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Hurricane Florence, TS Isaac, Hurricane Helene 2018

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Severe Weather and Climate Group @ Stanford

The Severe Weather and Climate Group at Stanford is led by Dr. Morgan O'Neill in the Department of Earth System Science. We study the dynamics and thermodynamics of multiscale severe events, including supercell thunderstorms and hurricanes. The two-way feedbacks between these storms and the climate in which they occur is of importance to meteorologists, climate scientists and planetary scientists. In a changing climate, it is critical to accurately predict how the extremes to which we are accustomed will change in the future. The past and present climates of Earth, as well as those of other planets in our solar system, serve as physical laboratories in which we can observe a range of extreme phenomena.

The tools that our group uses to address these questions are varied, from simple theory and observations to complex numerical models that simulate realistic atmospheric phenomena. Because of the impossibility of recreating all the complexities of the atmosphere in a laboratory, our laboratory is a hierarchy of numerical models that approximate the equations of motion. Ultimately, numerical results and theoretical understanding must be tested against observations. We collaborate with other scientists and institutions to take the observations we need to validate our work. Our focus is on the genesis, evolution and environmental interaction of convective storms in a range of climates.

Group Updates

  • March 2022: Morgan will speak on a panel at the 2022 March Meeting of the American Physical Society, Nobel Session on the Physics of Climate Change and the Physics of Complex Systems (13 March, streaming here)
  • May 2022: the group intends to go in-person to the AMS Tropical conference in New Orleans - see you there!
  • January 2022: Marty Singh (Monash U.) and Morgan O'Neill published a review on "The climate system and the second law of thermodynamics" in Rev. Mod. Phys.
  • December 2021: Hao Fu's paper, "The role of random vorticity stretching in tropical depression genesis", is out in JAS.
  • September 2021: the group participated remotely in the NOAA Hurricane Research Division field campaign, taking measurements of Hurricane Larry (see below).
  • September 2021: Morgan O'Neill and colleagues published a paper on hydraulic jumps in Science (see below).

New paper out in Science

10 September 2021


Hydraulic jump dynamics above supercell thunderstormsby Morgan O'Neill, Leigh Orf @ U. Wisconsin Madison, Gerald Heymsfield @ NASA Goddard, and Kelton Halbert @ U. Wisconsin Madison

We find that the above-anvil cirrus plume (AACP), found above some thunderstorms and before some of the most severe weather on Earth, is the visible manifestation of a new type of hydraulic jump: one that is forced by the overshooting top of the thunderstorm itself. The lower boundary of the jump is a moving fluid of nearly the same composition as the air above it. An open access link to the paper can be found on the Publications page.

See Science's video explainer here:


Image is of Hurricane Irma (2017) on Sept. 6th in the infrared, courtesy NOAA.

Image is of Hurricane Irma (2017) on Sept. 6th in the infrared, courtesy NOAA.

Two hurricane hunting aircraft flying side by side

Tropical Cyclone Diurnal Cycle Experiment

Our group is participating in the 2021 NOAA AOML/Hurricane Research Division field campaign: the Advancing the Prediction of Hurricanes EXperiment (APHEX). We deployed dropsondes from the NOAA Hurricane Hunter planes into Hurricane Larry this year and Hurricane Teddy last year to better understand the diurnal cycle, with scientists at NOAA, Florida State University and Purdue University. Due to the pandemic, we participate remotely. All observations from our and other HRD experiments are available to the public shortly after they are processed, and can be accessed here. Image courtesy the National Oceanographic and Atmospheric Administration (NOAA).

Gulfstream IV flight path through Hurricane Teddy, 6 September 2021

Observing Hurricane Larry (2021)

We had a successful diurnal cycle experiment flight through Hurricane Larry on 6 September, 2021, after a nearly identical flight pattern through Larry the previous day. The plane was the NOAA Gulfstream-IV, "Gonzo", with a flight crew of scientists and engineers. Each blue dot on the flight path indicates where a dropsonde was released to measure wind, temperature, humidity and pressure as it falls toward the ocean surface. These data, taken at different times for each flight day, will help us better understand the diurnal pulse of convection seen to propagate outward at the hurricane's cloud top.