diff --git a/doc/ChangeSum b/doc/ChangeSum index 34b3b0b71f..88caaeffdb 100644 --- a/doc/ChangeSum +++ b/doc/ChangeSum @@ -1,5 +1,6 @@ Tag Who Date Summary ============================================================================================================================ +release-clm5.0.15 sacks 12/06/2018 Option for rain-to-snow to immediately run off in some regions release-clm5.0.14 erik 11/29/2018 Update cime and fix surface dataset for f05 1850 non-crop case release-clm5.0.13 erik 11/14/2018 Update externals with new CO2/presearo/rtm/mosart, add science_support, change testing release-clm5.0.12 erik 11/03/2018 New IC files for clm45/clm50 coupled cases, add 2010 compset diff --git a/doc/release-clm5.0.ChangeLog b/doc/release-clm5.0.ChangeLog index fa91db9ae2..fafdfe6902 100644 --- a/doc/release-clm5.0.ChangeLog +++ b/doc/release-clm5.0.ChangeLog @@ -1,4 +1,178 @@ =============================================================== +Tag name: release-clm5.0.15 +Originator(s): sacks (Bill Sacks) +Date: Thu Dec 6 10:14:30 MST 2018 +One-line Summary: Option for rain-to-snow to immediately run off in some regions + +Purpose of this version: +------------------------ + +Up until now: When repartition_rain_snow is .true. (which is the default +for CLM5), rain that falls when the near-surface temperature is cold is +converted to snow. This repartitioning was put in place for two +reasons: (1) Downscaling to elevation classes: changing the balance +between rain and snow for different elevation classes; (2) Correcting +problems in CAM. However, members of the Land Ice Working Group would +like to change this behavior so that, when CAM produces cold-temperature +rain, this rain immediately runs off rather than being converted to +snow. The purpose of this is to reduce the too-high SMB over portions of +Greenland in CESM2 coupled runs (which results in part from CAM's +generation of liquid precipitation despite very cold temperatures). + +This new behavior is implemented in a glacier region-specific manner, +based on a new namelist flag, glacier_region_rain_to_snow_behavior. It +is not at all ideal to make this aspect of the physics differ by region, +but this has been requested by members of the Land Ice Working Group in +order to address biases over Greenland while having minimal impact on +the climate (so that the climate can stay very similar to that of the +official CMIP6 runs). Note that, unlike other glacier region-specific +behaviors, this one applies to all landunits, not just glaciers. This +also seems a bit non-ideal, but we want the physics to be the same for +all landunit types in a given region, and we also want this behavior to +apply to vegetated columns because they are used for glacial +inception (and we want this alternate behavior to apply to glacial +inception, too, in order to decrease some instances of inception). + +The justification for this new physics is: In the case of (1) above: If +CAM is generating rain at a given elevation / temperature, that doesn't +necessarily imply that an equal water equivalent of snow would be +generated at a higher elevation / lower temperature: indeed, in reality, +there might not be any precipitation falling at that higher elevation / +lower temperature. In the case of (2) above: There seem to be problems +with CAM's microphysics that cause it to produce too much rain when +temperatures are very cold; it seems (at least to some people) equally +justifiable to throw this cold rain away (by sending it to the ocean as +runoff) as it is to convert this cold rain to snow. + +Note: I don't think any changes are needed in +BalanceCheck (unfortunately), since BalanceCheck currently uses the +post-downscaling precipitation fluxes, and the pre-lnd2atm runoff +fluxes (i.e., the new runoff flux isn't included in the terms in +BalanceCheck, and it doesn't need to be because BalanceCheck uses the +post-downscaling precipitation fluxes). (See also +https://github.com/ESCOMP/ctsm/issues/201#issuecomment-444264954 .) + +CTSM Master Tag This Corresponds To: N/A + + At least for now, we are bringing this to the release branch but not to + master. Here is an excerpt from the email explaining this rationale: + + My question is: Should I do this: + + (1) Just on a branch off of the release-clm5.0 branch, with no plan to + bring it back to release-clm5.0 or master + + (2) On the release-clm5.0 branch, but not bring it back to master + + (3) On the release-clm5.0 branch and master + + My inclination right now is towards (2). I don't really like (1) because + this change will be wanted for a number of CMIP6-related experiments, + and it feels like it could be a pain to keep this branch up-to-date with + the evolving release-clm5.0 branch. However, the changes are going to be + a bit messy and having this be region-specific isn't really physically + justifiable (it's just being done that way to keep the climate as close + as possible to the official CMIP6 runs), so I'm not sure we really want + this on master. If we did anything on master, I could imagine having a + globally-applicable switch controlling this behavior, rather than having + it apply to just certain glacier regions. + + Bette: The main reason I could see for bringing this to master is if you + imagine needing to use this new option in isotope-enabled runs, since + the isotope-enabled version of CTSM won't be on the release-clm5.0 + branch. Do you think it's likely that you'd need to do that, or would + the isotope-enabled runs use the standard CMIP6 physics settings in this + respect? + +Summary of changes: +------------------- + +Science changes since: release-clm5.0.14 + None by default: just introduces a new option + +Software changes since: release-clm5.0.14 + Introduces a new option, glacier_region_rain_to_snow_behavior, + controlling whether would-be rain-to-snow conversion ends up as snow + or instead ends up as liquid runoff. + +Changes to User Interface since: release-clm5.0.14 + Introduces a new option, glacier_region_rain_to_snow_behavior, + controlling whether would-be rain-to-snow conversion ends up as snow + or instead ends up as liquid runoff. + +Testing: +-------- + + [PASS means all tests PASS and OK means tests PASS other than expected fails.] + + build-namelist tests: + + cheyenne - ok + + Tests pass, namelists differ as expected + + unit-tests (components/clm/src): + + cheyenne - pass + hobart --- not run + + tools-tests (components/clm/test/tools): + + cheyenne - not run + hobart --- not run + + PTCLM testing (components/clm/tools/shared/PTCLM/test): + + cheyenne - not run + hobart --- not run + + regular tests (aux_clm): + + cheyenne_intel ---- pass + cheyenne_gnu ------ pass + hobart_nag -------- pass + hobart_pgi -------- pass + hobart_intel ------ pass + + regular tests (prealpha): + + cheyenne_intel - not run + cheyenne_gnu --- not run + hobart_nag ----- not run + + regular tests (prebeta): + + cheyenne_intel - not run + cheyenne_gnu --- not run + hobart_nag ----- not run + +Summary of Answer changes: +------------------------- + +Baseline version for comparison: release-clm5.0.14 + +Changes answers relative to baseline: NO + +Detailed list of changes: +------------------------ + +Externals being used: + + cism: release-cesm2.0.04 + rtm: release-cesm2.0.02 + mosart: release-cesm2.0.03 + cime: cime_cesm2_1_rel_05 + FATES: fates_s1.8.1_a3.0.0 + PTCLM: PTCLM2_180611 + +CTSM Tag versions pulled over from master development branch: none + +Pull Requests that document the changes (include PR ids): + ESCOMP/ctsm#586 - Option for rain-to-snow to immediately run off in + some regions + +=============================================================== +=============================================================== Tag name: release-clm5.0.14 Originator(s): erik (Erik Kluzek) Date: Thu Nov 29 11:46:41 MST 2018