If avgflag /= 'I', time_bounds is present and time = mid of time_bounds

...and other mods that I'm preserving from closed PR ESCOMP#2019, such as
- changes to long_names and
- treating avgflag as a tape (not field) trait for 'I' and 'L' tapes

src/main/histFileMod.F90

@@ -1170,6 +1170,7 @@ subroutine htape_addfld (t, f, avgflag)
     integer :: beg1d,end1d          ! beginning and ending indices for this field (assume already set)
     integer :: num1d_out            ! history output 1d size
     type(bounds_type) :: bounds
+    character(len=avgflag_strlen) :: avgflag_temp  ! local copy of hist_avgflag_pertape(t)
     character(len=*),parameter :: subname = 'htape_addfld'
     !-----------------------------------------------------------------------
 
@@ -1300,6 +1301,19 @@ subroutine htape_addfld (t, f, avgflag)
        tape(t)%hlist(n)%avgflag = avgflag
     end if
 
+    ! Override this tape's avgflag if nhtfrq == 1
+    if (tape(t)%nhtfrq == 1) then  ! output is instantaneous
+       hist_avgflag_pertape(t) = 'I'
+    end if
+    ! Override this field's avgflag if the namelist or the previous line
+    ! has set this tape to
+    ! - instantaneous (I) or
+    ! - local time (L)
+    avgflag_temp = hist_avgflag_pertape(t)
+    if (avgflag_temp == 'I' .or. avgflag_temp(1:1) == 'L') then
+       tape(t)%hlist(n)%avgflag = avgflag_temp
+    end if
+
   end subroutine htape_addfld
 
   !-----------------------------------------------------------------------
@@ -3093,6 +3107,7 @@ subroutine htape_timeconst(t, mode)
     integer :: mcdate                     ! current date
     integer :: yr,mon,day,nbsec           ! year,month,day,seconds components of a date
     integer :: hours,minutes,secs         ! hours,minutes,seconds of hh:mm:ss
+    character(len= 12) :: step_or_bounds  ! string used in long_name of several time variables
     character(len= 10) :: basedate        ! base date (yyyymmdd)
     character(len=  8) :: basesec         ! base seconds
     character(len=  8) :: cdate           ! system date
@@ -3352,20 +3367,30 @@ subroutine htape_timeconst(t, mode)
 
        dim1id(1) = time_dimid
        str = 'days since ' // basedate // " " // basesec
-       call ncd_defvar(nfid(t), 'time', tape(t)%ncprec, 1, dim1id, varid, &
-            long_name='time',units=str)
+       if (tape(t)%hlist(1)%avgflag /= 'I') then  ! NOT instantaneous fields tape
+          step_or_bounds = 'time_bounds'
+          long_name = 'time at exact middle of ' // step_or_bounds
+          call ncd_defvar(nfid(t), 'time', tape(t)%ncprec, 1, dim1id, varid, &
+               long_name=long_name, units=str)
+          call ncd_putatt(nfid(t), varid, 'bounds', 'time_bounds')
+       else  ! instantaneous fields tape
+          step_or_bounds = 'time step'
+          long_name = 'time at end of ' // step_or_bounds
+          call ncd_defvar(nfid(t), 'time', tape(t)%ncprec, 1, dim1id, varid, &
+               long_name=long_name, units=str)
+       end if
        cal = get_calendar()
        if (      trim(cal) == NO_LEAP_C   )then
           caldesc = "noleap"
        else if ( trim(cal) == GREGORIAN_C )then
           caldesc = "gregorian"
        end if
        call ncd_putatt(nfid(t), varid, 'calendar', caldesc)
-       call ncd_putatt(nfid(t), varid, 'bounds', 'time_bounds')
 
        dim1id(1) = time_dimid
+       long_name = 'current date (YYYYMMDD) at end of ' // step_or_bounds
        call ncd_defvar(nfid(t) , 'mcdate', ncd_int, 1, dim1id , varid, &
-          long_name = 'current date (YYYYMMDD)')
+          long_name = long_name)
        !
        ! add global attribute time_period_freq
        !
@@ -3392,18 +3417,23 @@ subroutine htape_timeconst(t, mode)
        call ncd_putatt(nfid(t), ncd_global, 'time_period_freq',          &
                           trim(time_period_freq))
 
