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Ice caves are, similar to mountain glaciers, threatened by the warming climate. To better understand the response of perennial ice in caves to a changing climate, we analysed the thermal characteristics of a sag-type ice cave in the Austrian Alps (Hundsalm ice cave), based on long-term temperature measurements for the period 2008–2021. Observations show a warming trend in all parts of the cave as well as a distinct seasonal pattern with two main regimes, i.e. an open (winter) and a closed (summer) period. During the closed period, a persistent stable stratification prevails that largely decouples the cave from the external atmosphere. The open period is characterised by unstable to neutral stratification, which is an effect of convection during episodes when cold air can penetrate into the cave. Criteria to detect corresponding periods are investigated. Vertical temperature profiles also provide hints on corresponding circulation patterns and the spatial temperature variability in the cave. The positive air temperature trend is reflected in a decrease in perennial cave ice, derived from stake measurements. Besides surface melting, we find compelling evidence of basal melting of ice. The observed ablation rates can be well reproduced by applying a modified degree-day model, which, however, is less feasible regarding mass balance. Overall, we conclude that Hundsalm ice cave is highly impacted by regional warming, which will lead to the disappearance of its perennial ice deposits within the next decades.

Observations from six eddy-covariance stations in the Austrian Inn Valley reveal a strong spatial variability in near-surface turbulent fluxes. While the stations are located within an approximately 6.5 km long section of the valley and thus within an area similar or even smaller than a single grid cell in current global weather forecasting models, the sites strongly differ in terms of topography and land use. Observed magnitudes of sensible and latent heat fluxes are driven by the solar incoming radiation and thus affected by the local slope angle and orientation, with further influences from the land use on the partitioning of the available energy into sensible and latent heat fluxes. In addition, the locally induced thermal slope- and valley-wind circulation impact the diurnal cycles of the turbulent fluxes. To correctly represent turbulent exchange in mountainous terrain in numerical models, the models thus need to represent all these conditions and processes correctly. We are running WRF simulations with a 1-km grid spacing as part of an ongoing project to evaluate land-surface models and turbulence parameterizations over complex terrain. The simulations are used to determine how sensitive the modeled land-atmosphere exchange is to inaccuracies in the topography and land use, which are unavoidable at this spatial resolution, and whether the model can reproduce the observed spatial variability.

“Valley-wind days” are characterized by synoptically undisturbed, clear-sky conditions, which lead to the formation of thermally-driven slope- and valley-wind circulations in mountain regions. A simple method is presented to identify these conditions in the Inn Valley, Austria, using ERA-Interim geopotential height fields and a clear-sky index, which is calculated from measurements of longwave incoming radiation, air temperature, and humidity at a single site on the valley floor. As the method is based on identifying weak synoptic-scale flows and clear skies, it can also be applied to the identification of ideal conditions for other thermally-driven circulations. The mean diurnal cycle of the valley-wind circulation on these days is briefly discussed.

The scaled standard deviations of temperature and humidity are investigated in complex terrain. The study area is a steep Alpine valley, with six measurement sites of different slope, orientation and roughness (i-Box experimental site, Inn Valley, Austria). Examined here are several assumptions forming the basis of Monin–Obukhov similarity theory (MOST), including constant turbulence fluxes with height and the degree of self-correlation between the involved turbulence variables. Since the basic assumptions for the applicability of the MOST approach—horizontally homogeneous and flat conditions—are violated, the analysis is performed based on a local similarity hypothesis. The scaled standard deviations as a function of local stability are compared with previous studies from horizontally homogeneous and flat terrain, horizontally inhomogeneous and flat terrain, weakly inhomogeneous and flat terrain, as well as complex terrain. As a reference, similarity relations for unstable and stable conditions are evaluated using turbulence data from the weakly inhomogeneous and flat terrain of the Cabauw experimental site in the Netherlands, and assessed with the same post-processing method as the i-Box data. Significant differences from the reference curve and also among the i-Box sites are noted, especially for data derived from the i-Box sites with steep slopes. These differences concern the slope and the magnitude of the best-fit curves, illustrating the site dependence of any similarity theory.

