Propagating large-scale oceanic features - an analysis over time

Abstract

Oceanic large-scale westward propagating features are capable of transporting heat and momentum and their importance in the set-up of major climate oscillations is undeniable. The ability to monitor and understand climate change is one of the top priorities in research. The possibility of using of these waves as indicators of such changes was analysed by Fyfe and Saenko (2007) who found that the increasing temperatures of the ocean's upper layers caused wave speeds to increase 35% in the 2 centuries analysed. Given the reported changes in ocean stratification and heat content (IPCC, 2013), this work analyses 20 years of altimetry data for changes in the Rossby wave signatures that might result from changes in the oceans. The 'Rossby wave-like' (RW) variability and speed distribution is characterised on a global scale. In the Indian and Pacific, the ocean's RW variability is shown to be significantly correlated with the Niño time-series, proving the RW sensitivity to ocean changes. A second RW dataset, derived from NEMO SSHA outputs - NEMO RW - is produced and validated against the altimeter RW data, providing good results especially for latitudes up to 20º. Speeds over time of the RW signal are computed for both datasets for trend analysis. The altimeter data proved to be too short however, 42 years of NEMO RW data provided trend maps showing speed changes occurring in all ocean basins, albeit with a more complex distribution than the findings of Fyfe and Saenko (2007) suggested. The NEMO RW speed time-series shows signs of being modulated by ENSO and the South Atlantic Southern Dipole in the Pacific and the Atlantic, respectively. Results confirm that changes are occurring in the RW speeds over the time-series analysed and establish the RW sensitivity to changes over time in the ocean's properties.

More information

Identifiers

Catalogue record

Export record