SUBROUTINE GET_WACCMFILE_INTERP(DS_TIME,WACCM_DIR,WACCM_FILE,
     &IDATE1,IDATE2,WGHT)
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C
C This routine Assigns the file name for reading WACCM data and
C returns the IDATE parameters to use in reading the WACCM data
C The WACCM date corresponding to a particular year and month average 
C is yearmm01, where mm is month+1, so the January 2002 monthly average
C data is found using the date 20020201. We wish to read two months of
C data and interpolate to the desired date using the weight given by
C WGHT. So data=data1*wght+data2*(1.0-wght).  
C
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      IMPLICIT NONE
      INTEGER DAY,NCHAR,IC,ICC1,ICC2,YEAR,MONTH,IDATE1,IDATE2
      REAL*4 WGHT
      CHARACTER*(*) DS_Time,WACCM_DIR,WACCM_FILE
      CHARACTER*1 BLANK
      CHARACTER*60 DIR
      DATA BLANK/' '/
      NCHAR = LEN(WACCM_DIR)
      DIR = WACCM_DIR
      DO IC = 1, NCHAR
        ICC1 = IC
        IF(DIR(IC:IC).NE.BLANK) GO TO 1
      ENDDO
 1    DO IC = ICC1, NCHAR
        IF(DIR(IC:IC).EQ.BLANK.OR.DIR(IC:IC).EQ.char(0)) GO TO 2
        ICC2 = IC
      ENDDO
 2    READ(DS_Time,'(I4,I3)') YEAR,DAY
      WACCM_FILE=
     $   DIR(ICC1:ICC2)//'WACCM_SABER_2000-2020.nc'//char(0)
      WRITE(*,'(A)') WACCM_FILE
      IF ( (DAY .GT. 0) .AND. (DAY .LE. 31) )THEN
        MONTH=1
        WGHT=REAL(DAY-16.0)/31.0
      ELSE IF( (DAY .GT. 31) .AND. (DAY .LE. 59) )THEN
        MONTH=2
        WGHT=REAL(DAY-45.0)/28.0
      ELSE IF( (DAY .GT. 59) .AND. (DAY .LE. 90) )THEN  
        MONTH=3
        WGHT=REAL(DAY-75.0)/31.0
      ELSE IF( (DAY .GT. 90) .AND. (DAY .LE. 120) )THEN
        MONTH=4
        WGHT=REAL(DAY-105.0)/30.0
      ELSE IF( (DAY .GT. 120) .AND. (DAY .LE. 151) )THEN
        MONTH=5
        WGHT=REAL(DAY-136.0)/31.0
      ELSE IF( (DAY .GT. 151) .AND. (DAY .LE. 181) )THEN
        MONTH=6
        WGHT=REAL(DAY-166.0)/30.0
      ELSE IF( (DAY .GT. 181) .AND. (DAY .LE. 212) )THEN
        MONTH=7
        WGHT=REAL(DAY-197.0)/31.0
      ELSE IF( (DAY .GT. 212) .AND. (DAY .LE. 243) )THEN
        MONTH=8
        WGHT=REAL(DAY-228.0)/31.0
      ELSE IF( (DAY .GT. 243) .AND. (DAY .LE. 273) )THEN
        MONTH=9
        WGHT=REAL(DAY-258.0)/30.0
      ELSE IF( (DAY .GT. 273) .AND. (DAY .LE. 304) )THEN
        MONTH=10
        WGHT=REAL(DAY-289.0)/31.0
      ELSE IF( (DAY .GT. 304) .AND. (DAY .LE. 334) )THEN
        MONTH=11
        WGHT=REAL(DAY-319.0)/30.0
      ELSE IF( (DAY .GT. 334) .AND. (DAY .LE. 366) )THEN
        MONTH=12
        WGHT=REAL(DAY-350.0)/31.0
      ENDIF
      IF(WGHT.LE.0.0) THEN
        IF(MONTH.LT.12) THEN
          IDATE1=YEAR*10000+MONTH*100+1
          IDATE2=YEAR*10000+(MONTH+1)*100+1
        ELSE
          IDATE1=YEAR*10000+1201
          IDATE2=(YEAR+1)*10000+101
        ENDIF
        WGHT=-WGHT
      ELSE
        IF(MONTH.LT.11) THEN
          IDATE1=YEAR*10000+(MONTH+1)*100+1
          IDATE2=YEAR*10000+(MONTH+2)*100+1
        ELSEIF(MONTH.EQ.11) THEN
          IDATE1=YEAR*10000+1201
          IDATE2=(YEAR+1)*10000+101
        ELSE
          IDATE1=(YEAR+1)*10000+101
          IDATE2=(YEAR+1)*10000+201
        ENDIF
        WGHT=1.0-WGHT
      ENDIF
      RETURN
      END