MODULE MLS_HNO3_OBS_MOD

!
!
! Module MLS_HNO3_OBS contains all subroutines and variables needed for MLS HNO3 column data
!
!
! Module Routines:
!
! (1) READ_MLS_HNO3_FILE       : Read MLS hdf file

  IMPLICIT NONE

#include "CMN_SIZE"

  PRIVATE
      
  !PUBLIC READ_OMI_HNO3_FILE
  PUBLIC READ_MLS_HNO3_FILE
  PUBLIC CALC_MLS_HNO3_FORCE

  ! Module variables

  ! MLS data
  REAL*8, ALLOCATABLE :: MLS_LON(:)
  REAL*8, ALLOCATABLE :: MLS_LAT(:)
  REAL*8, ALLOCATABLE :: MLS_TIME(:)
  REAL*8, ALLOCATABLE :: MLS_HNO3(:,:)
  REAL*8, ALLOCATABLE :: MLS_HNO3_STD(:,:)
  REAL*8, ALLOCATABLE :: MLS_CN(:)
  REAL*8, ALLOCATABLE :: MLS_CON_QUAL(:)
  REAL*8, ALLOCATABLE :: MLS_STA_QUAL(:)
  REAL*8, ALLOCATABLE :: MLS_MAIN_QUAL(:)
  REAL*8, ALLOCATABLE :: MLS_VIEW_ZENITH(:)
  REAL*8, ALLOCATABLE :: MLS_SOLAR_ZENITH(:)
  REAL*8, ALLOCATABLE :: MLS_PRESSURE(:)
  
  ! MLS grid specification
  INTEGER :: N_MLS_OBS
  INTEGER :: N_MLS_ALT
  
CONTAINS

!-----------------------------------------------------------------------------!
  SUBROUTINE READ_MLS_HNO3_FILE ( YYYYMMDD, HHMMSS )
      
    USE ERROR_MOD, ONLY : ALLOC_ERR
    USE TIME_MOD,  ONLY : EXPAND_DATE, GET_MONTH, GET_YEAR
    USE HDF5

    ! Arguments
    INTEGER, INTENT(IN) :: YYYYMMDD, HHMMSS

    CHARACTER(LEN=255) :: DIR_MLS
    CHARACTER(LEN=255) :: DIR_MONTH_MLS
    CHARACTER(LEN=255) :: FILENAME_MLS
    CHARACTER(LEN=255) :: FILENAME_FULL
    CHARACTER(LEN=255) :: DSET_NAME

    INTEGER(HID_T) :: file_id, dset_id, dspace_id
    INTEGER(HSIZE_T) :: dims(2), maxdims(2), data_dims(2)
    INTEGER :: error

    CALL CLEANUP_MLS
    
    DIR_MLS = '/users/jk/15/xzhang/MLS_HNO3/'
    DIR_MONTH_MLS = '/YYYY/MM/'
    FILENAME_MLS = 'MLS-Aura_L2GP-HNO3_v04-22-c01_YYYYdMMDD.he5'
      
    CALL EXPAND_DATE(DIR_MLS, YYYYMMDD, 0)
    CALL EXPAND_DATE(DIR_MONTH_MLS, YYYYMMDD, 0)
    CALL EXPAND_DATE(FILENAME_MLS, YYYYMMDD, 0)

    FILENAME_FULL = TRIM(DIR_MLS) // TRIM(DIR_MONTH_MLS) // TRIM(FILENAME_MLS)
      
    PRINT *,"READING MLS File: ", FILENAME_FULL

    ! Initialize HDF5 Interface

    PRINT *,"INITIALIZE INTERFACE"

    CALL h5open_f(error)

    ! Open HDF5 file

    PRINT *,"OPEN FILE"

    CALL h5fopen_f (FILENAME_FULL, H5F_ACC_RDONLY_F, file_id, error)
      
    ! Read Time array

    PRINT *,"READING TIME ARRAY"

