Westward Traveling Speeds of Sea-level Variations in the North Pacific as Revealed by 2D Frequency-wavenumber Spectra From 9 Years of TOPEX Data

The spectral method is refined to better isolate traveling features from standing features, which include everything that does not propagate, such as the sea-level response to the seasonal heating and cooling. Examining the traveling spectra from the equatorial region to latitudes south of the Kuroshio Extension, it often appears that there is a dominant zonal speed such that the spectral energy tends to congregate around a straight line on the spectra representing this dominant speed of westward propagation. This qualitative description has been put on a quantitative basis. One certainly likes to know how much spectral energy is congregated around the line and how narrow is the concentration. Thus a speed range centered on the dominant speed is computed so that more than 50% of the westward propagating power is contained in this speed range. The computation has been carried out for 9 latitude zones centered on the midpoint latitudes with three estimates at each latitude zone representing respectively the entire ocean basin and the east and west basins. The results are discussed in the context of various existing theories.