An innovative approach to characterize concentration of atmospheric aerosol particles and air mass layering along the elevation profile of glaciers is presented for the first time and validated, exploiting low weight and fast response sensors deployed on a snowmobile. Two micro-Aethalometers for black carbon measurements and a miniature Diffusion Size Classifier (miniDisc) for total aerosol concentration (airborne particles) in the 14–260 nm range were used. Test experiments were conducted in the Arctic (Svalbard) in Spring (2016). Three glaciers in the Spitsbergen region were considered for this exploratory study, the Austre Broggerbreen, the Edithbreen and the Kongsvegen. The Austre Broggerbreen and Edithbreen were considered as test sites to setup the experiment, to optimize the sampling strategy and to identify some basic experimental artefacts. Kongsvegen glacier was chosen for the main case study, extending from the Kongsfjorden coast to roughly 700 m above sea level for a total length of ca. 25 km and with a nearly constant elevation gradient. The obtained results were rather consistent for the three glaciers and show an increase of nanoparticles with altitude. Black carbon concentration show stationary to decreasing trends going from the bottom to the top of the glaciers. These observations indicate a very active secondary aerosol formation at the highest elevations, responsible for the increase concentration of ultrafine particles at the glacier top. On the other side, black carbon shows higher levels at the lower altitudes of the glacier. This is indicative that in absence of a long-range transport as demonstrated by calculated back trajectories, black carbon might have accumulated due to the effect of katabatic winds flow along the glacier profile. The results obtained were compared and are largely consistent with the observations from concurrent soundings with a tethered balloon experiment conducted in the nearby site of Ny-Alesund. The proposed experimental design opens new perspectives for future experiments, which may be of relevance for the understanding of black carbon and dry dust deposition on the glacier surface, which may impact the melting of ice and snow. The investigations also contribute to better understanding of the transport and surface exchange processes acting within the atmospheric layer over glacier surface.

Although aerosols in the Arctic have multiple and complex impacts on the regional climate, their removal due to deposition is still not well quantified. We combined meteorological, aerosol, precipitation, and snow pack observations with simulations to derive information about the deposition of sea salt components and black carbon (BC) from November 2011 to April 2012 to the Arctic snow pack at two locations close to Ny-Ålesund, Svalbard. The dominating role of sea salt and the contribution of dust for the composition of atmospheric aerosols were reflected in the seasonal composition of the snow pack. The strong alignment of the concentrations of the major sea salt components in the aerosols, the precipitation, and the snow pack is linked to the importance of wet deposition for the transfer from the atmosphere to the snow pack. This agreement was less strong for monthly snow budgets and deposition indicating important relocation of the impurities inside the snow pack after deposition. Wet deposition was less important for the transfer of nitrate, non sea salt-sulfate, and BC to the snow during the winter period. The average BC concentration in the snow pack remains small with a limited impact on snow albedo and melting. Nevertheless, the observations also indicate an important redistribution of BC in the snowpack leading to layers with enhanced concentrations. The complex behavior of bromide due to modifications during the sea salt aerosol formation and remobilization in the atmosphere and in the snow were not resolved due to the lack of measurements in aerosols and precipitation.

The Austrian RADiation monitoring network (ARAD) has been established to advance the national climate monitoring and to support satellite retrieval, atmospheric modeling and the development of solar energy techniques. Measurements cover the downward solar and thermal infrared radiation using instruments according to Baseline Surface Radiation Network (BSRN) standards. A unique feature of ARAD is its vertical dimension of five stations, covering an altitude range between about 200 m a.s.l (Vienna) and 3100 m a.s.l. (BSRN site Sonnblick). The paper outlines the aims and scopes of ARAD, its measurement and calibration standards, methods, strategies and station locations. ARAD network operation uses innovative data processing for quality assurance and quality control, utilizing manual and automated control algorithms. A combined uncertainty estimate for the broadband shortwave radiation fluxes at all five ARAD stations, using the methodology specified by the Guide to the Expression of Uncertainty in Measurement indicates that relative accuracies range from 1.5 to 2.9 % for large signals (global, direct: 1000 W m−2, diffuse: 500 W m−2) and from 1.7 to 23 % (or 0.9 to 11.5 W m−2) for small signals (50 W m−2) (expanded uncertainties corresponding to the 95 % confidence level). If the directional response error of the pyranometers and the temperature response of the instruments and the data acquisition system (DAQ) are corrected, this expanded uncertainty reduces to 1.4 to 2.8 % for large signals and to 1.7 to 5.2 % (or 0.9–2.6 W m−2) for small signals. Thus, for large signals of global and diffuse radiation, BSRN target accuracies are met or nearly met (missed by less than 0.2 percentage points, pps) for 70 % of the ARAD measurements after this correction. For small signals of direct radiation, BSRN targets are achieved at two sites and nearly met (also missed by less than 0.2 pps) at the other sites. For small signals of global and diffuse radiation, targets are achieved at all stations. Additional accuracy gains can be achieved in the future through additional measurements, corrections and a further upgrade of the DAQ. However, to improve the accuracy of measurements of direct solar radiation, improved instrument accuracy is needed. ARAD could serve as a useful example for establishing state-of-the-art radiation monitoring at the national level with a multiple-purpose approach. Instrumentation, guidelines and tools (such as the data quality control) developed within ARAD are intended to increase monitoring capabilities of global radiation and thus designed to allow straightforward adoption in other regions, without high development costs.

