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Tim Woollings

Professor of Physical Climate Science

Research theme

  • Climate physics

Sub department

  • Atmospheric, Oceanic and Planetary Physics

Research groups

  • Climate dynamics
Tim.Woollings@physics.ox.ac.uk
Telephone: 01865 (2)82427
Atmospheric Physics Clarendon Laboratory, room 203
  • About
  • Publications

Spatio-temporal averaging of jets obscures the reinforcement of baroclinicity by latent heating

Weather and Climate Dynamics Copernicus Publications 5:4 (2024) 1269-1286

Authors:

Henrik Auestad, Clemens Spensberger, Andrea Marcheggiani, Paulo Ceppi, Thomas Spengler, Tim Woollings

Abstract:

Latent heating modifies the jet stream by modifying the vertical geostrophic wind shear, thereby altering the potential for baroclinic development. Hence, correctly representing diabatic effects is important for modelling the mid-latitude atmospheric circulation and variability. However, the direct effects of diabatic heating remain poorly understood. For example, there is no consensus on the effect of latent heating on the cross-jet temperature contrast. We show that this disagreement is attributable to the choice of spatio-temporal averaging. Jet representations relying on averaged wind tend to have the strongest latent heating on the cold flank of the jet, thus weakening the cross-jet temperature contrast. In contrast, jet representations reflecting the two-dimensional instantaneous wind field have the strongest latent heating on the warm flank of the jet. Furthermore, we show that latent heating primarily occurs on the warm flank of poleward directed instantaneous jets, which is the case for all storm tracks and seasons.
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An Ocean Memory Perspective: Disentangling Atmospheric Control of Decadal Variability in the North Atlantic Ocean

Geophysical Research Letters Wiley 51:20 (2024) e2024GL110333

Authors:

Hemant Khatri, Richard G Williams, Tim Woollings, Doug M Smith

Abstract:

An ocean memory framework is proposed to reveal the atmosphere's influence on ocean temperatures. Anomalous atmospheric forcing alters the ocean state through two mechanisms: short‐term, local effects involving air − ${-}$ sea heat fluxes and Ekman circulation, and long‐term, far‐field effects involving changes from overturning and gyre circulations. The framework employs the Green function's method to incorporate both effects, enabling the quantification of ocean memory and the contribution of atmospheric forcing to ocean thermal variability. The framework is employed to examine the North Atlantic Oscillation's (NAO) influence on the North Atlantic Ocean variability, including the Atlantic Multidecadal Variability, with its memory estimated to be 10 – 20 $10\mbox{--}20$ years. The NAO and variability in the North Atlantic jet speed explain up to 30% of ocean decadal variability, primarily driven by temporal changes in ocean heat transport. Therefore, decadal fluctuations in ocean temperatures cannot be accurately modeled solely as a passive response to stochastic atmospheric forcing.
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Intraseasonal shift in the wintertime North Atlantic jet structure projected by CMIP6 models

npj Climate and Atmospheric Science Nature Research 7:1 (2024) 234

Authors:

Marina García-Burgos, Blanca Ayarzagüena, David Barriopedro, Tim Woollings, Ricardo García-Herrera

Abstract:

The projected winter changes of the North Atlantic eddy-driven jet (EDJ) under climate change conditions have been extensively analysed. Previous studies have reported a squeezed and elongated EDJ. However, other changes present large uncertainties, specifically those related to the intensity and latitude. Here, the projections of the EDJ in a multimodel ensemble of CMIP6 are scrutinised by using a multiparametric description of the EDJ. The multimodel mean projects non-stationary responses of the EDJ latitude through the winter, characterised by a poleward shift in early winter and equator migration in late winter. These intraseasonal shifts (rather than a genuine narrowing) explain the previously established squeezing of the EDJ and are linked to the future changes in different drivers: the 200 hPa meridional temperature gradient and Atlantic warming hole in early winter, and the stratospheric vortex in late winter. Model biases also influence EDJ projections, contributing to the poleward shift in early winter.
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Emerging signals of climate change from the equator to the poles: new insights into a warming world

Frontiers in Science Frontiers Media 2 (2024) 1340323

Authors:

Matthew Collins, Jonathan D Beverley, Thomas J Bracegirdle, Jennifer Catto, Michelle McCrystall, Andrea Dittus, Nicolas Freychet, Jeremy Grist, Gabriele C Hegerl, Paul R Holland, Caroline Holmes, Simon A Josey, Manoj Joshi, Ed Hawkins, Eunice Lo, Natalie Lord, Dann Mitchell, Paul-Arthur Monerie, Matthew DK Priestley, Adam Scaife, James Screen, Natasha Senior, David Sexton, Emily Shuckburgh, Tim Woollings

Abstract:

The reality of human-induced climate change is unequivocal and exerts an ever-increasing global impact. Access to the latest scientific information on current climate change and projection of future trends is important for planning adaptation measures and for informing international efforts to reduce emissions of greenhouse gases (GHGs). Identification of hazards and risks may be used to assess vulnerability, determine limits to adaptation, and enhance resilience to climate change. This article highlights how recent research programs are continuing to elucidate current processes and advance projections across major climate systems and identifies remaining knowledge gaps. Key findings include projected future increases in monsoon rainfall, resulting from a changing balance between the rainfall-reducing effect of aerosols and rainfall-increasing GHGs; a strengthening of the storm track in the North Atlantic; an increase in the fraction of precipitation that falls as rain at both poles; an increase in the frequency and severity of El Niño Southern Oscillation (ENSO) events, along with changes in ENSO teleconnections to North America and Europe; and an increase in the frequency of hazardous hot-humid extremes. These changes have the potential to increase risks to both human and natural systems. Nevertheless, these risks may be reduced via urgent, science-led adaptation and resilience measures and by reductions in GHGs.
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Intraseasonal shift in the wintertime North Atlantic jet structure projected by CMIP6 models

Copernicus Publications (2024)

Authors:

Marina Garcia-Burgos, Blanca Ayarzagüena, David Barriopedro, Tim Woollings, Ricardo Garcia-Herrera
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