Revisiting the Vertical Structure of Dry and Moist Kelvin Waves.

Horizontal and vertical structure of Kelvin waves at different phase speeds

Regression maps of the tropospheric vertical structure of Kelvin waves at a different speeds and at wavenumber four are investigated. The role of the convection on tilting the vertical structure is examined by comparing the vertical structure at different equivalent depths ranging from 5 to 100 m. The dynamical field (zonal wind) data rather than the outgoing longwave radiation (OLR) data were used as a predictor to emphasize and enhance the filtration of the dry wave structure for comparison against moist waves structures. We filtered the data at the single wavelength to ensure that the vertical structure (especially the tilt of the wave) in a regression map is not a result of superposition between different wavelengths and that it is purely due to intrinsic wave properties at the selected scale. Results should enable us to shed light on the limitation on which stratiform instability could influence the Kelvin wave tilt at high speed (dry wave).

In the second part, we are focusing on studying the deviation of the dry and moist Kelvin wave from its theoretical structure found by Matsuno (1966). Preliminary results show that slow Kelvin wave structure rather than the fast tend to deviate more from the theoretical structure of the Kelvin wave. Preliminary results are in agreement with results shown by Roundy (2012). The deviation of the slow Kelvin wave from the theoretical one arises because the flow tends to follow the mass sink and source generated by diabatic heating rather than following the geostrophic dynamics associated with the pure Kelvin wave.

Matsuno, T., 1966. Quasi-geostrophic motions in the equatorial area. J. Meteor. Soc. Japan. Available at: http://www.mccrones.com/tropical/2008/NPS/MR4242/Week2/Matsuno.PDF [Accessed August 3, 2014].

Roundy, P.E., 2012. Observed Structure of Convectively Coupled Waves as a Function of Equivalent Depth: Kelvin Waves and the Madden–Julian Oscillation. Journal of the Atmospheric Sciences, 69(7), pp.2097–2106. Available at: http://journals.ametsoc.org/doi/abs/10.1175/JAS-D-12-03.1.