Sensible heat exchange at the Antarctic snow surface: a study with automatic weather stations

Broeke, Michiel van den; As, Dirk van; Reijmer, C. H.; Wal, Roderik van de

doi:10.1002/joc.1152

Cited by 53 publications

(66 citation statements)

References 41 publications

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“…This procedure left 417 hourly values of SHF and 223 of LHF. With regression coefficients of 0.68 and 0.74, agreement is reasonable, but with regression slopes less than unity and a significant bias, agreement is less good than for a similar comparison of Antarctic data (Van den Broeke et al, 2005). This can likely be attributed to the much greater seasonal variability in the nature of the GrIS surface, which introduces, e.g., an unknown displacement distance.…”

Section: Validation Of Calculated Turbulent Fluxesmentioning

confidence: 67%

“…At S5, in contrast, the largest absolute surface-to-air temperature gradients are found in summer, with daily mean values in excess of 4°C m −1 (Figure 6(a)). But strong inversions alone are not sufficient to generate large values of θ * : in order for the stability correction to remain small ( h in Equation (2)), L MO and thus wind shear u * must be sufficiently large; katabatic forcing ensures that this is the case (see Section 4.3 and Van den Broeke et al, 2005). The large temperature gradient in combination with strong mixing sustains large positive values of θ * at S5 during summer with typical values of 0.15-0.25 K (Figure 7(a)).…”

Section: Resultsmentioning

confidence: 99%

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Surface layer climate and turbulent exchange in the ablation zone of the west Greenland ice sheet

Broeke

Smeets

Ettema

2008

Intl Journal of Climatology

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ABSTRACT:A comprehensive description is presented of the surface layer (SL) wind, temperature and humidity climate and the resulting sensible and latent heat exchange in the ablation zone of the west Greenland ice sheet. Over a four-year period (August 2003-August 2007, data were collected using three automatic weather stations (AWS) located along the 67°N latitude circle at 6, 38 and 88 km from the ice sheet margin at elevations of 490, 1020 and 1520 m asl. In the lower ablation zone, surface momentum roughness peaks in summer, which enhances the mechanical generation of turbulence in the stable SL. The SL is stably stratified throughout the year: in summer, the surface temperature is maximised at the melting point and therefore remains colder than the overlying air, in winter the surface is cooled by a radiation deficit. The resulting downward directed sensible heat flux cools the SL air. Humidity gradients between surface and air are small in winter, in response to low temperatures, but peak in spring, when the surface is not yet melting and can freely increase its temperature. This is especially true for the lower ablation zone, where winter accumulation is small so that the dark ice surface is already exposed at the onset of spring, allowing significant convection and sublimation. During summer, when the surface is melting, the sensible heat flux becomes directed towards the surface and sublimation changes into deposition in the lower ablation zone. The SL wind climate is dominated by katabatic forcing, with high directional constancy in summer and winter. The katabatic forcing is important to maintain turbulent exchange in the stable Greenland SL.

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Section: Validation Of Calculated Turbulent Fluxesmentioning

confidence: 67%

Section: Resultsmentioning

confidence: 99%

Surface layer climate and turbulent exchange in the ablation zone of the west Greenland ice sheet

Broeke

Smeets

Ettema

2008

Intl Journal of Climatology

Self Cite

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“…We noted no substantial changes, i.e., no difference > 1 %, in the 30 min turbulent fluxes during these tests, however. The latent-heat flux data were corrected for oxygen absorption by the KH2O (Tanner et al, 1993) and for fluctuations in the water vapor density induced by high-frequency changes in air temperature (Webb-Pearman-Leuning correction;Webb et al, 1980). Finally, we applied a series of standardized processing steps consisting of corrections for potentially high-and low-frequency loss, and sensor separation (Ibrom et al, 2007;Moncrieff et al, 2004;Horst and Lenschow, 2009).…”

Section: Eddy-covariance Data Processingmentioning

confidence: 99%

“…Direct measurements of turbulent fluxes, by an eddy-covariance method, are relatively rare because they require sophisticated instrumentation requiring continuous maintenance, making them unsuitable for long-term operational purposes. Few studies exist that have directly measured turbulent fluxes over mountain glaciers, and all of these studies are restricted to shorter time intervals, e.g., weeks to a couple of months (e.g., Munro, 1989;Forrer and Rotach, 1997;van der Avoird and Duynkerke, 1999;Cullen et al, 2007;Guo et al, 2011;Conway and Cullen, 2013). A more common approach in the studies of SEB on glaciers is to derive the turbulent fluxes through parameterization schemes that utilize the observations of mean meteorological variables such as near-surface air temperature, wind, and relative humidity (e.g., Hock and Holmgren, 2005;Sicart et al, 2005;Mölg et al, 2008;Reijmer and Hock, 2008;Mölg et al, 2009;MacDougall and Flowers, 2011;Sicart et al, 2011;Huintjes et al, 2015;Prinz et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

