Analysis of blocking events from observations and ECHAM model
                        simulations

Sausen, R.; König, Winfried; Sielmann, Frank

doi:10.3402/tellusa.v48i4.12076

Cited by 11 publications

(23 citation statements)

References 20 publications

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“…It, however, suffers from arbitrary blocking anomaly thresholds and the need of a robust climatology to define anomalies (Doblas-Reyes et al 2002). In spite of refinements to the Dole-Gordon index, such as more severe threshold values (e.g., Sausen et al 1995) or defining anomalies relative to a sector mean (e.g., Mullen 1987), the possible misrepresentation still remains. In spite of refinements to the Dole-Gordon index, such as more severe threshold values (e.g., Sausen et al 1995) or defining anomalies relative to a sector mean (e.g., Mullen 1987), the possible misrepresentation still remains.…”

Section: A Backgroundmentioning

confidence: 99%

“…where Z is 500-hPa geopotential height normalized by the sine of latitude; Z is a running annual mean of Z centered on a given day; andẐ is a mean seasonal cycle derived from Z*, which is a running monthly mean of Z 2 Z centered on a given day (see Sausen et al 1995 for further details). This treatment effectively removes the seasonal cycle and long-term variability of the background field.…”

Section: ) Anomaliesmentioning

confidence: 99%

See 1 more Smart Citation

Evaluation of Northern Hemisphere Blocking Climatology in the Global Environment Multiscale Model

Dunn‐Sigouin

Son

Lin

2013

Monthly Weather Review

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The performance of the Global Environmental Multiscale (GEM) model, the Canadian operational numerical model, in reproducing atmospheric low-frequency variability is evaluated in the context of Northern Hemisphere blocking climatology. The validation is conducted by applying a comprehensive but relatively simple blocking detection algorithm to a 20-yr (1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006) integration of the GEM model in climate mode. The comparison to reanalysis reveals that, although the model can reproduce Northern Hemisphere blocking climatology reasonably well, the maximum blocking frequency over the North Atlantic and western Europe is generally underestimated and its peak season is delayed from late winter to spring. This contrasts with the blocking frequency over the North Pacific, which is generally overestimated during all seasons. These misrepresentations of blocking climatology are found to be largely associated with the biases in climatological background flow. The modeled stationary waves show a seasonal delay in zonal wavenumber 1 and an eastward extension in zonal wavenumber-2 components consistent with blocking frequency biases. High-frequency eddies are, however, consistently underestimated both in the North Atlantic and Pacific, indicating that the biases in eddy fields might not be the main reason for the blocking biases in the North Pacific.

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Section: A Backgroundmentioning

confidence: 99%

Section: ) Anomaliesmentioning

confidence: 99%

Evaluation of Northern Hemisphere Blocking Climatology in the Global Environment Multiscale Model

Dunn‐Sigouin

Son

Lin

2013

Monthly Weather Review

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“…Height anomalies have been often used for automatic identification of blocking events [ Dole and Gordon , 1983; Shukla and Mo , 1983; Mullen , 1986; Liu , 1994]. In this study the index described by Sausen et al [1995] (SKS) has been applied. This index reduces the number of empirical parameters to a minimum, although it requires time series long enough so as to be able to compute a reliable climatology.…”

Section: Data and Blocking Indicesmentioning

confidence: 99%

“…This uncertainty is a major difficulty that confronts researchers and hampers intercomparison of scientific results. Hence objective procedures for identifying blocking events are required, although almost all definitions contain some subjectivity [ Knox and Hay , 1984; Sausen et al , 1995]. Tibaldi et al [1990] compared several simulations with different horizontal resolutions.…”

Section: Introductionmentioning

confidence: 99%

Sensitivity of the Northern Hemisphere blocking frequency to the detection index

2002

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[1] The sensitivity of Northern Hemisphere blocking features to the use of two different blocking indices is investigated using European Centre for Medium-Range Weather Forecasts (ECMWF) reanalyses (ERA) and data from a climate simulation carried out with the atmospheric general circulation model Action de Recherche, Petite Echelle, Grande Echelle ARPEGE. The seasonal cycle of blocking frequency shows a good agreement between both indices, for both analyses and model, when the seasonal cycle of the 500-hPa geopotential height is previously removed from the data. Furthermore, the blocking frequency seasonal cycle agrees well with the 5-to 45-day bandpass-filtered standard deviation (a proxy indicator of blocking activity) seasonal cycle. In contrast to previous results, this demonstrates that a consensus estimate of blocking features may be obtained with two different blocking indices. Nevertheless, some differences in the results from the two indices have been detected, particularly for the Euro-Atlantic blocking. Regional differences suggest that on some occasions, an index may detect blocking events that the other index misses, and vice versa. An important consequence is that uncertainty in blocking interannual variability estimates, which depend on the index used, is expected to be high. The study shows that the model underestimates the blocking frequency regardless of the index used. However, the model proves to be able to simulate realistic blocks when removing an estimate of the geopotential time-mean bias. Blocking drawbacks in the model are interpreted as a consequence of a specific zonal wind forcing associated with a decrease in the frequency of large-scale ridges over the main blocking regions. These results strengthen the interest of analyzing model blocking as a complex phenomenon with regional dynamical differences and tight links with other atmospheric phenomena.

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“…Thus, a temporal succession of collocated blocks can imprint markedly upon a single winter's mean climate. Note however that, depending on the blocking index used, it is the central North Atlantic Ocean (e.g., Dole and Gordon 1983;Sausen et al 1995;Croci-Maspoli et al 2007b) as opposed to western Europe (e.g., Lejenä s and Økland 1983; Tibaldi and Molteni 1990;Pelly and Hoskins 2003) that is the most preferred location for blocking in the Euro-Atlantic sector.…”

Section: Introductionmentioning

confidence: 99%

Key Dynamical Features of the 2005/06 European Winter

Croci-Maspoli

Davies

2009

Monthly Weather Review

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A three-part study of the anomalously cold European winter of 2005/06 is undertaken. Climatological analysis indicates that the dominant pattern of climate variability in the Euro-Atlantic sector during this winter was not a negative phase of the North Atlantic Oscillation (NAO), but a pattern with a ''blocklike'' center located immediately upstream of the continent. Synoptic-dynamical diagnosis of the winter indicates the frequent occurrence of long-lasting blocks in this region, and a Lagrangian trajectory analysis points to the significant role of cloud-diabatic effects in the dynamics of block inception. A series of heuristic numerical simulations lend credence to the hypothesis that the occurrence of the blocks was sensitive to, and significantly influenced by, the warm surface temperature anomalies upstream over the western Atlantic Ocean and North America. Brief comments are made on the significance of the foregoing results for seasonal numerical weather prediction and also their relevance to the consideration of interannual climate variability.

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Analysis of blocking events from observations and ECHAM model simulations

Cited by 11 publications

References 20 publications

Evaluation of Northern Hemisphere Blocking Climatology in the Global Environment Multiscale Model

Evaluation of Northern Hemisphere Blocking Climatology in the Global Environment Multiscale Model

Sensitivity of the Northern Hemisphere blocking frequency to the detection index

Key Dynamical Features of the 2005/06 European Winter

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