+       long_name = 'current seconds of current date at end of ' // step_or_bounds
        call ncd_defvar(nfid(t) , 'mcsec' , ncd_int, 1, dim1id , varid, &
-          long_name = 'current seconds of current date', units='s')
+          long_name = long_name, units='s')
+       long_name = 'current day (from base day) at end of ' // step_or_bounds
        call ncd_defvar(nfid(t) , 'mdcur' , ncd_int, 1, dim1id , varid, &
-          long_name = 'current day (from base day)')
+          long_name = long_name)
+       long_name = 'current seconds of current day at end of ' // step_or_bounds
        call ncd_defvar(nfid(t) , 'mscur' , ncd_int, 1, dim1id , varid, &
-          long_name = 'current seconds of current day')
+          long_name = long_name)
        call ncd_defvar(nfid(t) , 'nstep' , ncd_int, 1, dim1id , varid, &
           long_name = 'time step')
 
        dim2id(1) = hist_interval_dimid;  dim2id(2) = time_dimid
-       call ncd_defvar(nfid(t), 'time_bounds', ncd_double, 2, dim2id, varid, &
-          long_name = 'history time interval endpoints')
+       if (tape(t)%hlist(1)%avgflag /= 'I') then  ! NOT instantaneous fields tape
+          call ncd_defvar(nfid(t), 'time_bounds', ncd_double, 2, dim2id, varid, &
+             long_name = 'history time interval endpoints')
+       end if
 
        dim2id(1) = strlen_dimid;  dim2id(2) = time_dimid
        call ncd_defvar(nfid(t), 'date_written', ncd_char, 2, dim2id, varid)
@@ -3431,13 +3461,16 @@ subroutine htape_timeconst(t, mode)
        call ncd_io('mscur' , mscur , 'write', nfid(t), nt=tape(t)%ntimes)
        call ncd_io('nstep' , nstep , 'write', nfid(t), nt=tape(t)%ntimes)
 
-       time = mdcur + mscur/secspday
+       timedata(1) = tape(t)%begtime  ! beginning time
+       timedata(2) = mdcur + mscur/secspday  ! end time
+       if (tape(t)%hlist(1)%avgflag /= 'I') then  ! NOT instantaneous fields tape
+          time = (timedata(1) + timedata(2)) * 0.5_r8
+          call ncd_io('time_bounds', timedata, 'write', nfid(t), nt=tape(t)%ntimes)
+       else
+          time = timedata(2)
+       end if
        call ncd_io('time'  , time  , 'write', nfid(t), nt=tape(t)%ntimes)
 
-       timedata(1) = tape(t)%begtime
-       timedata(2) = time
-       call ncd_io('time_bounds', timedata, 'write', nfid(t), nt=tape(t)%ntimes)
-
        call getdatetime (cdate, ctime)
        call ncd_io('date_written', cdate, 'write', nfid(t), nt=tape(t)%ntimes)
 
@@ -5254,6 +5287,10 @@ character(len=max_length_filename) function set_hist_filename (hist_freq, hist_m
       write(cdate,'(i4.4,"-",i2.2,"-",i2.2,"-",i5.5)') yr,mon,day,sec
    endif
    write(hist_index,'(i1.1)') hist_file - 1
+   ! TODO slevis: After hist_index add "i" or "a"
+   !              For guidance on how to split the files, search for
+   !              maxsplitfiles in https://github.com/ESCOMP/CAM/pull/903/files
+   !              See CAM#1003 for a bug-fix in monthly avged output
    set_hist_filename = "./"//trim(caseid)//"."//trim(compname)//trim(inst_suffix)//&
                        ".h"//hist_index//"."//trim(cdate)//".nc"