Bayesian calibration of firn densification models

Verjans, Vincent; Leeson, Amber; Nemeth, Christopher; Stevens, C. Max; Munneke, Peter Kuipers; Noël, Brice; Wessem, Jan Melchior van

doi:10.5194/tc-14-3017-2020

Cited by 18 publications

(36 citation statements)

References 55 publications

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“…Therefore, changes in elevation of an ice sheet can be modeled using accumulation and temperature data or estimates as inputs to a firn compaction model (FCM). We use accumulation and temperature changes from RACMO2.3p2 outputs and the model developed by Stevens et al (2020) to account for firn compaction [54]. Referring to the implementation by Stevens et al…”

Section: From Modelingmentioning

confidence: 99%

“…This depth, which is referred to as critical depth, depends on the climate conditions including rate of accumulation and average temperature. Even though critical depth varies across the AIS, we use a contant firn column of depth 220 m inspired from Verjans et al ( 2020) [55]. The rate of densification depends on accumulation rate and temperature changes; consequently, it varies across the AIS, along with the climatic conditions.…”

Section: From Modelingmentioning

confidence: 99%

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Inter-Annual Variability in the Antarctic Ice Sheets Using Geodetic Observations and a Climate Model

2021

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Quantifying the mass balance of the Antarctic Ice Sheet (AIS), and the resulting sea level rise, requires an understanding of inter-annual variability and associated causal mechanisms. Very few studies have been exploring the influence of climate anomalies on the AIS and only a vague estimate of its impact is available. Changes to the ice sheet are quantified using observations from space-borne altimetry and gravimetry missions. We use data from Envisat (2002 to 2010) and Gravity Recovery And Climate Experiment (GRACE) (2002 to 2016) missions to estimate monthly elevation changes and mass changes, respectively. Similar estimates of the changes are made using weather variables (surface mass balance (SMB) and temperature) from a regional climate model (RACMO2.3p2) as inputs to a firn compaction (FC) model. Elevation changes estimated from different techniques are in good agreement with each other across the AIS especially in West Antarctica, Antarctic Peninsula, and along the coasts of East Antarctica. Inter-annual height change patterns are then extracted using for the first time an empirical mode decomposition followed by a principal component analysis to investigate for influences of climate anomalies on the AIS. Investigating the inter-annual signals in these regions revealed a sub-4-year periodic signal in the height change patterns. El Niño Southern Oscillation (ENSO) is a climate anomaly that alters, among other parameters, moisture transport, sea surface temperature, precipitation, in and around the AIS at similar frequency by alternating between warm and cold conditions. This periodic behavior in the height change patterns is altered in the Antarctic Pacific (AP) sector, possibly by the influence of multiple climate drivers, like the Amundsen Sea Low (ASL) and the Southern Annular Mode (SAM). Height change anomaly also appears to traverse eastwards from Coats Land to Pine Island Glacier (PIG) regions passing through Dronning Maud Land (DML) and Wilkes Land (WL) in 6 to 8 years. This is indicative of climate anomaly traversal due to the Antarctic Circumpolar Wave (ACW). Altogether, inter-annual variability in the SMB of the AIS is found to be modulated by multiple competing climate anomalies.

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Section: From Modelingmentioning

confidence: 99%

Section: From Modelingmentioning

confidence: 99%

Inter-Annual Variability in the Antarctic Ice Sheets Using Geodetic Observations and a Climate Model

2021

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“…However, as our primary analysis focuses on lake coverage, and comparison to RCM for possible correlations, we limit our consideration of these uncertainties to prior literature. We also modelled the evolution of north GVIIS's firn layer using the ArMAP parameterization in the Community Firn Model (CFM; Stevens et al, 2020;Verjans et al, 2020), to derive monthly estimates of ice lens depth, refreezing, runoff and firn air content (FAC) in the upper 10 m of the snowpack, with FAC representing the pore space available for meltwater storage. We use ArMAP due to its relevance to the study region, as it is a reparameterization of the firn densification model developed by Arthern et al (2010) which uses a Bayesian calibration framework on a dataset of firn cores from both Antarctica and Greenland, as detailed in Verjans et al, (2020).…”

