Elmer/Ice News

New Elmer/Ice users workshop

CSC and IGE invite you to join the 2022 online Elmer/Ice workshop.  The idea behind this workshop is to listen to and discuss  talks given by developers and - most importantly - the users (=you). Hence we encourage you to submit a title (no abstract needed) of a 10 - 15 minute talk. You can do so in the registration form, which is accessible under the link https://ssl.eventilla.com/event/JBab5  There you need to provide your name + valid email address, else registration and attendance is free of charge

It will be held  as  a Zoom-Webinar on Wednesday,  2. February, 2022, from 9 am-12 am Central European Time (CET = UTC+1) . We apologize that this schedule leads to inconvenient times, mainly for the Americas and a wide range of the Pacific region. Nevertheless, we will record the event and make those talks for which we get permission available online.

Looking forward to seeing you, 

Olivier Gagliardini (IGE), Thomas Zwinger and the Elmer-Team at CSC

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Seasonal evolution of basal environment conditions of Russell sector, West Greenland, inverted from satellite observation of surface flow

Seasonal evolution of basal environment conditions of Russell sector, West Greenland, inverted from satellite observation of surface flow

https://tc.copernicus.org/articles/15/5675/2021/

Due to increasing surface melting on the Greenland ice sheet, better constraints on seasonally evolving basal water pressure and sliding speed are required by models. Here we assess the potential of using inverse methods on a dense time series of surface speeds to recover the seasonal evolution of the basal conditions in a well-documented region in southwest Greenland. Using data compiled from multiple satellite missions, we document seasonally evolving surface velocities with a temporal resolution of 2 weeks between 2015 and 2019. We then apply the inverse control method using the ice flow model Elmer/Ice to infer the basal sliding and friction corresponding to each of the 24 surface velocity data sets. Near the margin where the uncertainty in the velocity and bed topography are small, we obtain clear seasonal variations that can be mostly interpreted in terms of an effective-pressure-based hard-bed friction law. We find for valley bottoms or “troughs” in the bed topography that the changes in modelled basal conditions directly respond to local modelled water pressure variations, while the link is more complex for subglacial “ridges” which are often non-locally forced. At the catchment scale, in-phase variations in the water pressure, surface velocities, and surface runoff variations are found. Our results show that time series inversions of observed surface velocities can be used to understand the evolution of basal conditions over different timescales and could therefore serve as an intermediate validation for subglacial hydrology models to achieve better coupling with ice flow models.

Read more: Derkacheva, A., Gillet-Chaulet, F., Mouginot, J., Jager, E., Maier, N., Cook, S., 2021. Seasonal evolution of basal environment conditions of Russell sector, West Greenland, inverted from satellite observation of surface flow. The Cryosphere 15, 5675–5704. https://doi.org/10.5194/tc-15-5675-2021

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Modeling Ice-Crystal Fabric as a Proxy for Ice-Stream Stability

lilien2021Glacier ice is composed of individual grains, or crystals. These grains can have different orientations, similar to how a pile of snow has many flakes all pointing in different directions. When ice accumulates as snowfall, the grains point in approximately random directions. However, as glaciers move, the orientation of the grains is changed, leading to characteristic "fabrics," where the grains tend to point in distinctive directions. Here, we try to understand how one could work backwards, from the orientation of the grains, to determine how the ice flowed in the past. We use an ice-flow model to understand whether instabilities in ice streams, "rivers" of fast flowing ice in Greenland and Antarctica, would be recorded in the fabric. We find that changes in ice-stream flow could indeed be seen in the fabric for thousands or tens of thousands of years, depending on the exact type of change. We then show that these changes to fabric are large enough that they could be measured in ice cores or with specialized ice-penetrating radars. This helps lay the groundwork for better understanding of long-term changes to ice flow, which is important but hard-to-measure context for modern ice-stream retreat.

Read more: Lilien, D. A., N. M. Rathmann, C. S. Hvidberg and D. Dahl-Jensen, 2021. Modeling ice-crystal fabric as a proxy for ice-stream stability. Journal of Geophysical Research: Earth Surface, 126, e2021JF006306, doi: 10.1029/2021JF006306


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