Characteristics of northern hemisphere blocking as determined from a long time series of observational data

Lejenäs, Harald; Økland, Hans

doi:10.3402/tellusa.v35i5.11446

Cited by 249 publications

(102 citation statements)

References 8 publications

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“…We have therefore carried out studies like those described in but focusing on 60° longitude sectors of the Northern Hemisphere extratropics (20°–90°N) where the different blocks form. Although blocking appears to be primarily a local phenomenon (Lejenas and Okland, 1983; Lupo, 1997), the development of a block or the presence of a mature block in a given sector affects not only the error growth in the sector but tends to have a similar effect on sectors both upstream and downstream. For this reason, and because the Atlantic sector is a region for a major Northern Hemisphere storm track, we focus here on the sector 20°–90°N, 0°–60°W.…”

Section: Forecast Results For the Atlantic Sectormentioning

confidence: 99%

“…We examine the performance of the ensemble prediction method described in for initial conditions taken from the period between 0000 utc on 11 October 1979 and 1200 utc on 21 November 1979. We have focused on this interval because it was a time of large‐scale Northern Hemisphere blocking in the major blocking regions over the North Atlantic Ocean and over Europe and over the Gulf of Alaska (Dole and Gordon, 1983; Lejenas and Okland, 1983; Lupo and Smith, 1995a,b; Wiedermann et al, 2002) and as well over North America. As this time interval coincides with the First Global Atmospheric Research Programme Global Experiment (FGGE), observations are of the highest quality.…”

Section: Synoptic Situationsmentioning

confidence: 99%

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Ensemble prediction of blocking regime transitions

2004

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The skill of ensemble prediction during blocking regime transitions is examined for Northern Hemisphere flows within two atmospheric models. An ensemble prediction scheme based on fast growing perturbations has been implemented for conformal‐cubic and spectral general circulation models. The methodology uses a breeding method, based on an implicit linearization of the models, in which perturbations likened to leading Lyapunov vectors are obtained and used to perturb the initial conditions. Detailed comparisons of the skill of ensemble mean forecasts with control forecasts have been carried out for Northern Hemisphere initial conditions in October and November 1979. A particular focus has been the variability of forecast skill during the development, maturation and decay of the large‐scale blocking dipoles that occurred in the major blocking regions over Europe, over the Gulf of Alaska, over the North Atlantic and as well over North America. On average, the ensemble mean forecast performs better than the control forecast for forecast times longer than three or four days. Average error growth curves in the two models are quite similar with the conformal‐cubic model ensemble generally performing slightly better than for the lower‐resolution spectral model. Both ensemble and control forecasts initiated twice daily exhibit considerable variability in forecast skill that is shown to be related to instability regimes of particular synoptic events. At a given forecast lead time, errors tend to be larger for forecasts validating when blocks are developing or decaying and smaller for mature blocks. The spread of ensemble member forecasts has been studied and related to likely forecast skill. Comparison of results from the conformal‐cubic and spectral models initialized with two different analysis data sets has allowed the determination of the robustness of our findings relating error growth to instability regimes.

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Section: Forecast Results For the Atlantic Sectormentioning

confidence: 99%

Section: Synoptic Situationsmentioning

confidence: 99%

Ensemble prediction of blocking regime transitions

2004

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“…The atmospheric blocking frequency (see the method in Lejenäs & Økland, 1983;Tibaldi & Molteni, 1990) during winter shows upward trends over the west-central Northern Eurasia in the ERA-Interim data (Figure 13a, black curve). The upward trends in blocking frequency are particularly strong near the Ural area (around 60°E).…”

Section: The Trends In the Winter Atmospheric Blocking Frequency And mentioning

confidence: 99%

The Influences of the Arctic Troposphere on the Midlatitude Climate Variability and the Recent Eurasian Cooling

Jung

Semmler

2018

JGR Atmospheres

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Understanding the influence of the Arctic troposphere on the climate at midlatitudes is critical for projecting the impacts of ongoing and anticipated Arctic changes such as Arctic amplification and rapid sea ice decline over the Northern Hemisphere. In this study, we analyze a suite of atmospheric model experiments, with and without atmospheric relaxation toward reanalysis data, to study the impacts of the Arctic troposphere on the midlatitude atmospheric circulation and climate variability. The Arctic troposphere is found to strongly impact the interannual variability of the atmospheric circulation and temperature over the midlatitude continents. The major mechanisms for the impacts of Arctic troposphere include the modulation of the large‐scale atmospheric circulation, the associated heat transport over the continents, and the impacts on synoptic variations in the North Atlantic‐European sector. The impact of the Arctic troposphere on the intensity of the Siberian High is an important factor for how the Arctic can influence temperature variability in south Siberia and East Asia. The trends in the Arctic troposphere in recent decades are closely linked to the recent winter cooling in Northern Eurasia. These recent cooling trends are not driven by the trends in sea surface temperature/sea ice, tropical atmosphere, and the stratosphere. It is argued that the temperature trend pattern of warm Arctic‐cold Eurasia is a manifestation of two possibly independent phenomena and the cooling trend is contributed to by the Arctic troposphere through impacting the large‐scale atmospheric circulation, the atmospheric blocking frequency, and the intensity of the Siberian High.

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“…The original Lejenäs and Økland (1983) index, henceforth known as L&O83, forms the basis for the derivations of the most commonly used blocking indices. For this study, the Lupo et al (2008) blocking index dataset is used and this too is based off a modified version of the L&O83 index.…”

Section: Atmospheric Blocking Index Uncertaintymentioning

confidence: 99%

Quantifying the variability of potential black carbon transport from cropland burning in Russia driven by atmospheric blocking events

Hall

Loboda

2018

Environ. Res. Lett.

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The deposition of short-lived aerosols and pollutants on snow above the Arctic Circle transported from northern mid-latitudes have amplified the short term warming in the Arctic region. Specifically, black carbon has received a great deal of attention due to its absorptive efficiency and its fairly complex influence on the climate. Cropland burning in Russia is a large contributor to the black carbon emissions deposited directly onto the snow in the Arctic region during the spring when the impact on the snow/ice albedo is at its highest. In this study, our focus is on identifying a possible atmospheric pattern that may enhance the transport of black carbon emissions from cropland burning in Russia to the snow-covered Arctic. Specifically, atmospheric blocking events are large-scale patterns in the atmospheric pressure field that are nearly stationary and act to block migratory cyclones. The persistent low-level wind patterns associated with these mid-latitude weather patterns are likely to accelerate potential transport and increase the success of transport of black carbon emissions to the snow-covered Arctic during the spring. Our results revealed that overall, in March, the transport time of hypothetical black carbon emissions from Russian cropland burning to the Arctic snow is shorter (in some areas over 50 hours less at higher injection heights) and the success rate is also much higher (in some areas up to 100% more successful) during atmospheric blocking conditions as compared to conditions without an atmospheric blocking event. The enhanced transport of black carbon has important implications for the efficacy of deposited black carbon. Therefore, understanding these relationships could lead to possible mitigation strategies for reducing the impact of deposition of black carbon from crop residue burning in the Arctic.

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Characteristics of northern hemisphere blocking as determined from a long time series of observational data

Cited by 249 publications

References 8 publications

Ensemble prediction of blocking regime transitions

Ensemble prediction of blocking regime transitions

The Influences of the Arctic Troposphere on the Midlatitude Climate Variability and the Recent Eurasian Cooling

Quantifying the variability of potential black carbon transport from cropland burning in Russia driven by atmospheric blocking events

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