State-of-the-art numerical snowpack models essentially rely on observational data for initialization, forcing, parametrization, and validation. Such data are available in increasing amounts, but the propagation of related uncertainties in simulation results has received rather limited attention so far. Depending on their complexity, even small errors can have a profound effect on simulations, which dilutes our confidence in the results. This paper aims at quantification of the overall and fractional contributions of some archetypical measurement uncertainties on snowpack simulations in arctic environments. The sensitivity pattern is studied at two sites representing the accumulation and ablation area of the Kongsvegen glacier (Svalbard), using the snowpack scheme Crocus. The contribution of measurement errors on model output variance, either alone or by interaction, is decomposed using global sensitivity analysis. This allows one to investigate the temporal evolution of the fractional contribution of different factors on key model output metrics, which provides a more detailed understanding of the model's sensitivity pattern. The analysis demonstrates that the specified uncertainties in precipitation and long-wave radiation forcings had a strong influence on the calculated surface-height changes and surface-energy balance components. The model output sensitivity patterns also revealed some characteristic seasonal imprints. For example, uncertainties in long-wave radiation affect the calculated surface-energy balance throughout the year at both study sites, while precipitation exerted the most influence during the winter and at the upper site. Such findings are valuable for identifying critical parameters and improving their measurement; correspondingly, updated simulations may shed new light on the confidence of results from snow or glacier mass- and energy-balance models. This is relevant for many applications, for example in the fields of avalanche and hydrological forecasting.

A series of major eruptions of the Eyjafjallajökull volcano in Iceland started on 14 April 2010 and continued until the end of May 2010. The volcanic emissions moved over nearly the whole of Europe and were observed first on 16 April 2010 in Southern Germany with different remote sensing systems from the ground and space. Enhanced PM10 and SO2 concentrations were detected on 17 April at mountain stations (Zugspitze/Schneefernerhaus and Schauinsland) as well as in Innsbruck by in situ measurement devices. On 19 April intensive vertical mixing and advection along with clear-sky conditions facilitated the entrainment of volcanic material down to the ground. The subsequent formation of a stably stratified lower atmosphere with limited mixing near the ground during the evening of 19 April led to an additional enhancement of near-surface particle concentrations. Consequently, on 19 April and 20 April exceedances of the daily threshold value for particulate matter (PM10) were reported at nearly all monitoring stations of the North Alpine foothills as well as at mountain and valley stations in the northern Alps. The chemical analyses of ambient PM10 at monitoring stations of the North Alpine foothills yielded elevated Titanium concentrations on 19/20 April which prove the presence of volcanic plume material. Following this result the PM10 threshold exceedances are also associated with the volcanic plume. The entrainment of the volcanic plume material mainly affected the concentrations of coarse particles (>1 μm) – interpreted as volcanic ash – and ultrafine particles (

[1] Kongsvegen is an Arctic glacier located in northwest Spitzbergen. We use meteorological observations made near the average equilibrium line of Kongsvegen during the decade 2001 to 2010 to drive a glacier energy and mass balance model. Average daily and seasonal cycles are analyzed over the course of a full decade, as well as the interannual variations of the meteorological parameters and of the mass and energy balance components. The calculated average of net radiation is close to zero and the sensible heat flux is the most important and continuous source of energy at the surface. The latent heat flux is a weak source of energy as well. The resultant flux constellation yields a surplus of energy accumulating throughout the decade (9.5 W m–2) and fosters a negative specific surface mass balance throughout the investigated decade (–1.8 m w. eq.). The most significant mass loss occurred during the middle of the decade (2004 until 2006), with positive surface mass balances observed afterward when significant amounts of superimposed ice were formed. This development is well correlated to the total surface mass balance of the glacier. Application of monthly temperature and precipitation perturbations corroborates earlier studies indicating a high sensitivity of the mass balance to energy fluxes depending on temperature conditions during summer.

