Momme Hell | ASP Postdoctural Fellow | NSF NCAR






Air-Sea Interaction Across Scales
Winds | Waves | Sea Ice

Researcher Image

Momme C. Hell

Postdoctoral Fellow in the Advanced Study Program

NSF National Center for Atmospheric Research
CISL/CGD, Ocean Section
Boulder, CO
mhell @ ucar.edu

Curriculum Vitae

I joined NSF NCAR as a Postdoctoral Fellow in the ASP program in Fall 2023 to develop and implement and a fast and efficient wave model in coupled earth system models jointly between Computational and Information Systems Lab (CISL) and the Climate & Global Dynamics (CGD) section. Before that I was Postdoctoral Research Associate in the Department for Earth, Environmental and Planetary Sciences (DEEPS) at Brown Univeristy (now visiting Research Scholar) with Baylor Fox-Kemper and Chris Horvat.

I graduated from Scripps Institution of Oceanography (SIO) in November 2020 in Physical Oceanography with my advisors Arthur "Art" Miller, Sarah Gille, and Bruce Cornuelle, and short postdoc with Nick Lutsko. Prior to that I studied at GEOMAR in Kiel (2009-2012) and ETH Zurich (2013-2015) Atmosphere, Ocean, and Climate working with Tapio Schneider, Noel Keenlyside and Mojib Latif.

My research focuses on processes that are related to large biases in climate models and the predictability of mid-latitude weather. My topics spans from ocean surface waves to large-scale Rossby-waves and the atmospheric general circulation. I currently focus on:

• Stochastic air-sea fluxes
• Open-ocean surface wave modeling
• Sea ice-wave coupling
• Ocean remote sensing observations
• Climate dynamics and weather extremes

Research Projects


Research Example Image

Surface waves govern air-sea exchange

The sea state controls momentum transfer across the air-sea boundary and alters the surface stress, fluxes of CO2, and heat between the atmosphere and the ocean. I focus on how synoptic-scale variability influences Air-Sea exchange through waves or upper ocean turbulence. I combine simple models of surface wave generation with optimization methods to apply them to ensembles of wave observations.

Research Example Image

Swell generation under extra-tropical storms

Storms generate swell events that many like to surf. I study how the dynamics of the storm determine the generated swell. For that, I use idealized models, observations from wave buoys and remote sensing data, and non-linear optimization methods to understand the process of wave generation on the synoptic scale.

The key mechanism that leads to the generation of major swell events is trapping wave energy under the moving storm (figure on the left). To understand this, one has to think of wave energy propagation in the reference system of the moving storm. While the wave energy of a short wave travels slower and will be left behind, the wave energy of longer waves will keep up with the moving storm and be further enhanced.
This mechanism compresses the wave energy to a small area, appearing as a small, localized swell source in the open ocean. Stronger storms that move faster will generate larger swell events, while storms that propagate too fast are less efficient in creating strong swell events.

Surface Winds

always play a role for air-sea coupling. Surface winds force the ocean on synoptic scales, but they are also in constant feedback with the ocean. Surface temperature pattern can change the local winds, and current can change waves. Surface winds have to be seen as one aspect of the coupled air-sea boundary layer. In my research I focus on statistical representation of surface winds over the ocean. Remote sensing product, reanalysis data, and state-of-the-art high resolution models allow us to derive wind statistics that vary in space and time. A closer lock to these wind statistics show that their shape, i.e. the shape of their PDFs, is not gaussian and can be expressed as the superposition of empirical modes.

Leading modes of surface winds are driven by annular mode variability

The leading modes of the surface wind PDF are connected to large-scale drivers of in the atmosphere. For example, the statistics of winds in the mid-latitudes are driven by the momentum balance of the atmospheric column aloft. This provides new insight in how and where surface wind statistics and subsequent air-sea fluxes may change under global warming, as the global warming signal starts to emerge in the large-scale flow. That means we can use the leading mode of the scatterometer wind distribution (upper right panels) to infer the phase of the Annular Mode (black and blue line on the bottom). See more in the publication below

Research Example Image

Waves in Sea Ice

We start to observe waves in sea ice. Waves can break up, disperse, or drift sea ice and alter air-sea heat fluxes within the sea ice. They play a major role in globally retreating sea ice, but the interaction needs to be better understood. In my work, I use satellite and in situ observations to better understand how waves surface waves behave in sea ice. Waves in the Marginal Ice Zone (MIZ) are a dominant source for the mechanical breaking of sea ice with potentially enormous consequences for the air-sea exchange in the MIZ. I study the impact of waves on sea ice through remote sensing and idealized models to better represent these processes in climate models.

