High Mountain Station Research Articles

Constructing a long‐term monthly climate data set in central Asia

ABSTRACTWe compiled and merged in situ observation data from several sources, creating a comprehensive unified monthly air temperature and precipitation data set with 457 stations in central Asia (CA). Stations with a valid data rate higher than 80% were selected, and the remaining gaps in selected station time series were filled with an iterative‐principal component analysis (PCA) gap‐filling method. The result is a gap‐filled station data set for the period 1951–2010, with 369 and 381 stations for air temperature and precipitation, respectively. The cross‐validation shows that the iterative‐PCA gap‐filling algorithm provides stable and trustworthy estimations of gaps, with mean root mean squared error (RMSE) of 0.03 °C (in the range of 0.01–0.13 °C) for air temperature, and mean RMSE of 0.60 mm (in the range of 0.10–1.99 mm) for precipitation. A gridded data set was created by interpolating the gap‐filled station data set with the geographically weighted regression method. Comparison of the gridded data set with the National Centers for Environmental Prediction (NCEP) reanalysis data set shows that though both data sets present the long‐term mean climate situation similarly, the gridded data set exhibits less annual and monthly variability. And the gridded data set has stronger correlations with stations time series than the reanalysis data set (mean correlations are 0.994 vs 0.975 for air temperature, and 0.787 vs 0.515 for precipitation), especially for precipitation in high mountain stations. The gridded data set is more suitable for climate and hydrological studies in CA, especially in high mountains regions.

Influence of air mass origins on optical properties and PM concentrations measured at a high mountain station located in the southwestern Mediterranean

The influence of air mass origins on aerosol optical properties and particulate matter (PM) concentrations measured from January 2014 to December 2015 at a high mountain station in the southwestern Mediterranean was analyzed. Mean values of extensive aerosol optical properties (scattering, backscattering and absorption coefficients) and PM mass fractions: σsp (30.7±1.1Mm−1), σbsp (3.9±0.1Mm−1), σap (2.4±0.1Mm−1), PM10 (13.1±0.6μg·m−3) and PM1 (4.0±0.1μg·m−3) were in the range of values reported in most studies carried out at high altitude locations. Nevertheless, a significant variation of these concentrations according to the air mass origin has been noticed. Transport from North Africa (NAF back-trajectories) and regional recirculations (REG) were the two air mass types in which the highest values of PM concentrations and optical properties were registered. Alternatively, the lowest values were recorded under Atlantic advections. Noticeable differences between NAF and REG categories were observed when intensive optical properties of aerosols were analyzed. During NAF scenarios the lowest value of SAE (0.91±0.06) was obtained as well as the greatest AAE value (1.30±0.02), with daily levels higher than 1.90. This result suggests that OC and hematite compounds were relevant in the absorption process during NAF events. However, during REG episodes the AAE mean value declined to 1.18±0.01, since the highest mean concentration of BC was recorded under this category, and the SAE value was maximum (1.70±0.05) due to the smaller size of PM. It has also been documented that during the study period a great number of REG back-trajectories occurred just after the transport of air masses from North Africa. In these situations, AAE and SAE values showed slight variations due to the persistence of mineral dust in the local atmosphere.

Analysis of temperature variability in the mountain regions of the North Caucasus in 1961–2013

Annual and seasonal series of temperature values are analyzed using the data of Akhty, Teberda, and Terskol weather stations (the height above the sea level is >1000 m) for 1961-2013 as well as from 1976 to 2013 in order to reveal changes in the mountain climate in the period of contemporary global warming. Mean values, standard deviations, norms, and anomalies of annual and seasonal values of temperature as well as the rate of their variation in the mentioned periods are obtained. It is found that the temperature rise is observed in all seasons and for the year as a whole at the mountain weather stations except Terskol station. According to the results of studying temperature variability, Akhty and Teberda weather stations were united into the group “mountain weather stations” with the subsequent averaging of climatic variables. Terskol weather station was singled out as an independent high-mountain weather station.