    DSET_NAME = '/HDFEOS/SWATHS/HNO3/Data Fields/L2gpValue'

    PRINT *,"OPENING DATA SET"
      
    CALL h5dopen_f(file_id, DSET_NAME, dset_id, error)

    ! open dataspace

    CALL h5dget_space_f(dset_id, dspace_id, error)

    ! read in length of data arrays

    CALL h5sget_simple_extent_dims_f(dspace_id, dims, maxdims, error)

    ! close dataspace

    CALL h5sclose_f(dspace_id, error)

    N_MLS_ALT = dims(1)
    N_MLS_OBS = dims(2)

    ALLOCATE(MLS_TIME(N_MLS_OBS))
    ALLOCATE(MLS_LON(N_MLS_OBS))
    ALLOCATE(MLS_LAT(N_MLS_OBS))
    ALLOCATE(MLS_HNO3(N_MLS_ALT,N_MLS_OBS))
    ALLOCATE(MLS_CON_QUAL(N_MLS_OBS))
    ALLOCATE(MLS_HNO3_STD(N_MLS_ALT,N_MLS_OBS))
    ALLOCATE(MLS_MAIN_QUAL(N_MLS_OBS))
    ALLOCATE(MLS_STA_QUAL(N_MLS_OBS))
    ALLOCATE(MLS_CN(N_MLS_OBS))
    ALLOCATE(MLS_VIEW_ZENITH(N_MLS_OBS))
    ALLOCATE(MLS_SOLAR_ZENITH(N_MLS_OBS))
    ALLOCATE(MLS_PRESSURE(N_MLS_ALT))

    PRINT *,"ALLOCATING TIME ARRAY WITH LENGTH: ", N_MLS_OBS

    CALL h5dread_f(dset_id, H5T_NATIVE_DOUBLE, MLS_HNO3, data_dims, error)

    CALL h5dclose_f(dset_id,error)

    ! Read MLS HNO3 array

    DSET_NAME= '/HDFEOS/SWATHS/HNO3/Data Fields/L2gpValue'

    CALL h5dopen_f(file_id, DSET_NAME, dset_id, error)

    CALL h5dread_f(dset_id, H5T_NATIVE_DOUBLE, MLS_HNO3, data_dims, error)

    CALL h5dclose_f(dset_id,error)
    !PRINT *, "L2gpValue", MLS_HNO3(:,N_MLS_OBS)

    ! Read Time array

    DSET_NAME= '/HDFEOS/SWATHS/HNO3/Geolocation Fields/Time'

    CALL h5dopen_f(file_id, DSET_NAME, dset_id, error)

    CALL h5dread_f(dset_id, H5T_NATIVE_DOUBLE, MLS_TIME, (/data_dims(2),0/), error)

    CALL h5dclose_f(dset_id,error)

    ! Read Longitude array

    DSET_NAME= '/HDFEOS/SWATHS/HNO3/Geolocation Fields/Longitude'
      
    CALL h5dopen_f(file_id, DSET_NAME, dset_id, error)

    CALL h5dread_f(dset_id, H5T_NATIVE_DOUBLE, MLS_LON, (/data_dims(2),0/), error)

    CALL h5dclose_f(dset_id,error)

    ! Read Latitude array

    DSET_NAME= '/HDFEOS/SWATHS/HNO3/Geolocation Fields/Latitude'
      
    CALL h5dopen_f(file_id, DSET_NAME, dset_id, error)

    CALL h5dread_f(dset_id, H5T_NATIVE_DOUBLE, MLS_LAT, (/data_dims(2),0/), error)

    CALL h5dclose_f(dset_id,error)

    ! Read MLS HNO3 Precision array

    DSET_NAME= '/HDFEOS/SWATHS/HNO3/Data Fields/L2gpPrecision'

    CALL h5dopen_f(file_id, DSET_NAME, dset_id, error)

    CALL h5dread_f(dset_id, H5T_NATIVE_DOUBLE, MLS_HNO3_STD, data_dims, error)

