The Relationship between Northern Hemisphere Winter Blocking and Tropical Modes of Variability

Gollan, Gereon; Greatbatch, Richard John

doi:10.1175/jcli-d-16-0742.1

Cited by 14 publications

(21 citation statements)

References 58 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The results for ENSO agree well with Gollan and Greatbatch () over the Pacific, who found similar MLB anomalies in reanalysis data and in a seasonal forecasting model. Over the western NA, the increase of HLB frequency for both El Niño and La Niña is contrary to Gollan and Greatbatch () and also to Henderson and Maloney () who both find a weak decrease in HLB frequency for both cases. Over midlatitude Europe, results agree qualitatively with the model results of Gollan and Greatbatch (), who find a weak decrease (increase) in MLB frequency for El Niño (La Niña).…”

Section: Resultssupporting

confidence: 85%

“…Over the western NA, the increase of HLB frequency for both El Niño and La Niña is contrary to Gollan and Greatbatch () and also to Henderson and Maloney () who both find a weak decrease in HLB frequency for both cases. Over midlatitude Europe, results agree qualitatively with the model results of Gollan and Greatbatch (), who find a weak decrease (increase) in MLB frequency for El Niño (La Niña). Note again that there is no stratospheric polar vortex in the model used here, so that the response seen is purely due to a tropospheric pathway.…”

Section: Resultscontrasting

confidence: 71%

“…The above definition of BI inst measures the meridional gradient of Z that is usually negative in the Northern Hemisphere. An actual blocking event is then detected if BI inst is positive, meaning reversed, for at least 4 days and over at least 15° longitude (similar to previous studies, for example, Gollan et al, ; Gollan and Greatbatch, ).…”

Section: Methodssupporting

confidence: 75%

“…For example, the positive (negative) phase of El Niño Southern Oscillation (ENSO) is associated with reduced (increased) blocking over the midlatitude North Pacific (NP) (Renwick and Wallace, ; Barriopedro et al, ). Over the NA and European sector, results are less clear in reanalyses, and previous studies suggest only a weak ENSO influence in general (Henderson and Maloney, ) or slightly reduced high‐latitude blocking (HLB) over the NA during La Niña (Gollan and Greatbatch, ). Also, those phases of the Madden–Julian Oscillation (MJO, Wheeler and Hendon, ) characterized by enhanced convection over the Maritime Continent and the western tropical Pacific, are associated with enhanced blocking over the NA and Europe (e.g., Cassou, ; Gollan et al, ; Henderson et al, ).…”

Section: Introductionmentioning

confidence: 88%

See 3 more Smart Citations

Tropical precipitation influencing boreal winter midlatitude blocking

Gollan

Bastin

Greatbatch

2019

Atmospheric Science Letters

Self Cite

View full text Add to dashboard Cite

Recent studies using reanalysis data and complex models suggest that the Tropics influence midlatitude blocking. Here, the influence of tropical precipitation anomalies is investigated further using a dry dynamical model driven by specified diabatic heating anomalies. The model uses a quasi-realistic setup based on idealized orography and an idealized representation of the land-ocean thermal contrast. Results concerning the El Niño Southern Oscillation and the Madden-Julian Oscillation are mostly consistent with previous studies and emphasize the importance of tropical dynamics for driving the variability of blocking at midlatitudes. It is also shown that a common bias in models of the Coupled Model Intercomparison Project Phase 5 (CMIP5), namely, excessive tropical precipitation, leads to an underestimation of midlatitude blocking in our model, also a common bias in the CMIP5 models. The strongest blocking anomalies associated with the tropical precipitation bias are found over Europe, where the underestimation of blocking in CMIP5 models is also particularly strong. K E Y W O R D S blocking bias, CMIP5, dry atmospheric general circulation model, ENSO, Midlatitude blocking, MJO, precipitation bias

