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Dr Scott Osprey FRMetS

Senior NCAS Research Scientist

Research theme

  • Climate physics

Sub department

  • Atmospheric, Oceanic and Planetary Physics

Research groups

  • Climate dynamics
Scott.Osprey@physics.ox.ac.uk
Telephone: 01865 (2)82434,01865 (2)72923
Atmospheric Physics Clarendon Laboratory, room 111
National Centre for Atmospheric Science
SPARC QBOi
Explaining & Predicting Earth System Change
  • About
  • Publications

Impacts, processes and projections of the quasi-biennial oscillation

Nature Reviews Earth and Environment Springer Nature 3 (2022) 588-603

Authors:

James Anstey, Scott Osprey, Joan Alexander, Mark Baldwin, Neal Butchart, Lesley Gray, Yoshio Kawatani, Paul Newman, Jadwiga Richter

Abstract:

In the tropical stratosphere, deep layers of eastward and westward winds encircle the globe and descend regularly from the upper stratosphere to the tropical tropopause. With a complete cycle typically lasting almost 2.5 years, this quasi-biennial oscillation (QBO) is arguably the most predictable mode of atmospheric variability that is not linked to the changing seasons. The QBO affects climate phenomena outside the tropical stratosphere, including ozone transport, the North Atlantic Oscillation and the Madden–Julian Oscillation, and its high predictability could enable better forecasts of these phenomena if models can accurately represent the coupling processes. Climate and forecasting models are increasingly able to simulate stratospheric oscillations resembling the QBO, but exhibit common systematic errors such as weak amplitude in the lowermost tropical stratosphere. Uncertainties about the waves that force the oscillation, particularly the momentum fluxes from small-scale gravity waves excited by deep convection, make its simulation challenging. Improved representation of the processes governing the QBO is expected to lead to better forecasts of the oscillation and its impacts, increased understanding of unusual events such as the two QBO disruptions observed since 2016, and more reliable future projections of QBO behaviour under climate change.
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Surface-to-space atmospheric waves from Hunga Tonga-Hunga Ha’apai eruption

Nature Springer Nature 609 (2022) 741-746

Authors:

Corwin J Wright, Neil P Hindley, M Joan Alexander, Mathew Barlow, Lars Hoffmann, Cathryn N Mitchell, Fred Prata, Marie Bouillon, Justin Carstens, Cathy Clerbaux, Scott Osprey, Nick Powell, Cora E Randall, Jia Yue

Abstract:

The January 2022 Hunga Tonga–Hunga Haʻapai eruption was one of the most explosive volcanic events of the modern era1,2, producing a vertical plume which peaked > 50km above the Earth3. The initial explosion and subsequent plume triggered atmospheric waves which propagated around the world multiple times4. A global-scale wave response of this magnitude from a single source has not previously been observed. Here we show the details of this response, using a comprehensive set of satellite and ground-based observations to quantify it from surface to ionosphere. A broad spectrum of waves was triggered by the initial explosion, including Lamb waves5,6 propagating at phase speeds of 318.2±6 ms-1 at surface level and between 308±5 to 319±4 ms-1 in the stratosphere, and gravity waves7 propagating at 238±3 to 269±3 ms-1 in the stratosphere. Gravity waves at sub-ionospheric heights have not previously been observed propagating at this speed or over the whole Earth from a single source8,9. Latent heat release from the plume remained the most significant individual gravity wave source worldwide for >12 hours, producing circular wavefronts visible across the Pacific basin in satellite observations. A single source dominating such a large region is also unique in the observational record. The Hunga Tonga eruption represents a key natural experiment in how the atmosphere responds to a sudden point-source-driven state change, which will be of use for improving weather and climate models.

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Autonomous balloons take flight with artificial intelligence

Nature Springer Science and Business Media LLC 588:7836 (2020) 33-34
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An unexpected disruption of the atmospheric quasi-biennial oscillation

Science American Association for the Advancement of Science 353:6306 (2016) 1424-1427

Authors:

Scott Osprey, Neal Butchart, Jeff R Knight, Adam A Scaife, Kevin Hamilton, James A Anstey, Verena Schenzinger, Chunxi Zhang

Abstract:

One of the most repeatable phenomena seen in the atmosphere, the quasi-biennial oscillation (QBO) between prevailing eastward and westward wind-jets in the equatorial stratosphere (~16-50 km altitude), was unexpectedly disrupted in February 2016. An unprecedented westward jet formed within the eastward phase in the lower stratosphere and cannot be accounted for by the standard QBO paradigm based on vertical momentum transport. Instead the primary cause was waves transporting momentum from the Northern Hemisphere. Seasonal forecasts did not predict the disruption but analogous QBO disruptions are seen very occasionally in some climate simulations. A return to more typical QBO behavior within the next year is forecast, though the possibility of more frequent occurrences of similar disruptions is projected for a warming climate.
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QBOi El Niño–Southern Oscillation experiments: overview of the experimental design and ENSO modulation of the QBO

Weather and Climate Dynamics Copernicus GmbH 6:4 (2025) 1045-1073

Authors:

Yoshio Kawatani, Kevin Hamilton, Shingo Watanabe, Masakazu Taguchi, Federico Serva, James A Anstey, Jadwiga H Richter, Neal Butchart, Clara Orbe, Scott M Osprey, Hiroaki Naoe, Dillon Elsbury, Chih-Chieh Chen, Javier García-Serrano, Anne Glanville, Tobias Kerzenmacher, François Lott, Froila M Palmeiro, Mijeong Park, Stefan Versick, Kohei Yoshida

Abstract:

<jats:p>Abstract. The Atmospheric Processes And their Role in Climate (APARC) Quasi-Biennial Oscillation initiative (QBOi) has conducted new experiments to explore the modulation of the QBO by El Niño–Southern Oscillation (ENSO). This paper provides an overview of the experimental design and investigates the modulation of the QBO by ENSO using nine climate models used in QBOi. A key finding is a consistent lengthening of the QBO period during La Niña compared to El Niño across all models, aligning with observational evidence. Although several models simulate QBO periods that deviate from the observed mean of approximately 28 months, the relative difference between La Niña and El Niño remains interpretable within each model. The simulated QBO periods during La Niña tend to be longer than those during El Niño, although, in most models, the differences are small compared to that observed. However, the magnitude of this lengthening shows large inter-model differences. By contrast, even the sign of the ENSO effect on QBO amplitude varies among models. Models employing variable parameterized gravity wave sources generally exhibit greater sensitivity of the QBO amplitude to the presence of ENSO than those models using fixed sources. The models capture key observed ENSO-related characteristics, including a weaker Walker circulation and increased equatorial precipitation during El Niño compared to La Niña, as well as a characteristic response in zonal mean zonal wind and temperature. All models also simulate stronger equatorial tropical upwelling in El Niño compared to La Niña up to ∼ 10 hPa, consistent with ERA5 reanalysis. These modulations influence the propagation and filtering of gravity waves. Notably, models with variable parameterized gravity wave sources show stronger wave forcing during El Niño, potentially explaining the shorter QBO period modulation in these models. Further investigation into the complex interplay between ENSO, gravity waves, and the QBO can contribute to improved model formulations. </jats:p>
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