The influence of the circulation on surface temperature and precipitation patterns over Europe (original) (raw)
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Attribution of European precipitation and temperature trends to changes in circulation types
Surface climate in Europe is changing and patterns in trends have been found to vary at sub-seasonal scales. This study aims to contribute to a better understanding of these changes across space and time by analysing to what degree observed climatic trends can be attributed to changes in synoptic atmospheric circulation. The relative importance of synoptic circulation changes (i.e. trends in synoptic type frequencies) as opposed to trends in the hydrothermal properties of synoptic types (within-type trends) on precipitation and temperature trends in Europe is assessed on a monthly basis. The study is based on mapping spatial and temporal trend patterns and their variability at a relatively high resolution (0.5 • × 0.5 • ; monthly) across Europe. Gridded precipitation and temperature data (1963-2001) originate from the Watch Forcing Data set and synoptic types are defined by the objective SynopVis Grosswetterlagen (SVG). During the study period, relatively high influence of synoptic circulation changes are found from January to March, contributing to wetting trends in northern Europe and drying in the south. Simultaneously, particularly dry synoptic types get warmer first in southwestern Europe in November and/or December and affect most of Europe in March and/or April. Strong influence of synoptic circulation changes is again found in June and August. In general, changes in synoptic circulation has a stronger effect on climate trends in northwestern Europe than in the southeast. The exact locations of the strongest influence of synoptic circulation changes vary with the time of year and to some degree between precipitation and temperature. Throughout the year and across the whole of Europe, precipitation and temperature trends are caused by a combination of synoptic circulation changes and withintype changes with their relative influence varying between regions, months and climate variables.
Spatial response of two European atmospheric circulation classifications (data 1901–2010)
Theoretical and Applied Climatology, 2013
Air pressure field and circulation pattern frequencies were investigated to (1) locate and compare positions of the underlying pressure fields, (2) analyse the spatial dimension of affected areas, (3) create schematic maps of important circulation types and (4) compare the classification types in their response to the data. Two manual classifications were used, selected for the length of their time series and their applicability to a larger region: the Grosswetterlagen classification (GWLc) and the Vangengeim-Girs classification (VGc). Their time series were correlated with a global set of gridded monthly sea-level pressure data. Results show the different conceptual orientation of VGc (hemispheric) and GWLc (continental). The highest correlation values and the largest affected areas are visible in winter, where patterns frequently extended into northern Africa and western Asia. Schematic maps, illustrating the average location of main pressure centres, are provided for basic classes of both classifications. Rearranging GWLc subtypes increases the classifications comparability with the VGc. Analysis of moving correlation coefficients reveals high fluctuations in the relation of both classifications over time.
Influence of circulation types on temperature extremes in Europe
Theoretical and Applied Climatology, 2010
The aim of this study is to determine the influence of atmospheric circulation on the recently observed changes in the number of warm days and cold days in Europe. The temperature series for stations in the European Climate Assessment and Dataset project and the Grosswetterlagen (GWL) were used here. The temperature series were first adjusted for global warming before determining the indices for cold and warm extremes.
Climate Dynamics, 2011
Using pressure fields classified by the SANDRA algorithm, this study investigates the changes in the relationship between North Atlantic/European sea level pressure (SLP) and gridded European winter (DJF) temperature and precipitation back to 1750. Important changes in the frequency of the SLP clusters are found, though none of them indicating significant long-term trends. However, for the majority of the SLP clusters a tendency toward overall warmer and partly wetter winter conditions is found, most pronounced over the last decades. This suggests important within-type variations, i.e. the temperature and precipitation fields related to a particular SLP pattern change their characteristics over time. Using a decomposition scheme we find for temperature and precipitation that within-type-related variations dominate over those due to changed frequencies of the SLP clusters: Approximately 70% (60%) of European winter temperature (precipitation) variations can be explained by within-type changes, most strongly expressed over Eastern Europe and Scandinavia. This indicates that the current European winter warming cannot be explained by changed frequencies of the SLP patterns alone, but to a larger degree by changed characteristics of the patterns themselves. Potential sources of within-type variations are discussed.
Attribution of European precipitation and temperature trends to changes in synoptic circulation
2015
Abstract. Surface climate in Europe is changing and patterns in trends have been found to vary at sub-seasonal scales. This study aims to contribute to a better understanding of these changes across space and time by analysing to what degree observed climatic trends can be attributed to changes in synoptic atmospheric circulation. The relative importance of synoptic circulation changes (i.e. trends in synoptic type frequencies) as opposed to trends in the hydrothermal prop-erties of synoptic types (within-type trends) on precipitation and temperature trends in Europe is assessed on a monthly basis. The study is based on mapping spatial and temporal trend patterns and their variability at a relatively high res-olution (0.5◦ × 0.5◦; monthly) across Europe. Gridded pre-cipitation and temperature data (1963–2001) originate from the Watch Forcing Data set and synoptic types are defined
A European pattern climatology 1766–2000
Climate Dynamics, 2007
Using monthly independently reconstructed gridded European fields for the 500 hPa geopotential height, temperature, and precipitation covering the last 235 years we investigate the temporal and spatial evolution of these key climate variables and assess the leading combined patterns of climate variability. Seasonal European temperatures show a positive trend mainly over the last 40 years with absolute highest values since 1766. Precipitation indicates no clear trend. Spatial correlation technique reveals that winter, spring, and autumn covariability between European temperature and precipitation is mainly influenced by advective processes, whereas during summer convection plays the dominant role. Empirical Orthogonal Function analysis is applied to the combined fields of pressure, temperature, and precipitation. The dominant patterns of climate variability for winter, spring, and autumn resemble the North Atlantic Oscillation and show a distinct positive trend during the past 40 years for winter and spring. A positive trend is also detected for summer pattern 2, which reflects an increased influence of the Azores High towards central Europe and the Mediter-ranean coinciding with warm and dry conditions. The question to which extent these recent trends in European climate patterns can be explained by internal variability or are a result of radiative forcing is answered using cross wavelets on an annual basis. Natural radiative forcing (solar and volcanic) has no imprint on annual European climate patterns. Connections to CO 2 forcing are only detected at the margins of the wavelets where edge effects are apparent and hence one has to be cautious in a further interpretation.
