Convectively coupled Kelvin waves

Observations of tropical outgoing longwave radiation (OLR) show coherent signatures of fast eastward-propagating convection, moving to the east at approximately 17 m/s. Wheeler and Kiladis (1999) designate these waves as "convectively coupled Kelvin waves" because their signature in the space-time spectrum of tropical OLR stands well above the background spectrum within a region bounded by the dispersion curves for shallow water Kelvin waves. This study will investigate the spatial and temporal behavior of these convectively coupled Kelvin waves, in both the troposphere and stratosphere, in more detail.

An EOF analysis is used to capture the dominant modes of OLR variability in this Kelvin wave band for both the NH summer and winter seasons. Results show that the temporal spectra of the principal modes of variability differ quite substantially between summer and winter, with a 10-day mode dominant in the NH summer, while a 20-day mode is dominant in the NH winter. Regression techniques are used to determine the relationships between the Kelvin wave OLR field and dynamical fields such as winds and temperature, through use of the ECMWF and NCEP/NCAR Reanalysis datasets. Radiosonde data are used to verify these analyses. The seasonal and interannual variability of these waves will also be discussed.