Presented on October 11, 2023, by
Kevin Hamilton, Emeritus Professor of Atmospheric Sciences
School of Ocean and Earth Sciences
University of Hawaii at Manoa
Abstract
A fundamental and long-standing issue in dynamical meteorology is how the global atmosphere resonates. Unlike many familiar finite mechanical systems (such as a violin string, a drum membrane, or an elastic sphere) that feature a complete set of possible normal mode oscillations, the unbounded nature of the atmosphere introduces complications and leads to the expectation that the normal modes may not be a complete set. A true normal mode oscillation of the atmosphere must be described by solutions of the inviscid governing equations with no vertical energy flux at “infinite height.” It turns out that dealing with this subtlety has sustained a two-century-long search for theoretical understanding and observational evidence of atmospheric resonance.
The study of this issue has a particularly long and interesting history and my lecture will begin with a historical review providing context for this classic problem and introducing the physical and
mathematical issues that are involved. Then I will discuss recent work with my collaborators analyzing hourly atmospheric data that detected a rich spectrum of distinct modes with periods from a few hours to a few days.
I will then show that an understanding of the global modes provides a context for interpreting observations of the atmospheric pulses resulting from the explosive eruption of the Hunga Tonga–Hunga Ha‘apai volcano on 15 January 2022. Observations of this event were supplemented with detailed computer simulations using a state-of-the-art global atmospheric model conducted by colleagues at JAMSTEC. Our analysis demonstrated for the first time the existence of an elusive internal vertical mode that has been a feature of theoretical solutions obtained by investigators in studies over the last nine decades.
Finally I will show that global resonance is key to understanding the strong daily atmospheric pressure oscillation seen in observations taken at the Martian surface by the NASA Curiosity rover.
Attendees may find the following two brief articles intended for the general public to be useful
background:
https://www.theatlantic.com/science/archive/2020/08/centuries-old-theory-finally-confirmed/615295/