Publications

Accepted Papers

Hell, M. C., and Horvat, C. Directional Surface Wave Spectra And Sea Ice Structure from ICEsat-2 Altimeter,The Cryosphere,(accepted)
https://doi.org/10.5194/egusphere-2022-842

Woollings, T., and Coauthors including Hell, M., The role of Rossby waves in polar weather and climate. Weather and Climate Dynamics Discussions, (2022), 1–32,
https://doi.org/10.5194/wcd-2022-43

Lutsko, N. J., Hell, M. C. Moisture and the Persistence of Annular Modes (2021). Journal of Atmospheric Science.
https://doi.org/10.1175/JAS-D-21-0055.1

Hell, M. C., Ayet, A, Chapron, B. (2021) Swell Generation under Extra-Tropical Storms. Journal of Geophysical Research: Oceans, 126, e2021JC017637, 2021.
https://doi.org/10.1029/2021JC017637 [preprint]

Hell, M. C., Cornuelle, B. D., Gille, S. T., Lutsko, N. J., 2021: Time-Varying Empirical Probability Densities of Southern Ocean Surface Winds: Linking the Leading Mode to SAM and Quantifying Wind Product Differences. Journal of Climate
https://doi.org/10.1175/JCLI-D-20-0629.1. [conference talk]

Hell, M. C., Gille, S. T., Cornuelle, B., Miller, A. J., Bromirski, P. D., & Crawford, A. D, 2020: Estimating Southern Ocean storm position with seismic observations. Journal of Geophysical Research: Oceans, 125, e2019JC015898.
https://doi.org/10.1029/2019JC015898

Hell, M., Schneider, T., Li, C.,2019: Atmospheric Circulation Response to Episodic Arctic Warming in an Idealized Model. Journal of Atmospheric Science,https://journals.ametsoc.org/doi/10.1175/JAS-D-19-0133.1

Hell, M. C., B. D. Cornuelle, S. T. Gille, A. J. Miller, and P. D. Bromirski, 2019: Identifying ocean swell generation events from Ross Ice Shelf seismic data. J. Atmos. Oceanic Technol.,https://doi.org/10.1175/JTECH-D-19-0093.1

Villas Bôas, A. B., and Coauthors, 2019: Integrated Observations of Global Surface Winds, Currents, and Waves: Requirements and Challenges for the Next Decade. Front. Mar. Sci., 6, https://doi.org/10.3389/fmars.2019.00425

Cohen, J., and Coauthors, 2018: Arctic change and possible influence on mid-latitude climate and weather. US clivar Rep, N/A,
https://doi.org/10.5065/D6TH8KGW

King, M.P., Hell, M. & Keenlyside, N. Investigation of the atmospheric mechanisms related to the autumn sea ice and winter circulation link in the Northern Hemisphere. Clim Dyn ,2016, 46: 1185. https://doi.org/10.1007/s00382-015-2639-5

Theses

Momme Hell, Einfluss der atlantischen Meeresoberflächentemperatur auf Niederschläge in Indien und dem Sahel im Kieler Klimamodell, Bachelor Thesis, University of Kiel, 2012, Advisors: Mojib Latif and Claus Boening

Momme Hell, High Arctic-Stratosphere-Feedback on Sub-Seasonal Scale, Master Thesis, Swiss Federal Institute of Technology in Zurich, 2015, Advisors: Tapio Schneider and Noel Keenlyside

Hell, M., Einfluss der atlantischen Meeresoberflächentemperatur auf Niederschläge in Indien und dem Sahel im Kieler Klimamodell, 2012, Bachelor Thesis, University of Kiel, Advisors: Mojib Latif and Claus Boening [PDF]

Invited Talks & Presentations

2023

Hell, M. C. and Chris Horvat. Learning surface wave spectra and sea ice structure from icesat-2 altimeter - an path to better wave attenuation parametrization in the marginal ice zone. ICESat-2 Science Team Meeting, La Jolla, CA, USA, 2023-10-03
 Hell, M. C. and Baylor Fox-Kemper. Bulk fluxes in earth system models and beyond - how converging scales may lead to diverging results. Workshop at the Lorenz Center: Atmosphere-ocean coupling at (sub)mesoscales, Leiden, Nederlands, 2023-09-26
 Hell, M. C., Baylor Fox-Kemper, Bertrand Chapron, and Chris Horvat. Modeling and observing waves in sea ice. SASIP Annual Project meeting, Bergen, Norway, 2023-06-29
 Hell, M. C.. Southern ocean extreme wind statistics and their effect on resonant swell generation under storms. BCCR seminar, GFI, Bergen, Norway, 2023-06-26
 Hell, M. C.. When the ocean is not flat - Rough challenges of waves in sea-ice, models, and air-sea coupling. Woods Hole Oceanographic Institution, PO Seminar, 2023-05-03
 Hell, M. C.. Southern ocean extreme wind statistics and their effect on resonant swell generation under storms (virtual). MAXSS 2023 : Marine Atmosphere eXtreme Satellite Synergy workshop, Brest, France, 2023-04-04
 Hell, M. C. and Baylor Fox-Kemper. A particle-in-cell wave model for efficient sea-state and swell estimates in coupled models (virtual). CESM Ocean Model Winter Working Group meeting - Boulder, CO, USA, 2023-02-10
 Hell, M. C., Alex Ayet, and B. Chapron. Swell generation under extra-tropical storms. AMS 2023 Session on Extreme Maritime Weather, Denver, 2023-01-10

