Spiral Gravity Waves Radiating From Tropical Cyclones: Observations, Simulations, and Analysis
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Spiral Gravity Waves Radiating From Tropical Cyclones: Observations, Simulations, and Analysis
Dr. David Nolan
Professor and Chair of Department of Atmospheric Sciences
University of Miami
Monday, October 26, 2020, 2 PM
Abstract:
While it has been known for some time that tropical cyclones (TCs) produce gravity waves that propagate upward into the stratosphere, a recent study brought new attention to small-scale waves that radiate outward in the troposphere, with their phase lines wrapped into tight spirals. Evidence for these waves can be found in flight-level data obtained from research aircraft flying in tropical cyclones, and the waves can be detected in pressure anomalies observed by surface instruments. Examination of numerical simulations of tropical cyclones suggests that the waves are caused by convective asymmetries rotating around the TC eyewall, that are amplified as they pass through the “downshear-left” quadrant. This hypothesis is tested by using rotating and pulsing heat sources in a linear dynamical model of perturbations to stationary, balanced, TC-like vortices. The model shows that such forcing produces two types of waves: a fast, deep wave with a strong signal at the surface, followed by a packet of slower waves with shorter radial and vertical wavelengths. The observed peak in the power spectrum of surface pressure anomalies, corresponding to periods of 1000-3000 seconds, is connected to the pulsation frequency of the rotating convective anomalies in the eyewall. The talk will conclude by describing our efforts to obtain more in-situ observations of spiral gravity waves.
Bio-sketch:
David Nolan is a professor and chair of the Department of Atmospheric Sciences in the Rosenstiel School of Marine and Atmospheric Sciences at the University of Miami. He earned a B.A. in Physics and a Ph.D. in Earth and Planetary Sciences from Harvard University. After research positions at UC Berkeley, Colorado State, and GFDL, he joined the faculty at Rosenstiel in 2002. He has published over 80 journal articles on the dynamics and impacts of tropical cyclones, the structure of the intertropical convergence zone, tornadoes, and other topics. In both 2016 and 2020 he and his co-authors earned the AMS Banner Miller Award for papers that contribute to improvements in tropical cyclone forecasting.
Webinar info:
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Event site: https://go.umd.edu/nolan
Webinar number: 120 033 0104
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