Presented on November 15, 2023, by

Pao-Shin Chu, PhD
Professor of Atmospheric Sciences
School of Ocean and Earth Sciences
University of Hawaii at Manoa

ABSTRACT

Intense tropical cyclones (TCs), which often peak in autumn, have destructive impacts on life and property, making it crucial to determine whether any changes in intense TCs are likely to occur. Since the 1980s there has been a significant seasonal advance of intense TCs in most tropical oceans, with an earlier shifting rate of 3 to 4 days in each passing decade for both the Northern and Southern Hemispheres. This seasonal advance of intense TCs is closely related to the seasonal advance of rapid intensification (RI) events, bolstered by the observed earlier onset of favorable oceanic conditions. Using simulations from multiple global climate models, large ensembles, and individual forcing experiments, the earlier onset of favorable oceanic conditions is detectable and primarily driven by greenhouse gas forcing. The seasonal advance of intense TCs will increase the likelihood of intersecting with other extreme rainfall events, which usually peak in summer, thereby leading to disproportionate impacts.

Presented on November 8, 2023, by

Derek Wroe, MS
National Weather Service Fire Weather Focal Point
Honolulu Forecast Office

Yi-Leng Chen, PhD
Professor of Atmospheric Sciences
School of Ocean and Earth Sciences
University of Hawaii at Manoa

ABSTRACT

The NWS Fire Weather Focal Point will present a brief overview of fire weather forecasting in Hawaii, the conditions leading up to Aug 8, and how NWS dealt with uncertainty, interpreted global numerical model data, communicated information, and issued products leading up to the event.

The UH team will review and evaluation the performance of the experimental high-resolution numerical weather model, and present the diagnosis of this event, based on model output and observational data.

The team (NWS, UHM and USFS) will discuss possible value aided model products and other products to benefit fire weather forecasts in Hawaii.

At the beginning of the seminar, the MIX peer advisors will present international exchange opportunities for UHM students.

Presented on November 1, 2023, by

Daniel R. Chavas
Associate Professor of Atmospheric Science
Department of Earth, Atmospheric, and Planetary Sciences
Purdue University

ABSTRACT

Tropical cyclones cause widespread damage and loss of life globally each year. In a future warmer climate, tropical cyclones are expected to have stronger maximum wind speeds, but could they also get larger? This talk will discuss how I integrate theory, observations, idealized models, and global climate models to understand what sets the size of tropical cyclones on Earth. I will focus in particular on how size depends on both the Coriolis parameter and its meridional gradient. The latter acts as a strong dynamical constraint on size in the Earth’s tropics, via a length scale traditionally known as the “Rhines scale”. This length scale has long been used to explain properties of jet streams and the size of extratropical cyclones. I will demonstrate how the Rhines scale can be applied in a very simple manner to explain why it limits the size of any isolated vortex, including the tropical cyclone. These results suggest that storm size should not change strongly with warming, which is corroborated by results from idealized and real-world GCM simulations. The above insights will be combined with recent work linking hurricane physics to economic damage to discuss implications for tropical cyclone risk and risk communication under climate change.

BIO

I am currently Associate Professor of Atmospheric Science at Purdue University in the Department of Earth, Atmospheric, and Planetary Sciences. I study the physics of tropical cyclones and severe thunderstorms, why the climate system produces them, and how we can better predict their hazards and impacts. I work across theory, idealized numerical models, and observations. I am an NSF CAREER awardee (2020). Before starting at Purdue, I was an NSF Postdoctoral Research Fellow in Civil and Environmental Engineering at Princeton University, and I received my PhD in Atmospheric Science from MIT and my BS in Atmospheric and Oceanic Sciences and Applied Mathematics from the University of Wisconsin-Madison.

Presented on October 25, 2023, by

Dr. Steven Businger
Professor of Atmospheric Sciences
School of Ocean and Earth Sciences
University of Hawaii at Manoa

ABSTRACT

This talk will present preliminary results regarding, i) the role of the large scale weather pattern – e.g., the role of the subtropical high and Hurricane Dora, ii) the mesoscale weather pattern – e.g., the role of the orography in the generation of hurricane force winds, iii) the climatology of downslope windstorms in Hawaii, and iv) the role of climate change in setting the stage for the firestorm. There will be time at the end for a discussion of what actions we might take in SOEST and UHM to support the State is preventing future firestorms.

BIOGRAPHICAL SKETCH

Dr. Steven Businger is Professor in the Department of Atmospheric Sciences at the University of Hawaii. For the past 30 years Dr. Businger has been active in researching the evolution and structure of destructive atmospheric storms, resulting in fundamental contributions to our understanding of the formation of storm systems in cold air streams and in the tropics (e.g., kona lows and tropical cyclones). Dr. Businger has also made pioneering contributions to the development of GPS meteorology, long-range lightning detection, and autonomous constant-level balloons. To date he has over 100 peer-reviewed journal publications, published 2 academic textbooks, and seven book chapters. Dr. Businger was elected Fellow of the American Meteorological Society (AMS) in 2010. He is an AMS Certified Consulting Meteorologist, and in 2011 Professor Businger received the UH Mānoa Chancellor’s Citation for Meritorious Teaching.

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/

https://theconversation.com/tonga-eruption-was-so-intense-it-caused-the-atmosphere-to-ring-like-a-bell-175311