Simulated and Observed Gravity Waves Radiating from Tropical Cyclones and Prospects for Remote Monitoring

Theoretical understandings of atmospheric convection and tropical cyclone dynamics indicate that TCs must radiate gravity waves, and they are often visible in satellite animations. A number of studies have considered whether these waves play some role in the angular momentum or energy budgets of TCs, or in the formation and propagation of rainbands, but many results have been either negative, contradictory, or inconclusive. With recent increases in computer power and data storage, numerical simulations can be regularly performed with 1 km grid spacing and 2 minute output. The field of radiating gravity waves, with several different radial wavelengths and vertical structures simultaneously, can be clearly seen in the vertical wind fields of these simulations. Power spectral analyses of simulated time series of surface pressure and surface wind speed suggest these waves can also be detected from fixed surface instruments. We have in fact found evidence for these same waves in high frequency observations of pressure and wind from instruments in the Pacific ocean during the passage of typhoons at distances of several hundred kilometers, and also in flight level data from NOAA research aircraft. The amplitudes and peak frequencies appear to depend on the storm intensity and storm position relative to the observer. We will discuss whether and how such observations might be used to remotely monitor TC position and intensity.