    CALL h5dclose_f(dset_id,error)

    ! Read Quality array

    DSET_NAME= '/HDFEOS/SWATHS/HNO3/Data Fields/Quality'

    CALL h5dopen_f(file_id, DSET_NAME, dset_id, error)

    CALL h5dread_f(dset_id, H5T_NATIVE_DOUBLE, MLS_MAIN_QUAL, (/data_dims(2),0/), error)

    CALL h5dclose_f(dset_id,error)
    ! Read Status array

    DSET_NAME= '/HDFEOS/SWATHS/HNO3/Data Fields/Status'

    CALL h5dopen_f(file_id, DSET_NAME, dset_id, error)

    CALL h5dread_f(dset_id, H5T_NATIVE_DOUBLE, MLS_STA_QUAL, (/data_dims(2),0/), error)

    CALL h5dclose_f(dset_id,error)
    ! Read ChunkNumber array

    DSET_NAME= '/HDFEOS/SWATHS/HNO3/Geolocation Fields/ChunkNumber'

    CALL h5dopen_f(file_id, DSET_NAME, dset_id, error)

    CALL h5dread_f(dset_id, H5T_NATIVE_DOUBLE, MLS_CN, (/data_dims(2),0/), error)

    CALL h5dclose_f(dset_id,error)
    ! Read LineofSightAngle array

    DSET_NAME= '/HDFEOS/SWATHS/HNO3/Geolocation Fields/LineOfSightAngle'

    CALL h5dopen_f(file_id, DSET_NAME, dset_id, error)

    CALL h5dread_f(dset_id, H5T_NATIVE_DOUBLE, MLS_VIEW_ZENITH, (/data_dims(2),0/), error)

    CALL h5dclose_f(dset_id,error)
    ! Read Solar zenith Angle array

    DSET_NAME= '/HDFEOS/SWATHS/HNO3/Geolocation Fields/SolarZenithAngle'

    CALL h5dopen_f(file_id, DSET_NAME, dset_id, error)

    CALL h5dread_f(dset_id, H5T_NATIVE_DOUBLE, MLS_SOLAR_ZENITH, (/data_dims(2),0/), error)

    CALL h5dclose_f(dset_id,error)

    ! Read Convergence quality array

    DSET_NAME= '/HDFEOS/SWATHS/HNO3/Data Fields/Convergence'

    CALL h5dopen_f(file_id, DSET_NAME, dset_id, error)

    CALL h5dread_f(dset_id, H5T_NATIVE_DOUBLE, MLS_CON_QUAL, (/data_dims(2),0/), error)

    CALL h5dclose_f(dset_id,error)

    ! Read Convergence quality array

    DSET_NAME= '/HDFEOS/SWATHS/HNO3/Geolocation Fields/Pressure'

    CALL h5dopen_f(file_id, DSET_NAME, dset_id, error)

    CALL h5dread_f(dset_id, H5T_NATIVE_DOUBLE, MLS_PRESSURE, (/data_dims(1),0/), error)

    CALL h5dclose_f(dset_id,error)

    ! close HDF5 file

    CALL h5fclose_f(file_id,error)

    ! close HDF5 interface

    CALL h5close_f(error)


  END SUBROUTINE READ_MLS_HNO3_FILE
!-----------------------------------------------------------------------------!
  SUBROUTINE CALC_MLS_HNO3_FORCE

!!
!! Subroutine CALC_OMI_HNO3_FORCE computes the HNO3 adjoint forcing from OMI column data
!!

