Time-Frequency Characteristics of the Pressure Term of the Eaam Excitation Functions in Some Geographic Regions

Abstract

Regional values of the Effective Atmospheric Angular Momentum (EAAM) functions were computed from the Japan Meteorological Agency Global Objective Analysis data for the period 1988–1997. Time-variable amplitude spectra of the pressure terms (including or not the inverted barometric (IB) correction) of the complex-valued equatorial components of EAAM functions χ₁, χ₂ were computed for the selected geographic regions covering mid-latitude Europe, Asia with part of Siberia, North America and parts of northern Atlantic, and Pacific. These spectra of short period variations of pressure terms of χ₁, χ₂ show distinct time variations of amplitudes of the prograde and retrograde oscillations with periods of about 40–60 and 90–120 days. Amplitudes of these oscillations depend also on latitude and longitude. The computed coherence between regional and global pressure terms of the χ₁, χ₂ and between these regional terms and polar motion exciatation functions show that the regional pressure terms over Eurasia in the latitude belt 45° - 60° N give the most important contribution to polar motion excitation.