An observational dataset from a wintertime field campaign in the Inn Valley, Austria, is analysed in order to study mechanisms of air pollution transport in an Alpine valley. The results illustrate three types of mechanisms: transport by a density current, back-and-forth transport by valley winds, and transport by slope winds. The first type is associated with an air mass difference along the valley. Cooler air located in the lower part of the valley behaves like a density current and produces the advection of pollutants by upvalley winds. In the second type, strong horizontal gradients in pollution concentrations exist close to ground. Multiple wind reversals result in a back-and-forth transport of pollutants by weak valley winds. In the third type, upslope winds during daytime decrease low-level pollution concentrations and cause the formation of elevated pollution layers.

The aim of this study is to investigate the skill of the High Resolution Limited Area Model (HIRLAM) to reproduce the near-surface atmospheric conditions across the Vatnajokull Ice Cap in Iceland. This model-observation comparison study is based on a mesoscale glaciometeorological observation campaign, which has been performed during summer 1996 and provided a wealth of meteorological and glaciological data. Fine-scale hydrostatic HIRLAM experiments are based on downscaling ERA-40 analyses and the application of upper-air and surface data assimilation. The simulation results are compared to a subset of observations following a height transect across Breidamerkurjokull, a southern outlet glacier of Vatnajokull. After introduction of improvements, suggested by comparison of a reference run with observations, HIRLAM successfully simulates the surface energy balance and the driving meteorological parameters. For a correct simulation, a proper description of the constant and temporary varying physical properties of the underlying surface turned out to be crucial. The results are valuable for further improvement of operational mesoscale NWP in mountainous and high latitude environments.

Air quality is mainly determined by traffic, industrial and urban emissions as well as by specific meteorological and topographic conditions. Focussing on nitrogen oxides and particulate matter, the temporal and spatial differences in air pollution in a deep Alpine valley with a major motorway were studied by a measurement campaign between November 2005 and February 2006 near Schwaz, Austria. The variation of air pollutant concentrations near the motorway was determined on the basis of path-averaged (DOAS) and in situ measurements. The layering of the valley atmosphere and the mixing-layer height were observed continuously by SODAR and ceilometer measurements. The winter-time weather conditions were characterized by exceptionally low temperature and high amount of snow in the valley. This resulted in the development of very stable cold pools with low wind speeds and an accordingly high air pollution burden. During several periods the air pollutants accumulated from day to day and frequent exceedances of NO 2 and PM 10 thresholds were detected. Furthermore it could be concluded that the emission situation was not unusually high during these periods, at least concerning road traffic as the dominant source for nitrogen oxides. Analysis confirmed that the typical weather phenomena associated with stable high-pressure regimes were the main factor for the observed pollution burden. During foehn and cold front passages, which interrupted these high pressure periods, concentration levels generally decreased at the valley ground and increased at the slope. Analysis revealed that this is a consequence of vertical mixing due to the influence of mountain specific wind systems, like thermally driven and quasi-periodic valley or slope winds. NO 2 concentration levels are a matter of concern regarding annual mean values as well as - previously not recorded - exceedances of the half-hourly threshold in severe winter conditions. Compared to previous investigations an increased NO 2 /NO 2 ratio was observed during the measurement campaign which is related to enhanced N0 2 emissions from road traffic in consequence to fleet composition and emission changes.

This paper investigates the influence of the planetary boundary-layer (PBL) parameterization and the vertical distribution of model layers on simulations of an Alpine foehn case that was observed during the Mesoscale Alpine Programme (MAP) in autumn 1999. The study is based on the PSU/NCAR MM5 modelling system and combines five different PBL schemes with three model layer settings, which mainly differ in the height above ground of the lowest model level (z1). Specifically, z1 takes values of about 7 m, 22 m and 36 m, and the experiments with z1 = 7 m are set up such that the second model level is located at z = 36 m. To assess if the different model setups have a systematic impact on the model performance, the simulation results are compared against wind lidar, radiosonde and surface measurements gathered along the Austrian Wipp Valley. Moreover, the dependence of the simulated wind and temperature fields at a given height (36 m above ground) on z1 is examined for several different regions.

