Kelvin wave-CISK: a possible mechanism for the 30-50 day oscillations

Abstract

Two categories of theories have been proposed to explain the observed tropical intraseasonal oscillations whose main periodicity is between 30-50 days: 1) those based on eastward propagating Kelvin waves maintained by cumulus heating; and 2) those based on interactions with stationary oscillations of the basic state. Recent numerical modeling studies have simulated certain important aspects of the oscillations, particularly the slower propagation speed as compared with the normal Kelvin waves. Motivated by these results which lend support to the first category, a linear theoretical analysis of the equatorial β-plane wave-CISK was carried out with a focus on the Kelvin modes. The results further imply that, in the absence of wave-CISK, the observed oscillation cannot be excited by stationary oscillations. -from Authors