Add the WhatsNew markdown file

README

@@ -76,7 +76,7 @@ README ------------------- This file
 README.md ---------------- File that displays on github under https::/github.com/ESCOMP/CTSM.git
 README.rst --------------- File that displays under the project in github
 README_GITFLEXIMOD.rst --- Information on how to work with git-fleximod for CTSM
-WhatsNewinCTSM5.3.md ----- Overview document of the changes between ctsm5.2.0 and ctsm5.3.0
+WhatsNewInCTSM5.3.md ----- Overview document of the changes between ctsm5.2.0 and ctsm5.3.0
 CODE_OF_CONDUCT.md ------- Code of Conduct for how to work with each other on the CTSM project
 Copyright ---------------- CESM Copyright file
 doc/UpdateChangeLog.pl --- Script to add documentation on a tag to the

WhatsNewInCTSM5.3.md

@@ -0,0 +1,53 @@
+Purpose and description of changes since ctsm5.2.005
+----------------------------------------------------
+
+Bring in updates needed for the CESM3.0 science capability/functionality "chill". Most importantly bringing
+in: CN Matrix to speed up spinup for the BGC model, updated surface datasets, updated Leung 2023 dust emissions,
+explicit Air Conditioning for the Urban model, updates to crop calendars. For clm6_0 physics these options are now
+default turned on in addition to Sturm snow, and excess ice.
+
+Changes to CTSM Infrastructure:
+===============================
+
+ - manage_externals removed and replaced by git-fleximod
+ - Ability to handle CAM7 in LND_TUNING_MODE
+
+Changes to CTSM Answers:
+========================
+
+ Changes to defaults for clm6_0 physics:
+  - Urban explicit A/C turned on
+  - Snow thermal conductivity is now Sturm_1997
+  - New IC file for f09 1850
+  - New crop calendars
+  - Dust emissions is now Leung_2023
+  - Excess ice is turned on
+  - Updates to MEGAN for BVOC's
+  - Updates to BGC fire method
+
+ Changes for all physics versions:
+
+  - Parameter files updated
+  - FATES parameter file updated
+  - Glacier region 1 is now undefined
+  - Update in FATES transient Land use
+  - Pass active glacier (CISM) runoff directly to river model (MOSART)
+  - Add the option for using matrix for Carbon/Nitrogen BGC spinup
+
+New surface datasets:
+=====================
+
+- With new surface datasets the following GLC fields have region "1" set to UNSET:
+     glacier_region_behavior, glacier_region_melt_behavior, glacier_region_ice_runoff_behavior
+- Updates to allow creating transient landuse timeseries files going back to 1700.
+- Fix an important bug on soil fields that was there since ctsm5.2.0. This results in mksurfdata_esmf now giving identical answers with a change in number of processors, as it should.
+- Add in creation of ne0np4.POLARCAP.ne30x4 surface datasets.
+- Add version to the surface datasets.
+- Remove the --hires_pft option from mksurfdata_esmf as we don't have the datasets for it.
+- Remove VIC fields from surface datasets.
+
+New input datasets to mksurfdata_esmf:
+======================================
+
+- Updates in PFT/LAI/soil-color raw datasets (now from the TRENDY2024 timeseries that ends in 2023), as well as two fire datasets (AG fire, peatland), and the glacier behavior dataset.
+