    USE ADJ_ARRAYS_MOD,     ONLY : STT_ADJ
    USE CHECKPT_MOD,        ONLY : CHK_STT
    USE COMODE_MOD,         ONLY : JLOP
    USE COMODE_MOD,         ONLY : CSPEC_AFTER_CHEM
    USE COMODE_MOD,         ONLY : CSPEC_AFTER_CHEM_ADJ
    USE DAO_MOD,            ONLY : AD
    USE DAO_MOD,            ONLY : AIRDEN
    USE DAO_MOD,            ONLY : BXHEIGHT
    USE GRID_MOD,           ONLY : GET_IJ
    USE TIME_MOD,           ONLY : GET_HOUR
    USE TROPOPAUSE_MOD,     ONLY : ITS_IN_THE_TROP
    USE ADJ_ARRAYS_MOD,     ONLY : ID2C
    USE TRACERID_MOD,       ONLY : IDHNO3, IDTHNO3
    USE ADJ_ARRAYS_MOD,     ONLY : COST_FUNC
    USE TRACER_MOD,         ONLY : XNUMOLAIR
    USE TRACER_MOD,         ONLY : TCVV
    USE PRESSURE_MOD,       ONLY : GET_PCENTER, GET_PEDGE
      
#include "CMN_SIZE" ! size parameters

    INTEGER :: I,J,K,L
    INTEGER :: I_MLS, J_MLS, JLOOP
    INTEGER :: IIJJ(2)
      
    ! variables for time unit conversion
    REAL*8 :: tai93
    INTEGER :: iy,im,id,ih,imin
    REAL*8 :: sec
    INTEGER :: GC_HOUR

    ! variables for observation operator and adjoint thereof

    REAL*8 :: GC_HNO3(LLPAR)
    REAL*8 :: GC_HNO3_COL
    REAL*8 :: GC_HNO3_ADJ(IIPAR,JJPAR,LLPAR)
    REAL*8 :: CM22DU
    REAL*8 :: DIFF
    REAL*8 :: OBS_ERROR

    LOGICAL :: MLS_MATCH
    REAL*8  :: OMI_MLS_DIST
    REAl*8  :: OMI_MLS_DIST_LON
    REAl*8  :: OMI_MLS_DIST_LAT
    REAL*8  :: MLS_HNO3_GC(LLPAR)
    REAL*8  :: MLS_HNO3_GC_STD(LLPAR)
    REAL*8  :: NCP(LLPAR)
    REAL*8  :: COUNT_GRID(IIPAR,JJPAR)
    REAL*8  :: COST_CONTRIB(LLPAR)
    ! arrays needed for superobservations
    LOGICAL :: SUPER_OBS = .TRUE.                       ! do super observations?
    REAL*8 ::  SOBS_COUNT(IIPAR,JJPAR)                   ! super observation count
    REAL*8 ::  SOBS_ADJ_FORCE(IIPAR,JJPAR,LLPAR)        ! super observation adjoint forcing
    REAL*8 ::  GC_ADJ_COUNT(IIPAR,JJPAR,LLPAR)
    REAL*8 ::  NEW_COST(IIPAR,JJPAR)       ! super observation cost function contribution
    REAL*8 ::  SOBS_GC(IIPAR,JJPAR)
    REAL*8 ::  SOBS_OMI(IIPAR,JJPAR)
    REAL*8 ::  SOBS_BIAS(IIPAR,JJPAR)
    REAL*8 ::  SOBS_CHISQUARED(IIPAR,JJPAR)

    ! Loop through data to find observations

    CM22DU = 2.69E16 ! conversion factor for DU -> #/cm2
    
    GC_HOUR = GET_HOUR()

    ! initialize needed arrays and variables

    COUNT_GRID = 0d0
    COST_CONTRIB = 0d0
    GC_HNO3 = 0d0
    GC_HNO3_ADJ = 0d0
    GC_HNO3_COL = 0d0
    MLS_HNO3_GC = 0d0
    MLS_HNO3_GC_STD = 0d0
    NCP = 0d0
    SOBS_COUNT = 0d0
    SOBS_ADJ_FORCE = 0d0
    NEW_COST = 0d0
    GC_ADJ_COUNT = 0d0

    OMI_MLS_DIST = 10000d0
    
    DO I_MLS = 1, N_MLS_OBS
       IF(MLS_TIME(I_MLS)>0) THEN
          ! There is an observation in the MLS grid box.
          ! Check if it was made within the current hour.
          tai93 = MLS_TIME(I_MLS)