Patterns and trends of high-impact weather in China during 1959–2014

Abstract. The spatial and temporal characteristics of the frequencies of four types of high-impact weather (HIW), i.e. snowfall, thunderstorms, fog and hailstorms, were analysed in China during 1959–2014. Results indicate a significant decrease in the number of snowfall days, thunderstorm days and thunderstorm spells in all six regions of China, with regional decreasing rates of 0.1–3.4 days, 1.6–5.1 days and 0.23–0.77 times per decade respectively. The number of foggy days, hailstorm days and snowfall spells decreased at rates of 0.2–1.8 days, 0.1–0.7 days and 0.14–0.44 times per decade respectively in almost all regions and fog and hailstorm spells decreased at rates of 0.06–0.17 and 0.001–0.043 times per decade respectively in most regions of China. Spatially, there was more snowfall in northeastern China and western China, and more thunderstorms in southern China and southwestern China. The number of fog events was larger in some high mountain stations, eastern China and central China. Hailstorms were concentrated on Qinghai–Tibet Plateau. Over the past 56 years, snowfall days, thunderstorm days and thunderstorm spells decreased in most parts of China, and hailstorm days decreased in northeastern China, most parts of northern China and Tibet, southern Qinghai and western Sichuan. The spatial trends of foggy days, foggy spells, snowfall spells and hailstorm spells were not significant in most parts of China. With global warming, some types of HIW are likely to increase in their intensities, so more mitigation and adaptation strategies are still essential for local government and the public in China.

Contribution of cosmic ray particles to radiation environment at high mountain altitude: Comparison of Monte Carlo simulations with experimental data

A numerical model for assessment of the effective dose due to secondary cosmic ray particles of galactic origin at high mountain altitude of about 3000 m above the sea level is presented. The model is based on a newly numerically computed effective dose yield function considering realistic propagation of cosmic rays in the Earth magnetosphere and atmosphere. The yield function is computed using a full Monte Carlo simulation of the atmospheric cascade induced by primary protons and α− particles and subsequent conversion of secondary particle fluence (neutrons, protons, gammas, electrons, positrons, muons and charged pions) to effective dose. A lookup table of the newly computed effective dose yield function is provided. The model is compared with several measurements. The comparison of model simulations with measured spectral energy distributions of secondary cosmic ray neutrons at high mountain altitude shows good consistency. Results from measurements of radiation environment at high mountain station - Basic Environmental Observatory Moussala (42.11 N, 23.35 E, 2925m a.s.l.) are also shown, specifically the contribution of secondary cosmic ray neutrons. A good agreement with the model is demonstrated.

Measurements of the atmospheric electric field under high-mountain conditions in the vicinity of Mt. Elbrus

The measurements of the atmospheric electric field potential gradient are analyzed simultaneously at the two high-mountain stations in the vicinity of Mt. Elbrus: Cheget Peak and Terskol Peak, as well as the Kyzburun mountain station located at the end of the Baksan ravine. A global component in the diurnal variation in the electric field is revealed: the morning minimum (01-04 UT) and the evening maximum (19-21 UT), which conforms to the unitary variation in the ionospheric potential, as well as the daylight maximum (08-12 UT) caused by the action of the local generators in the surface layer. The features of the seasonal variation in the electric field are studied.

PM1 variability and transport conditions between an urban coastal area and a high mountain site during the cold season

During late autumn and winter, the western Mediterranean basin is often affected by severe pollution episodes (SPE) caused by stagnant weather conditions that produce a notable increase in particulate matter (PM) levels. The main objective of the present study is to evaluate the impact of these episodes on the variability of PM1 concentrations at an urban and a high mountain station in the western Mediterranean. At the urban site, SPEs caused increases in PM1 levels of up to 20 μg m−3 at 20:00–21:00 UTC due to a decrease in the mixing layer depth during the evening rush hour. In contrast, the highest increments at the high mountain station (∼12 μg m−3) were observed around midday. Since there are little anthropogenic emissions in the surroundings of the mountain station, this was most likely the result of aerosol transport from coastal urban areas and photochemical formation of secondary particles during transport. The transport of air pollutants through a complex orography occurs under specific weather conditions.

