby radius, theoretical dispersion relations appear to be relatively insensitive to variations in the mean flow.
 
Angela Maharaj
Climate Change Research Centre and ARC Centre of Excellence for Climate System Science
Australia
a.maharaj@unsw.edu.au