Surface energy budget on Larsen and Wilkins ice shelves in the Antarctic Peninsula: results based on reanalyses in 1989–2010

Välisuo, Ilona; Vihma, Timo; King, John C.

doi:10.5194/tc-8-1519-2014

Cited by 18 publications

(22 citation statements)

References 51 publications

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“…They found a consistent warm bias and significant biases in wind components. Välisuo et al () supported the conclusion of Stössel et al () that the coarse resolution of reanalyses did not represent the complex orography of the Antarctic Peninsula accurately enough from the point of view of modelling of the wind field. Due to the inadequate resolution, the westerlies were overestimated and the northward wind component was underestimated.…”

Section: Introductionmentioning

confidence: 84%

Validation of eight atmospheric reanalyses in the Antarctic Peninsula region

Nygård

Vihma

Birnbaum

et al. 2015

Quart J Royal Meteoro Soc

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Eight atmospheric reanalyses were compared against observed vertical profiles of temperature, specific humidity and wind speed collected by two research aircraft in February-March 2010 in the Antarctic Peninsula region. These data offered a rare possibility to validate reanalyses against independent in-situ data which have not been assimilated into the reanalyses. The reanalyses had generally too moist profiles with too low wind speeds, but otherwise the errors in the reanalyses had large spatial differences. On the eastern side of the peninsula, the near-surface temperatures were largely overestimated. None of the reanalysis outperformed the others in all variables, at all altitudes and on both sides of the peninsula. Generally, NCEP-CFSR and MERRA had the smallest errors in temperature profiles, JRA-55 had marginally the most accurate specific humidity profiles and NCEP-CFSR had the best wind profiles. The reanalyses were coherent, although biased, on the western side of the Antarctic Peninsula, but on the eastern side the spread was large. All the reanalyses underestimated the variability between the individual profiles of temperature and wind speed. The modern reanalyses with a sufficient spatial resolution and an adequate data assimilation method outperformed the others, especially on the eastern side.

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Section: Introductionmentioning

confidence: 84%

Validation of eight atmospheric reanalyses in the Antarctic Peninsula region

Nygård

Vihma

Birnbaum

et al. 2015

Quart J Royal Meteoro Soc

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“…Välisuo et al . [] found biases in summertime radiative fluxes over Larsen Ice Shelf from three atmospheric reanalyses that were similar in both magnitude and sign to those found in the present study. Cloud microphysical parameterizations in atmospheric models are largely based on data gathered at low and middle latitudes and measurements of the microphysical properties of Antarctic clouds are limited [ Lachlan‐Cope , ].…”

Section: Discussionmentioning

confidence: 99%

Validation of the summertime surface energy budget of Larsen C Ice Shelf (Antarctica) as represented in three high‐resolution atmospheric models

et al. 2015

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We compare measurements of the turbulent and radiative surface energy fluxes from an automatic weather station (AWS) on Larsen C Ice Shelf, Antarctica with corresponding fluxes from three high-resolution atmospheric models over a 1 month period during austral summer. All three models produce a reasonable simulation of the (relatively small) turbulent energy fluxes at the AWS site. However, biases in the modeled radiative fluxes, which dominate the surface energy budget, are significant. There is a significant positive bias in net shortwave radiation in all three models, together with a corresponding negative bias in net longwave radiation. In two of the models, the longwave bias only partially offsets the positive shortwave bias, leading to an excessive amount of energy available for heating and melting the surface, while, in the third, the negative longwave bias exceeds the positive shortwave bias, leading to a deficiency in calculated surface melt. Biases in shortwave and longwave radiation are anticorrelated, suggesting that they both result from the models simulating too little cloud (or clouds that are too optically thin). We conclude that, while these models may be able to provide some useful information on surface energy fluxes, absolute values of modeled melt rate are significantly biased and should be used with caution. Efforts to improve model simulation of melt should initially focus on the radiative fluxes and, in particular, on the simulation of the clouds that control these fluxes.