Measurements of the energy and mass budgets have beenmade at the equilibrium line ofBreidamerkurjokull, a southern outlet glacier ofVatnajokull, Iceland. The glacier's surface wasmelting for most of the measurement period, whichallowed for a reliable closure of the energy budget.Sensitivity studies focussed mainly on potentialeffects of measurement errors, site-specificmicrometeorological conditions, surface developmentand different parameterization of the turbulentfluxes. Although the high stability and a roughnessdisturbance imposed certain restrictions, thesestudies confirmed the applicability of theMonin–Obukhov framework for the evaluation of turbulentfluxes.

We give an overview of a glacio-meteorological experiment carried out in the summer (melt season) of 1996 on the largest European ice cap, Vatnajökull, Iceland (area 8000 km2; altitude range: from sea level to about 2000 m). The main goal was to understand how the energy used in the melting of snow and ice is delivered to the surface. Many meteorological stations were operated simultaneously on the ice cap, at almost all of which profile measurements were made. Cable balloons and radiosondes were used to probe the vertical structure of the boundary layer. It appears that the flow near the surface is katabatic most of the time, with the height of the wind maximum varying between a few metres and a few tens of metres. It is only during the passage of intense storms that the katabatic wind in the melt zone disappears. Global radiation increases significantly with altitude. Surface albedo varies enormously in space and time, with very low values (≈ 0.1) being found at many places because of the melt out of volcanic ash layers. If we consider the total melt in the period 22 May–31 August 1996, we conclude that radiation typically provides two-thirds of the melt energy, and turbulent exchange of heat one-third. At locations high on the glacier, turbulent exchange becomes less significant.

As an important deliverable of a glaciometeorological experiment the participating research institutes produced a common data set that consists of temperature, humidity, wind and radiation data collected by different types of weather station at an elevation of 2 m above the glacier surface. Although all of the instruments had been calibrated in laboratories, intercomparison measurements were carried out under field conditions before and after the Vatnajokull experiment. This note deals with the intercomparison measurements and considers the observed differences in sensor characteristics. In spite of the fact that different types and brands of sensors were used under difficult field circumstances, the estimated accuracy of the common data set obtained is almost as good as suggested by the manufacturers' specifications. The long-term stability of the sensor calibrations also proved to be good. The reliability of the observed values included in the common Vatnajokull dataset is therefore considered to be high.

An impressive cloud wall has frequently been observed on the southern slopes of the Vatnajokull ice sheet, which is located in south-eastern Iceland. Its optical and dynamic features suggest a delicate balance of the atmospheric agents involved. This has been confirmed by a thorough analysis of a well documented event and by statistics covering a whole summer season. As an exemplary event, the regional development of the associated cloud has basically been documented with synchronous surface data along a suitable transect of the glacier. Data from tethered balloons, radiosoundings and routine synoptic data have also been exploited extensively. Cloud development was generally aided by a high moisture potential because of proximity to the open seas and the remnants of a frontal system. Furthermore the occurrence of the cloud phenomenon was associated with onshore (southerly) surface winds, assisting advection and lifting of the associated air masses above the slopes of the ice sheet. Northward protrusion of the associated cloud was apparently opposed by continuous katabatic winds and topographically induced lee effects.

We present data from two eddy covariance systems for determining the sensible and latent heat flux and the shear stress near the earth's surface. One measures continuously since September 2010 close to the village Ny-Ålesund, Svalbard, the other one was located on Kongsvegen glacier for a short period in April 2011. Two examples for small-scale variability are discussed: near surface external gravity waves associated with katabatic wind from the Broggerbreen glacier located a few kilometres southwestern of Ny-Ålesund, and an episode when the two eddy systems at the different measurement sites captured very different conditions at the same time. In case of gravity wave motion the eddy covariance method results in fictitious positive fluxes due to the strong correlation between temperature and vertical wind, which has to be considered carefully. The comparison between the two sites showed that generally the dynamical processes near the Earth’s surface for Ny-Ålesund and the Kongsvegen glacier are different and local. But there are also cases of synchronization due to synoptic influences, and then the same processes are visible at the two measurement sites. Both examples show that the boundary layer in Ny-Ålesund is not only affected by the main glaciers in the east of the village, but also by other orographical characteristics and synoptic issues. Therefore, the only meaningful way to deal with point measurements is to consider them in context with the surrounding orography and the general meteorological conditions.

