Glacier Surface Mass Balance Research Articles

Evolution of the Lower Barun lake and its exposure to potential mass movement slopes in the Nepal Himalaya

The Lower Barun Lake, the largest glacier-fed lake in the Nepal Himalaya, has been designated as critically or highly vulnerable to Glacier Lake Outburst Floods (GLOFs) due to the lake's massive volume and steep side walls that are susceptible to mass movements. The current study estimates the future evolution of the lake's extent and its exposure to potential avalanche under different climate scenarios by simulating the evolution of the Lower Barun glacier, which feeds the lake. We then assess this exposure (i) at the lake's current extent, (ii) when the lake length grows to 75 % of its maximum length, and (iii) when the lake length reaches its maximum possible length. We use a mass conservation based numerical flowline model for our analyses. The model was forced by the glacier surface mass balance (SMB) and meteorological data collected from weather stations in Kathmandu, Nepal and Darjeeling, India. Modelled lake lengths matched measured lengths within an RMSE of ∼200 m. Analyses show that under SSP2–4.5 and SSP5–8.5 scenarios, the lake will reach its maximum length by 2075 ± 2 and 2061 ± 1, respectively. The largest uncertainty in future lake length fluctuations is approximately 200 m. Our study reveals that in current conditions, the zone where the angle of reach of potential avalanches is highest lies on the slopes along the right shore (south side) of the lake. The angle of reach shifts upstream and steepens—and the mass movement hazard increases—as the lake grows in the future.

A low-cost and open-source approach for supraglacial debris thickness mapping using UAV-based infrared thermography

Abstract. Debris-covered glaciers exist in many mountain ranges and play an important role in the regional water cycle. However, modelling the surface mass balance, runoff contribution and future evolution of debris-covered glaciers is fraught with uncertainty as accurate observations on small-scale variations in debris thickness and sub-debris ice melt rates are only available for a few locations worldwide. Here we describe a customised low-cost unoccupied aerial vehicle (UAV) for high-resolution thermal imaging of mountain glaciers and present a complete open-source pipeline that facilitates the generation of accurate surface temperature and debris thickness maps from radiometric images. First, a radiometric orthophoto is computed from individual radiometric UAV images using structure-from-motion and multi-view-stereo techniques. User-specific calibration and correction procedures can then be applied to the radiometric orthophoto to account for atmospheric and environmental influences that affect the radiometric measurement. The thermal orthophoto reveals distinct spatial variations in surface temperature across the surveyed debris-covered area. Finally, a high-resolution debris thickness map is derived from the corrected thermal orthophoto using an empirical or inverse surface energy balance model that relates surface temperature to debris thickness and is calibrated against in situ measurements. Our results from a small-scale experiment on the Kanderfirn (also known as Kander Neve) in the Swiss Alps show that the surface temperature and thickness of a relatively thin debris layer (ca. 0–15 cm) can be mapped with high accuracy using an empirical or physical model. On snow and ice surfaces, the mean deviation of the mapped surface temperature from the melting point (∼ 0 ∘C) was 0.6 ± 2.0 ∘C. The root-mean-square error of the modelled debris thickness was 1.3 cm. Through the detailed mapping, typical small-scale debris features and debris thickness patterns become visible, which are not spatially resolved by the thermal infrared sensors of current-generation satellites. The presented approach paves the way for comprehensive high-resolution supraglacial debris thickness mapping and opens up new opportunities for more accurate monitoring and modelling of debris-covered glaciers.