          ! Convert TAI93 to UTC
          CALL TAI2UTC(tai93,iy,im,id,ih,imin,sec)

          IF ( ( GC_HOUR .EQ. ih                        ) .AND. & 
               ( MLS_MAIN_QUAL(I_MLS) > 0.5             ) .AND. &
               ( MLS_STA_QUAL(I_MLS) < 250              ) .AND. &
               ( MLS_CON_QUAL(I_MLS) < 1.4    ) ) THEN

             ! Get model grid coordinate indices that correspond to the observation
             IIJJ = GET_IJ(REAL(MLS_LON(I_MLS),4),REAL(MLS_LAT(I_MLS),4))

             I = IIJJ(1)
             J = IIJJ(2)

             ! Get GEOS-CHEM HNO3 values

             GC_HNO3 = 0d0
             GC_HNO3_COL = 0d0
             MLS_HNO3_GC = 0d0
             MLS_HNO3_GC_STD = 0d0
             NCP = 0d0
             COST_CONTRIB = 0d0
             DO L = 1, LLPAR

                JLOOP = JLOP(I,J,L)

                IF( ( GET_PCENTER(I,J,L) < 151 ) .AND. ( GET_PCENTER(I,J,L) > 15 ) ) THEN


                   !IF ( JLOOP > 0 ) THEN

                   !GC_HNO3(L) = CSPEC_AFTER_CHEM(JLOOP,ID2C(IDHNO3)) * 1d6 / ( AIRDEN(L,I,J) * XNUMOLAIR )

                   !ELSE

                   !GC_HNO3(L) = CHK_STT(I,J,L,IDTOX) * TCVV(IDTOX) / AD(I,J,L)

                   !ENDIF

                   ! CHK_STT is in units of [kg/box] here. Convert to ppb
                   GC_HNO3(L) =  CHK_STT(I,J,L,IDTHNO3) * TCVV(IDTHNO3) / AD(I,J,L)

                   DO J_MLS = 1, N_MLS_ALT

                      IF( ( MLS_PRESSURE(J_MLS) >= GET_PEDGE(I,J,L+1)   ) .AND. &
                          ( MLS_PRESSURE(J_MLS) < GET_PEDGE(I,J,L)      ) .AND. &
                          ( MLS_PRESSURE(J_MLS) < 151                   ) .AND. &
                          ( MLS_PRESSURE(J_MLS) > 15                    ) .AND. &
                          ( MLS_HNO3(J_MLS,I_MLS) > 0 ) ) THEN
                         
                         MLS_HNO3_GC(L) = MLS_HNO3_GC(L) + MLS_HNO3(J_MLS,I_MLS)

                         MLS_HNO3_GC_STD(L) = MLS_HNO3_GC_STD(L) + MLS_HNO3_STD(J_MLS,I_MLS)**2
                         
                         NCP(L) = NCP(L) + 1
                      ENDIF
                   ENDDO

                   IF (NCP(L)>0) THEN

                      MLS_HNO3_GC(L) = MLS_HNO3_GC(L)/NCP(L)
                      MLS_HNO3_GC_STD(L) = (MLS_HNO3_GC_STD(L)**(0.5))/NCP(L)
                      OBS_ERROR = MLS_HNO3_GC_STD(L)
                      DIFF = GC_HNO3(L) - MLS_HNO3_GC(L)
                      COST_CONTRIB(L) = 0.5 * (DIFF/OBS_ERROR)**2
                      IF ( ( COST_CONTRIB(L) > 0d0) .AND. &
                           ( GET_PCENTER(I,J,L) < 151 ) .AND. &
                           ( GET_PCENTER(I,J,L) > 15 ) ) THEN
                         