Atmospheric circulation and surface temperature in Europe from the 18th century to 1995
International Journal of Climatology, 2001
The relationship between surface atmospheric circulation and temperature in Europe from the 1770s to 1995 is examined using correlation analysis. The atmospheric circulation is represented by six indices: the three leading principal components (PCs) of an empirical orthogonal function (EOF) analysis of 20 European pressure series from 1822 to 1995, which represent the central tendency of European pressure (EOF 1), a zonal circulation pattern (EOF 2) and a meridional pattern (EOF 3), a North Atlantic zonal index constructed from Gibraltar and Reykjavik pressure series for 1821-1995; a Western European zonal index constructed from Madrid, Barcelona, Lund and Trondheim for 1786-1995; and an index constructed from Paris and London, 1774-1995. Eight long temperature series from northwestern and central Europe were correlated with these circulation indices. European temperatures in general had the highest correlations with the zonal circulation indices in winter, with almost 70% of the variability in the temperature records explained by variations in the zonal index. The correlation coefficients between PC 3 (representing meridional circulation) and temperatures were highest in spring and autumn, particularly for Scandinavia. Running correlation series calculated over 25-year windows reveal significant non-stationarities in the relationship between surface temperature and atmospheric circulation on decadal time scales, suggesting caution must be used in extrapolating current relationships between circulation and temperature for future climate predictions based on downscaling or past palaeoclimatic reconstructions.
Spatial and Temporal Variations of Climate in Europe
Atmospheric and Climate Sciences, 2012
Temperature series of the original individual measurements of the minimum and maximum daily temperatures from 24 stations located in different regions of Europe are considered with the objective of studying the stability or the variability of the "climate" in time and space. The patterns of the temperature statistics, the shapes of probability density functions, in particular, at different places and times allow comparisons based on the Kolmogorov-Smirnov test, the Shannon entropy, and cluster analysis, used separately or in combination for the purposes of quantitative climate classification.
International Journal of Climatology, 2007
This study investigates the importance of large-scale atmospheric circulation changes for Central European climate variations during the last two centuries. On the basis of an objective classification of monthly mean sea level pressure (SLP) grids reconstructed back to 1780 and monthly historical station data for the same period, temperature and precipitation changes in Central Europe since 1780 are decomposed into two parts; one part due to frequency changes of large-scale circulation types, and the other part caused by (dynamic and climatic) changes within these circulation types. This is achieved by applying a particular decomposition scheme for moving 31-year time windows during the 1780-1995 period. Results indicate that large parts of the long-term variations in Central European climate cannot be explained sufficiently by frequency changes of circulation types. Roughly one half of these variations -even up to 80% during July -can be ascribed to varying internal properties of some major circulation types. Percentages of frequency-related and within-typerelated climate changes are seen to vary on decadal to multidecadal time scales, thus implying that relationships between large-scale circulation patterns and regional climates are characterised by distinct instationarities. Furthermore, regional climate variations, being attributable to within-type changes of major circulation types, can only partly be explained by corresponding variations in dynamic properties (vorticity, intensity) of these circulation types. This points to the importance of further sources for within-type variability, including subgrid-scale processes, synoptic-scale variations, and modifications of the climatic boundary conditions.
Emerging regional climate change signals for Europe under varying large-scale circulation conditions
Climate Research, 2013
A large ensemble of regional climate model projections was investigated regarding if and when they show an emergence of significant climate change signals in seasonal temperature and precipitation within Europe. The influence of the North Atlantic Oscillation (NAO), as simulated in the projections, was investigated. In most parts of Europe, the projections indicate robust emergence of temperature change in the first 2 decades of the 21st century, typically earlier for summer than for winter. For precipitation changes, signals generally emerge much later than for temperature. For Europe as a whole, the precipitation signals tend to emerge some 40 to 60 yr later than the temperature signals. In some sub-regions, robust signals for precipitation are not found within the studied period, i.e. until 2100. Some sub-regions, notably the Mediterranean area and Scandinavia, show different behaviour in some aspects compared to the ensemble-based results as a whole. NAO has some influence on the temperature change signals, which emerge earlier in winter for some models and regions if NAO is accounted for. For summer temperatures, the influence of NAO is less evident. Similarly, for precipitation, accounting for NAO leads to an earlier emergence in some regions and models. Here, we find an impact for both summer and winter.