Comparison of measured and modelled spectral UV irradiance at Izaña high mountain station: estimation of the underlying effective albedo

In this work, we have carried out a comparison study between measured and modelled direct and global ultraviolet (UV) (300–400 nm) spectral irradiances and the determination of the surface effective albedo at the high altitude Izana Observatory [IZO; 2400 m above sea level (a.s.l.)] located in Tenerife (Canary Islands, Spain). The spectral measurements were performed with a Bentham spectroradiometer during the Quality Assurance of Solar Ultraviolet Spectral Irradiance Measurements (QASUME) comparison campaign in June 2005. The simulations were obtained with the LibRadtran radiative transfer model. The model input parameters, such as total ozone and aerosol optical depth (AOD), were measured at IZO. The comparison between measured and modelled direct solar radiation component was made at 0.5 nm spectral resolution, showing excellent agreement, with differences below 5% for solar zenith angle (SZA) < 60°. These differences were attributed to the effect of the underlying surface albedo due to the frequent existence of a sea of clouds below the station altitude. The underlying surface albedo was determined using different methods. In spite of the variability of this parameter through the day due to the strong influence and variable structure of these underlying clouds, the mean of this effective surface albedo in the UV region gives a value between 0.2 and 0.5 in the UV range, 10 times higher than the local surface albedo (0.02–0.05).

Long-term dynamics of nival processes in the Khibiny Mountains

Period of warming is registered at Khibiny Mountains in the end of XX century. Sensible rise in temperature occur in winter. The one of general indicators of present climate changes is multiyear dynamic of nival processes not only for contrast high-mountain conditions but also for more temperate green belt. Compatible variability of both data sets from high-mountain (1050 m) and green belt (320 m) stations allows to full appreciation of present changes. The results of data evaluation shows stability of snow cover characteristics against changing of winter temperature conditions and avalanche activity.

3-year chemical composition of free tropospheric PM1 at the Mt. Cimone GAW global station – South Europe – 2165 m a.s.l.

Nocturnal organic and inorganic chemical characterization of fine (PM1) aerosol was carried out at the GAW global high mountain station of Mt. Cimone (CMN), from January 2009 to December 2011, in the framework of the EU-EUSAAR and ACTRIS programs. The station is located at the summit of the Northern Italian Apennines (2165 m a.s.l.) overlooking the polluted Po river basin and is considered representative of background conditions for Southern Europe/Northern Mediterranean.The concentrations of carbonaceous and ionic aerosol follow a typical seasonal trend, with maxima during summer and minima during winter. The average PM1 mass apportioned by the chemical analyses ranged between 1.2 ± 0.68 μg m−3 (winter) and 5.0 ± 2.7 μg m−3 (summer), with ca. 80% and 60%, respectively, accounted for by organic matter, mainly water-soluble (yearly average WSOC/TC ratio 0.67 ± 0.18), the remainder taking the form of ammonium salts. The fine fraction turned out to be mostly neutralized by ammonia, with a slight tendency to acidity during colder months.This seasonal cycle can be explained by the interplay between the local/mesoscale (vertical) and large-scale (advective) circulations. From mid-spring to late summer, stable anticyclonic conditions and increased turbulent mixing in the lower troposphere, associated to the thermal mountain wind system, induce convective/thermal uplift of air masses from the Po Valley to CMN, strongly altering the free tropospheric aerosol features. Conversely, higher vertical stability at the low levels and variable transport patterns related to the passage of synoptic disturbances over Northern Italy, determine a weaker influence of vertical transport of pollution on aerosol composition, during midfall-winter.At CMN, the synoptic-scale circulation regimes presented four principal contributions: Mediterranean, Western Europe, continental Europe and Eastern Europe.

Observation of double extensive air showers

Double extensive air showers were studied at the Tien Shan high-mountain scientific station of the Lebedev Physical Institute using two different installations. One measured the electron-photon shower component, the other measured Cherenkov radiation. Double showers separated by a time interval of ∼100 ns were detected by both setups. The frequency of the occurrence of such showers in each setup is analyzed. It is shown that these frequencies are identical when observing vertical showers (the zenith angle ϑ < 60°).