The spatial structure and the progression speed of the first ash layer from the Icelandic Eyjafjallajökull volcano which reached Germany on 16/17 April is investigated from remote sensing data and numerical simulations. The ceilometer network of the German Meteorological Service was able to follow the progression of the ash layer over the whole of Germany. This first ash layer turned out to be a rather shallow layer of only several hundreds of metres thickness which was oriented slantwise in the middle troposphere and which was brought downward by large-scale sinking motion over Southern Germany and the Alps. Special Raman lidar measurements, trajectory analyses and in-situ observations from mountain observatories helped to confirm the volcanic origin of the detected aerosol layer. Ultralight aircraft measurements permitted the detection of the arrival of a second major flush of volcanic material in Southern Germany. Numerical simulations with the Eulerian meso-scale model MCCM were able to reproduce the temporal and spatial structure of the ash layer. Comparisons of the model results with the ceilometer network data on 17 April and with the ultralight aircraft data on 19 April were satisfying. This is the first example of a model validation study from this ceilometer network data.

The spatial structure and the progression speed of the first ash layer from the Icelandic Eyjafjallajökull volcano which reached Germany on 16/17 April is investigated from remote sensing data and with numerical simulations. The ceilometer network of the German Weather Service was able to follow the progression of the ash layer over the whole of Germany. This first ash layer turned out to be a rather shallow layer of only several hundreds of metres thickness which was oriented slantwise in the middle troposphere and which was brought downward by large-scale sinking motion over Southern Germany and the Alps. Special Raman lidar measurements, trajectory analyses and in-situ observations from mountain observatories helped to confirm the volcanic origin of the detected aerosol layer. Ultralight aircraft measurements permitted the detection of the arrival of a second major flush of volcanic material in Southern Germany. Numerical simulations with the Eulerian meso-scale model MCCM were able to reproduce the temporal and spatial structure of the ash layer. Comparisons with the ceilometer network data on 17 April and with the ultralight aircraft data on 19 April were satisfying. This is the first example of a model validation study from this ceilometer network data.

Concurrent measurements of meteorological parameters, traffic flow and vehicle composition, NOx concentrations and noise levels have been performed during a consecutive 166-hour (approx. one week) episode in the Austrian Inn valley. The study elaborates the meteorologically induced effects on the transport and dispersion of air pollutants (NOx) and the propagation of sound waves from the motorway in the valley towards two receptor/receiver sites, one at the valley bottom, the other one at an elevated slope position. Due to complex transmission effects only a small portion of the observed variations in the air and noise pollution at the two sites can be explained by the varying emission at the motorway. With the help of simple models it is shown that by adding merely one or two meteorological parameters a substantially larger portion of the variation can be explained. The vertical temperature gradient turned out to be the meteorological key parameter. It controls the mixing volume (confined by the valley sides and the mixing-layer top) and the sound wave refraction which strongly determine air pollution and noise level, respectively.

Spectral actinometric measurements of direct solar radiation were made on all 17 clear days during 1981/82. From broadband measurements using cutoff fillers, a number of common measures for aerosol extinction as well as precipitable-water content of the atmosphere were derived by numerical analysis. Average Angstrom's turbidity coefficient β = 0.017 ± 0.006, wavelength exponent α1.6 ± 0.2, aerosol optical depth at 0,5 μm D(O.5) = 0.05 ± 0.001, and mean precipitable water w = 0.2 ± 0.1 cm were determined, matching the regional pattern known until now. Monthly, as well as daily,variations of observed atmospheric turbidity are discussed with respect to prevailing winds, synoptic patterns, and topography, revealing lowest turbidity for southwesterly flow. A review on 30 years of compatible aerosol optical thickness measurements at Antarctic coastal stations is added.