Section: Climate and Firn Datamentioning

confidence: 99%

“…We also modelled the evolution of north GVIIS's firn layer using the ArMAP parameterization in the Community Firn Model (CFM; Stevens et al, 2020;Verjans et al, 2020), to derive monthly estimates of ice lens depth, refreezing, runoff and firn air content (FAC) in the upper 10 m of the snowpack, with FAC representing the pore space available for meltwater storage. We use ArMAP due to its relevance to the study region, as it is a reparameterization of the firn densification model developed by Arthern et al (2010) which uses a Bayesian calibration framework on a dataset of firn cores from both Antarctica and Greenland, as detailed in Verjans et al, (2020). The CFM was forced with daily data from MAR between 1979-2020, specifically surface temperature, surface melting and precipitation for all grid cells within our study area.…”

Section: Climate and Firn Datamentioning

confidence: 99%

Changes in Supraglacial Lakes on George VI Ice Shelf, Antarctic Peninsula: 1973–2020

Barnes

Leeson

McMillan

et al. 2021

Preprint

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Abstract. High densities of supraglacial lakes have been associated with ice shelf instability and collapse. 2020 was a record melt year on George VI ice shelf with ~12 % of its northernmost portion being covered by lakes. We use 208 Sentinel-2 and Landsat-1-8 satellite images from the past 47 years, together with climate data and firn modelling, to assess the long-term presence of lakes on George VI, thus placing 2020 within a historical context. We find that the ~12 % lake coverage observed in 2020 is not unprecedented and similar to previous high lake years; events of similar magnitude occurred at least five times previously. Secondly, we find lake coverage is controlled by a combination of melting, accumulation, firn air content and firn build-up strong melting alone does not entail high lake coverage. Instead, while melting contributes positively to lake formation, we find accumulation to act as a limiting factor on the formation of lakes in response to melt, introducing new frozen material to the surface, thus cooling and storing meltwater. We find accumulation’s ability to limit melt to be further enhanced by its build-up, increasing available firn air content, and thus meltwater storage capacity. Our findings are supported by comparative analysis, showing years such as 1989 to have 55 % less melt, but similar lake coverage to 2020. Finally, we find that climate projections suggest future temperature increases, but steady snowfall in this region. Thus, in future there will be a greater propensity for higher lake densities on North George VI ice shelf, and associated risk of instability.

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“…The resulting firn profile is then compared to the measured profile. Unlike other recent studies (Lundin et al, 2017;Verjans et al, 2020) we use the objective measure of the root mean square deviation between measured and modelled density, which allows a simple and good comparability between the simulation result and the density measurement. To calculate the deviation, simulated density values are interpolated linearly to the measurement locations along the profile.…”

Section: Optimisationmentioning

confidence: 99%

Comment on tc-2021-75

2021

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Physics based simulation approaches to firn densification often rely on the assumption that grain boundary sliding, first introduced by Alley (1987) to firn, is the leading process driving the first stage of densification. However, often so called semi empirical models are favored against the description of grain boundary sliding due to simplicity and uncertainties regarding model parameters. In this study, we are assessing the applicability of grain boundary sliding to firn using a numeric firn densification model and an optimisation approach, for which we formulate variants of the constitutive relation by Alley (1987).The efficient model implementation based on an updated Lagrangian numerical scheme enables us to perform a large number of simulations testing different model parameters, to find simulation results suiting 159 firn density profiles from Greenland and Antarctica best. For most of the investigated locations a good agreement of simulated and measured firn density profiles was found. This implies that the constitutive relation by Alley (1987) characterises the fist stage of firn densification well, if suitable model parameter are used. An analysis of the parameters that lead to best matches reveals a dependency on the mean surface mass balance. This may indicate an insufficient description of the load situation, as horizontal components of the stress tensor are usually neglected in one dimensional models of the firn column.

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Bayesian calibration of firn densification models

Cited by 18 publications

References 55 publications

Inter-Annual Variability in the Antarctic Ice Sheets Using Geodetic Observations and a Climate Model

Inter-Annual Variability in the Antarctic Ice Sheets Using Geodetic Observations and a Climate Model

Changes in Supraglacial Lakes on George VI Ice Shelf, Antarctic Peninsula: 1973–2020

Comment on tc-2021-75

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