Multidecadal Changes in the Flow Velocity and Mass Balance of the Hailuogou Glacier in Mount Gongga, Southeastern Tibetan Plateau

Maritime glaciers in the southeastern Tibetan Plateau (TP) have experienced important changes in mass and dynamics over the past decades, challenging the regional water supply and glacier-related hazards. However, knowledge about long-term variations in the surface velocity and mass balance of maritime glaciers remains incomplete due to the lack of representative observations in the southeastern TP. In this study, offset tracking is employed to measure spatiotemporal variation in the surface velocity of the Hailuogou Glacier (HLG) in Mount Gongga of the southeastern TP using Sentinel-1A imagery, while the time series of the HLG mass balance is reconstructed since 1950 by a physically based energy–mass balance model. Our satellite-based results find that HLG surface velocity shows significant spatial heterogeneity with a double-peak pattern along the flow line, and sustained slowdown below the icefall zone has been observed during the past nearly 40 years, although the icefall zone and the area above it have become relatively active. Our modeling indicates a persistent increase in mass loss over the last seven decades with an average rate of −0.58 m water equivalent (w.e.) year−1, which has accelerated in the past two decades. Sustained slowdown on the glacier is concomitant with pronounced negative mass balance, thereby enhancing glacier wastage in recent decades. The long-term trend in HLG mass loss is mainly driven by an increase in positive air temperature that decreases surface albedo and solid precipitation ratio and increases longwave incoming radiation, besides the influence of supraglacial debris cover. Large-scale atmospheric circulation patterns in the Eurasian region provide important implications for regional-to-local climate variability, unsustainably intensifying the trend of the negative mass balance of the HLG in the southeastern TP in the past two decades.

Analysis of gap filling techniques for GRACE/GRACE-FO terrestrial water storage anomalies in Canada

Terrestrial water storage anomaly (TWSA) data derived from the Gravity Recovery and Climate Experiment (GRACE/GRACE-FO) have become indispensable for hydrological monitoring since the first mission launched in 2002. Evaluation of basin dynamics is enabled through TWSA integration with independent hydrological and climate datasets such as precipitation, evapotranspiration, and surface runoff. With over 20 years of observations, long-term statistical analysis reveals water storage trends, provided the 11-month gap between the two missions is filled. This study compares four methods for reconstructing GRACE-like TWSA over Canada, namely: extreme gradient boosting, artificial neural networks, automated machine learning, and projection onto convex sets. The GRACE mascon product released by the Jet Propulsion Laboratory is used over the study region. Nine sets of hydrological and climate parameters are used as predictors for the machine learning models, namely GRACE average seasonal signals, TWSA from the GLDAS Catchment Land Surface Model, precipitation, air temperature, glacier surface mass balance, ocean tides, the North Atlantic Oscillation, the Multivariate ENSO Index, and sea surface temperature. For each of the four methods, 20 % of the GRACE TWSA data (the ‘testing data’) is omitted from the model training, and the model is used to fill the artificial gap. Root mean square error (RMSE) is computed using the difference between testing data and model predictions. Normalized RMSE expresses the RMSE as a proportion of the range of the GRACE TWSA data. The automated machine learning algorithm performs best in terms of mean normalized root mean square error, with 6 % (2.4 cm equivalent water height RMSE), followed by projection onto convex sets, extreme gradient boosting, and artificial neural networks. Inclusion of glacier surface mass balance models derived from the GMAO Modern-Era Retrospective Analysis for Research and Applications Version 2 reanalysis and the Randolph Glacier Inventory improved the automated machine learning average root mean square error by 70 %. Results indicate that filling the gap between missions allows for more comprehensive analysis of terrestrial water storage changes, including basin-by-basin analysis, which is ongoing.

Surface mass balance and energy balance of the 79N Glacier (Nioghalvfjerdsfjorden, NE Greenland) modeled by linking COSIPY and Polar WRF – CORRIGENDUM

Surface mass balance and energy balance of the 79N Glacier (Nioghalvfjerdsfjorden, NE Greenland) modeled by linking COSIPY and Polar WRF – CORRIGENDUM

Exploring the ability of the variable-resolution Community Earth System Model to simulate cryospheric–hydrological variables in High Mountain Asia

