Atmospheric circulation variability in the North-Atlantic-European area since the mid-seventeenth century. Climate Dyn

Institute of Geography, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany
Climate Dynamics (Impact Factor: 4.67). 01/2003; 20(4):341-352. DOI: 10.1007/s00382-002-0278-0

ABSTRACT Based on monthly mean sea level pressure grids objectively reconstructed by Luterbacher et al. variations of dynamical modes of the atmospheric circulation for January and July are described by novel indices for running 31-year periods between 1659 and 1999. These indices reflect the continuous evolution of the atmospheric circulation not only with regard to frequency changes of major dynamical modes but also in terms of internal changes within each mode concerning both dynamic (vorticity, intensity) and climatic properties (Central European temperature and precipitation during occurrence of each mode, respectively). Results indicate the great importance of within-mode variations: the zonal circulation mode in January, varying in frequency with long-term cycles, primarily changed its dynamic and climatic properties (towards higher indices) during the transition from the Little Ice Age to modern conditions between 1800 and 1930. Within the Russian High mode of January a change in preference from easterly to westerly patterns above Central Europe occurred around 1850. For July, a striking frequency maximum of the westerly mode at the end of the eighteenth century coincided with a period of marked summer warmth in Central Europe due to negative/positive deviations in vorticity/temperature during occurrence of this mode. The long-term evolution in July indicates a general increase of anticyclonic conditions strengthening during the last 50 years towards a unique phenomenon within the last centuries. The strong increase in the winter-time westerly circulation during the last decades, however, does not appear extraordinary in view of the low-frequency variations of this mode.