A comparative study of wintertime NO and NO 2 concentrations and the investigation of the influences of meteorological conditions upon air quality in a valley near a motorway was performed in the Inn valley near Innsbruck, Austria. A DOAS with emitter/receiver unit and three retroreflectors was used for this study. One retroreflector was installed at a mast on the other side of the motorway (120 m path length) so that the path was about 10 m above motorway level. Another retroreflector was set up for a path parallel to the motorway and the third retroreflector was used to measure at a path perpendicular and away from the motorway. The path across the motorway was directly above the air quality monitoring station Vomp of Land Tyrol which is only three meters away from the motorway. The first measurement campaign was performed during winter 2005 / 2006 and the second one during the winter 2007 / 2008. The concentrations above the motorway are clearly dominated by the traffic volume. Higher concentration values are found during week days than during the weekend. The diurnal differences in air pollution e.g. due to temporal variations of motorway emissions (10 times higher during peak hours in the morning and afternoon compared to night hours) and meteorological conditions (stable from late afternoon until mid-morning) are investigated. The mean NO 2 / NO x ratio from these DOAS measurements is 0.3 which can be caused by the high amount of heavy duty vehicles at that motorway. During synoptically undisturbed winter periods persistent inversion conditions determined by a SODAR as mixing layer heights lead to relatively high air pollutant concentrations from late afternoon until mid-morning. In this context the influence of the quasi-regular mountain wind system (valley and slope winds) is studied. The colder winter 2005 / 2006 with a persistent snow cover is characterised by higher concentration of pollutants (e.g. NO 2 ).

[1] This snow modeling study investigates two methods to artificially reduce ablation in Alpine glacier ski resorts. Using the snow cover model SNTHERM, a first set of sensitivity studies focuses on the potential effects of artificial compaction of snow during winter. In comparison to a reference run representing the natural conditions, a stepwise increase of the model's new snow density toward 500 kg m−3 yields no more than 218 kg m−2 water equivalent being saved at the end of the ablation period. Further studies consider effects of covering the snow surface with different materials in spring. The physical properties and the energetic processes at the model's surface node are parameterized accordingly. The results show that 2489 kg m−2 water equivalent are saved compared to the reference run. Thus 15% of the winter snow cover as well as the whole amount of the underlying glacier ice are preserved. This indicates that surface covering reduces snow and ice ablation more effectively than snow compaction, which is confirmed by field measurements.

The Alpine environment as a sensitive region is heavily influenced by major traffic routes. Within the project ALPNAP (Monitoring and Minimisation of Traffic-Induced Noise and Air Pollution along Major Alpine Transport Routes) the integration of advanced scientific methods of monitoring and simulating the air quality distribution and noise propagation is a key aspect for the impact analysis on human health. A methodology for measurement strategies and model simulations for air pollutants will be demonstrated for the Brenner traverse. First results of a field measurement campaign give detailed insights of the complexity of the atmospheric conditions and the distribution of air pollutants in the Inn valley. Introduction Road traffic emissions combined with unfavourable meteorological conditions like calm winds and low inversion layers have severe impacts on the natural environment as well as on the socio-economic development of regions in the vicinity of major Alpine traffic routes. Increasing amounts of heavy duty vehicles and passenger cars force the increase of traffic emissions, which continually violate the EU air quality thresholds of e.g. PM

[1] We estimate annual anomalies of the surface mass balance of glaciers on Svalbard for the period 2000–2005 (six years), by calculating the so-called ‘‘satellite-derived mass balance’’ (Bsat) from time series of satellite-derived surface albedos. The method needs no other input variables. Surface albedos are extracted from the Moderate Resolution Imaging Spectroradiometer (MODIS)/Terra albedo product. We validate the MODIS albedos by comparing them with in situ measurements on Kongsvegen, and we find a low root-meansquare error of 0.04 for higher-quality MODIS data. Confidence in the MODIS product is also provided by realistic profiles of albedo along glacier centerlines. We apply the method to 18 glaciers that are evenly distributed over the archipelago. Correlation coefficients of time series of Bsat and direct measurements of the annual mass balance on Kongsvegen and Hansbreen are highly significant (0.94 and 0.82, respectively). Moreover, spatial distributions of the anomalies for individual years are coherent. Disadvantages of the method are that absolute values of the mass balance cannot be determined and that the interannual variability is underestimated. The latter might be corrected by equations to be established with mass balance models.

