Evaluation of different methods to model near-surface turbulent fluxes for a mountain glacier in the Cariboo Mountains, BC, Canada

Radić, Valentina; Menounos, Brian; Shea, J. M.; Fitzpatrick, Noel; Tessema, Mekdes Ayalew; Déry, Stephen J.

doi:10.5194/tc-11-2897-2017

Cited by 36 publications

(83 citation statements)

References 76 publications

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“…Thus, it is vital to improve current understanding of the turbulent exchanges between glaciers and the atmosphere in order to understand how the changing climate influences glaciers, as well as how changing glacier surfaces might influence future atmospheric states and microclimates. However, the present paucity of suitable data over glacier surfaces limits deeper investigation of the processes of turbulence at the glacier-atmosphere boundary (Radic and others, 2017).…”

Section: Introductionmentioning

confidence: 99%

Comparison of turbulent structures and energy fluxes over exposed and debris-covered glacier ice

Nicholson

Stiperski

2020

J. Glaciol.

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We present the first direct comparison of turbulence conditions measured simultaneously over exposed ice and a 0.08 m thick supraglacial debris cover on Suldenferner, a small glacier in the Italian Alps. Surface roughness, sensible heat fluxes (~20–50 W m−2), latent heat fluxes (~2–10 W m−2), topology and scale of turbulence are similar over both glacier surface types during katabatic and synoptically disturbed conditions. Exceptions are sunny days when buoyant convection becomes significant over debris-covered ice (sensible heat flux ~ −100 W m−2; latent heat flux ~ −30 W m−2) and prevailing katabatic conditions are rapidly broken down even over this thin debris cover. The similarity in turbulent properties implies that both surface types can be treated the same in terms of boundary layer similarity theory. The differences in turbulence between the two surface types on this glacier are dominated by the radiative and thermal contrasts, thus during sunny days debris cover alters both the local surface turbulent energy fluxes and the glacier component of valley circulation. These variations under different flow conditions should be accounted for when distributing temperature fields for modeling applications over partially debris-covered glaciers.

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Section: Introductionmentioning

confidence: 99%

Comparison of turbulent structures and energy fluxes over exposed and debris-covered glacier ice

Nicholson

Stiperski

2020

J. Glaciol.

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“…Assuming similarity, fluxes are derived through the so-called bulk approach, in which the turbulence characteristics are captured in a single bulk transfer coefficient. This can be challenging on glacier surfaces (Conway and Cullen, 2013;Fitzpatrick et al, 2017;Radić et al, 2017), and becomes even more difficult for debris-covered glaciers, which show strong variations in surface temperature (Steiner and Pellicciotti, 2016;Kraaijenbrink et al, 2018) and humidity. Relative humidity at the surface is difficult to measure on a debris-covered glacier, and therefore the latent heat flux is often neglected (Lejeune et al, 2013;Rounce and McKinney, 2014) or calculated with the assumption of either full saturation or a completely dry surface (Rounce et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

The Importance of Turbulent Fluxes in the Surface Energy Balance of a Debris-Covered Glacier in the Himalayas

