Seasonal changes in dynamic heights based on altimetric data

One year of TOPEX/POSEIDON altimeter data have been evaluated to study seasonal changes in the ocean dynamic heights. The authors modeled these heights by a spherical harmonics expansion up to degree 30 for each 10-day cycle covering the year 1993. The global mean sea level rate is estimated at -1.3 mm/yr. The seasonal sea height variability shows the anticipated behavior of most of the western boundary currents; relatively high levels in spring/fall, and low in winter/summer. The Agulhas Retroflection Front, however, shows the opposite. It also shifts to the west in spring and fall. Local harmonic analyses (FFT) of the dynamic heights reveal a dominant annual cycle for most areas, whereas the semi-annual cycle is confined to the western boundary currents. Dominant cycles of about 100 days are found in highly instable areas like the Brazil-Malvinas Confluence and the Agulhas Retroflection. A longitude-time diagram of a section in the Pacific along the equator gives evidence of equatorial Kelvin waves