Influence of the Shallow Seas on the Pressure Terms of the EAAM Function

Abstract

It is likely that the inverted barometer (IB) response breaks down in the shallow seas and ocean shelves. This paper is intended to show the contribution of the shallow seas and sea shelves to the pressure terms of the Effective Atmospheric Angular Momentum (EAAM) excitation function, by computing three residuals of the equatorial components of the EAAM function on the basis of two ocean response models. In the first model, the IB correction is assumed to be valid for the whole ocean, while in the second model the correction is valid only for ocean deeper than 500 m. The equatorial components of the EAAM function, X ₁ and X ₂, are computed from the Japanese Meteorological Agency’s Global Objective Analysis data for the period from 1988 to 1995. The computed residuals are separated into three spectral ranges namely, 2 – 10 days, 10 – 150 days and over 150 days. The residuals exhibit maximum amplitudes in the order of 10⁻⁷ rad, which are smaller than differences of X ₁ and X ₂ components with IB corrections from those without the correction. However, they are more significant than the differences between those obtained by Barnes et al. (1983) and Eubanks (1993) who use different dynamical parameters of the Earth. In addition to this result we show spectral variations of the residuals. In the spectral range from 10 to 150 days, 59 day retrograde and 75 day prograde oscillations are strongest, while in the spectral range shorter than 10 days, 8 day retrograde oscillation is most significant.

On leave from Space Research Center of the PAS, Poland