Publications by Tim Woollings

Seasonal Sensitivity of the Hadley Cell and Cross-Hemispheric Responses to Diabatic Heating in an Idealized GCM


HS Baker, C Mbengue, T Woollings

Daily to Decadal Modulation of Jet Variability

JOURNAL OF CLIMATE 31 (2018) 1297-1314

T Woollings, E Barnes, B Hoskins, Y-O Kwon, RW Lee, C Li, E Madonna, M McGraw, T Parker, T Parker, R Rodrigues, C Spensberger, K Williams

Higher CO<inf>2</inf>concentrations increase extreme event risk in a 1.5 °C world

Nature Climate Change (2018) 1-5

HS Baker, RJ Millar, DJ Karoly, U Beyerle, BP Guillod, D Mitchell, H Shiogama, S Sparrow, T Woollings, MR Allen

© 2018 The Author(s) The Paris Agreement1aims to ‘pursue efforts to limit the temperature increase to 1.5 °C above pre-industrial levels.’ However, it has been suggested that temperature targets alone are insufficient to limit the risks associated with anthropogenic emissions2,3. Here, using an ensemble of model simulations, we show that atmospheric CO2increase—an even more predictable consequence of emissions than global temperature increase—has a significant direct impact on Northern Hemisphere summer temperature, heat stress, and tropical precipitation extremes. Hence in an iterative climate mitigation regime aiming solely for a specific temperature goal, an unexpectedly low climate response may have corresponding ‘dangerous’ changes in extreme events. The direct impact of higher CO2concentrations on climate extremes therefore substantially reduces the upper bound of the carbon budget, and highlights the need to explicitly limit atmospheric CO2concentration when formulating allowable emissions. Thus, complementing global mean temperature goals with explicit limits on atmospheric CO2concentrations in future climate policy would limit the adverse effects of high-impact weather extremes.

The Met Office Global Coupled Model 3.0 and 3.1 (GC3.0 and GC3.1) Configurations


KD Williams, D Copsey, EW Blockley, A Bodas-Salcedo, D Calvert, R Comer, P Davis, T Graham, HT Hewitt, R Hill, P Hyder, S Ineson, TC Johns, AB Keen, RW Lee, A Megann, SF Milton, JGL Rae, MJ Roberts, AA Scaife, R Schiemann, D Storkey, L Thorpe, IG Watterson, DN Walters, A West, RA Wood, T Woollings, PK Xavier

AN INTERDISCIPLINARY APPROACH TO THE STUDY OF EXTREME WEATHER EVENTS Large-Scale Atmospheric Controls and Insights from Dynamical Systems Theory and Statistical Mechanics


G Messori, R Caballero, F Bouchet, D Faranda, R Grotjahn, N Harnik, S Jewson, JG Pinto, G Riviere, T Woollings, P Yiou

The roles of static stability and tropical–extratropical interactions in the summer interannual variability of the North Atlantic sector

Climate Dynamics (2018) 1-17

CO Mbengue, T Woollings, HF Dacre, KI Hodges

© 2018 The Author(s) Summer seasonal forecast skill in the North Atlantic sector is lower than winter skill. To identify potential controls on predictability, the sensitivity of North Atlantic baroclinicity to atmospheric drivers is quantified. Using ERA-INTERIM reanalysis data, North Atlantic storm-track baroclinicity is shown to be less sensitive to meridional temperature-gradient variability in summer. Static stability shapes the sector’s interannual variability by modulating the sensitivity of baroclinicity to variations in meridional temperature gradients and tropopause height and by modifying the baroclinicity itself. High static stability anomalies at upper levels result in more zonal extratropical cyclone tracks and higher eddy kinetic energy over the British Isles in the summertime. These static stability anomalies are not strongly related to the summer NAO; but they are correlated with the suppression of convection over the tropical Atlantic and with a poleward-shifted subtropical jet. These results suggest a non-local driver of North Atlantic variability. Furthermore, they imply that improved representations of convection over the south-eastern part of North America and the tropical Atlantic might improve summer seasonal forecast skill.

