Propagating vs. Stationary Intraseasonal Oscillations in the Tropical Atmosphere: What May Have Caused the Difference?

ECMWF Reanalysis data from 1974-2002 (29 years) covering the globe with horizontal resolution of 2.5º×2.5º in longitude and latitude were used to identify the events of intraseasonal oscillation/variation (ISO) in atmospheric convection in the tropical Indian and Pacific Ocean region. In addition, the outgoing longwave radiation (OLR) data from NOAA-CIRES Climate Diagnostics Center for the same 29 years were used to examine the ISO. The identified events were examined for their source regions of the oscillation using the beamforming method that traces the source of wave/oscillation activity in interpolated data grids, such as the ECMWF dataset. Upon finding the sources regions of the ISO events in those 29 years we examined the conditions in the source regions for development of the ISO. Two kinds of ISO were identified: 1) the kind that propagates eastward in a fashion similar to the classic 40-50 day Madden-Julian Oscillation (MJO), and 2) the kind that is either stationary in the source region or even propagates westward. The latter kind was similar to some of those also reported in previous literature. The atmospheric conditions were examined to aid understanding of what may have caused the two rather different kinds of ISO in the tropical Pacific and Indian Ocean region. Questions of how such different conditions may develop in that region and hence result in different ISO are raised.