Monitoring snow avalanches with seismic stations in north-eastern Italy: a test case

The Regional Agency for the Environmental Prevention and Protection of Veneto (Agenzia Regionale per la Prevenzione e Protezione Ambientale del Veneto, ARPAV) was established in October 2007 to monitor and prevent environmental risks in the Veneto region, in north-eastern Italy. The Italian National Institute for Oceanography and Experimental Geophysics (Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, OGS), after the strong earthquake (magnitude M=6.4) occurred in 1976 in the Friuli-Venezia Giulia region, started to operate the North- East Italy (NI) seismic network: it currently consists of 11 very sensitive broad band seismic stations and 21 more simple short period seismic stations, all acquired in real time. OGS also exchanges seismic data with other Italian, Austrian and Slovenian agencies in the surrounding areas, which gives a total number of 73 stations acquired in real time. This makes the OGS the reference agency for the monitoring of the seismic activity in north-eastern Italy. Detecting avalanches by means of seismic stations is indeed a difficult job because of the poor snow-to-earth coupling and the high dumping of the snow. In June 2007 OGS installed in cooperation with the Italian National Institute for Geophysics and Volcanology (Istituto Nazionale di Geofisica e Vulcanologia, INGV) a broad band seismic station in Agordo, a site located on the Dolomites mountains in Veneto. In the first half of December 2008, the Southern Alps have been affected by 2 episodes of intense snowfall: in the whole Dolomites, above the altitude of 1200 m, between 250 and 350 cm of fresh snow have fallen: similar snowfall events occurred in the last 80 years only in December 1979, 1960, 1959 and 1951. The large amount of snow fell in the 2 episodes, on November 28th - December 6th and on December 10th-17th, failed to consolidate and for several days over a large part of the Alps the danger of avalanches was high (grade 4 out of 5 of the European level system). In the Dolomites, the area of interest of this work, the spontaneous avalanche phenomena was very intense, both during the snowfalls and subsequently. During the 2 periods several large avalanches have fallen reaching the bottom of the valley and were detected by the seismic stations: avalanches of such characteristics were not observed since 1987 (January) and 1977 (February). Given the intensity of the snowfalls, it has not been possible to date all the big avalanches, but only those closest to the towns. In this work we analyze the seismic recordings and relate them to the main characteristics of the avalanches

The influence of the synoptic regime on stable water isotopes in precipitation at Dome C, East Antarctica

Abstract. The correct derivation of paleotemperatures from ice cores requires exact knowledge of all processes involved before and after the deposition of snow and the subsequent formation of ice. At the Antarctic deep ice core drilling site Dome C, a unique data set of daily precipitation amount, type, and stable water isotope ratios is available that enables us to study in detail atmospheric processes that influence the stable water isotope ratio of precipitation. Meteorological data from both automatic weather station and a mesoscale atmospheric model were used to investigate how different atmospheric flow patterns determine the precipitation parameters. A classification of synoptic situations that cause precipitation at Dome C was established and, together with back-trajectory calculations, was utilized to estimate moisture source areas. With the resulting source area conditions (wind speed, sea surface temperature, and relative humidity) as input, the precipitation stable isotopic composition was modeled using the so-called Mixed Cloud Isotope Model (MCIM). The model generally underestimates the depletion of 18O in precipitation, which was not improved by using condensation temperature rather than inversion temperature. Contrary to the assumption widely used in ice core studies, a more northern moisture source does not necessarily mean stronger isotopic fractionation. This is due to the fact that snowfall events at Dome C are often associated with warm air advection due to amplification of planetary waves, which considerably increases the site temperature and thus reduces the temperature difference between source area and deposition site. In addition, no correlation was found between relative humidity at the moisture source and the deuterium excess in precipitation. The significant difference in the isotopic signal of hoarfrost and diamond dust was shown to disappear after removal of seasonality. This study confirms the results of an earlier study carried out at Dome Fuji with a shorter data set using the same methods

Precipitation and synoptic regime in two extreme years 2009 and 2010 at Dome C, Antarctica - implications for ice core interpretation

