Aliasing of high‐frequency variability by altimetry: Evaluation from bottom pressure recorders

In spectra computed from bottom pressure records, 18% to 63% of non‐tidal energy is associated with frequencies greater than 1 cycle per 20 days, the approximate Nyquist frequency for the TOPEX/Poseidon (T/P) satellite. Since bottom pressure measurements are correlated with coincident sea surface height measurements from the T/P satellite, hourly bottom pressure data are used here to characterize the aliasing expected from T/P. As numerical modeling studies have also demonstrated, spectra computed from data sampled at 10‐day intervals are likely to alias substantial amounts of unresolved high‐frequency variability, particularly at frequencies greater than 0.2 times the Nyquist frequency.