The Izaña BSRN station

The BSRN (Baseline Surface Radiation Network) is a project of the Radiation Panel from the Global Energy and Water Cycle Experiment (GEWEX) under the umbrella of the World Climate Research Programme (WCRP). Since March 2009 the Izana Atmospheric Observatory belongs to the BSRN network. The Izana Observatory is a Global Atmospheric Watch station. It is a high mountain station, located at Tenerife Island (2.367 m. above sea level). The measurements recorded in this station are sent on a monthly basic to the BSRN database are: global, direct, diffuse, longwave downward, net, UV-A, UV-B radiation and the data obtained with rawinsondes launched daily from the Santa Cruz de Tenerife station, located 30 km from the Izana station. In this work we focused on the study of the global, direct and diffuse radiation measurements, performed at the Izana Observatory during 2009. The results show a high quality of BSRN measurements. Although Izana is a high mountain station there are 357 days with valid measurements for 2009. A 99% of the measurements are within the limits recommended by the BSRN. Furthermore there is a very good agreement between the measurements and the simulated values with the radiative transfer model LibRadtran using a sample set of 129 days with cloud free sky conditions. The daily values of the global and direct radiation show a RMSE lower than 2%, while the diffuse radiation shows a RMSE of about 10%.

Surface ozone at the Caucasian site Kislovodsk High Mountain Station and the Swiss Alpine site Jungfraujoch: data analysis and trends (1990–2006)

Abstract. Long-term ozone measurements of two background mountain sites, namely the Kislovodsk High Mountain Station in Caucasus, Russia (KHMS, 43.70° N, 42.70° E, 2070 m a.s.l.) and the Jungfraujoch in Switzerland (JFJ, 46.55° N, 7.98° E, 3580 m a.s.l.) are compared. Despite of more than 1.5 km altitude difference ozone mixing ratios are comparable at JFJ an KHMS in the beginning of measurements (1990–1993) while the annually averaged levels at JFJ are around 15 ppb higher than the ones at KHMS for the most recent years (1997–2006). The seasonal cycle of the surface ozone mixing ratios is characterized by a double spring-summer maximum at both sites with a spring one being more pronounced for the air masses with the longest contact with the upper free troposphere and stratosphere. Ozone mixing ratio increased at JFJ but decreased at KHMS for the period 1990–2006. Trends are more pronounced for the 1990s (+0.73±0.20 ppb/year at JFJ and −0.91±0.17 ppb/year at KHMS for the period 1991–2001) in comparison with the later years (+0.04±0.21 ppb/year at JFJ and −0.37±0.14 ppb/year at KHMS for the period 1997–2006). Trends show a distinct seasonality, which is different for the different periods. To investigate possible reasons for this remarkable trends difference 3-D trajectories using LAGRANTO trajectory model are used. Effects of horizontal and vertical transport on ozone trends are considered. No substantial systematic changes in the transport patterns were detected which could lead to strong changes in the trend magnitude between 1991–2001 and 1997–2006. The geographical position of the sites relative to the main topographic features and emission sources as well as distance from the coast are interpreted to be among the main reasons for the opposite surface ozone trends. During the 90s the JFJ trend reflects increase of the ozone in the upper free troposphere/lower stratosphere, while KHMS is not sensitive to this change or even showing the opposite tendency. The analysis provided evidence for a stronger influence of processes in the lower troposphere, in particular the dramatic emission decrease in the earlier 1990s in former USSR and emissions regulations in Western Europe on the surface ozone trend at KHMS.

A method to generate near real time UV-Index maps of Austria

Abstract. A method is presented that combines individual ground based ultraviolet (UV) measurements and satellite data from MSG (Meteosat Second Generation) to generate a UV-Index map all over the region of Austria. Cloud modification factors (CMFs) gathered from satellite images give an area wide information of the cloud situation but compared to ground based measurements significant discrepancies have been found. These discrepancies are especially large for high mountain stations but also for low altitude sites differences between satellite derived and ground based data in the order of 15% have been found. To overcome these discrepancies a correction procedure based on the correlation of both data sets at the pixel of the measurement stations is developed. The uncertainty of the final UV-Index map is evaluated exemplarily for the pixel of the measurement sites Bad Vöslau and München by eliminating the information of both sites from the UV-Index map generation process and comparing afterwards calculated and measured results. More than 5000 maps for all weather conditions have been evaluated leading to a mean agreement of 1.02 (standard deviation ±0.31, Bad Vöslau) and 1.01 (standard deviation ±0.34, München) between calculated and measured UV-Indexes.