At the East Antarctic deep ice core drilling site Dome C, daily precipitation measurements were initiated in 2006 and are being continued until today. The amounts and stable isotope ratios of the precipitation samples as well as crystal types are determined. Within the measuring period, the two years 2009 and 2010 showed striking contrasting temperature and precipitation anomalies, particularly in the winter seasons. The reasons for these anomalies are analysed using data from the mesoscale atmospheric model WRF (Weather Research and Forecasting Model) run under the Antarctic Mesoscale Prediction System (AMPS). 2009 was relatively warm and moist due to frequent warm air intrusions connected to amplification of Rossby waves in the circumpolar westerlies, whereas the winter of 2010 was extremely dry and cold. It is shown that while in 2010 a strong zonal atmospheric flow was dominant, in 2009 an enhanced meridional flow prevailed, which increased the meridional transport of heat and moisture onto the East Antarctic plateau and led to a number of high-precipitation/warming events at Dome C. This was also evident in a positive (negative) SAM (Southern Annular Mode) index and a negative (positive) ZW3 (zonal wave number three) index during the winter months of 2010 (2009). Changes in the frequency or seasonality of such event-type precipitation can lead to a strong bias in the air temperature derived from stable water isotopes in ice cores

Modelling stable water isotopes during “high-precipitation” events at Dome C, Antarctica

For a correct paleoclimatologic interpretation of stable water isotopes from ice cores both pre- and postdepositional processes and their role for isotope fractionation have to be better understood. Our study focuses on “pre-depositional processes”, namely the atmospheric processes that determine moisture transport and precipitation formation. At the deep ice core drilling site "Dome C", East Antarctica, fresh snow samples have been taken since 2006. These samples have been analysed crystallographically, which enables us to clearly distinguish between blowing snow, diamond dust, and "synoptic precipitation". Also the stable oxygen/hydrogen isotope ratios of the snow samples were measured, including measurements of 17-O. This is the first and only multi-year fresh-snow data series from an Antarctic deep drilling site. The Antarctic Mesoscale Prediction System (AMPS) employs Polar WRF for aviation weather forecasts in Antarctica. The data are archived and can be used for scientific purposes. The mesoscale atmospheric model was adapted especially for polar regions. The horizontal resolution for the domain that covers the Antarctic continent is 10 km. It was shown that precipitation at Dome C is temporally dominated by diamond dust. However, comparatively large amounts of precipitation are observed during several “high-precipitation” events per year, caused by synoptic activity in the circumpolar trough and related advection of relatively warm and moist air from lower latitudes to the interior of Antarctica. AMPS archive data are used to investigate the synoptic situations that lead to “high-precipitation” events at Dome C; in particular, possible moisture sources are determined using back-trajectories. With this meteorological information, the isotope ratios are calculated using two different isotope models, the Mixed Cloud Isotope Model, a simple Rayleigh-type model, and the LMDZ-iso (Laboratoire de Météorologie Dynamic Zoom), a General Circulation Model (GCM) with implementation of stable isotopes. The results are compared to the measured stable isotope ratios of the fresh snow samples

Three-year monitoring of stable isotopes of precipitation at Concordia Station, East Antarctica

