A climatology of waves in the equatorial region

Abstract

Propagating anomalies of moisture and moist deep convection in the Tropics are organized into a variety of large-scale modes. These include (but are not limited to) the so-called intraseasonal oscillations, convectively coupled waves similar to those predicted by shallow water theory on the equatorial beta plane, and tropical-depression-type disturbances. Along with the annual and diurnal cycles, these modes act and interact to control much of the variance of tropical convection. Analyses of 10 yr of outgoing longwave radiation (OLR) and precipitable water (PW) data are carried out to develop comparative climatologies of these wavelike modes. The analysis relaxes the commonly used cross-equatorial symmetry constraints, which allows study of the portions of the wavelike processes that are asymmetric across the equator. Mean background states are found for OLR and for PW as functions of day of the year. Examination of anomalies together with the background reveals much about how the waves are affected by their environments. Zonal wavenumber-frequency spectral analyses are performed on these anomalies. Following the spectral analyses, the OLR and the PW data are then filtered for specific regions of the wavenumber-frequency domain. Results show how variance generated by propagating modes is distributed in time and space, approximately illustrating the relative contributions of the wave modes to regional OLR and PW variability. © 2004 American Meteorological Society.