The blocking of middle latitude westerly winds by planetary waves

Austin, J. B.

doi:10.1002/qj.49710644807

Cited by 113 publications

(67 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Systematic errors from outside the blocking area could also influence the development or removal of blocks, but the corrections applied here cannot directly compensate for those errors. This is particularly relevant for errors in the high-frequency transient eddy activity, which can act from upstream to amplify and sustain a downstream blocking high (Austin, 1980;Illari 1984;Shutts 1983). For example, a positive bias in high-frequency synoptic activity could enhance blocking activity downstream (according to current understanding of the dynamical mechanisms linking eddies and blocking).…”

Section: Summary and Interpretation Of Resultsmentioning

confidence: 94%

Assessment of atmosphere-ocean general circulation model simulations of winter northern hemisphere atmospheric blocking

Vial

Osborn

2011

Clim Dyn

View full text Add to dashboard Cite

An assessment of six coupled AtmosphereOcean General Circulation Models (AOGCMs) is undertaken in order to evaluate their ability in simulating winter atmospheric blocking highs in the northern hemisphere. The poor representation of atmospheric blocking in climate models is a long-standing problem (e.g. D'Andrea et al. in Clim Dyn 4:385-407, 1998), and despite considerable effort in model development, there is only a moderate improvement in blocking simulation. A modified version of the Tibaldi and Molteni (in Tellus A 42:343-365, 1990) blocking index is applied to daily averaged 500 hPa geopotential fields, from the ERA-40 reanalysis and as simulated by the climate models, during the winter periods from 1957 to 1999. The two preferred regions of blocking development, in the Euro-Atlantic and North Pacific, are relatively well captured by most of the models. However, the prominent error in blocking simulations consists of an underestimation of the total frequency of blocking episodes over both regions. A more detailed analysis revealed that this error was due to an insufficient number of medium spells and long-lasting episodes, and a shift in blocking lifetime distributions towards shorter blocks in the Euro-Atlantic sector. In the Pacific, results are more diverse; the models are equally likely to overestimate or underestimate the frequency at different spell lengths. Blocking spatial signatures are relatively well simulated in the Euro-Atlantic sector, while errors in the intensity and geographical location of the blocks emerge in the Pacific. The impact of models' systematic errors on blocking simulation has also been analysed. The time-mean atmospheric circulation biases affect the frequency of blocking episodes, and the maximum event duration in the Euro-Atlantic region, while they sometimes cause geographical mislocations in the Pacific sector. The analysis of the systematic error in timevariability has revealed a negative relationship between the high-frequency variability of the transient eddies in the areas affected by blocking and blocking frequency. The blocking responses to errors in the low-frequency variability are different according to the region considered; the amplitude of the low-frequency variability is positively related to the blocking frequency and persistence in the Euro-Atlantic sector, while no such consistency is observed in the Pacific.

show abstract

Section: Summary and Interpretation Of Resultsmentioning

confidence: 94%

Assessment of atmosphere-ocean general circulation model simulations of winter northern hemisphere atmospheric blocking

Vial

Osborn

2011

Clim Dyn

View full text Add to dashboard Cite

show abstract

“…Blocking is also associated with a reduction in the westerly geostrophic flow, leading many studies to identify blocking events as a persistent, synoptic-scale reversal of the 500-hPa geopotential height gradient (Rex 1950a,b;Austin 1980;Lejen€ as and Økland 1983;Tibaldi and Molteni 1990;Tibaldi et al 1994;Lupo and Smith 1998;Barriopedro et al 2006;Diao et al 2006;Barnes and Hartmann 2010). Recent studies have also modeled blocking as a breaking wave that cuts off from the westerly flow and produces a local reversal of the potential gradient on the dynamic tropopause.…”

Section: Overview and Critique Of Existing Blocking Indicesmentioning

confidence: 95%

An Objectively Determined Blocking Index and its Northern Hemisphere Climatology

2013

View full text Add to dashboard Cite

A modified blocking index is defined based on vertically integrated potential vorticity. The application of this index identifies blocking activity over the Northern Hemisphere during all seasons. The index is developed by systematically identifying the magnitude and spatial scale that best characterizes persistent anticyclonic circulation anomalies in different seasons. By applying a systematic approach to the detection of blocking, the interannual, seasonal, and intraseasonal patterns of blocking frequency across the Northern Hemisphere are able to be characterized. The results are consistent with previous studies in finding that blocking is more frequent in the cold season months than in the warm season, although the results suggest that blocking occurs much more frequently in the summer and fall than many studies have previously reported. By examining blocking frequency monthly, interesting patterns of intraseasonal variability are found, especially over the central Pacific in August and the eastern Pacific in September and October, where blocking is nearly as frequent as in the winter. Possible explanations for this intraseasonal variability are discussed.

show abstract

“…Because of the importance of atmospheric blocking in affecting the regional shortterm climate, it is imperative to study this atmospheric phenomenon. Many theoretical and observational studies have investigated the onset of atmospheric blocking from distinct perspectives (Rex 1950;Egger 1978;Charney and De Vore 1979;Tung and Lindzen 1979a,b;Hoskins and Karoly 1981;Austin 1980;Colucci et al 1981;Frederiksen 1982;Shutts 1983;Tsou and Smith 1990;Tracton 1990;Alberta et al 1991;Colucci 2001;Dong andColucci 2005, 2007). Despite the extensive diagnostic and theoretical studies of atmospheric blocking over the last several decades, the current prediction skill of blocking by comprehensive numerical models is still far from satisfactory (Tracton 1990;Tibaldi et al 1994;Watson and Colucci 2002).…”

Section: Introductionmentioning

confidence: 95%

Interdecadal Trend and ENSO-Related Interannual Variability in Southern Hemisphere Blocking

2008

View full text Add to dashboard Cite

The interdecadal trend and ENSO-related interannual variability in the frequency and intensity of atmospheric blocking in the Southern Hemisphere are analyzed by a statistical model that takes account of serial correlation in the datasets. Results suggest that an autoregressive process AR(1) fits the error term of the Southern Hemisphere blocking occurrence series, and a white-noise process AR(0) fits the error term of the Southern Hemisphere blocking intensity series reasonably well. It is found that the Southern Hemisphere blocking days have decreased over the past 52 yr (1948-99) but with an enhanced intensity. In addition, the Southern Hemisphere atmospheric blocking is found to occur more frequently in the warm phase of ENSO cycles, whereas the intensity of the Southern Hemisphere atmospheric blocking does not appear to be affected by ENSO cycles.

show abstract

The blocking of middle latitude westerly winds by planetary waves

Cited by 113 publications

References 11 publications

Assessment of atmosphere-ocean general circulation model simulations of winter northern hemisphere atmospheric blocking

Assessment of atmosphere-ocean general circulation model simulations of winter northern hemisphere atmospheric blocking

An Objectively Determined Blocking Index and its Northern Hemisphere Climatology

Interdecadal Trend and ENSO-Related Interannual Variability in Southern Hemisphere Blocking

Contact Info

Product

Resources

About