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“…Previous iceshelf collapses are thought to have been accomplished by surface meltwater-driven crevassing (van der Veen, 1998;van den Broeke, 2005;Banwell et al, 2013) and ice-front retreat past a "compressive arch" in strain rates (Doake et al, 1998;Kulessa et al, 2014). We conceive several interconnected mechanisms by which LCIS stability could be compromised: (1) ice-front retreats past a compressive arch; (2) increased surface melting causes firn depletion and meltwater-driven crevassing; (3) decreased ocean freezing or increased melting depletes marine ice, permitting the propagation of crevasses; (4) collapse of the remnant LBIS opens a new ice front at the northern margin of LCIS; (5) ungrounding from Bawden Ice Rise removes an ice-front pinning point; (6) ice thinning and acceleration enhances the propagation of crevasses and weakens shear zones.…”

Section: Ice-shelf Stabilitymentioning

confidence: 99%

“…Observed AP surface melt days and modelled meltwater fluxes both lack significant trends during 1979-2010 and have trends that are strongly negative during 1989(Kuipers Munneke et al, 2012a). An automatic weather station on LCIS lacks any significant 1985-2011 trend in air temperature in any season (Valisuo et al, 2014), and there is no convincing evidence of trends in melting derived from reanalysis models during recent decades (Valisuo et al, 2014). Even without a trend in atmospheric forcing within recent decades, the period could still be anomalous relative to the long-term mean, and so an atmosphere-driven lowering remains viable.…”

Section: Introductionmentioning

confidence: 99%

“…These ice-shelf collapses are thought to have been accomplished by surface meltwater-driven crevassing (van der Veen, 1998;van den Broeke, 2005;Banwell et al, 2013) and ice-front retreat past a "compressive arch" in strain rates (Doake et al, 1998;Kulessa et al, 2014). However, longer-term processes such as ice thinning and firn compaction must first have driven these ice shelves into a state liable to collapse by weakening the ice and enabling meltwater to pool on the ice surface.…”

Section: Introductionmentioning

confidence: 99%

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Oceanic and atmospheric forcing of Larsen C Ice-Shelf thinning

et al. 2015

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Abstract. The catastrophic collapses of Larsen A and B ice shelves on the eastern Antarctic Peninsula have caused their tributary glaciers to accelerate, contributing to sea-level rise and freshening the Antarctic Bottom Water formed nearby. The surface of Larsen C Ice Shelf (LCIS), the largest ice shelf on the peninsula, is lowering. This could be caused by unbalanced ocean melting (ice loss) or enhanced firn melting and compaction (englacial air loss). Using a novel method to analyse eight radar surveys, this study derives separate estimates of ice and air thickness changes during a 15-year period. The uncertainties are considerable, but the primary estimate is that the surveyed lowering (0.066 ± 0.017 m yr −1 ) is caused by both ice loss (0.28 ± 0.18 m yr −1 ) and firn-air loss (0.037 ± 0.026 m yr −1 ). The ice loss is much larger than the air loss, but both contribute approximately equally to the lowering because the ice is floating. The ice loss could be explained by high basal melting and/or ice divergence, and the air loss by low surface accumulation or high surface melting and/or compaction. The primary estimate therefore requires that at least two forcings caused the surveyed lowering. Mechanisms are discussed by which LCIS stability could be compromised in the future. The most rapid pathways to collapse are offered by the ungrounding of LCIS from Bawden Ice Rise or ice-front retreat past a "compressive arch" in strain rates. Recent evidence suggests that either mechanism could pose an imminent risk.

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Surface energy budget on Larsen and Wilkins ice shelves in the Antarctic Peninsula: results based on reanalyses in 1989–2010

Cited by 18 publications

References 51 publications

Validation of eight atmospheric reanalyses in the Antarctic Peninsula region

Validation of eight atmospheric reanalyses in the Antarctic Peninsula region

Validation of the summertime surface energy budget of Larsen C Ice Shelf (Antarctica) as represented in three high‐resolution atmospheric models

Oceanic and atmospheric forcing of Larsen C Ice-Shelf thinning

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