Dynamics-Based Analysis of Waves in the Tropics

Tropical waves are often locally excited by convective heating. When tropical waves propagate away from their exciting locations in a dissipative atmosphere, they tend to attenuate and disappear. The distances from exciting locations that tropical waves can reach are characterized by the product of group velocities and damping timescale. Observed tropical waves over the whole tropical belt are rarely synchronized; rather, they are spatiotemporally local, especially these waves of small group velocities, such as mixed Rossby-gravity waves. For spatiotemporally local tropical waves, the Fourier transform-based analysis methods are less effective in accurately extracting wave characteristics.

This study focus on developing a new analysis tool that can effectively determine characteristics of local waves and then projecting them onto tropical wave dispersion relationship represented by wavenumber-frequency-energy-equivalent depth diagram, the widely called Wheeler-Kiladis diagram. The fundamental component of our tool is a spatiotemporally local analysis method, called multidimensional ensemble empirical mode decomposition, that can naturally isolate spatiotemporally local tropical waves, facilitating the determination of tropical wave characteristics. This analysis tool also takes advantage of known theoretical understanding of tropical waves of different types and use them to design effective algorithms in determining wave characteristic parameters. To illustrate the details of our new tropical wave analysis package and its advantages, the procedure of isolating various types of waves and obtaining their climatology are presented. These extracted characteristics are further utilized to infer and refine the physical aspects of tropical convection and tropical waves.