Impact of Gulf Stream SST biases on the global atmospheric circulation

Climate Dynamics (2018) 1-19

RW Lee, TJ Woollings, BJ Hoskins, KD Williams, CH O Reilly, G Masato

© 2018 The Author(s) The UK Met Office Unified Model in the Global Coupled 2 (GC2) configuration has a warm bias of up to almost (Formula presented.) in the Gulf Stream SSTs in the winter season, which is associated with surface heat flux biases and potentially related to biases in the atmospheric circulation. The role of this SST bias is examined with a focus on the tropospheric response by performing three sensitivity experiments. The SST biases are imposed on the atmosphere-only configuration of the model over a small and medium section of the Gulf Stream, and also the wider North Atlantic. Here we show that the dynamical response to this anomalous Gulf Stream heating (and associated shifting and changing SST gradients) is to enhance vertical motion in the transient eddies over the Gulf Stream, rather than balance the heating with a linear dynamical meridional wind or meridional eddy heat transport. Together with the imposed Gulf Stream heating bias, the response affects the troposphere not only locally but also in remote regions of the Northern Hemisphere via a planetary Rossby wave response. The sensitivity experiments partially reproduce some of the differences in the coupled configuration of the model relative to the atmosphere-only configuration and to the ERA-Interim reanalysis. These biases may have implications for the ability of the model to respond correctly to variability or changes in the Gulf Stream. Better global prediction therefore requires particular focus on reducing any large western boundary current SST biases in these regions of high ocean-atmosphere interaction.

Skilful Seasonal Predictions of Summer European Rainfall


N Dunstone, D Smith, A Scaife, L Hermanson, D Fereday, C O'Reilly, A Stirling, R Eade, M Gordon, C Maclachlan, T Woollings, K Sheen, S Belcher

The Gulf Stream influence on wintertime North Atlantic jet variability


CH O'Reilly, S Minobe, A Kuwano-Yoshida, T Woollings

Assessing mid-latitude dynamics in extreme event attribution systems

CLIMATE DYNAMICS 48 (2017) 3889-3901

D Mitchell, P Davini, B Harvey, N Massey, K Haustein, T Woollings, R Jones, F Otto, B Guillod, S Sparrow, D Wallom, M Allen

Variability in seasonal forecast skill of Northern Hemisphere winters over the twentieth century


CH O'Reilly, J Heatley, D MacLeod, A Weisheimer, TN Palmer, N Schaller, T Woollings

Low-frequency nonlinearity and regime behavior in the Northern Hemisphere extratropical atmosphere

REVIEWS OF GEOPHYSICS 55 (2017) 199-234

A Hannachi, DM Straus, CLE Franzke, S Corti, T Woollings

The Dynamical Influence of the Atlantic Multidecadal Oscillation on Continental Climate

JOURNAL OF CLIMATE 30 (2017) 7213-7230

CH O'Reilly, T Woollings, L Zanna

Nonstationarity in Southern Hemisphere Climate Variability Associated with the Seasonal Breakdown of the Stratospheric Polar Vortex

JOURNAL OF CLIMATE 30 (2017) 7125-7139

NJ Byrne, TG Shepherd, T Woollings, RA Plumb

Impact of Atmospheric Blocking on South America in Austral Summer

JOURNAL OF CLIMATE 30 (2017) 1821-1837

RR Rodrigues, T Woollings

The link between eddy-driven jet variability and weather regimes in the North Atlantic-European sector


E Madonna, C Li, CM Grams, T Woollings

A "Cold Path'' for the Gulf Stream-Troposphere Connection

JOURNAL OF CLIMATE 30 (2017) 1363-1379

BT Vanniere, A Czaja, H Dacre, T Woollings

Eddy-Driven Jet Sensitivity to Diabatic Heating in an Idealized GCM

JOURNAL OF CLIMATE 30 (2017) 6413-6431

HS Baker, T Woollings, C Mbengue

Influence of the Ocean and Greenhouse Gases on Severe Drought Likelihood in the Central United States in 2012

JOURNAL OF CLIMATE 30 (2017) 1789-1806

DE Rupp, S Li, PW Mote, N Massey, SN Sparrow, DCH Wallom

A potential vorticity signature for the cold sector of winter extratropical cyclones


B Vanniere, A Czaja, H Dacre, T Woollings, R Parfitt