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

Abstract

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.

The relation between circulation types and regional Alpine climate. Part II: the dependence of the predictive skill on the vertical level of the classification for Trentino

“…Looking for the vertical layer which provides the highest predictive skill, this study is the natural continuation of Panziera et al (), from now on P15, who developed a synoptic climatology of Trentino by using the same classification method of Beck () and the same data set of this study. In fact, they showed that even though most circulation types exhibit distinct seasonal anomalies of mean daily temperature, daily rainfall, daily solar irradiation and mean daily wind intensity, their magnitude varies not only among weather types but also within the same type for different seasons and vertical levels.…”

“…A database of the numerous circulation type classifications available for Europe has been recently developed within the COST Action 733 (e.g. Philipp et al, 2010).…”

“…The extent to which classifications reach these goals determines their practical efficiency, which ultimately depends on how strict is the relation between the circulation types and the target variable. Different terms were used by several authors to denominate this ability of a synoptic classification: discriminative power (Beck and Philipp, 2010), synoptic-climatological applicability (Huth, 2010), predictive capability (Schiemann and Frei, 2010), within-type variability (e.g. Beck et al, 2007), synoptic skill (Beck et al, 2013).…”

“…Several studies quantitatively assess the predictive skill of circulation classifications for various atmospheric quantities by using different metrics (e.g. Yarnal, 1993;Brinkmann, 1999;Beck and Philipp, 2010;Huth, 2010;Schiemann and Frei, 2010;Beck et al, 2013;Casado and Pastor, 2013). In general, they show that the predictive skill varies significantly not only among the methods and for different target variables but also within the same method and target variable, depending on other factors such as the geographical region, the season, the spatial domain used for the classification, the number of circulation types, the number of variables and the period considered for the classification.…”

Estimating Hourly Beam and Diffuse Solar Radiation in an Alpine Valley: A Critical Assessment of Decomposition Models

“…To this respect, the usefulness of the locally-calibrated decomposition model could be tested, e.g., for the assessment of the solar resource in the surrounding Alpine valleys (cf. [57]), as well as for the improvement of local solar radiation forecasts, in connection with weather forecasting schemes based on climatological analogs for the region of interest (e.g., [84,85]). …”