Past temperature reconstructions from Antarctic ice cores require a good quantification and understanding of the relationship between snow isotopic composition and 2m air or inversion (condensation) temperature. Here, we focus on the French-Italian Concordia Station, central East Antarctic plateau, where the European Project for Ice Coring in Antarctica (EPICA) Dome C ice cores were drilled. We provide a multi-year record of daily precipitation types identified from crystal morphologies, daily precipitation amounts and isotopic composition. Our sampling period (2008-2010) encompasses a warmer year (2009, +1.2 degrees C with respect to 2m air temperature long-term average 1996-2010), with larger total precipitation and snowfall amounts (14 and 76% above sampling period average, respectively), and a colder and drier year (2010, -1.8 degrees C, 4% below long-term and sampling period averages, respectively) with larger diamond dust amounts (49% above sampling period average). Relationships between local meteorological data and precipitation isotopic composition are investigated at daily, monthly and inter-annual scale, and for the different types of precipitation. Water stable isotopes are more closely related to 2m air temperature than to inversion temperature at all timescales (e.g. R-2 = 03 and 0.44, respectively for daily values). The slope of the temporal relationship between daily delta O-18 and 2m air temperature is approximately 2 times smaller (0.49 parts per thousand degrees C-1) than the average Antarctic spatial (0.8 parts per thousand degrees C-1) relationship initially used for the interpretation of EPICA Dome C records. In accordance with results from precipitation monitoring at Vostok and Dome F, deuterium excess is anticorrelated with delta O-18 at daily and monthly scales, reaching maximum values in winter. Hoar frost precipitation samples have a specific fingerprint with more depleted delta O-18 (about 5% below average) and higher deuterium excess (about 8% above average) values than other precipitation types. These datasets provide a basis for comparison with shallow ice core records, to investigate post-deposition effects. A preliminary comparison between observations and precipitation from the European Centre for Medium-RangeWeather Forecasts (ECMWF) reanalysis and the simulated water stable isotopes from the Laboratoire de Meteorologie Dynamique Zoom atmospheric general circulation model (LMDZiso) shows that models do correctly capture the amount of precipitation as well as more than 50% of the variance of the observed delta O-18, driven by large-scale weather patterns. Despite a warm bias and an underestimation of the variance in water stable isotopes, LMDZiso correctly captures these relationships between delta O-18, 2m air temperature and deuterium excess. Our dataset is therefore available for further in-depth model evaluation at the synoptic scale

Monitoring snow avalanches with seismic stations in north-eastern Italy: a test case

The Regional Agency for the Environmental Prevention and Protection of Veneto (Agenzia Regionale per la Prevenzione e Protezione Ambientale del Veneto, ARPAV) was established in October 2007 to monitor and prevent environmental risks in the Veneto region, in north-eastern Italy. The Italian National Institute for Oceanography and Experimental Geophysics (Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, OGS), after the strong earthquake (magnitude M=6.4) occurred in 1976 in the Friuli-Venezia Giulia region, started to operate the North- East Italy (NI) seismic network: it currently consists of 11 very sensitive broad band seismic stations and 21 more simple short period seismic stations, all acquired in real time. OGS also exchanges seismic data with other Italian, Austrian and Slovenian agencies in the surrounding areas, which gives a total number of 73 stations acquired in real time. This makes the OGS the reference agency for the monitoring of the seismic activity in north-eastern Italy. Detecting avalanches by means of seismic stations is indeed a difficult job because of the poor snow-to-earth coupling and the high dumping of the snow. In June 2007 OGS installed in cooperation with the Italian National Institute for Geophysics and Volcanology (Istituto Nazionale di Geofisica e Vulcanologia, INGV) a broad band seismic station in Agordo, a site located on the Dolomites mountains in Veneto. In the first half of December 2008, the Southern Alps have been affected by 2 episodes of intense snowfall: in the whole Dolomites, above the altitude of 1200 m, between 250 and 350 cm of fresh snow have fallen: similar snowfall events occurred in the last 80 years only in December 1979, 1960, 1959 and 1951. The large amount of snow fell in the 2 episodes, on November 28th - December 6th and on December 10th-17th, failed to consolidate and for several days over a large part of the Alps the danger of avalanches was high (grade 4 out of 5 of the European level system). In the Dolomites, the area of interest of this work, the spontaneous avalanche phenomena was very intense, both during the snowfalls and subsequently. During the 2 periods several large avalanches have fallen reaching the bottom of the valley and were detected by the seismic stations: avalanches of such characteristics were not observed since 1987 (January) and 1977 (February). Given the intensity of the snowfalls, it has not been possible to date all the big avalanches, but only those closest to the towns. In this work we analyze the seismic recordings and relate them to the main characteristics of the avalanches.PublishedVienna, Austria1.8. Osservazioni di geofisica ambientaleope