show abstract

Section: Resultssupporting

confidence: 85%

Section: Resultscontrasting

confidence: 71%

Section: Methodssupporting

confidence: 75%

Section: Introductionmentioning

confidence: 88%

See 2 more Smart Citations

Tropical precipitation influencing boreal winter midlatitude blocking

Gollan

Bastin

Greatbatch

2019

Atmospheric Science Letters

Self Cite

View full text Add to dashboard Cite

show abstract

“…We cannot rule out the possibility that model deficiencies in, for example, the representation of blocking in this region (biases are present in CMIP5 models and persist even at high resolutions; Dunn‐Sigouin & Son, ; Masato et al, ; Schiemann et al, ) may have led to the modeled rapid decay in height anomalies in this region; this possibility deserves future research, though a thorough investigation of blocking frequency and duration in S2S models, or of the effect of climate change on blocking in this region, is beyond the scope of this work. However, connections between ENSO and blocking in western Eurasia are weak (Cheung et al, ; Gollan & Greatbatch, ), and hence, even the ridging over western Siberia/eastern Europe apparent in the composited difference LN‐EN appears to reflect internal midlatitude atmospheric variability and not a forced response to ENSO.…”

Section: Discussion and Summarymentioning

confidence: 99%

Weakening of the Teleconnection From El Niño–Southern Oscillation to the Arctic Stratosphere Over the Past Few Decades: What Can Be Learned From Subseasonal Forecast Models?

et al. 2019

View full text Add to dashboard Cite

While a connection between the El Niño–Southern Oscillation (ENSO) and the Northern Hemisphere wintertime stratospheric polar vortex appears robust in observational studies focusing on the period before 1979 and in many modeling studies, this connection is not evident over the past few decades. In this study, the factors that have led to the disappearance of the ENSO‐vortex relationship are assessed by comparing this relationship in observational data and in operational subseasonal forecasting models over the past few decades. For reforecasts initialized in December, the models simulate a significantly weaker vortex during El Niño than La Niña (LN) as occurred before 1979, but no such effect was observed to have occurred. The apparent cause of this is the eastern European and western Siberian height anomalies present during ENSO. The observed LN events were associated with persistent ridging over eastern Europe as compared to El Niño. Although the Subseasonal‐to‐Seasonal models are initialized with this ridge, the ridge quickly dissipates. As ridging over this region enhances wave flux entering the stratosphere, the net effect is no robust stratospheric response to ENSO in the observations despite a North Pacific teleconnection that would, in isolation, lead to less wave flux for LN. The anomalies in the eastern European sector in response to ENSO likely reflect unforced internal atmospheric variability.

show abstract

Predictability of European winter 2019/20: Indian Ocean dipole impacts on the NAO

Hardiman

Dunstone

Scaife

et al. 2020

Atmospheric Science Letters

Self Cite

View full text Add to dashboard Cite

Northern Europe and the UK experienced an exceptionally warm and wet winter in 2019/20, driven by an anomalously positive North Atlantic Oscillation (NAO). This positive NAO was well forecast by several seasonal forecast systems, suggesting that this winter the NAO was highly predictable at seasonal lead times. A very strong positive Indian Ocean dipole (IOD) event was also observed at the start of winter. Here we use composite analysis and model experiments, to show that the IOD was a key driver of the observed positive NAO. Using model experiments that perturb the Indian Ocean initial conditions, two teleconnection pathways of the IOD to the north Atlantic emerge: a tropospheric teleconnection pathway via a Rossby wave train travelling from the Indian Ocean over the Pacific and Atlantic, and a stratospheric teleconnection pathway via the Aleutian region and the stratospheric polar vortex. These pathways are similar to those for the El Niño Southern Oscillation link to the north Atlantic which are already well documented. The anomalies in the north Atlantic jet stream location and strength, and the associated precipitation anomalies over the UK and northern Europe, as simulated by the model IOD experiments, show remarkable agreement with those forecast and observed.

show abstract

The Relationship between Northern Hemisphere Winter Blocking and Tropical Modes of Variability

Cited by 14 publications

References 58 publications

Tropical precipitation influencing boreal winter midlatitude blocking

Tropical precipitation influencing boreal winter midlatitude blocking

Weakening of the Teleconnection From El Niño–Southern Oscillation to the Arctic Stratosphere Over the Past Few Decades: What Can Be Learned From Subseasonal Forecast Models?

Predictability of European winter 2019/20: Indian Ocean dipole impacts on the NAO

Contact Info

Product

Resources

About