Dear Martin, it should be a weighted time mean, as we also request for sea-ice thickness, for example.
Thanks! Dirk ---- Dr. Dirk Notz http://www.mpimet.mpg.de/~notz.dirk Am 02.08.2016 um 13:37 schrieb martin.juc...@stfc.ac.uk: > Dear Dirk, > > OK. For the snow thickness, do you want a weighted time mean? For example, if > there is a 1m snow layer over 50% of a grid cell for half the month and 3m > over 25% for the 2nd half of the month (the rest of the cell being snow > free), do you want a weighted time mean of 1.6667m or a simple mean of 2m? > > regards, > Martin > ________________________________________ > From: Dirk Notz [dirk.n...@mpimet.mpg.de] > Sent: 02 August 2016 11:59 > To: Juckes, Martin (STFC,RAL,RALSP); j.m.greg...@reading.ac.uk; Pamment, > Alison (STFC,RAL,RALSP) > Cc: cf-metadata@cgd.ucar.edu > Subject: Re: [CF-metadata] CMIP6 Sea Ice MIP: Ice thickness > > Dear Martin, > >> It looks as though you have resolved all the issues nicely, but I have one >> concern about Jonathan's suggestion for dealing with the thickness of ice >> floating in melt ponds on the surface of sea ice. The suggestion is to use >> the existing standard name "floating_ice_thickness" with a cell methods term >> of the form "area: mean where sea_ice_melt_pond". My concern is that there >> is some ambiguity here between the thickness of the ice floating in the melt >> pond and the thickness of the sea ice underneath the melt pond, which is >> floating in the sea. This might be resolved if "floating_ice_thickness" was >> to be defined in such a way as to exclude sea ice, but the current >> definition does not do this. (It states that '"Floating ice" means any ice >> that is floating on water, e.g. on a sea or lake surface.') > > This is an important point, thanks for raising it. It might then be > necessary to indeed introduce a new variable as initially suggested to > avoid this ambiguity. This variable was initially called > "thickness_of_sea_ice_melt_pond_refrozen_ice ". > >> I have a 2nd comment about the suggested area type of snow_covered_sea_ice: >> this has been proposed for use with variables which represent the amount of >> snow on sea ice (m) and the heat content of that snow (J m-2). In both cases >> these are quantities which can be considered as zero on snow-free sea ice, >> in which case there is no need to mask them by the area of snow cover (I >> believe Jonathan has advanced this argument in another thread recently). In >> this case, amount of snow on sea ice would just be represented by >> "surface_snow_thickness" with cell methods "area: mean where sea_ice over >> all_area_types" (or "area: mean where sea_ice over sea"). > > This is certainly true for the heat content. For snow thickness, > however, we would like to be able to consider partial snow coverage. We > would like to record the thickness of the actual snow, not the average > thickness including those parts of sea ice that are ice free. Hence, for > snow thickness, I believe that the area type "snow_covered_sea_ice" > should still be applied. > > Thanks in any case for your helpful feedback, > > best, > > Dirk > _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
