Circulation types related to lightning activity over Catalonia and the Principality of Andorra

This study evaluates the classifications of atmospheric circulation patterns collected in the COST733 database (COST733cat) in terms of their ability to stratify daily surface temperature and precipitation in 12 domains covering the whole of Europe. The classifications differ in the classification methods used, in the number of types, the variable(s) classified, the number of days in a sequence that are classified and in whether the classification is based on year-round or seasonal data. Several classification methods that perform fairly well are identified; they include a simple k-means clustering, a k-means clustering preceded by hierarchical cluster analysis, Litynski's method, and a classification based on circulation prototypes. On the other hand, there are a couple of classification methods that do not provide a good stratification of temperature and precipitation: orthogonally and obliquely rotated principal component analysis in a T-mode, Lund's correlation method, Kirchhofer's sums-of-squares method, and Erpicum's method. Some methods tend to perform better on large domains, while others tend to perform better on smaller domains; however, the sensitivity of most classification methods to the domain size appears to be small. Several methods exhibit a geographical dependence of their performance, e.g. the method based on circulation prototypes tends to perform better in the northern domains, while Jenkinson-Collison and Erpicum's methods perform better in the southern domains. Classifications of 4-day sequences are usually better in stratifying surface temperature than ordinary instantaneous classifications; the opposite is true for precipitation. Adding a mid-tropospheric variable (500 hPa heights or 1000/500 hPa thickness) to sea level pressure as a classified variable improves the skill of classifications in stratifying temperature.

Section: General Issuesmentioning

confidence: 99%

Synoptic‐climatological evaluation of the classifications of atmospheric circulation patterns over Europe

Huth

Beck

Kučerová

2015

“…Trigo and DaCamara, ; Goodess and Jones, ; Kyselý, ; Lupikasza, ; Penalba et al ., ; Plavcová et al ., ; Ramos et al ., ) or atmospheric phenomena (e.g. Vicente‐Serrano and López‐Moreno, ; Leckebusch et al ., ; Kassomenos, ; Pineda et al ., ; Hoffmann and Schlünzen, ; Wastl et al ., ). In most of the papers dealing with Alpine climate, however, the synoptic analysis is limited to single case studies or to a number of events sharing some common features, mainly the occurrence of intense precipitation.…”

Section: Introductionmentioning

confidence: 99%

The relation between circulation types and regional Alpine climate. Part I: synoptic climatology of Trentino

Panziera

Giovannini

Laiti

et al. 2015

A comprehensive data set of surface temperature, rainfall, solar radiation and wind measurements was composed to investigate the relation between synoptic circulation types and the climate of Trentino, a mountainous region in the South-Eastern Alps. Synoptic patterns are classified over different levels by means of an existing classification method according to their degree of zonality, meridionality and vorticity. Distinct seasonal anomalies of mean daily temperature, total daily rainfall, daily solar irradiation and mean daily wind intensity are associated with most circulation types. Their magnitude varies not only among weather types, but also within the same type for different isobaric levels and seasons. The largest positive temperature anomalies are observed in correspondence with high-pressure and westerly circulations, whereas southerly circulation in the upper levels and low-pressure systems at lower altitudes produce the largest positive deviations of daily rainfall. Daily solar irradiation and mean daily wind intensity are larger than average with northerly circulations. Particular emphasis is given to extreme meteorological events, which occur with preferential circulation types. In fact, the frequency of occurrence of extremes of any variable for each synoptic pattern rarely coincides with the climatological value. Even though extremes in daily rainfall are observed with almost all synoptic circulations, most of them occur with the south-westerly circulation at 500 hPa, a frequent configuration contributing more than 50% to the total rainfall. Moreover, they occur with a larger variety of weather types at the lower levels and in spring and summer with respect to the upper levels and the colder seasons. The large number of statistical indices presented in this paper reveals that the climate of Trentino is strongly influenced not only by the synoptic circulation, but also by the mesoscale mechanisms resulting from the interaction of the large-scale flow with the local orography.

“…We intend to make the best use of this catalogue and perform an objective comparison on the ability of each classification to explain wildfire variability in the IP domain. Numerous objective comparisons for the catalogue have been performed on several areas of study, such as heavy precipitation occurrence (Lupikasza, 2010;Twardosz, 2010), extreme values of air temperature (Ustrnul et al, 2010), lightning activity (Pineda et al, 2010), air pollution (Lésniok et al, 2010. Preliminary works relating WTC with wildfire occurrences have been developed for Iberia (Rasilla et al, 2010) and Greece (Kassomenos, 2010).…”

Section: Introductionmentioning

confidence: 99%

Modelling wildfire activity in Iberia with different atmospheric circulation weather types

Trigo

Sousa

Pereira

et al. 2013

106

This work focuses on the spatial and temporal variability of burnt area (BA) in the entire Iberian Peninsula (IP) and on the construction of statistical models to reproduce the inter‐annual variability. A novel common dataset was assembled for the whole IP by merging the registered BA from 66 administrative regions of both Portugal and Spain. We applied a cluster analysis to identify larger regions with similar fire regimes and results point to the existence of four clusters (Northwestern, Northern, Southwestern and Eastern) whose spatial patterns and seasonal fire regimes are shown to be related with constraining factors such as topography, vegetation cover and climate conditions. The relationship between BA at monthly time scale with both long‐term climatic pre‐conditions and short‐term synoptic forcing was assessed using correlation and regression analysis based on: (1) temperature and precipitation from 2 to 7 months in advance to fire peak season, (2) synoptic weather patterns derived from 11 distinct Weather Types Classifications (WTC). Different relations were obtained for each IP region with a relevant link being identified between BA and short‐term synoptic forcing for all clusters, while the relation with long‐term climatic preconditioning was relevant for all but one cluster. Stepwise regression models based on the best climatic and synoptic circulation predictors were developed with cross‐validation to avoid over fitting. The performance of the models varies within IP regions, though models exclusively based on WTC tend to better reproduce the annual BA time series than those merely based on pre‐conditioning climatic information. Nevertheless, the use of both synoptic and climatic predictors provides the best results, particularly for the two western clusters, with Pearson correlation coefficient values higher than 0.7. Finally, it is shown that typical synoptic configurations that favour high values of BA correspond to dry and warm wind flows associated with anti‐cyclonic regimes.