Abstract. Earth system models (ESMs) can help to improve the understanding of climate-induced cryospheric–hydrological impacts in complex mountain regions, such as High Mountain Asia (HMA). Coarse ESM grids, however, have difficulties in representing cryospheric–hydrological processes that vary over short distances in complex mountainous environments. Variable-resolution (VR) ESMs can help to overcome these limitations through targeted grid refinement. This study investigates the ability of the VR Community Earth System Model (VR-CESM) to simulate cryospheric–hydrological variables such as the glacier surface mass balance (SMB) over HMA. To this end, a new VR grid is generated, with a regional grid refinement up to 7 km over HMA. Two coupled atmosphere–land simulations are run for the period 1979–1998. The second simulation is performed with an updated glacier cover dataset and includes snow and glacier model modifications. Comparisons are made to gridded outputs derived from a globally uniform 1∘ CESM grid, observation-, reanalysis-, and satellite-based datasets, and a glacier model forced by a regional climate model (RCM). Climatological biases are generally reduced compared to the coarse-resolution CESM grid, but the glacier SMB is too negative relative to observation-based glaciological and geodetic mass balances, as well as the RCM-forced glacier model output. In the second simulation, the SMB is improved but is still underestimated due to cloud cover and temperature biases, missing model physics, and incomplete land–atmosphere coupling. The outcomes suggest that VR-CESM could be a useful tool to simulate cryospheric–hydrological variables and to study climate change in mountainous environments, but further developments are needed to better simulate the SMB of mountain glaciers.

Reconstructing 32 years (1989–2020) of annual glacier surface mass balance in Chandra Basin, Western Himalayas, India

Reconstructing 32 years (1989–2020) of annual glacier surface mass balance in Chandra Basin, Western Himalayas, India

The importance of regional sea-ice variability for the coastal climate and near-surface temperature gradients in Northeast Greenland

Abstract. The climate in Northeast Greenland is shaped by complex topography and interaction with the cryosphere. Since the regional ecosystem processes are sensitive to atmospheric stability conditions, it is crucial to capture this complexity including adequate cryosphere coupling. This study uses an observational dataset from the Zackenberg region (Northeast Greenland) to investigate the local- and large-scale factors that determine the slope temperature gradient (STG), i.e., the temperature gradient along the mountain slope. A synthesis of automated weather stations, reanalysis, and a regional climate model simulations was used. For all seasons, our results show that snow cover and near-fjord ice conditions are the dominating factors governing the temporal evolution of the STG in the Zackenberg region. Considering large-scale drivers of the STG, we find that temperature inversions are associated with positive 500 hPa geopotential height and surface pressure anomalies over East Greenland. A strong connection between fractional sea-ice cover (SIF) in the Greenland Sea and the terrestrial climate of the Zackenberg region is found. A positive SIF anomaly coincides with a shallow STG, i.e., more positive (inversions) or less negative than the mean STG, since the temperature at the bottom of the valley decreases more than at the top. For example, the mean STG varies by ∼4 ∘C km−1 for a corresponding ∼27 % change in SIF. Reduction in temperature and precipitation (snowfall) during the days with high sea ice also affects the surface mass balance (SMB) of nearby glaciers and ice caps as shown for the A. P. Olsen Ice Cap. During summer, days with high SIF are associated with a positive SMB anomaly in the ablation area (∼16 mm w.e. d−1; indicating less melt) and a negative anomaly in the accumulation area (∼-0.3 mm w.e. d−1; indicating less accumulation). Based on our findings, we speculate that the local conditions in the Zackenberg region associated with anomalously low sea ice (i.e., a decrease in atmospheric stability) will be more prominent in the future with climate warming.

