On the Effect of Surface Friction and Upward Radiation of Energy on Equatorial Waves
Name
atsc-JAS-D-21-0199.1.pdf
Description
Published version
Size
2.08 MB
Format
Adobe PDF
Checksum (MD5)
9c45dcebeccb870cf905dabe7a67adf5
Author(s)
Lin, Jonathan
Emanuel, Kerry
Date Issued
March 11, 2022
Journal
Journal of the Atmospheric Sciences
Publisher
American Meteorological Society
Citation
Lin, J., and K. Emanuel, 2022: On the Effect of Surface Friction and Upward Radiation of Energy on Equatorial Waves. J. Atmos. Sci., 79, 837–857.
Version
Final published version
Abstract
In theoretical models of tropical dynamics, the effects of both surface friction and upward wave radiation through interaction with the stratosphere are oft-ignored, as they greatly complicate mathematical analysis. In this study, we relax the rigid-lid assumption and impose surface drag, which allows the barotropic mode to be excited in equatorial waves. In particular, a previously developed set of linear, strict quasi-equilibrium tropospheric equations is coupled with a dry, passive stratosphere, and surface drag is added to the troposphere momentum equations. Theoretical and numerical model analysis is performed on the model in the limits of an inviscid surface coupled to a stratosphere, as well as a frictional surface under a rigid lid. This study confirms and extends previous research that shows the presence of a stratosphere strongly shifts the growth rates of fast-propagating equatorial waves to larger scales, reddening the equatorial power spectrum. The growth rates of modes that are slowly propagating and highly interactive with cloud radiation are shown to be negligibly affected by the presence of a stratosphere. Surface friction in this model framework acts as purely a damping mechanism and couples the baroclinic mode to the barotropic mode, increasing the poleward extent of the equatorial waves. Numerical solutions of the coupled troposphere–stratosphere model with surface friction show that the stratosphere stratification controls the extent of tropospheric trapping of the barotropic mode, and thus the poleward extent of the wave. The superposition of phase-shifted barotropic and first baroclinic modes is also shown to lead to an eastward vertical tilt in the dynamical fields of Kelvin wave–like modes.
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DOI of Published Version
https://doi.org/10.1175/JAS-D-21-0199.1