                         IF (SUPER_OBS) THEN
                            NEW_COST(I,J) = NEW_COST(I,J) + COST_CONTRIB(L)
                            SOBS_COUNT(I,J) = SOBS_COUNT(I,J) + 1
                            SOBS_ADJ_FORCE(I,J,L) = SOBS_ADJ_FORCE(I,J,L) + DIFF/(OBS_ERROR**2) * TCVV(IDTHNO3) / AD(I,J,L)
                            GC_ADJ_COUNT(I,J,L) = GC_ADJ_COUNT(I,J,L) + 1
                         ENDIF
                      ENDIF
                   ENDIF
                ENDIF

             ENDDO
             !PRINT *, "MODELLED HNO3", GC_HNO3
             !PRINT *, "OBSERVED HNO3", MLS_HNO3_GC

             ! Compute stratospheric HNO3 column value [v/v*cm]

             !GC_HNO3_COL = SUM(GC_HNO3(:) * BXHEIGHT(I,J,:) * 100d0)

             !PRINT *, "GC_HNO3_COL", GC_HNO3_COL

             !PRINT *, "MLS_HNO3_COL", MLS_HNO3_COL(I_MLS)

             !DIFF = GC_HNO3_COL - MLS_HNO3_COL(I_MLS)

             !OBS_ERROR = (MLS_HNO3_COL_STD(I_MLS))**0.5

             !DO L = 1, LLPAR
                !IF( ( GET_PCENTER(I,J,L) < 151 ) .AND. ( GET_PCENTER(I,J,L) > 15 ) ) THEN

                   !JLOOP = JLOP(I,J,L)
                   
                   !IF (SUPER_OBS) THEN

                      !SOBS_ADJ_FORCE(I,J,L) = SOBS_ADJ_FORCE(I,J,L) + DIFF/(OBS_ERROR**2) * BXHEIGHT(I,J,L) * 100d0 &
                           !* TCVV(IDTHNO3) / (AD(I,J,L) * 1d6)
                   !ELSE
                      !STT_ADJ(I,J,L,IDTHNO3) = STT_ADJ(I,J,L,IDTHNO3) + DIFF/(OBS_ERROR**2) * BXHEIGHT(I,J,L) * 100d0 &
                           !* TCVV(IDTHNO3) / (AD(I,J,L) * 1d6)

                   !ENDIF
                !ENDIF
             !ENDDO
             !PRINT *, "SUPER_OBS_FORCE", SOBS_ADJ_FORCE
          ENDIF
       
       ENDIF
    ENDDO
    !PRINT *, "SUPER_OBS_FORCE", SOBS_ADJ_FORCE

    IF (SUPER_OBS) THEN

       DO J = 1,JJPAR
          DO I = 1, IIPAR

             IF(SOBS_COUNT(I,J) > 0d0) THEN

                DO L = 1,LLPAR
                   IF( ( GET_PCENTER(I,J,L) < 151 ) .AND. & 
                       ( GET_PCENTER(I,J,L) > 15 ) .AND. &
                       ( GC_ADJ_COUNT(I,J,L) > 0 ) ) THEN

                      !JLOOP = JLOP(I,J,L)

                      STT_ADJ(I,J,L,IDTHNO3) = STT_ADJ(I,J,L,IDTHNO3) + SOBS_ADJ_FORCE(I,J,L)/GC_ADJ_COUNT(I,J,L)