Everest South Col Glacier did not thin during the period 1984–2017

Abstract. The South Col Glacier is a small body of ice and snow (approx. 0.2 km2) located at the very high elevation of 8000 m a.s.l. (above sea level) on the southern ridge of Mt. Everest. A recent study by Potocki et al. (2022) proposed that South Col Glacier is rapidly losing mass. This is in contradiction to our comparison of two digital elevation models derived from aerial photographs taken in December 1984 and a stereo Pléiades satellite acquisition from March 2017, from which we estimate a mean elevation change of 0.01 ± 0.05 m a−1. To reconcile these results, we investigate some aspects of the surface energy and mass balance of South Col Glacier. From satellite images and a simple model of snow compaction and erosion, we show that wind erosion has a major impact on the surface mass balance due to the strong seasonality in precipitation and wind and that it cannot be neglected. Additionally, we show that the melt amount predicted by a surface energy and mass balance model is very sensitive to the model structure and implementation. Contrary to previous findings, melt is likely not a dominant ablation process on this glacier, which remains mostly snow-covered during the monsoon.

Brief communication: Non-linear sensitivity of glacier mass balance to climate attested by temperature-index models

Abstract. Temperature-index models have been widely used for glacier-mass projections spanning the 21st century. The ability of temperature-index models to capture non-linear responses of glacier surface mass balance (SMB) to high deviations in air temperature and solid precipitation was recently discussed in the context of mass-balance simulations employing advanced machine-learning techniques. Here, we performed numerical experiments with a classic temperature-index model and confirmed that such models are capable of detecting non-linear responses of glacier SMB to temperature and precipitation changes. Non-linearities derive from the change in the degree-day factor over the ablation season and from the lengthening of the ablation season.

Response of the Thick and Thin Debris-Covered Glaciers between 1971 and 2019 in Ladakh Himalaya, India—A Case Study from Pensilungpa and Durung-Drung Glaciers

This paper aims to broadly understand the response of glaciers to thick and thin debris cover from one of the less explored regions (Zanskar) of the Himalaya. The present study is based on ground-based measurements (from 2015 to 2019), satellite data (since 1971), and available topographic maps (at a 1:50,000 scale). The study includes snout retreat, changes in equilibrium line altitude (ELA), surface elevation, and modeled mass balance of thick and thin debris-covered Pensilungpa (Suru River basin) and Durung-Drung (Doda River basin) glaciers in the western Indian Himalaya, Ladakh, for the past five decades. The Durung-Drung Glacier (DDG) receded ~−624 ± 547 m with an average rate of −12 ± 11 m a−1 between 1971 and 2019. The frontal part of the DDG is broad (~2 km wide), which shows wide discrepancies in its retreat. Compared to DDG, the small and narrow snout of the Pensilungpa Glacier (PG) retreated −270.5 ± 27.5 m (1971 to 2019), with an average rate of −5.6 ± 0.57 m a−1. Similarly, the four years (2015–2019) of field observations suggest that the retreat rate of PG and DDG is −6.7 ± 3 and −18 ± 15 m a−1, and the rate of modeled glacier mass loss is −0.29 ± 0.3 and −0.3 ± 0.3 m w.e. a−1, respectively. Furthermore, the ELA of the DDG and PG between 1971 and 2019 increased by ~59 ± 38 and ~23 ± 19 m, respectively. The change in the longitudinal profile of the glaciers along the centerline between 2000 and 2017 shows the DDG and PG lost ~17 and 15 m surface ice thickness. The change in debris cover plays a critical role in the glacier surface lowering, shrinkage, retreat, and mass balance. Hence, we quantitatively evaluated the influence of the debris cover on summer ablation and terminus recession on two different characteristic glaciers (DDG and PG) with its potential effect on the mass balance process (area-volume loss).

