Relation between sea level and bottom pressure and the vertical dependence of oceanic variability

[1] The relation between large-scale sea level and bottom pressure variability is studied using long (50-yr) simulations of a general circulation model under realistic forcing. Admittance and coherence analyses are used to characterize the bottom pressure and sea level relationship as a function of period, horizontal spatial scale, and location. At the model grid scale (1 degrees), bottom pressure is found to be essentially equivalent to sea level at periods <30 days, except in the tropics. This equivalence still holds for longer periods (similar to 100 days), but only at high latitudes (>60 degrees) and in shallow depths (<200 m). Elsewhere, bottom pressure and sea level fields can differ significantly. Results indicate an increase of the importance of baroclinic signals with decreasing latitude and spatial scale, with significant baroclinic signals at intra-seasonal and longer periods present in many subtropical and mid-latitude regions. Variability is clearly baroclinic at inter-annual periods, regardless of location and spatial scale. Results have broad implications for the interpretation and processing of both satellite altimetry and gravity data and for their assimilation into numerical models.