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Available from: Andreas Philipp, Sep 29, 2015
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    • "This reduced storminess in the Cors Fochno reconstruction may in part result from the bog's location making it sensitive to westerly tracking storms. Westerly airflow was suggested as the cause of the increased flooding at the LIA transitions (Rumsby and Macklin, 1996), while at the peak of the LIA (the Maunder Minimum, 1645–1715 AD) documentary and modelling evidence has indicated that there were more meridional circulation patterns, blocking high pressures across northern Europe, a southerly storm track in winter and lower precipitation particularly on Britain's west coast (Lamb, 1966; Luterbacher et al., 2001; Jacobeit et al., 2003; Raible et al., 2007). In support of this, reconstructions from across southern Europe suggest precipitation and flooding increased between 0.45 and 0.25/0.15 "
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    ABSTRACT: Future anthropogenic climate forcing is forecast to increase storm intensity and frequency over Northern Europe, due to a northward shift of the storm tracks, and a positive North Atlantic Oscillation. However understanding the significance of such a change is difficult because the natural variability of storminess beyond the range of instrumental data is poorly known. Here we present a decadal-resolution record of storminess covering the Late Holocene, based on a 4-m-long core taken from the peat bog of Cors Fochno in mid-Wales, UK. Storminess is indicated by variations in the minerogenic content as well as bromine deposited from sea spray. Twelve episodes of enhanced storm activity are identified during the last 4.5 cal ka BP. Although the age model gives some uncertainty in the timings, it appears that storminess increased at the onset and close of North Atlantic cold events associated with oceanic changes, with reduced storm activity at their peak. Cors Fochno is strongly influenced by westerly moving storms, so it is suggested that the patterns were due to variations in the intensity of westerly airflow and atmospheric circulation during times when the latitudinal temperature gradient was steepened.
    Journal of Quaternary Science 07/2015; 30(5):478-488. DOI:10.1002/jqs.2792 · 3.36 Impact Factor
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    • "The systematic categorization of atmospheric behaviour into a series of discrete archetypal circulation patterns, provides a means for studying the dynamics of large-scale circulation and its relationship with variability in surface weather and climate (Barry and Perry, 1973; Sweeney and O'Hare, 1992; Buishand and Brandsma, 1997; Jacobeit et al., 2003; Ustrnul, 2006; Beck et al., 2007; Esteban et al., 2009). Previously synoptic typing has been used to investigate the link between distinct modes of circulation and a multitude of 'exotic' or environmental variables including: human mortality rates (Kassomenos et al., 2001); hydrological drought (Stahl and Siegfreid, 1999; Vicente-Serrano and Lopez-Moreno, 2006; Fleig et al., 2010) and flooding (Samaniego and Bárdossy, 2007; Pattison and Lane, 2011; Prudhomme and Genevier, 2011); viticulture (Jones and Davis, 2000); urban heat islands (Unger, 1996; Mihalakakou et al., 2002; Wilby, 2003); * Correspondence to: C. Broderick, Department of Geography, NUI Maynooth, Co. Kildare, Ireland. "
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    ABSTRACT: Circulation type classifications (CTCs) compiled as part of the COST733 Action, entitled 'Harmonisation and Application of Weather Type Classifications for European Regions', are examined for their synoptic and climatological applicability to Ireland based on their ability to characterise surface temperature and precipitation. In all 16 different objective classification schemes, representative of four different methodological approaches to circulation typing (optimization algorithms, threshold based methods, eigenvector techniques and leader algorithms) are considered. Several statistical metrics which variously quantify the ability of CTCs to discretize daily data into well-defined homogeneous groups are used to evaluate and compare different approaches to synoptic typing. The records from 14 meteorological stations located across the island of Ireland are used in the study. The results indicate that while it was not possible to identify a single optimum classification or approach to circulation typing - conditional on the location and surface variables considered - a number of general assertions regarding the performance of different schemes can be made. The findings for surface temperature indicate that that those classifications based on predefined thresholds (e.g. Litynski, GrossWetterTypes and original Lamb Weather Type) perform well, as do the Kruizinga and Lund classification schemes. Similarly for precipitation predefined type classifications return high skill scores, as do those classifications derived using some optimization procedure (e.g. SANDRA, Self Organizing Maps and K-Means clustering). For both temperature and precipitation the results generally indicate that the classifications perform best for the winter season - reflecting the closer coupling between large-scale circulation and surface conditions during this period. In contrast to the findings for temperature, spatial patterns in the performance of classifications were more evident for precipitation. In the case of this variable those more westerly synoptic stations open to zonal airflow and less influenced by regional scale forcings generally exhibited a stronger link with large-scale circulation.
    International Journal of Climatology 03/2015; 35(4):1636-. DOI:10.1002/joc.3996 · 3.16 Impact Factor
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    • "This process suffers from different sources of uncertainty, such as those derived from non-stationary relationships between the proxy and the local climate and between the local climate and the largerscale atmospheric circulation itself (e.g., Schmutz et al. 2000; Jung et al. 2003; Vicente-Serrano and López-Moreno 2008). The lack of stationary relationships between atmospheric circulation and European climate can be even larger in the context of the last centuries (Jacobeit et al. 2003; Casty et al. 2005; Pauling et al. 2006; Küttel et al. 2011), and could influence the reconstructions of atmospheric circulation, as the statistical models would be sensitive to the specific time periods chosen for calibration and validation (e.g., Slonosky and Yiou 2002). "
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    ABSTRACT: A monthly index based on the persistence of the westerly winds over the English Chanel is constructed for 1685–2008 using daily data from ships' logbooks and comprehensive marine meteorological datasets. The so-called Westerly Index (WI) provides the longest instrumental record of atmospheric circulation currently avail-able. Anomalous WI values are associated with spatially coherent climatic signals in temperature and precipitation over large areas of Europe, which are stronger for precipitation than for temperature and in winter and summer than in transitional seasons. Overall, the WI series accord with the known European climatic history, and reveal that the frequency of the westerlies in the eastern Atlantic during the twentieth century and the Late Maunder Minimum was not exceptional in the context of the last three centuries. It is shown that the WI provides additional and complementary information to the North Atlantic Oscillation (NAO) indices. The analysis of WI series during the industrial era indicates an overall good agreement with the winter and high-summer NAO, with the exception of several multidecadal periods of weakened correlation. These decoupled periods between the frequency and the intensity of the zonal flow are interpreted on the basis of several sources of non-stationarity affecting the centres of the variability of the North Atlantic and their teleconnections. Comparisons with NAO reconstructions and long instrumental indices extending back to the seventeenth century suggest that similar situations have occurred in the past, which call for caution when reconstructing the past atmospheric circulation from climatic proxies. The robustness and extension of its climatic signal, the length of the series and its instrumental nature make the WI an excellent benchmark for proxy calibration in Europe and Greenland.
    Climate Dynamics 10/2013; 43(3-4). DOI:10.1007/s00382-013-1957-8 · 4.67 Impact Factor
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