Periodicity of the Southern Annular Mode in Southern Patagonia, insight from the Lago Argentino varve record

Climatic variability across a large fraction of the Southern Hemisphere is controlled by the Southern Annular Mode and associated latitudinal shifts in the Southern Westerly Wind belt. In Patagonia, these changes control the large-scale temperature and precipitation trends – and resulting glacier surface mass balance. Our understanding of recent changes in this climatic oscillation is, however, limited by the number of paleo-environmental records in the mid to high-latitude Southern Hemisphere. Here, we first use a synthetic proxy record to demonstrate that periodicity may be preserved in a wider range of records than can be used for quantitative paleoclimatic reconstructions. We then analyze a 5000-year-long sedimentation record derived from Lago Argentino, a 1500 km2 ice-contact lake in Southern Patagonia. We extract a mass accumulation rate and greyscale pixel intensity record from 28 cores across all of Lago Argentino's main depositional environments. We align the mass accumulation rate and pixel intensity records to a common time axis through multivariate dynamic-time-warping, and investigate their spectral properties using the multi-taper Lomb Scargle periodogram. We find statistically significant spectral peaks at 200 ± 20, 150 ± 16, and 85 ± 9 years in two thirds of mass accumulation rate and one third of the pixel intensity records. These periodicities reveal the centennial periodicity of the Southern Annular Mode, which is the key climatic driver of sedimentation at Lago Argentino.

Modelling evolution of a large, glacier-fed lake in the Western Indian Himalaya

In this study, we simulated the evolution of a large glacier-fed lake called the Gepan Gath lake located in Western Himalayas by numerically modelling the evolution of the Gepan Gath glacier that feeds the lake. Due to the extremely large volume and steep lake sidewalls, the lake has been classified as ‘critical’ or prone to hazards such as lake outburst floods in the future, by various scientific investigations. This modelling was carried out by a 1D model that is based on the principle of mass conservation. The 1D model was forced with the glacier surface mass balance (SMB). Due to non-availability of published in-situ estimates, the SMB was estimated using an energy balance-based model on station derived and reanalysis derived meteorological data. Modelled glacier length fluctuations for over 134 years matched reasonably well with that of observed within the RMSE error ~ 320 m. In addition to that, between 2004 and 2019, the modelled and observed lake lengths were in agreement with each other with the RMSE ~ 110 m. Modelled glacier lake lengths also match well with published, satellite imagery derived lengths within 15% uncertainty. The uncertainty in future lake length fluctuations is within 100–200 m. Our ultimate aim is to show that numerical ice-flow modelling can be an asset in modelling glacier-fed lake evolution even in the case of highly data-sparse regions of the IHR.

Reconstruction of Annual Glacier Mass Balance from Remote Sensing-Derived Average Glacier-Wide Albedo

Annual mass balance is an important reflection of glacier status that is also very sensitive to climate fluctuations. However, there is no effective and universal albedo-based method for the reconstruction of annual mass balance due to the scarcity of field observations. Here, we present an improved albedo–mass balance (IAMB) method to estimate annual glacier surface mass balance series using remote sensing techniques. The averaged glacier-wide albedo derived with the MODImLab algorithm during the summer season provides an effective proxy of the annual mass change. Defined as the variation in the albedo as a function of elevation change, the altitude–albedo gradient (∂z/∂α) can be obtained from a glacier digital elevation model (DEM) and optical images. The Chhota Shigri glacier situated in the western Himalayas was selected to test and assess the accuracy of this method over the period from 2003 to 2014. Reconstructed annual mass budgets correlated well with those from the observed records, with an average difference and root mean square error (RMSE) of −0.75 mm w.e. a−1 and 274.91 mm w.e. a−1, respectively, indicating that the IAMB method holds promise for glacier mass change monitoring. This study provides a new technique for annual mass balance estimation that can be applied to glaciers with no or few mass balance observations.

What drives the decrease of glacier surface albedo in High Mountain Asia in the past two decades?