[1] Multiyear glaciometeorological data have been collected at about the equilibrium line of Kongsvegen glacier in Svalbard. During the first summer of the investigation period, about 0.6 m of superimposed ice (SI) was built up because of effective meltwater refreeze upon the former glacier surface. Thus winter accumulation is completely retained from runoff, and latent heat is released equivalent to 27% of July net radiation. This ice layer, as well as part of the former year's ice, disappeared during the subsequent summer. Using a physically based snow model, the evolution of the snow pack properties as well as the observed amount of SI is successfully reproduced. However, the latter is only possible by modifying the model's water transport routine to also treat effects of ponding water, which have been observed. Two distinct phases of SI formation can be distinguished. A first one (15 cm) is initiated as soon as meltwater has penetrated to the underlying cold glacier ice. Toward the end of the melt period, however, the remaining body of SI is rapidly formed because of intense atmospheric cooling. The availability of ponding water plays an essential role in this context. During the following summer the initial refreezing phase was terminated by exposure of the newly built SI at the surface. The whole amount of the actual year and the major part of the former year's SI was melted then. A positive ice-albedo feedback process plays an additional role there. Sensitivity studies prove that the model results and their interpretation do not critically depend on possible uncertainties of input data and model parameters. Despite their local nature these studies are valuable steps toward understanding the regional distribution of SI on Arctic glaciers as well as their climate sensitivity. Remote sensing studies indicate that SI presently covers 35% of Kongsvegen's surface area.

Glacier surface melt dynamics throughout Novaya Zemlya (NovZ) and Severnaya Zemlya (SevZ) serve as a good indicator of ice mass ablation and regional climate change in the Russian High Arctic. Here we report trends of surface melt onset date (MOD) and total melt days (TMD) by combining multiple resolution-enhanced active and passive microwave satellite datasets and analyze the TMD correlations with local temperature and regional sea ice extent. The glacier surface snowpack on SevZ melted significantly earlier (−7.3 days/decade) from 1992 to 2012 and significantly longer (7.7 days/decade) from 1995 to 2011. NovZ experienced large interannual variability in MOD, but its annual mean TMD increased. The snowpack melt on NovZ is more sensitive to temperature fluctuations than SevZ in recent decades. After ruling out the regional temperature influence using partial correlation analysis, the TMD on both archipelagoes is statistically anti-correlated with regional late summer sea ice extent, linking land ice snowmelt dynamics to regional sea ice extent variations.

The energy fluxes over dry tundra were measured during the period mid-May to mid-June 1988 in Western Greenland at 67?N as contribution to a field campaign of the International Satellite Land Surface Climatology Experiment (ISLSCP). In addition to the energy balance station, which was situated about 4 km west of the margin of the inland ice, standard meteorological data were collected at two stations a few kilometers south and west, respectively, from the energy balance site. While air temperature shows little differences between the stations, the wind patterns are strongly modified by comparatively small-scale topography and show clearly decreasing influence of catabatic flow already at scales of a few kilometers from the ice margin. The temporal variations of the energy fluxes are dominated by the incoming solar radiation and the availability of moisture at the soil surface. Desiccation of the soil crust during the first 2 wk of the observation period resulted in decrease of evaporation. On the average, the sensible heat flux clearly surpassed the latent heat flux. Evapotranspiration sums of various surface types, including dry tundra and a swamp, were measured twice daily with lysimeters. Daily evapotranspiration was found to be closely related to net radiation and to the difference between air temperature and surface temperature, which offers the opportunity to apply satellite data for estimation of the latent heat flux.

In order to investigate the spatial distribution of air pollutants in the Inn valley (Tyrol, Austria) during wintertime, a joint field campaign of the three research projects ALPNAP (Monitoring and Minimisation of Traffic-Induced Noise and Air Pollution Along Major Alpine Transport Routes), INNAP (Boundary Layer Structure in the Inn Valley during high Air Pollution) and INNOX (NOx-structure in the Inn Valley during High Air Pollution) was carried out in January/February 2006. In addition to continuous ground based measurements, vertical profiles of various air pollutants and meteorological parameters were obtained on six selected days. For in-situ investigations, a tethered balloon was used to analyse the lowest atmospheric layers, 0–500 m above the valley bottom (a.v.b.), and a research aircraft sampled at 150–2200 m a.v.b. An aircraft equipped with an aerosol backscatter lidar performed nadir measurements at 3000 m a.v.b. Combined results from a typical day show a strongly polluted layer up to about 125 m a.v.b. in the morning. Around midday concentrations on the valley floor decrease indicating some vertical air exchange despite thermally stable conditions. Strong vertical and horizontal gradients with enhanced pollution levels along the sunny side of the valley up to 1300 m a.v.b. were observed in the afternoon. This vertical mixing due to thermally or dynamically driven slope winds reduces the concentration of air pollutants at the bottom of the valley and causes the formation of elevated pollution layers.