Global Interannual Trends and Amplitude Modulations of the Sea Surface Height Anomaly from the TOPEX/Jason-1 Altimeters

Abstract

This study uses the global Ocean Topography Experiment (TOPEX)/Jason-1 altimeters' time series to estimate the 13-yr trend in sea surface height anomaly. These trends are estimated at each grid point by two methods: one fits a straight line to the time series and the other is based on the difference between the average height between the two halves of the time series. In both cases the trend shows large regional variability, mostly where the intense western boundary currents turn. The authors hypothesize that the regional variability of the sea surface height trends leads to changes in the local geostrophic transport. This in turn affects the instability-related processes that generate mesoscale eddies and enhances the Rossby wave signals. This hypothesis is verified by estimates of the trend of the amplitude of the filtered sea surface height anomaly that contains the spectral bands associated with Rossby waves and mesoscale eddies. The authors found predominantly positive tendency in the amplitude of Rossby waves and eddies, which suggests that, on average, these events are becoming more energetic. In some regions, the variation in amplitude over 13 yr is comparable to the standard deviation of the data and is statistically significant according to both methods employed in this study. It is plausible that in this case, the energy is transferred from the mean currents to the waves and eddies through barotropic and baroclinic instability processes that are more pronounced in the western boundary current extension regions. If these heat storage patterns and trends are confirmed on longer time series, then it will be justified to argue that the warming trend of the last century provides the energy that amplifies both Rossby waves and mesoscale eddies.

Regional Patterns of Sea Level Change Related to Interannual Variability and Multidecadal Trends in the Atlantic Meridional Overturning Circulation*

“…The difference in SSH patterns suggests that over the mid-latitude NA, the manifestation of changes in MOC transport critically depends on the time scales of interest. A general implication is that trend studies of SSH patterns based on available, relatively short (13-year) altimeter records [Bindoff et al, 2007;Cromwell et al, 2007;Polito and Sato, 2008] have to be interpretated with caution, especially along the GS in the mid-latitude western North Atlantic where the SSH variability is dominated by strong intra-seasonal-to-interannual fluctuations. Because of this intense, high-frequency "noise" in SSH time series, the manifestation of a gradual trend in the MOC would effectively be masked in the GS regime.…”

Global changes in oceanic mesoscale currents over the satellite altimetry record

“…Over recent decades, sea water thermal expansion and melting of land ice have led to an increase of SSH 1, 25 (Fig. 1a).…”

Observação da Variação Espectral e Posicional da Frente Brasil-Malvinas por Sensoriamento Remoto

“…Contudo, ainda há espaço para avançar o conhecimento acerca da variabilidade da posição dessa frente, principalmente quanto ao período interanual devidoà curta extensão das séries temporais estudadas previamente nessa região. Em face disso, foram estabelecidos os objetivos do presente trabalho.De acordo com os objetivos estabelecidos, foram elaborados estudos de variação do espectro de ondas de Rossby para a região da CBM, mapas de distribuição horizontal da velocidade geostrófica oriunda de altímetro, mapas de distribuição horizontal do gradiente de temperatura da superfície do mar (TSM) e por meio destes feita a digitalização da FBM Polito & Sato [2008]. observaram tendência de aumento da inclinação da superfície associada a um aumento na intensidade ou a uma mudança na posição das correntes de contorno oeste (CCO).…”