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--- pmip3:design:pi:final:icesheet [2009/12/04 13:19]
pasb
+++ pmip3:design:pi:final:icesheet [2010/03/25 12:51]
jypeter Moved a bit of text from 21k:final
@@ Line 4: / Line 4: @@
 ===== Introduction =====
+//Note: use paragraph below...
+The ice sheet provided for PMIP3/CMIP5 LGM experiments is a blended product obtained by averaging three different ice sheets:
+  * ICE6G provided by Dick Peltier
+  * MOCA provided by Lev Tarasov
+  * ANU provided by Kurt Lambeck
+A short description and references for the different ice sheets is provided under the link below:
+[[pmip3:design:pi:final:icesheet|LGM icesheet description]]
+This solution was proposed by PMIP bureau in light of a community checking. Given the uncertainties that still exist on the reconstruction of the ice-sheet, resulting from uncertainties in datation for the data used for global or regional constraints, climate intput from ice core temperature reconstructions or climate model simulations, etc... it sounds reasonable to consider that the average is a best estimate of the LGM ice-sheet.//
 Several PMIP participants were in favour of using a new ice-sheet reconstruction for PMIP3/CMIP5 that better matches the geomorphologic and glaciological constraints than the ICE-5G reconstruction used in PMIP2.
@@ Line 15: / Line 29: @@
 ===== Ice-sheet reconstruction to be used for PMIP3/CMIP5 simulations =====
+ Procedure to make the averages.
+. Sources:
+   - <H, RSL>  ANU ice model (2009) incl. British area (*1)
+   - <s, mask> ICE-6G v1.02
+   - <H, s>    GLAC-1 nn454 model for North America, and ne8234 for Eurasia
+   H:    thickness
+   s:    surface topography
+   mask: ice or not
+ *1 Only the ice thickness at 20ka is provided for the British region
+    at the moment.  RSL is computed with assumption of mantle density
+kg m-3.
+    Surface elevation at LGM is computed as follows:
+      s[LGM,ANU] = s[present,ICE-6G] + H[LGM,ANU] - RSL[LGM,ANU]
+. Interpolation on to ICE-6G domain
+  /ICE-6G domain/
+    lon [0, 1, ..., 359]
+    lat [-89.5, -88.5, ..., 89.5]
+  Gridpoints out of the sources are set `Undefined'
+  *Resolution Notes*
+    ANU    Antarctica         [-179,180]      x [-89.5,-61.5]   1 deg
+           Eurasia            [0,115.5]       x [50.25,83]      0.5 deg
+           North AMerica      [-139,-7]       x [38,84.5]       0.5 deg
+           British            [-10,-2]        x [52,59]         1 deg
+    GLAC-1 North America      [187.5,354.5]   x [34.75,84.25]   1 x 0.5 deg
+           Eurasia            [347.25,479.25] x [48.125,83.125] 0.5 x 0.25 deg
+. Average
+  The average is computed as follows:
+    X(ave) = [X(ANU) + X (6G) + X(GLAC-1)] / <Number of `defined' grids>
+  X(ANU or GLAC-1) = X (if defined)
+                or = 0 (if undefined)
+. Plots
+{{:pmip3:design:pi:final:antarctica21ka.pdf|}}
+  In the surface topography plots, light green indicates that the
+  elevation at the gridpoint is below zero;  brown is above zero but
+  not covered by ice; grey or blank region are `undefined' gridpoints.
+  Number of `defined` grids are plotted besides the average in the
+  NH figure.  Red = 1, Blue = 2, Magenta = 3.
+  By this configuration; Magenta corresponds to the ANU domain,
+  magenta and blue to GLAC-1 domain, and all region to the ICE-6G
+  domain, respectively.
+  There is a region of isolated red at the north of Alaska.  This is
+  because of the `undefined' grids in the GLAC-1 source.  I have no
+  idea why this isolated region is undefined in the GLAC-1.
+  Average surface topography shows straight coastline at the Bering
+  strait on the Alaska part.  This reflects the original GLAC-1 data.
+  I think this region should be skipped when averaging, but this is
+  just a quick-look.
+  Number of `defined` grids are NOT plotted in the SH figure.
+  But, this is easily deduced by other two plots.

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