initial changelog

doc/ChangeLog

@@ -1,5 +1,83 @@
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+Tag name:
+Originator(s): peverwhee
+Date:
+One-line Summary: Separate history tapes into hXi and hXa
+Github PR URL: https://github.com/ESCOMP/CAM/pull/903
+
+Purpose of changes (include the issue number and title text for each relevant GitHub issue):
+ - Change "time" value for averaged quantities to midpoint of averaging period (#159)
+ - Modify naming and attributes of time variables on history files to be
+   consistent with other CESM components (#554)
+
+Describe any changes made to build system: N/A
+
+Describe any changes made to the namelist: N/A
+
+List any changes to the defaults for the boundary datasets: N/A
+
+Describe any substantial timing or memory changes: N/A
+
+Code reviewed by: cacraigucar brian-eaton nusbaume
+
+List all files eliminated: N/A
+
+List all files added and what they do: N/A
+
+List all existing files that have been modified, and describe the changes:
+M        cime_config/SystemTests/sct.py
+ - change references to history file to include "i" flag
+
+M        src/control/cam_history.F90
+ - change 'time_bnds' to 'time_bounds'
+ - split history stream into two files: instantaneous and accumulated
+   - accumulated file has all non-instantaneous fields and 'time', 'date',
+    'datesec' fields are the midpoint time
+      - accumulated file is only generated when one or more accumulated fields
+      - filename includes 'a' flag
+      is included in the fincl list
+   - instantaneous file has all instantaneous fields (including scalars that
+     are always written) and 'time', 'date', and 'datesec' fields are the end
+     time
+       - instantaneous file is always generated (with, at minimum, those
+       scalars like VMRs, current timestep, etc
+       - filename includes 'i' flag
+ - change 'cell_methods' to always include 'time: x' attribute to specify flag
+   - "time: point" for instantaneous fields
+
+M        src/control/cam_history_support.F90
+ - add functionality for multiple files per history stream
+
+M        src/control/filenames.F90
+ - update interpret_filename_spec to include 'a' or 'i' flag in filename
+
+M        src/control/sat_hist.F90
+ - update to comply with new Files array (multiple files per stream)
+
+M        src/utils/cam_grid_support.F90
+ - updates to get around logic that prevented fields to be written twice (need
+   to be written once per file instead of once overall)
+
+
+If there were any failures reported from running test_driver.sh on any test
+platform, and checkin with these failures has been OK'd by the gatekeeper,
+then copy the lines from the td.*.status files for the failed tests to the
+appropriate machine below.  All failed tests must be justified.
+
+cheyenne/intel/aux_cam:
+
+derecho/intel/aux_cam:
+
+izumi/nag/aux_cam:
+
+izumi/gnu/aux_cam:
+
+Summarize any changes to answers: No answer changes except midpoint time,
+date, datesec for accumulated files/fields
+
+===============================================================
+
 Tag name: cam6_3_139
 Originator(s): fvitt, tilmes
 Date: 1 Dec 2023