Publications by Tim Woollings

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 20th century

Geophysical Research Letters American Geophysical Union (AGU) (2017)

C O'Reilly, MacLeod, A Weisheimer, T Palmer, 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

Quarterly Journal of the Royal Meteorological Society 143 (2017) 2960-2972

E Madonna, C Li, CM Grams, T Woollings

© 2017 The Authors. Quarterly Journal of the Royal Meteorological Society published by John Wiley & Sons Ltd on behalf of the Royal Meteorological Society. This study reconciles two perspectives on wintertime atmospheric variability in the North Atlantic–European sector: the zonal-mean framework comprising three preferred locations of the eddy-driven jet (southern, central, northern), and the weather regime framework comprising four classical North Atlantic-European regimes (Atlantic ridge AR, zonal ZO, European/Scandinavian blocking BL, Greenland anticyclone GA). A k-means clustering algorithm is used to characterize the two-dimensional variability of the eddy-driven jet stream, defined by the lower tropospheric zonal wind in the ERA-Interim reanalysis. The first three clusters capture the central jet and northern jet, along with a new mixed-jet configuration; a fourth cluster is needed to recover the southern jet. The mixed cluster represents a split or strongly tilted jet, neither of which is well described in the zonal-mean framework, and has a persistence of about one week, similar to the other clusters. Connections between the preferred jet locations and weather regimes are corroborated – southern to GA, central to ZO, and northern to AR. In addition, the new mixed cluster is found to be linked to European/Scandinavian blocking, whose relation to the eddy-driven jet was previously unclear.

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

Impact of atmospheric blocking on south america in austral summer

Journal of Climate 30 (2017) 1789-1806

RR Rodrigues, T Woollings

© 2017 American Meteorological Society. This study investigates atmospheric blocking over eastern South America in austral summer for the period of 1979-2014. The results show that blocking over this area is a consequence of propagating Rossby waves that grow to large amplitudes and eventually break anticyclonically over subtropical South America (SSA). The SSA blocking can prevent the establishment of the South Atlantic convergence zone (SACZ). As such, years with more blocking days coincide with years with fewer SACZ days and reduced precipitation. Convection mainly over the Indian Ocean associated with Madden-Julian oscillation (MJO) phases 1 and 2 can trigger the wave train that leads to SSA blocking whereas convection over the western/central Pacific associated with phases 6 and 7 is more likely to lead to SACZ events. It is found that the MJO is a key source of long-term variability in SSA blocking frequency. The wave packets associated with SSA blocking and SACZ episodes differ not only in their origin but also in their phase and refraction pattern. The tropopause-based methodology used here is proven to reliably identify events that lead to extremes of surface temperature and precipitation over SSA. Up to 80% of warm surface air temperature extremes occur simultaneously with SSA blocking events. The frequency of SSA blocking days is highly anticorrelated with the rainfall over southeast Brazil. The worst droughts in this area, during the summers of 1984, 2001, and 2014, are linked to record high numbers of SSA blocking days. The persistence of these events is also important in generating the extreme impacts.

Annular modes and apparent eddy feedbacks in the Southern Hemisphere.

Geophysical research letters 43 (2016) 3897-3902

NJ Byrne, TG Shepherd, T Woollings, RA Plumb

Lagged correlation analysis is often used to infer intraseasonal dynamical effects but is known to be affected by nonstationarity. We highlight a pronounced quasi 2 year peak in the anomalous zonal wind and eddy momentum flux convergence power spectra in the Southern Hemisphere, which is prima facie evidence for nonstationarity. We then investigate the consequences of this nonstationarity for the Southern Annular Mode and for eddy momentum flux convergence. We argue that positive lagged correlations previously attributed to the existence of an eddy feedback are more plausibly attributed to nonstationary interannual variability external to any potential feedback process in the midlatitude troposphere. The findings have implications for the diagnosis of feedbacks in both models and reanalysis data as well as for understanding the mechanisms underlying variations in the zonal wind.

Diabatic heating and jet stream shifts: A case study of the 2010 negative North Atlantic Oscillation winter


T Woollings, L Papritz, C Mbengue, T Spengler

A regime analysis of Atlantic winter jet variability applied to evaluate HadGEM3-GC2


G Masato, T Woollings, KD Williams, BJ Hoskins, RW Lee

The signature of low-frequency oceanic forcing in the Atlantic Multidecadal Oscillation


CH O'Reilly, M Huber, T Woollings, L Zanna

Eleven-year solar cycle signal in the NAO and Atlantic/European blocking


LJ Gray, TJ Woollings, M Andrews, J Knight

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


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

Robust Future Changes in Temperature Variability under Greenhouse Gas Forcing and the Relationship with Thermal Advection

JOURNAL OF CLIMATE 29 (2016) 2221-2236

CR Holmes, T Woollings, E Hawkins, H de Vries

The response of high-impact blocking weather systems to climate change


D Kennedy, T Parker, T Woollings, B Harvey, L Shaffrey

Contrasting interannual and multidecadal NAO variability

CLIMATE DYNAMICS 45 (2015) 539-556

T Woollings, C Franzke, DLR Hodson, B Dong, EA Barnes, CC Raible, JG Pinto