Spiral Gravity Waves Radiating from Tropical Cyclones

Internal gravity waves are ubiquitous in the atmosphere and are continuously generated by deep moist convection around the globe. Satellite images suggest that tropical cyclones produce short-wavelength, high-frequency waves that radiate outward, with the wave fronts wrapped into tight spirals by the very large differential advection of the radially sheared tangential flow. Flight level data from research aircraft show radial wavelengths of 2-10 km and vertical velocity magnitudes from 0.1-1.0 ms-1. Surface observations from a research buoy in the Pacific also indicate the passage of gravity waves overhead as tropical cyclones passed by at distances of 100 to 300 km. Numerical simulations are used to interpret these observations and to understand the broader horizontal and vertical structures of the radiating waves. The simulations also suggest a correlation between wave amplitude and cyclone intensity, which could be used to make remote estimates of peak wind speeds.