Atmospheric circulations associated to the interannual variability of cumulonimbus cloud frequency in the southern part of Romania

Annual and seasonal maximum daily rainfall time series from 44 rain gages in Romania, Ukraine, and Moldova are used to examine questions related to the validity of the stationarity assumption, the dependence of extreme rainfall on elevation, and its upper tail properties during the 20th century. Analyses are performed both at the annual and seasonal scales. The validity of the stationarity assumption is examined by testing the records for abrupt and slowly varying changes. The presence of change-points in the mean and variance of the daily maximum rainfall distribution is assessed using the nonparametric Pettitt test, while the presence of monotonic patterns is examined using the nonparametric Mann-Kendall and Spearman tests. These results indicate that most of the violations of the stationarity assumption are related to abrupt rather than slowly varying changes, and that it is difficult to detect an anthropogenic climate change signal in these records. The generalized extreme value (GEV) distribution is used as modelling framework to investigate the dependence of extreme rainfall on elevation and its upper tail properties. Both at the annual and seasonal scales there is no strong dependence of the parameters of the GEV distribution on elevation. These records point to an unbounded-above and heavy-tail behaviour, and discussion of these upper tail properties in light of mixtures of different rainfall-generating mechanisms is provided.

Section: Methodsmentioning

confidence: 97%

Analyses of annual and seasonal maximum daily rainfall accumulations for Ukraine, Moldova, and Romania

Villarini

2011

“…Obtaining synoptic patterns associated with particular weather conditions contributes to a wide range of purposes (climatological studies, weather forecasting, biometeorology, environmental studies), and in recent years several authors have established the impact of different circulation types on convective activity (Kolendowicz, 2006;Paraschivescu et al, 2012), and lightning activity (Tomás et al, 2004;Mikus et al, 2012). In particular, Ramos et al (2011) reported that the highest number of CG lightning flashes in Portugal was associated with northeastern circulation over Portugal due to an extension * Correspondence to: Dr. L. Rivas Soriano, Departamento de Física de la Atmósfera, Facultad de Ciencias, Universidad de Salamanca, Pl.…”

Section: Introductionmentioning

confidence: 99%

Atmospheric background associated with severe lightning thunderstorms in Central Spain

Mora

Riesco

Dávila

et al. 2014

A study of electrically severe thunderstorms (>2000 cloud-to-ground flashes per day) in the Spanish territory of Castilla-Leon (northern plateau of the Iberian Peninsula) has been performed using 11 years (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010) of data. These episodes were classified according to average upper-level synoptic patterns. Seven synoptic patterns emerged: shortwave and very shortwave troughs, three types of lows, cyclonic vortex and ridge. The moisture content at low levels and static instability were also considered. In general, all the episodes were associated with instability and moderate moisture (11 g kg −1 for the average mixing ratio at 925 hPa). The electrically severe thunderstorms associated with five synoptic patterns (shortwave and very shortwave troughs, and three types of lows) generated hail, strong winds, and intense precipitation. By contrast, the cyclonic vortex and ridge synoptic types were not associated with severe weather.

“…The winter season is characterized by large‐scale weather patterns that are better captured by the climate indices, in particular NAO. On the other hand, summertime precipitation is associated with convective activity (Paraschivescu et al , 2011), that is more spatially localized and less directly related to NAO or SOI. Moreover, different covariates are retained depending on the season, with NAO that is mostly related to fall–winter rainfall, while SOI to spring–summer rainfall (see also Busuioc and von Storch, 1996; Van Oldenborgh et al , 2000; Mares et al , 2002; Lloyd‐Hughes and Saunders, 2002; Tomozeiu et al , 2005).…”

Section: Resultsmentioning

confidence: 99%

Development of statistical models for at‐site probabilistic seasonal rainfall forecast

Villarini

Serinaldi

2011

A probabilistic seasonal rainfall forecasting system for the Bucharest-Filaret (Romania) station based on Generalized Additive Models in Location, Scale and Shape (GAMLSS) is proposed. First we develop statistical models to describe seasonal rainfall over the period 1926-2000, both considering the seasonal record as a continuous time series and accounting for seasonal changes, and by developing ad hoc models for each individual season. The Southern Oscillation Index (SOI), the North Atlantic Oscillation (NAO) and the seasonal rainfall for the previous year are included as possible covariates. Model selection is performed with respect to two penalty criteria [Akaike Information Criterion (AIC) and Schwarz Bayesian Criterion (SBC)], each of them leading to different final model configurations in terms of predictors and their functional relation to the parameters of the probability distribution. Retrospective forecast, in which the parameters of the models are re-estimated every time new information becomes available, is performed on a yearly basis for the period 1986-2000. The quality of the forecasts is assessed in terms of several accuracy measures and by visual examination of the forecasts' probability distributions. The best forecasts are obtained for the winter season. While it is not possible to identify a single 'best' model according to all the forecast measures, we recommend using the model that considers the seasonal rainfall as a continuous time series and penalized with respect to AIC.