2022

Hell, M. C.. Towards data-driven parameterizations with directional surface wave spectra from icesat-2 altimetry. IMSI Remote Sensing for Climate Analysis - Chicago, US, 2022-12-01
 Hell, M. C.. Southern ocean surface winds - how annular modes are linked to surface wave events and wind-driven mixing. NOAA Earth System Research Laboratories in Boulder, Colorado, 2022-11-02
 Hell, M. C. and Chris Horvat. Directional surface wave spectra and sea ice structure from ICESat-2 altimeter. SASIP Meeting 2022 - Grenoble, France, 2022-06-21
 Hell, M. C.. How annular modes are linked surface wave events and wind-driven mixing. Atmosphere Ocean Science Colloquium, NYU, New York, 2022-03-30
 Hell, M. C. and Chris Horvat. Directional surface wave spectra and sea-ice structure from ICESat-2 altimeter. ICESat-2 Science Team - Sea Ice Group, (virtual), 2022-03-17
 Hell, M. C. and Chris Horvart. Constraining frequency dependent wave attenuation in sea ice using ICESat-2 photon heights. Ocean Sciences Meeting, (virtual), 2022-02-24
 Hell, M. C., Bruce D. Cornuelle, S. T. Gille, and Nicholas J. Lutsko. Time-varying empirical probability densities of Southern Ocean surface winds: Leading modes linked to SAM, the annual cycle, and product differences. PO Seminar, Woods Hole, MA, 2022-01-18

2021

Hell, M. C., Alex Ayet, and B. Chapron. Swell generation under extra-tropical storms. MIT, virtual, 2021-10-06
 Hell, M. C. and Laurence Armi. Atmospheric zonal flows and blocks from the perspective of Rossby-beta hydraulics (talk). Atmospheric Blocking Virtual Workshop, (virtual), 2021-09-27
 Hell, M. C., Bruce D. Cornuelle, and Sarah T Gille. Leading modes and biases of Southern Ocean Surface Wind from time-varying Distributions. SOCCOM Annual Meeting, (virtual), 2021-06
 Hell, M. C., Bruce D. Cornuelle, S. T. Gille, and Nicholas J. Lutsko. Time-varying empirical probability densities of Southern Ocean surface winds: Leading modes linked to SAM, the annual cycle, and product differences. IOVWST Meeting, (virtual), 2021-02-24

2015-2019

Hell, M. C., Schneider, T., Li, C. Atmospheric Circulation Response to Episodic Arctic Warming in an Idealized Model, 22th Atmosphere and Ocean Fluid Dynamics Meeting, June 2019
 Hell, M. C., Cornuelle, B., Gille, S. T., Miller, A., Bromirski, P., Crawford A. D., Southern Ocean Storm positions and wave attenuation under sea ice estimated with seismic observations in the Ross Ice Shelf, ACDC 10-year anniversary conference, March 2018, Rondanau, Norway
 Hell, M. C., Cornuelle, B., Gille, S. T., Miller, A., Bromirski, P., Crawford A. D., Biases in Southern Ocean storm positions from seismic observations in the Ross Ice Shelf. Or, why is the SoCal south swell forecast often wrong?, Scripps Student Symposium 2018, La Jolla, September 2018
 Hell, M. C., Cornuelle, B., Gille, S. T., Miller, A., Bromirski, P., Crawford A. D., Ross Ice Shelf Seismic Data, Southern Ocean Storms and Antarctic Sea Ice Thickness, Multi-Modal Oscillations in Ocean Basins, Symposium, La Jolla, September 2018
 Hell, M. C., T. Schneider and N. Keenlyside Stratospherically-mediated Long-term Response to Polar Surface Heating, 20th Atmosphere and Ocean Fluid Dynamics Meeting, June 2015
 Hell, M. C., Martin King and Noel Keenlyside, Investigation of the atmospheric mechanisms related to the autumn sea ice and winter circulation link in the Northern Hemisphere, EGU Meeting, Mai 2015