Atmospheric Equatorial Kelvin Waves in Lagrantian Framework - Interactions with Local Environment and Its Impact for Their Propagation

Atmospheric Kelvin waves (KWs) propagate eastward in the equatorial belt and represent one of key modes of the intraseasonal variability in the topical atmosphere. Convectively coupled waves also create building blocks of the Madden-Julian Oscillations (MJO), but their activity is not limited to the MJO itself.

In this study, we utilize Lagrangian analysis based on FFT filtering, which allows tracking individual events. Such an approach has been successfully used in analysis based on 15-year-long TRMM satellite data. It enabled identification of initiation and decay of convective events as well as analysis of environmental conditions throughout the lifetime of convectively coupled KWs. Here we extend this approach to other remote sensing (OLR, GPM) and modeling (ERA-I) datasets to investigate fully three-dimensional structure of such events, their interaction with local environment and evolution.

Based on conjoint analysis of zonal winds at upper and lower levels, and convective signal (precipitation and OLR) we show where and under which environmental conditions dynamic only KWs become convectively coupled as well as where the opposite process takes place. It is shown that substantial fraction of all convectively coupled KWs originate from dynamic signals and persist as such after decoupling from convection.

The new database is used to investigate changes in the vertical structure (temperature, humidity and winds) of KWs along their trajectories, with particular interest in the eastern Indian Ocean, Maritime Continent and western Pacific. It is shown that KW circulation strengthens as an event propagate eastward across Indian Ocean but the process is stopped when it’s affected by the Maritime Continent. It is shown that propagating KWs alter characteristics of the local diurnal cycle of convection and this interaction also affects propagation properties of KWs. This two-way interaction is such that it favors propagation of events, which are in phase with local diurnal cycle of convection.