Documentation for PISM, the Parallel Ice Sheet Model

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aboutpism [2017/10/20 02:40]
Constantine Khroulev [What has PISM been used for?]
aboutpism [2019/06/10 23:12] (current)
Ed Bueler [Are you formally collaborating with international partners?]
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 Ice sheets, which are just big, continent-size glaciers, are moving ice fluids, like the ocean is a fluid and the atmosphere is a fluid. ​ Glaciers flow downhill, driven by gravity. ​ PISM simulates the movement of the ice fluid, and its temperature,​ and so on, just as a weather forecasting model simulates the atmosphere. ​ Scientists are interested in how changing climate might affect the ice flow.  Ice moves slower than the ocean or the atmosphere, so they use PISM to simulate decades, centuries, or millenia of flow, while a weather model works over just days. Ice sheets, which are just big, continent-size glaciers, are moving ice fluids, like the ocean is a fluid and the atmosphere is a fluid. ​ Glaciers flow downhill, driven by gravity. ​ PISM simulates the movement of the ice fluid, and its temperature,​ and so on, just as a weather forecasting model simulates the atmosphere. ​ Scientists are interested in how changing climate might affect the ice flow.  Ice moves slower than the ocean or the atmosphere, so they use PISM to simulate decades, centuries, or millenia of flow, while a weather model works over just days.
  
-[[http://​imaginary.org/​film/​the-future-of-glaciers|See this excellent 5 minute movie introducing what a glacier flow model does.]]  (It is not the PISM model but a new model by Guillaume Jouvet.)+See this [[http://​imaginary.org/​film/​the-future-of-glaciers|excellent 5 minute movie]] introducing what a glacier flow model does.  ​The model shown is not PISM but a new glacier-scale ​model by Guillaume Jouvet.  PISM does this kind of thing too, but for each part of a big ice sheet like Greenland or Antarctica.)
 ==== Why is it important? ==== ==== Why is it important? ====
  
-Ice sheets contain a large amount of (frozen) water which is currently above sea level.  ​Ice sheets are not sea ice---sea ice is already floating and changing will not change sea level directly.  Ice sheets in Greenland and Antarctica are more than two miles (more than four kilometers) thick and sitting on land.  If ice sheets flow faster or slower, or the way they flow changes, then this affects the rate at which they can raise sea level. ​ The potential amount is big---tens of meters---but the question is how fast these changes can happen. ​ In the past, as the earth went in and out of the ice ages, there were huge changes over very short periods. ​ If the present-day ice sheets flow faster into the ocean in the next century then sea level will rise and there may be other relatively-fast affects on the climate. ​ The question is whether sea level will rise a fraction of a meter or up to one or two meters in the next century or two.  And there could be tipping points we don't see now.  An ice sheet flow model like PISM is part of understanding such possibilities.+Ice sheets ​in Greenland and Antarctica are more than two miles (more than four kilometers) thick and sitting on land.  They contain a large amount of (frozen) water which is currently above sea level.  ​Note that ice sheets are not sea ice---sea ice is already floating and changing ​its thickness ​will not change sea level directly.
  
-Of coursebig part of understanding the ice sheets is to observe them better, and do field work, and so on ... not just work on a computer simulation.  ​Computers ​can only integrate the observations ​we have into a more complete picturethey do not create new facts.+If ice sheets flow faster or sloweror their flow direction changes, then this affects the rate at which they can raise sea level. ​ The potential amount is big---tens of meters---but the question is how fast these changes can happen. ​ In the past, as the earth went in and out of the ice ages, there were huge changes over very short periods. ​ In the future there could be tipping points we don't see now.  An ice sheet flow model like PISM is part of understanding ​such possibilities. 
 + 
 +If present-day Antarctic ice sheet flows faster into the ocean during the next century then sea level will rise.  There may be other relatively-fast effects on the climate. ​ One question is whether sea level will rise a only a fraction of a meter, or up to one or two meters, in the next century. 
 + 
 +A major part of predicting ​the ice sheets is to observe them better ​now through ​field work.  ​Computer simulations depend on observations;​ they can can only integrate the data we have into a more complete picture, and they do not create new facts.
  
 ==== Are you formally collaborating with international partners? ==== ==== Are you formally collaborating with international partners? ====
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 We have written software which is free and open source. ​ Our international partners, like the Potsdam Institute (PIK) and other groups in Denmark, Germany, New Zealand, and the Netherlands,​ use our software, and they even add to it.  The collaboration is not very formal, but we have traveled both ways across the pole quite a bit!  They have chosen PISM over the several other available ice sheet models because it works well for them. We have written software which is free and open source. ​ Our international partners, like the Potsdam Institute (PIK) and other groups in Denmark, Germany, New Zealand, and the Netherlands,​ use our software, and they even add to it.  The collaboration is not very formal, but we have traveled both ways across the pole quite a bit!  They have chosen PISM over the several other available ice sheet models because it works well for them.
  
-The purpose of a model like this is to put your imperfect understanding of ice sheets into a form where you can see the consequences of your current understanding,​ and then try to understand better, and then change the model accordingly. ​ That's what we do, and that's what they do. 
  
 ==== What have researchers discovered since adopting the model? ==== ==== What have researchers discovered since adopting the model? ====
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   * The [[http://​www.pism-docs.org/​sphinx/​manual|PISM User's Manual]] shows some realistic and idealized cases.   * The [[http://​www.pism-docs.org/​sphinx/​manual|PISM User's Manual]] shows some realistic and idealized cases.
-  * The [[old_paotm|PISM Applications of the Month]] list shows a large sample of applications. +  * The [[publications|publications page]] shows published ​applications ​of PISM from hundreds of different scientists all over the world.
- +
-Also see+
  
-  * the [[publications|publications page]], 
-  * and the [[worked_examples|worked examples page]]. 
aboutpism.1508467244.txt.gz · Last modified: 2017/10/20 02:40 by Constantine Khroulev
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