Changes in the mesoscale variability and in extreme sea levels over two decades as observed by satellite altimetry

A data set of precise radar altimeter sea surface heights obtained from the same 10-day repeat ground track has been analysed to determine the magnitude of change in the ocean ‘mesoscale’ variability over two decades. Trends in the standard deviation of sea surface height variability each year are found to be small (typically ~0.5 percent/yr) throughout the global ocean. Trends in positive and negative extreme sea level in each region are in general found to be similar to those of mean sea level, with some small regional exceptions. Generalised Extreme Value Distribution (GEVD) analysis also demonstrates that spatial variations in the statistics of extreme positive sea levels are determined largely by the corresponding spatial variations in mean sea level changes, and are related to regional modes of the climate system such as the El Niño – Southern Oscillation. Trends in the standard deviation of along-track sea level gradient variability are found to be close to zero on a global basis, with regional exceptions. Altogether our findings suggest an ocean mesoscale variability that displays little change when considered over an extended period of two decades, but that is superimposed on a spatially and temporally varying signal of mean sea level change. This article is protected by copyright. All rights reserved.