Synoptic control over winter snowfall variability observed in a remote site of Apennine Mountains (Italy), 1884–2015

Abstract

Abstract. This work presents a new, very long snowfall time series collected in a remote site of Italian Apennine mountains (Montevergine Observatory, 1280 m above sea level). After a careful check, based on quality control tests and homogenization procedures, the available data (i.e. daily height of new snow) have been aggregated over winter season (December–February) to study the long-term variability for the period 1884–2020. The main evidence emerging from this analysis lies in (i) the strong interannual variability of winter snowfall amounts, (ii) the absence of a relevant trend from the late 19th century to the mid-1970s, (iii) the strong reduction in the snowfall amount and frequency of occurrence from the mid-1970s to the end of the 1990s and (iv) the increase in average snowfall amount and frequency of occurrence in the past 20 years. Moreover, this study shed light on the relationship between the snowfall variability observed in Montevergine and the large-scale atmospheric circulation. Six different synoptic types, describing the meteorological scenarios triggering the snow events in the study area, have been identified by means of a cluster analysis, using two essential atmospheric variables, the 500 hPa geopotential height and the sea level pressure (both retrieved from the third version of the Twentieth Century Reanalysis dataset, which is available for the 1884–2015 period). Such patterns trace out scenarios characterized by the presence of a blocking high-pressure anomaly over Scandinavia or the North Atlantic and by a cold air outbreak involving both maritime and continental cold air masses. A further analysis demonstrates that the identified synoptic types are strongly related with different teleconnection patterns, i.e. the Arctic Oscillation (AO), the Eastern Atlantic Western Russia (EAWR), the Eastern Mediterranean Pattern (EMP), the North Atlantic Oscillation (NAO) and the Scandinavian pattern (SCAND), that govern the European winter atmospheric variability. The relevant decline in snowfall frequency and amounts between the 1970s and 1990s can be mainly ascribed to the strong positive trend of AO and NAO indices, which determined, in turn, a decrease in the incidence of patterns associated with the advection, in central Mediterranean area, of moist and cold arctic maritime air masses. The recent increase in average snowfall amounts can be explained by the reverse trend of the AO index and by the prevalence of a neutral or negative EAWR pattern.

Diverging snowfall trends across months and elevation in the northeastern Italian Alps

“…Notice that during that year a temporary decrease in average European temperatures was registered (Cattiaux et al ., 2010; Seager et al ., 2010; Wang et al ., 2010). In the most recent years a tendency toward a positive phase of both NAO and AO has been observed (Capozzi et al ., 2021).…”

“…As further potential drivers of HN variability, the 1980–2020 monthly series of NAO and AO were retrieved from the National Oceanic and Atmospheric Administration (NOAA) website (https://psl.noaa.gov/data/climateindices/list). These indices are called “teleconnection indices” and are used as descriptive parameters of the synoptic conditions that can occur over Europe, especially from autumn to spring (Bartolini et al ., 2010; Capozzi et al ., 2021). We selected NAO and AO since those indices explain most of the Alpine precipitation variance (Quadrelli et al ., 2001).…”

On the role of local and large-scale atmospheric variability in snow cover duration: a case study of Montevergine Observatory (Southern Italy)

“…/phase (associated with a weak polar vortex allowing cold air outbreaks across mid-latitudes(Thompson and Wallace 1998)) and the positive EMP pattern (characterized by positive 500-hPa geopotential height anomalies over northern Atlantic and by negative anomalies over Central and Eastern Mediterranean basins(Hatzaki et al (2007)) are both synonymous of synoptic weather types that promote snowfall events in Montevergine as recently demonstrated inCapozzi et al (2022). The strong impact that AO and EMP indices have on local weather conditions is highlighted in table…”

“…Recent studies have employed snowfall data collected at Montevergine Observatory. For instance, Capozzi et al (2022) examined the winter variability of fresh snow depth for the period 1884-2020 and performed a cluster analysis to identify the meteorological scenarios that triggered the snow events. In Diodato et al (2022), annual snow cover duration values recorded at this site from 1952 to 1996 were used to develop a semi-empirical model relating this variable to meteorological conditions and elevation inputs.…”

“…To investigate about the relationship between large-scale atmospheric circulation and SCD variability in Montevergine, we have selected several large-scale patterns that are known to exert a relevant influence on Central Mediterranean area (Brunetti and Kutiel 2011, Caloiero et al 2011, Capozzi et al 2022. The large-scale patterns considered in this work are: the North Atlantic Oscillation (NAO), the Arctic Oscillation (AO), the Eastern Mediterranean Pattern (EMP), the Atlantic Multidecadal Variability (AMV), the Mediterranean Circulation (MC), the Western European Zonal Circulation (WEZC) and the North Sea-Caspian Pattern (NCP).…”