Patterns of sea surface height and heat storage associated to intraseasonal Rossby waves in the tropics

Abstract

Propagating signals with periods of ∼50 days are detected in global sea surface height anomaly data from the TOPEX/Poseidon altimeter. The sea surface height anomaly is converted into heat storage because of its thermodynamical and biological interest. Both height and heat storage time series are organized in zonal-temporal diagrams for each latitude and band-pass filtered. The filters separate the spectral band with periods on the order of 35-65 days and wavelengths on the order of 500-2000 km within 12.5° of the equator. The main objectives are to identify the dynamical regime of the observed variability, locate regions with persistent variability in this spectral band, characterize the propagation patterns, and analyze their temporal dependence. Comparison with theoretical dispersion curves indicates that the observed signal behaves as short, dispersive baroclinic Rossby waves in all tested cases in the Atlantic, Pacific, and Indian Oceans. The group speed differs significantly from the phase speed and tends to smaller values away from the equator. The spatial and temporal pattern analysis is done by two independent methods: decomposition in complex empirical orthogonal functions and correlation-weighted averages. Both methods show essentially the same results within their inherent features and limitations. The correlation between the amplitude of these waves and the phase of the seasonal and El Niño cycles is estimated and discussed. Similarly, the correlation between the amplitude of these high-frequency Rossby waves and those of low-frequency Kelvin and Rossby waves is also estimated and discussed. Copyright 2003 by the American Geophysical Union.