Dynamics and Propagation of Tropospheric Gravity Waves Radiating from Tropical Cyclones As Seen in a Linear Nonhydrostatic Model (3DVPAS)

Recent work by Nolan and Zhang (2017, GRL) showed observational and numerical evidence for small-scale gravity waves that radiate outward from tropical cyclones. These waves are wrapped into tight spirals by the shear of the tangetial wind but they can be detected hundreds of kilometers from the storm center. A linearized, nonhydrostatic model for peturbations to a balanced vortex (3DVPAS) is used to study these waves. Tests with different diabatic heating functions show that the forcing that best reproduces the observed wave structures is an asymmetric, stationary pulsation in the eyewall, perhaps representative of time variations of enhanced convection on the downshear left quadrant. The forcing generates waves with multiple vertical and horizontal structures, with different radial wavelengths evident in the mid-tropospheric winds and in the surface pressure field. One feature that is not well represented in the linear model is an apparent ducting of waves in the upper-level outflow layer that can be seen in high-resolution simulations. Modifications to the basic state to match this behavior show mixed results.