Evaluation of the NCEP–NCAR reanalysis in terms of synoptic‐scale phenomena: a case study from the Midwestern USA

Schoof, J. T.; Pryor, Sara C.

doi:10.1002/joc.969

Cited by 16 publications

(9 citation statements)

References 26 publications

(32 reference statements)

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“…The 10-cluster solution derived from clustering the first four PCs was successful in grouping 61% of the variance between clusters. Although these levels of explanation are similar to those encountered in other eigenvector-based studies of mid-tropospheric circulation (Horel, 1981;Kidson and Sinclair, 1995;Rohli et al, 1999;Schoof and Pryor, 2003), the remaining unexplained variation represents a source of considerable uncertainty. One example of the causes of intra-cluster variability included difficulties in classifying zonal flow.…”

Section: Discussionsupporting

confidence: 76%

Synoptic controls on summer evapotranspiration from a bog peatland in southern Canada

2005

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The relationship between surface hydrometeorological variables and mid-tropospheric circulation was used to describe and model the synoptic controls on daily and monthly evapotranspiration (ET) and potential evapotranspiration (PET) measured above a peat bog near Ottawa, Ontario. The four most dominant modes of variability in daily 500 hPa geopotential height over eastern North America were defined by S-mode principal component analysis and subjected to K-means clustering in order to produce discrete patterns of 500 hPa height. A total of 10 clusters were retained, based on a compromise between the number of legitimate patterns defined in a separate manual classification scheme and the proportion of variance grouped between clusters (61%) by the K-means algorithm.Height patterns defined by the 10-cluster scheme exhibited differences in their control over bog ET. Pre-high anticyclonic conditions were most efficient at drying the bog, whereas conditions prior to and during the passage of cyclonic systems were the least efficient at drying the bog. The remaining seven clusters exhibited insignificant control over ET on a seasonal basis. Variability in heights directly over the study site, associated with the second principal component, exhibited the closest relationship with hydrometeorological fluxes at the bog surface. However, attempts to model daily ET based, first, on multiple linear regression using principal components and, second, on cluster analogues of ET produced unsatisfactory skill. The inability to forecast daily ET was attributed to the influence of non-linear variation in the rate at which mid-tropospheric circulation controls propagated down to the surface and also to unresolved hydrological controls at the bog surface. Days following rainfall frequently resulted in amplified ET, regardless of cluster type, indicating that the control of ET by antecedent moisture conditions was a limiting factor in downscaling ET from large-scale atmospheric predictors. On a monthly time scale, however, the circulation indices explained 64% and 45% of the variation in monthly ET and PET respectively.

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Section: Discussionsupporting

confidence: 76%

Synoptic controls on summer evapotranspiration from a bog peatland in southern Canada

2005

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“…In the second step, a nonhierarchical technique is used, while in the first step hierarchical clustering, e.g., Ref. 166, or T‐mode PCA 158 is employed. The use of T‐mode PCA in this context is methodologically different from the use of S‐mode PCA as a mere preprocessor: in the former case, PCA is a classification tool and the whole procedure can be regarded as eigenvector‐based, contrary to the latter case.…”

Section: Overview and Systematization Of Classification Methodsmentioning

confidence: 99%

Classifications of Atmospheric Circulation Patterns

Huth

Beck

Philipp

et al. 2008

Annals of the New York Academy of Sciences

555

508

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We review recent advances in classifications of circulation patterns as a specific research area within synoptic climatology. The review starts with a general description of goals of classification and the historical development in the field. We put circulation classifications into a broader context within climatology and systematize the varied methodologies and approaches. We characterize three basic groups of classifications: subjective (also called manual), mixed (hybrid), and objective (computer-assisted, automated). The roles of cluster analysis and principal component analysis in the classification process are clarified. Several recent methodological developments in circulation classifications are identified and briefly described: the introduction of nonlinear methods, objectivization of subjective catalogs, efforts to optimize classifications, the need for intercomparisons of classifications, and the progress toward an optimum, if possible unified, classification method. Among the recent tendencies in the applications of circulation classifications, we mention a more extensive use in climate studies, both of past, present, and future climates, innovative applications in the ensemble forecasting, increasing variety of synoptic-climatological investigations, and steps above from the troposphere. After introducing the international activity within the field of circulation classifications, the COST733 Action, we briefly describe outputs of the inventory of classifications in Europe, which was carried out within the Action. Approaches to the evaluation of classifications and their mutual comparisons are also reviewed. A considerable part of the review is devoted to three examples of applications of circulation classifications: in historical climatology, in analyses of recent climate variations, and in analyses of outputs from global climate models.

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“…Although these discontinuities are most pronounced in the Southern Hemisphere (Kistler et al, 2001) and at higher altitudes (Trenberth and Stepanik, 2002), changes in the number and nature of data sets assimilated by the reanalysis process will inevitably lead to some temporal inconsistencies. Hence, despite the clear utility of the reanalysis data sets, there is a recognized need to evaluate the reanalysis projects relative both to other reanalysis data sets and to independent data not assimilated within the reanalysis process (Hines et al, 2000;Hastenrath and Greischar, 2001;Smith et al, 2001;Marshall, 2002;Schoof and Pryor, 2003). This comparison is particularly relevant to the current application because, as described above, observations of near-surface winds over land are not assimilated by either the ECMWF or the NCEP-NCAR reanalysis models (Kalnay and Cai, 2003).…”

Section: Analysis and Comparison Of The Reanalysis Data Setsmentioning

confidence: 99%

The impact of non-stationarities in the climate system on the definition of ‘a normal wind year’: a case study from the Baltic

2005

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Wind speeds over the Baltic significantly increased over the second half of the 20th century (C20th), with the majority of the increase being focused on the upper quartile of the wind speed distribution and in the southwest of the region. These changes have potentially profound implications for the wind energy resource. For example, based on the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis data it is shown that, owing to this non-stationarity, using the normalization period of 1987-98 to determine the wind resource (as in the Danish wind index) leads to overestimation of the wind energy index (and hence the wind energy resource) in western Denmark relative to 1958-2001 by approximately 10%. To address whether the increased prevalence of high wind speeds at the end of the C20th will be maintained in the future, we provide a first prognosis of annual wind indices from the HadCM3 coupled atmosphere-ocean general circulation model. The results suggest the 21st century (C21st) will be similar to the 1958-2001 period with respect to the wind energy density, but that the northeastern Baltic will exhibit slightly higher wind energy indices over the course of the C21st relative to the latter half of the C20th, whereas the southwest of the Baltic exhibits some evidence of declining wind indices towards the end of the C21st. These changes may indicate a tendency in HadCM3 towards more northerly tracking of mid-latitude cyclones in the future, possibly due to evolution of the North Atlantic oscillation. As a caveat to this finding, it should be noted that the NCEP-NCAR and European Centre for Medium-Range Weather Forecasts reanalysis data sets and HadCM3 simulations, although exhibiting commonalities during the period of overlap, differ quantitatively in terms of the spatial fields and empirical cumulative probability distributions at individual grid cells.

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Evaluation of the NCEP–NCAR reanalysis in terms of synoptic‐scale phenomena: a case study from the Midwestern USA

Cited by 16 publications

References 26 publications

Synoptic controls on summer evapotranspiration from a bog peatland in southern Canada

Synoptic controls on summer evapotranspiration from a bog peatland in southern Canada

Classifications of Atmospheric Circulation Patterns

The impact of non-stationarities in the climate system on the definition of ‘a normal wind year’: a case study from the Baltic

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