“…Without them, roughness lengths from other studies are used assuming that the values are universally applicable on similar glacier surfaces (e.g., Greuell and Oerlemans, 1989;Konzelmann and Braithwaite, 1995). Values of z 0v derived at glacier ice surfaces widely vary in space and time (Bintanja and van den Broeke, 1995;van den Broeke, 1996). There are few directly measured values for the scalar roughness lengths (z 0t and z 0q ) for mountain glaciers, which has led to approaches that assume their values approximate z 0v .…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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Abstract. As part of surface energy balance models used to simulate glacier melting, choosing parameterizations to adequately estimate turbulent heat fluxes is extremely challenging. This study aims to evaluate a set of four aerodynamic bulk methods (labeled as C methods), commonly used to estimate turbulent heat fluxes for a sloped glacier surface, and two less commonly used bulk methods developed from katabatic flow models. The C methods differ in their parameterizations of the bulk exchange coefficient that relates the fluxes to the near-surface measurements of mean wind speed, air temperature, and humidity. The methods' performance in simulating 30 min sensible-and latent-heat fluxes is evaluated against the measured fluxes from an open-path eddycovariance (OPEC) method. The evaluation is performed at a point scale of a mountain glacier, using one-level meteorological and OPEC observations from multi-day periods in the 2010 and 2012 summer seasons. The analysis of the two independent seasons yielded the same key findings, which include the following: first, the bulk method, with or without the commonly used Monin-Obukhov (M-O) stability functions, overestimates the turbulent heat fluxes over the observational period, mainly due to a substantial overestimation of the friction velocity. This overestimation is most pronounced during the katabatic flow conditions, corroborating the previous findings that the M-O theory works poorly in the presence of a low wind speed maximum. Second, the method based on a katabatic flow model (labeled as the K Int method) outperforms any C method in simulating the friction velocity; however, the C methods outperform the K Int method in simulating the sensible-heat fluxes. Third, the best overall performance is given by a hybrid method, which combines the K Int approach with the C method; i.e., it parameterizes eddy viscosity differently than eddy diffusivity. An error analysis reveals that the uncertainties in the measured meteorological variables and the roughness lengths produce errors in the modeled fluxes that are smaller than the differences between the modeled and observed fluxes. This implies that further advances will require improvement to model theory rather than better measurements of input variables. Further data from different glaciers are needed to investigate any universality of these findings.

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Polynya dynamics drive primary production in the Larsen A and B embayments following ice shelf collapse

et al. 2014

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[1] The climate-driven collapses of the Larsen A and B ice shelves have opened up new regions of the coastal Antarctic to the influence of sea ice resulting in increases in seasonal primary production. In this study, passive microwave remote sensing of sea ice concentration and satellite imagery of ocean color are employed to quantify the magnitude of and variability in open water area and net primary productivity (NPP) in the Larsen embayments between 1997 and 2011. Numerical model output provides context to analyze atmospheric forcing on the coastal ocean. Following ice shelf disintegration the embayments function as coastal, sensible heat polynyas. The Larsen A and B are as productive as other Antarctic shelf regions, with seasonally averaged daily NPP rates reaching 1232 and 1127 mg C m 22 d 21 and annual rates reaching 200 and 184 g C m 22 yr 21 , respectively. A persistent cross-shelf gradient in NPP is present with higher productivity rates offshore, contrasting with patterns observed along the West Antarctic Peninsula. Embayment productivity is intimately tied to sea ice dynamics, with large interannual variability in NPP rates driven by open water area and the timing of embayment opening. Opening of the embayment is linked to periods of positive Southern Annular Mode and stronger westerlies, which lead to the vertical deflection of warm, maritime air over the peninsula and down the leeward side causing increases in surface air temperature and wind velocity. High productivity in these new polynyas is likely to have ramifications for organic matter export and marine ecosystem evolution.Citation: Cape, M. R., M. Vernet, M. Kahru, and G. Spreen (2014), Polynya dynamics drive primary production in the Larsen A and B embayments following ice-shelf collapse,

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Sensible heat exchange at the Antarctic snow surface: a study with automatic weather stations

Cited by 53 publications

References 41 publications

Surface layer climate and turbulent exchange in the ablation zone of the west Greenland ice sheet

Surface layer climate and turbulent exchange in the ablation zone of the west Greenland ice sheet

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

Polynya dynamics drive primary production in the Larsen A and B embayments following ice shelf collapse

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