Background ozone in the southern Europe and Mediterranean area: Influence of the transport processes

The troposphere is subject to continuous inputs, production and removal processes of ozone and its precursors from natural processes and human activities acting together within a very complex system. In order to assess the behaviour of background ozone in the Mediterranean area, a description of trends, seasonal and diurnal behaviours of free tropospheric ozone is provided. In the Mediterranean area and southern Europe the background tropospheric ozone concentration appears significantly affected by three main air mass transport processes: (i) transport of polluted air masses on regional and long-range scales, (ii) downward transport of stratospheric air masses, and (iii) transport of mineral dust from the Sahara desert. In this review of the literature of the last two decades, we present an overview of these phenomena, mainly monitored at high baseline mountain stations representative of background atmospheric conditions.

Gamma-emission of very high energy from the metagalactic sources Mkn421, Mkn501, NGC1275 and 3c454.3, 1739+522

Observations of two type of metagalactic sources: BLLacs Mkn 421 ( z = 0.031 ), Mkn 501 ( z = 0.034 ) and Seyfert galaxy NGC 1275 ( z = 0.0179 ) are presented. The integral average gamma-ray fluxes of Mkn 421 and Mkn 501 were estimated as ( 0.63 ± 0.14 ) × 10 −12 cm −2 s −1 and ( 0.86 ± 0.13 ) × 10 −12 cm −2 s −1 respectively. NGC 1275 is being intensively studied by SHALON and the gamma-ray flux is found to be ( 0.78 ± 0.13 ) × 10 −12 cm −2 s −1 . The new distant metagalactic sources 1739 + 522 ( z = 1.375 ) and 3c454.3 ( z = 0.857 ) are detected at energies > 0.8 TeV with fluxes ( 0.53 ± 0.10 ) × 10 −12 cm −2 s −1 and ( 0.43 ± 0.13 ) × 10 −12 cm −2 s −1 respectively. The gamma spectra and images of the sources are presented. The spectra and fluxes of known blazars Mkn 421, Mkn 501 and far FSRQs 1739 + 522 and 3c454.3 are discussed. These observations are carrying out using the SHALON mirror telescope at the Tien-Shan high mountain station of the P.N. Lebedev Physical Institute.

Localization of source regions of selected hydrofluorocarbons combining data collected at two European mountain stations

Ground-based in situ measurements of hydrofluorocarbons HFC-125, HFC-134a, and HFC-152a, which are regulated under the Kyoto Protocol, are carried out at four European sites within the SOGE (System of Observation of Halogenated Greenhouse Gases in Europe) program. Concentrations measured at the high mountain stations of Jungfraujoch (Switzerland) and Mte Cimone (Italy) together with back-trajectory statistical analysis are used in order to identify potential source regions on a European scale. Combining concentration data recorded at the two sites allows to reduce one of the problem which is inherent to the back-trajectory approach, i.e. the localisation of “ghost” sources in the wake of real sources. In this way, a more reliable picture of the location of European potential source regions is given.

Analyses and comparisons of variations of 7Be, 210Pb, and 7Be/210Pb with ozone observations at two Global Atmosphere Watch stations from high mountains