Glacier surface albedo is an important factor affecting glacier ablation, and a positive feedback mechanism has been observed between the surface albedo and mass balance of glaciers. It is important to understand the driving factors and mechanisms of glacier albedo changes (GAC). Based on the MODIS (Moderate resolution imaging spectroradiometer)-derived MOD10A1 and MYD10A1 albedo products, the glacier albedo trends in each MODIS grid cell during each melt season in High-Mountains Asia (HMA) from 2000 to 2020 were calculated. Decreasing glacier albedo trends were found, with a decline rate of 0.25 × 10−2 yr−1; in addition, the GACs exhibited great spatial differences among the 15 subregions. The geographical detector model (GDM) is a new spatial statistical method that can quantitatively reveal the driving forces of climate factors and light-absorbing particles on GAC under single-factor and two-factor interactions. These driving forces can be measured by the corresponding q value. The results showed that on the whole, solid precipitation (snowfall) had the strongest impact on GAC, followed by the glacier surface temperature. The q values of black carbon (BC) and dust were <0.1, but BC or dust had the greatest q value in the 9 subregions. The effects of each factor differed among different elevation zones. The interaction detector indicated that the q value under the influence of two factors was greater than that under a single factor, and the strongest interaction was between snowfall and BC, followed by between snowfall and dust. In 15 subregions, most of the greatest q values in each region corresponded to an interaction with BC or dust. Here, we obtained the main driving factors of GAC in different regions and emphasized the interactions between climatic factors and light-absorbing particles; these results provide references for further studies of glacier mass balance and surface albedo.

Light absorption and albedo reduction by pigmented microalgae on snow and ice

AbstractPigmented microalgae inhabiting snow and ice environments lower the albedo of glacier and ice-sheet surfaces, significantly enhancing surface melt. Our ability to accurately predict their role in glacier and ice-sheet surface mass balance is limited by the current lack of empirical data to constrain their representation in predictive models. Here we present new empirical optical properties for snow and ice algae and incorporate them in a radiative transfer model to investigate their impact on snow and ice surface albedo. We found ice algal cells to be more efficient absorbers than snow algal cells, but their blooms had comparable impact on surface albedo due to the different photic conditions of their habitats. We then used the model to reconstruct the effect of ice algae on bare ice albedo spectra collected at our field site in southern Greenland, where blooms dropped the albedo locally by between 3 and 43%, equivalent to 1–10 L m$^{-2}$ d$^{-1}$ of melted ice. Using the newly parametrized model, future studies could investigate biological albedo reduction and algal quantification from remote hyperspectral and multispectral imagery.

Accelerated Shrinkage of Glaciers in the Altai Mountains From 2000 to 2020

Mountain glaciers are an important component of the global hydrological cycle. Existing research about glacier changes in the Altai focused on limited regions. Study about recent glacier changes in the entire Altai Mountains is still lacking. We presented a consistent method for identifying glacier margins. The two new glacier inventories in 2000 and 2020 were derived from Landsat satellite imagery. Glacier surface elevation change and mass balance were obtained by comparing the 2000 Shuttle Radar Topography Mission (SRTM) and 2020 Digital Elevation Models (DEMs) generated from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images. The spatial pattern of glacier changes was discussed in conjunction with climate trends. We mapped a total area of 1,096.06 ± 53.32 km2around 2020, which amounts to 1,927 glaciers in the Altai Mountains. That was 12.02 ± 3.01% (or 0.60 ± 0.15%·a−1) less than the 1,245.75 ± 58.52 km2around 2000. The geodetic mass balance of the monitoring glaciers in the Aktru basin for the period 2000–2011 was used to validate the geodetic survey. The average geodetic mass balance of -0.32 ± 0.09 m w. e.·a−1on monitoring glaciers was slightly exaggerated than the observed mass balance of -0.26 m w. e.·a−1, but it was proved that the geodetic mass balance could reflect glacier changes in the Altai Mountains. An average mass loss of 14.55 ± 1.32 m w. e. (or 0.74 ± 0.07 m w. e.·a−1) was found during 2000–2020 in the Altai Mountains. Although the glacier area changes and mass balance were characterized by spatial heterogeneity, the glaciers in the Altai had experienced an accelerated shrinkage from 2000 to 2020 compared to the 20th century. The rising temperature is the foremost reason for glacier area shrinkage and mass loss according to the Climatic Research Unit (CRU) reanalysis data.