et al. 2018

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Surface energy balance models are common tools to estimate melt rates of debris-covered glaciers. In the Himalayas, radiative fluxes are occasionally measured, but very limited observations of turbulent fluxes on debris-covered tongues exist to date. We present measurements collected between 26 September and 12 October 2016 from an eddy correlation system installed on the debris-covered Lirung Glacier in Nepal during the transition between monsoon and post-monsoon. Our observations suggest that surface energy losses through turbulent fluxes reduce the positive net radiative fluxes during daylight hours between 10 and 100%, and even lead to a net negative surface energy balance after noon. During clear days, turbulent flux losses increase to over 250 W m −2 mainly due to high sensible heat fluxes. During overcast days the latent heat flux dominates the turbulent losses and together they reach just above 100 W m −2. Subsequently, we validate the performance of three bulk approaches in reproducing the observations from the eddy correlation system. Large differences exist between the approaches, and accurate estimates of surface temperature, wind speed, and surface roughness are necessary for their performance to be reasonable. Moreover, the tested bulk approaches generally overestimate turbulent latent heat fluxes by a factor 3 on clear days, because the debris-covered surface dries out rapidly, while the bulk equations assume surface saturation. Improvements to bulk surface energy models should therefore include the drying process of the surface. A sensitivity analysis suggests that, in order to be useful in distributed melt models, an accurate extrapolation of wind speed, surface temperature and surface roughness in space is a prerequisite. By applying the best performing bulk model over a complete melt period, we show that turbulent fluxes reduce the available energy for melt at the debris surface by 17% even at very low wind speeds. Overall, we conclude that turbulent fluxes play an essential role in the surface energy balance of debris-covered glaciers and that it is essential to include them in melt models.

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“…In addition, the surface temperature controls the sensible heat flux, which plays an important role in the energy balance of debris-covered glaciers and ice cliffs (Steiner et al, 2015;Buri et al, 2016a,b;Steiner and Pellicciotti, 2016). A comparison of thermal imagery collected before and after precipitation events might also help identify the role of moisture in the debris layer and its effect on latent heat fluxes, and lead to an overall improvement in turbulent flux parameterizations (e.g., Radić et al, 2017). Thirdly, thermal UAV imagery could be applied in understanding the surface and subsurface hydrology.…”

Section: Applications Of Thermal Uav Imagerymentioning

confidence: 99%

Mapping Surface Temperatures on a Debris-Covered Glacier With an Unmanned Aerial Vehicle

et al. 2018

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A layer of debris cover often accumulates across the surface of glaciers in active mountain ranges with exceptionally steep terrain, such as the Andes, Himalaya, and New Zealand Alps. Such a supraglacial debris layer has a major influence on a glacier's surface energy budget, enhancing radiation absorption, and melt when the layer is thin, but insulating the ice when thicker than a few cm. Information on spatially distributed debris surface temperature has the potential to provide insight into the properties of the debris, its effects on the ice below and its influence on the near-surface boundary layer. Here, we deploy an unmanned aerial vehicle (UAV) equipped with a thermal infrared sensor on three separate missions over one day to map changing surface temperatures across the debris-covered Lirung Glacier in the Central Himalaya. We present a methodology to georeference and process the acquired thermal imagery, and correct for emissivity and sensor bias. Derived UAV surface temperatures are compared with distributed simultaneous in situ temperature measurements as well as with Landsat 8 thermal satellite imagery. Results show that the UAV-derived surface temperatures vary greatly both spatially and temporally, with −1.4 ± 1.8, 11.0 ± 5.2, and 15.3 ± 4.7 • C for the three flights (mean ± sd), respectively. The range in surface temperatures over the glacier during the morning is very large with almost 50 • C. Ground-based measurements are generally in agreement with the UAV imagery, but considerable deviations are present that are likely due to differences in measurement technique and approach, and validation is difficult as a result. The difference in spatial and temporal variability captured by the UAV as compared with much coarser satellite imagery is striking and it shows that satellite derived temperature maps should be interpreted with care. We conclude that UAVs provide a suitable means to acquire surface temperature maps of debris-covered glacier surfaces at high spatial and temporal resolution, but that there are caveats with regard to absolute temperature measurement.

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Evaluation of different methods to model near-surface turbulent fluxes for a mountain glacier in the Cariboo Mountains, BC, Canada

Cited by 36 publications

References 76 publications

Comparison of turbulent structures and energy fluxes over exposed and debris-covered glacier ice

Comparison of turbulent structures and energy fluxes over exposed and debris-covered glacier ice

The Importance of Turbulent Fluxes in the Surface Energy Balance of a Debris-Covered Glacier in the Himalayas

Mapping Surface Temperatures on a Debris-Covered Glacier With an Unmanned Aerial Vehicle

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