Simultaneous measurements of 7Be and 210Pb and the analyses of activity ratio, i.e., 7Be/210Pb, offer another useful analytical tool for improving our understanding of ozone variability occurring at high altitude because they can provide diagnostic indicators of horizontal and vertical transport processes. Generally, the increase (decrease) of 7Be with decrease (increase) of 210Pb in association with high (low) values of 7Be/210Pb indicates the mechanisms associated with vertical (for being favorable to the horizontal) transport processes. For the purpose of demonstrating these mechanisms for ozone transport, we have presented the distinct transport processes of ozone and background conditions for two Global Atmosphere Watch (GAW) stations: Mount Cimone station (44.18°N, 10.7°E, 2165 m asl) and Mount Waliguan station (36.29°N, 100.90°E, 3816 m asl), located high in the mountains of Italy and China, respectively. We have performed the frequency distribution analyses and various comparisons of variations of 7Be with 210Pb and variations of 7Be, 210Pb, and 7Be/210Pb with surface ozone. The maximum ozone levels occur in the summer, and minimum levels occur in the winter at these two high mountain stations. Our analyses suggest that the processes of the stratospheric intrusions/upper tropospheric transport combined with the long‐range transport from polluted areas over eastern central China are the mechanisms that cause the ozone summer peak at the Mount Waliguan station. The ozone summer peak at the Mount Cimone station is mainly the result of photochemical production in the lower atmosphere associated with the transport of polluted air masses on regional and continental scales. Frequency distributions of 7Be, 210Pb, 7Be/210Pb, and surface ozone can be well represented by the lognormal distributions. Strikingly, we have found that the similarities of bimodal distributions for 7Be/210Pb at these two stations are clearly exhibited except for the magnitude, although the lognormal distributions of 7Be and 210Pb, with the noteworthy difference in altitude of these two stations, are significantly different. The measurements of 7Be and 210Pb combined with the analyses using 7Be/210Pb activity ratio can enhance our understanding of the transport processes in the atmosphere.

Anomalous high ozone concentrations recorded at a high mountain station in Italy in summer 2003

In order to evaluate the possible effects of heatwave phenomena on background O 3 concentrations, the average summer O 3 concentrations at the high mountain station of Mt. Cimone (MTC—2165 m a.s.l.) have been analyzed. In particular, at this baseline station unusually high O 3 concentrations were recorded during August 2003, when an intense heatwave (the “August heatwave”) affected Europe. During this heatwave, the highest O 3 concentrations were recorded at MTC in connection with air masses coming from continental Europe and the Po basin boundary layer as shown by three-dimensional air mass back-trajectory and mixing height analyzes. However, high O 3 concentrations were also recorded in air masses coming from the middle troposphere (above 3000 m a.s.l.), thus suggesting the presence of O 3-rich atmospheric layers over Europe. This could be due to the large extension of the mixing layer which favoured the transport of high concentrations of O 3 and its precursors to altitudes that would usually be in the free troposphere. Other than from traffic and industrial activities, a contribution to the high O 3 concentrations recorded at MTC during the August heatwave could derive from fires in the North of Italy, as suggested by a well-documented episode and supported by in situ CO 2 measurements used as non-conventional tracer for fire emissions.

A 6‐year analysis of stratospheric intrusions and their influence on ozone at Mt. Cimone (2165 m above sea level)

In this paper we present a study on stratospheric intrusion (SI) events recorded at a high mountain station in the Italian northern Apennines. Six years (1998–2003) of surface ozone and beryllium‐7 concentration measurements as well as relative humidity values recorded at the GAW Mt. Cimone research station (44°11′N, 10°42′E; 2165 m asl) were analyzed. Moreover, three‐dimensional backward trajectories calculated by the FLEXTRA model and potential vorticity values along these trajectories were used. In order to identify SI and evaluate their contribution to the tropospheric ozone at Mt. Cimone, a statistical methodology was developed. This methodology consists of different selection criteria based on observed and modeled stratospheric tracers as well as on tropopause height values recorded by radio soundings. On average, SI effects affected Mt. Cimone for about 36 days/year. The obtained 6‐year SI climatology showed a clear seasonal cycle with a winter maximum and a spring‐summer minimum. The seasonal cycle was also characterized by an interannual variation. In particular, during winter (autumn), SI frequency could be related to the intensity of the positive (negative) NAO phase. In order to separate direct SI from indirect SI, a restrictive selection criterion was set. This criterion, named Direct Intrusion Criterion (DIC), requested that all the analyzed tracers were characterized by stratospheric values. Direct SI affected Mt. Cimone for about 6 days/year, with frequency peaks in winter and early summer. At Mt. Cimone, SI contribution to background ozone concentrations was largest in winter. On average, an ozone increase of 8% (3%) with respect to the monthly running mean was found during direct (indirect) SI. Finally, the typical variations of stratospheric tracers during SI events were analyzed. The analysis of in situ atmospheric pressure values suggested that direct SI were connected with intense fronts affecting the region, while indirect SI were possibly connected with subsiding structures related with anticyclonic areas.