                   ENDIF
                ENDDO

                COST_FUNC = COST_FUNC + NEW_COST(I,J)/SOBS_COUNT(I,J)
             ENDIF
          ENDDO
       ENDDO
    ENDIF

    PRINT *, "COST FUNCTION OF MLS HNO3", COST_FUNC

  END SUBROUTINE CALC_MLS_HNO3_FORCE

!----------------------------------------------------------------------------!
  SUBROUTINE CLEANUP_MLS

    IF (ALLOCATED( MLS_LON ))  DEALLOCATE( MLS_LON )      
    IF (ALLOCATED( MLS_LAT ))  DEALLOCATE( MLS_LAT )
    IF (ALLOCATED( MLS_TIME ))  DEALLOCATE( MLS_TIME )
    IF (ALLOCATED( MLS_HNO3 ))  DEALLOCATE( MLS_HNO3 )
    IF (ALLOCATED( MLS_HNO3_STD ))  DEALLOCATE( MLS_HNO3_STD )
    IF (ALLOCATED( MLS_CON_QUAL ))  DEALLOCATE( MLS_CON_QUAL )
    IF (ALLOCATED( MLS_MAIN_QUAL ))  DEALLOCATE( MLS_MAIN_QUAL )
    IF (ALLOCATED( MLS_STA_QUAL ))  DEALLOCATE( MLS_STA_QUAL )
    IF (ALLOCATED( MLS_CN ))  DEALLOCATE( MLS_CN )
    IF (ALLOCATED( MLS_SOLAR_ZENITH ))  DEALLOCATE( MLS_SOLAR_ZENITH )
    IF (ALLOCATED( MLS_VIEW_ZENITH ))  DEALLOCATE( MLS_VIEW_ZENITH )
    IF (ALLOCATED( MLS_PRESSURE ))   DEALLOCATE( MLS_PRESSURE )

  END SUBROUTINE CLEANUP_MLS
  
!-----------------------------------------------------------------------------!
  
  SUBROUTINE TAI2UTC(tai93,iy,im,id,ih,imin,sec)
    
    !!
    !! SUBROUTINE TAI2UTC converts TAI93 time (seconds since 1.1.1993) to UTC 
    !!
    !! adapted from 
    !! code.google.com/p/miyoshi/source/browse/trunk/common/common.f90
    
    IMPLICIT NONE
    
    INTEGER,PARAMETER :: n=7  ! number of leap seconds after Jan. 1, 1993
    INTEGER,PARAMETER :: leapsec(n) = (/ 15638399, 47174400, 94608001, 141868802, 189302403, 410227204, 504921605/)
    REAL*8,INTENT(IN) :: tai93
    INTEGER,INTENT(OUT) :: iy,im,id,ih,imin
    REAL*8,INTENT(OUT) :: sec
    REAL*8,PARAMETER :: mins = 60.0d0
    REAL*8,PARAMETER :: hour = 60.0d0*mins
    REAL*8,PARAMETER :: day = 24.0d0*hour
    REAL*8,PARAMETER :: year = 365.0d0*day
    INTEGER,PARAMETER :: mdays(12) = (/31,28,31,30,31,30,31,31,30,31,30,31/)
    REAL*8 :: wk,tai
    INTEGER :: days,i,leap
    
    tai = tai93
    sec = 0.0d0
    
    DO i=1,n
       
       IF(FLOOR(tai93) == leapsec(i)+1) THEN
          sec = 60.0d0 + tai93-FLOOR(tai93)
       ENDIF
       
       IF(FLOOR(tai93) > leapsec(i)) tai = tai -1.0d0
       
    END DO
    
    iy = 1993 + FLOOR(tai /year)
    wk = tai - REAL(iy-1993)*year - FLOOR(REAL(iy-1993)/4.0)*day
    
    IF(wk < 0.0d0) THEN
       iy = iy -1
       wk = tai - REAL(iy-1993)*year - FLOOR(REAL(iy-1993)/4.0)*day
    END IF
    
    days = FLOOR(wk/day)
    wk = wk - REAL(days)*day
    im = 1
    
    DO i=1,12
       
       leap = 0
       IF(im == 2 .AND. MOD(iy,4)==0) leap=1
       IF(im == i .AND. days >= mdays(i)+leap) THEN
          im = im + 1
          days = days - mdays(i)-leap
       END IF
       
    END DO
    
    id = days +1
    
    ih = FLOOR(wk/hour)
    wk = wk - REAL(ih)*hour
    imin = FLOOR(wk/mins)
    
    IF(sec < 60.0d0) sec = wk - REAL(imin)*mins
    
    RETURN
    
  END SUBROUTINE TAI2UTC
  
END MODULE MLS_HNO3_OBS_MOD