Understanding monsoon controls on the energy and mass balance of glaciers in the Central and Eastern Himalaya

Abstract. The Indian and East Asian summer monsoons shape the melt and accumulation patterns of glaciers in High Mountain Asia in complex ways due to the interaction of persistent cloud cover, large temperature ranges, high atmospheric water content and high precipitation rates. Glacier energy- and mass-balance modelling using in situ measurements offers insights into the ways in which surface processes are shaped by climatic regimes. In this study, we use a full energy- and mass-balance model and seven on-glacier automatic weather station datasets from different parts of the Central and Eastern Himalaya to investigate how monsoon conditions influence the glacier surface energy and mass balance. In particular, we look at how debris-covered and debris-free glaciers respond differently to monsoonal conditions. The radiation budget primarily controls the melt of clean-ice glaciers, but turbulent fluxes play an important role in modulating the melt energy on debris-covered glaciers. The sensible heat flux decreases during core monsoon, but the latent heat flux cools the surface due to evaporation of liquid water. This interplay of radiative and turbulent fluxes causes debris-covered glacier melt rates to stay almost constant through the different phases of the monsoon. Ice melt under thin debris, on the other hand, is amplified by both the dark surface and the turbulent fluxes, which intensify melt during monsoon through surface heating and condensation. Pre-monsoon snow cover can considerably delay melt onset and have a strong impact on the seasonal mass balance. Intermittent monsoon snow cover lowers the melt rates at high elevation. This work is fundamental to the understanding of the present and future Himalayan cryosphere and water budget, while informing and motivating further glacier- and catchment-scale research using process-based models.

Large‐eddy simulations of the atmospheric boundary layer over an Alpine glacier: Impact of synoptic flow direction and governing processes

AbstractThe mass balance of mountain glaciers is of interest for several applications (e.g., local hydrology or climate projections), and turbulent fluxes can be an important contributor to glacier surface mass balance during strong melting events. The underlying complex terrain leads to spatial heterogeneity and non‐stationarity of turbulent fluxes. Owing to the contribution of thermally induced flows and gravity waves, exchange mechanisms are fully three‐dimensional, instead of only vertical. Additionally, glaciers have their own distinct microclimate, governed by a down‐glacier katabatic wind, which protects the glacier ice and interacts with the surrounding flows on multiple scales. In this study, we perform large‐eddy simulations with the Weather Research and Forecasting model at a horizontal grid spacing of 48 m to gain insight into the boundary‐layer processes over an Alpine valley glacier, the Hintereisferner. We choose two case studies from the Hintereisferner experiment measurement campaign with different synoptic wind directions (southwest and northwest). Model evaluation with an array of eddy‐covariance stations on the glacier tongue and surroundings reveals that the Weather Research and Forecasting model is able to simulate the general glacier boundary‐layer structure. Under a southwesterly airflow, the down‐glacier wind is supported by the synoptic wind parallel to the glacier axis, a stable boundary layer is present over the ice surface, and local processes govern the turbulence kinetic energy production. Under northwesterly airflow, a cross‐glacier valley flow and a breaking gravity wave lead to strong turbulent mixing and to the subsequent erosion of the glacier boundary layer. Stationarity analysis of the sensible heat flux suggests non‐stationary behaviour for both case study days, whereas non‐stationarity is highest on the northwesterly day during the gravity‐wave event. These results suggest that the synoptic wind direction has, in addition to upstream topography and the atmospheric stability, a strong impact on whether a local glacier boundary layer can form or not, influencing whether a glacier is able to maintain its own microclimate.

Reconstructed annual glacier surface mass balance in the Ányêmaqên Mountains, Yellow River source, based on snow line altitude

Reconstructed annual glacier surface mass balance in the Ányêmaqên Mountains, Yellow River source, based on snow line altitude