A 5 year record of surface energy and mass balance from the ablation zone of Storbreen, Norway

Andreassen, Liss M.; Broeke, M. R. van den; Giesen, Rianne H.; Oerlemans, J.

doi:10.3189/002214308784886199

Cited by 41 publications

(47 citation statements)

References 34 publications

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“…Relevant techniques to estimate turbulent fluxes, such as the bulk aerodynamic method widely used in glacio-meteorological investigations, should be usable only within the lowest several metres above the surface (e.g. Davies 1977, 1978;Denby and Greuell 2000;Andreassen et al 2008;Oerlemans 2010). As Hock (2005) argued, the determination of turbulent fluxes still constitutes a major uncertainty in energy-balance melt models, partly due to potential errors in the scalar roughness length parametrization.…”

Section: Introductionmentioning

confidence: 99%

Critical Evaluation of Scalar Roughness Length Parametrizations Over a Melting Valley Glacier

Guo

Yang

Zhao

et al. 2011

Boundary-Layer Meteorol

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We present a field investigation over a melting valley glacier on the Tibetan Plateau. In the ablation zone, aerodynamic roughness lengths (z 0M ) vary on the order of 10 −4 -10 −2 m, whose evolution corresponds to three melt phases with distinct surface cover and moisture exchange: snow (sublimation/evaporation), bare ice (deposition/condensation), and ice hummocks (sublimation/evaporation). Bowen-ratio similarity is validated in the stably stratified katabatic winds, which suggests a useful means for data quality check. A roughness sublayer is regarded as irrelevant to the present ablation season, because selected characteristics of scalar turbulence over smooth snow are quite similar to those over hummocky ice. We evaluate three parametrizations of the scalar roughness lengths (z 0T for temperature and z 0q for humidity), viz. key factors for the accurate estimation of sensible heat and latent heat fluxes using the bulk aerodynamic method. The first approach is based on surface-renewal models and has been widely applied in glaciated areas; the second has never received application over an ice/snow surface, despite its validity in (semi-)arid regions; the third, a derivative of the first, is proposed for use specifically over rough ice defined as z 0M > 10 −3 m or so. This empirical z 0M threshold value is deemed of general relevance to glaciated areas (e.g. ice sheet/cap and valley/outlet glaciers), above which the first approach gives notably underestimated z 0T,q . The first and the third approaches tend to underestimate and overestimate turbulent heat/moisture exchange, respectively, frequently leading to relative errors higher than 30%. Comparatively, the second approach produces fairly low errors in energy flux estimates both in individual melt phases and over the whole ablation season; it thus emerges as a practically useful choice to parametrize z 0T,q in glaciated areas. Moreover, we find all 123 308 X. Guo et al. three candidate parametrizations unable to predict diurnal variations in the excess resistances to humidity transfer, thus encouraging more efforts for improvement.

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Section: Introductionmentioning

confidence: 99%

Critical Evaluation of Scalar Roughness Length Parametrizations Over a Melting Valley Glacier

Guo

Yang

Zhao

et al. 2011

Boundary-Layer Meteorol

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“…with Q R and Q G often deemed negligible in studies on mid-latitude glaciers (Sicart et al, 2005;Andreassen et al, 2008;Gillet and Cullen, 2011). For the direct measurement of Q H and Q L , the EC technique correlates high frequency measurements of the turbulent components of vertical wind speed (w) with those of potential temperature (θ ) and specific humidity (q), to determine the magnitude and direction of the fluxes:…”

Section: Seb Backgroundmentioning

confidence: 99%

“…In a number of studies (e.g., Andreassen et al, 2008), a 24 h running mean value for albedo (α) is calculated from the 30 min S i and S r data, and used to generate a new parameterized dataset for S i . This correction method, however, does not account for sub-daily variations that can occur in α, due to snowfall, snow aging and removal, changing water content of the surface, and cloud amount.…”

Section: Radiation Measurementsmentioning

confidence: 99%

Surface Energy Balance Closure and Turbulent Flux Parameterization on a Mid-Latitude Mountain Glacier, Purcell Mountains, Canada

2017

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In the majority of glacier surface energy balance studies, parameterization rather than direct measurement is used to estimate one or more of the individual heat fluxes, with others, such as the rain and ground heat fluxes, often deemed negligible. Turbulent fluxes of sensible and latent heat are commonly parameterized using the bulk aerodynamic technique. This method was developed for horizontal, uniform surfaces rather than sloped, inhomogeneous glacier terrain, and significant uncertainty remains regarding the selection of appropriate roughness length values, and the validity of the atmospheric stability functions employed. A customized weather station, designed to measure all relevant heat fluxes, was installed on an alpine glacier over the 2014 melt season. Eddy covariance techniques were used to observe the turbulent heat fluxes, and to calculate site-specific roughness values. The obtained dataset was used to drive a point ablation model, and to evaluate the most commonly used bulk methods and roughness length schemes in the literature. Modeled ablation showed good agreement with observed rates at seasonal, daily, and sub-daily timescales, effectively closing the surface energy balance, and giving a high level of confidence in the flux observation method. Net radiation was the dominant contributor to melt energy over the season (65.2%), followed by the sensible heat flux (29.7%), while the rain heat flux was observed to be a significant contributor on daily timescales during periods of persistent heavy rain (up to 20% day −1 ). Momentum roughness lengths observed for the study surface (snow: 10 −3.8 m; ice: 10 −2.2 m) showed general agreement with previous findings, while the scalar values (temperature: 10 −4.6 m; water vapor: 10 −6 m) differed significantly from those for momentum, disagreeing with the assumption of equal roughness lengths. Of the three bulk method stability schemes tested, the functions based on the Monin-Obukhov length returned mean daily flux values closest to those observed, but displayed poor performance on sub-daily timescales, and periods of substantial flux overestimation.

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“…An automatic weather station (AWS) has been operated in the ablation zone of the glacier since September 2001 providing a near-continuous series of meteorological parameters and surface energy balance. Analysis of the first five years of data revealed that variations in temperature and reflected shortwave radiation (albedo) explained most of the inter-annual variation in melt, whereas the seasonal mean incoming shortwave radiation was remarkably constant between the years (Andreassen et al, 2008). Within the CES project, a mass balance model was applied and tested for Storbreen (Andreassen and Oerlemans, 2009).…”

Section: Storbreen Southern Norwaymentioning

confidence: 99%

Climate Change and Energy Systems

Björnsson¹,

Þorsteinsson²

2012

TemaNord

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A 5 year record of surface energy and mass balance from the ablation zone of Storbreen, Norway

Cited by 41 publications

References 34 publications

Critical Evaluation of Scalar Roughness Length Parametrizations Over a Melting Valley Glacier

Critical Evaluation of Scalar Roughness Length Parametrizations Over a Melting Valley Glacier

Surface Energy Balance Closure and Turbulent Flux Parameterization on a Mid-Latitude Mountain Glacier, Purcell Mountains, Canada

Climate Change and Energy Systems

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