Documentation for PISM, the Parallel Ice Sheet Model

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applications:201710 [2017/10/18 03:28]
Ed Bueler created by copy of future_applications:201710
applications:201710 [2017/10/18 16:25] (current)
Ed Bueler [October 2017] small edits (thanks Johannes)
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 | **journal**:​ | [[http://​www.the-cryosphere.net/​index.html|The Cryosphere]] | | **journal**:​ | [[http://​www.the-cryosphere.net/​index.html|The Cryosphere]] |
  
-When thermodynamics are coupled to basal sliding through the production of liquid water in a modeled basal till layer, PISM may exhibit cyclic, surge-like behavior. ​ This paper studies such ice-discharge instabilities in PISM for a buttressed ice-sheet-stream-shelf system. ​ When present the simulated surge cycles, which are believed to be fundamentally physical, have 1000 to 5000 year periods in the studied parameter ranges. ​ This work extends prior work on cyclic PISM behavior ([[http://​dx.doi.org/​10.1029/​2008JF001179|Bueler & Brown 2009]], [[http://​dx.doi.org/​10.3189/​2012JoG11J217|van Pelt & Oerlemans 2012]]) to marine ice sheet conditions, but the 1 km resolution model here is significantly more complete than in those studies. ​ It includes ''​stable0.7''​ version implementations of enthalpy-based thermodynamics,​ an improved till-layer hydrology model ([[http://​dx.doi.org/​10.5194/​gmd-8-1613-2015|Bueler & van Pelt 2015]]), a sub-grid scheme at the grounding line ([[http://​dx.doi.org/​10.3189/​2014JoG13J093|Feldman et al 2014]]), and a buttressed ice shelf. ​ The surface conditions are all constant, independent even of surface elevation, so the cyclic behavior arises purely internally in the ice and the basal layer. ​ This paper includes a new and careful analysis of cyclic behavior, identifying three competing time-scales controlling such cycles. ​ Results suggest that ice sheets of medium thickness may be more susceptible to surging than thin or thick ones.  The mechanisms studied here may play a role in the Heinrich events of the late-LGM Laurentide Ice Sheet and/or in ice-stream shutdown and reactivation observed in West Antarctica. ​ This is the now the definitive study of the PISM parameter space for modeled ice stream-shelf systems.+When thermodynamics are coupled to basal sliding through the production of liquid water in a modeled basal till layer, PISM may exhibit cyclic, surge-like behavior. ​ This paper studies such ice-discharge instabilities in PISM for a buttressed ice-sheet-stream-shelf system. ​ When present the simulated surge cycles, which are believed to be fundamentally physical, have 1000 to 5000 year periods in the studied parameter ranges. ​ This work extends prior work on cyclic PISM behavior ([[http://​dx.doi.org/​10.1029/​2008JF001179|Bueler & Brown 2009]], [[http://​dx.doi.org/​10.3189/​2012JoG11J217|van Pelt & Oerlemans 2012]]) to marine ice sheet conditions, but the 1 km resolution model here is significantly more complete than in those studies. ​ It includes ''​stable0.7''​ version implementations of enthalpy-based thermodynamics,​ an improved till-layer hydrology model ([[http://​dx.doi.org/​10.5194/​gmd-8-1613-2015|Bueler & van Pelt 2015]]), a sub-grid scheme at the grounding line ([[http://​dx.doi.org/​10.3189/​2014JoG13J093|Feldman et al 2014]]), and a buttressed ice shelf. ​ The surface conditions are all constant, independent even of surface elevation, so the cyclic behavior arises purely internally in the ice and the basal layer. ​ This paper includes a new and careful analysis of cyclic behavior, identifying three competing time-scales controlling such cycles. ​ Results suggest that ice sheets of medium thickness may be more susceptible to surging than thin or thick ones.  The mechanisms studied here may play a role in Heinrich events of the late-LGM Laurentide Ice Sheet and/or in ice-stream shutdown and reactivation observed in West Antarctica. ​ This is the definitive study of the PISM parameter space for modeled ice stream-shelf systems.
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applications/201710.txt ยท Last modified: 2017/10/18 16:25 by Ed Bueler
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