Seasonal and Low-Frequency Variability in Basin-Scale Sea Level

Seasonal and low-frequency variations in basin-scale mean sea level are studied for the period 1950 to 2000 by interpolating sparse tide gauge data to a global grid using empirical orthogonal functions (EOFs) of sea level variability determined from TOPEX/Poseidon (T/P) altimeter data. Results are based on data and with no long term trends. The fact that the results do not have secular trends is an artifact of the analysis, and should not be interpreted as an indication that sea level is not rising. Reconstructions using global EOF modes compare better with T/P for basin-scale averages than reconstructions based on basin EOF modes. An analysis of mean sea level in the North Pacific and North Atlantic suggests both basins have a significant trend in the mean annual amplitude over time and that the North Atlantic has a significant trend in the mean annual phase. It is also demonstrated that volume changes of the upper layer thickness in the tropical Pacific can be calculated from the reconstructed data with an accuracy comparable to other methods.