source: flexpart.git/src/juldate.f90

! SPDX-FileCopyrightText: FLEXPART 1998-2019, see flexpart_license.txt
! SPDX-License-Identifier: GPL-3.0-or-later

function juldate(yyyymmdd,hhmiss)

  !*****************************************************************************
  !                                                                            *
  !     Calculates the Julian date                                             *
  !                                                                            *
  !     AUTHOR: Andreas Stohl (15 October 1993)                                *
  !                                                                            *
  !     Variables:                                                             *
  !     dd             Day                                                     *
  !     hh             Hour                                                    *
  !     hhmiss         Hour, minute + second                                   *
  !     ja,jm,jy       help variables                                          *
  !     juldate        Julian Date                                             *
  !     julday         help variable                                           *
  !     mi             Minute                                                  *
  !     mm             Month                                                   *
  !     ss             Second                                                  *
  !     yyyy           Year                                                    *
  !     yyyymmddhh     Date and Time                                           *
  !                                                                            *
  !     Constants:                                                             *
  !     igreg          help constant                                           *
  !                                                                            *
  !*****************************************************************************

  use par_mod, only: dp

  implicit none

  integer           :: yyyymmdd,yyyy,mm,dd,hh,mi,ss,hhmiss
  integer           :: julday,jy,jm,ja
  integer,parameter :: igreg=15+31*(10+12*1582)
  real(kind=dp)     :: juldate

  yyyy=yyyymmdd/10000
  mm=(yyyymmdd-10000*yyyy)/100
  dd=yyyymmdd-10000*yyyy-100*mm
  hh=hhmiss/10000
  mi=(hhmiss-10000*hh)/100
  ss=hhmiss-10000*hh-100*mi

  if (yyyy.eq.0) then
     print*, 'there is no year zero.'
     stop
  end if
  if (yyyy.lt.0) yyyy=yyyy+1
  if (mm.gt.2) then
    jy=yyyy
    jm=mm+1
  else
    jy=yyyy-1
    jm=mm+13
  endif
  julday=int(365.25*jy)+int(30.6001*jm)+dd+1720995
  if (dd+31*(mm+12*yyyy).ge.igreg) then
    ja=int(0.01*jy)
    julday=julday+2-ja+int(0.25*ja)
  endif

  juldate=real(julday,kind=dp)   + real(hh,kind=dp)/24._dp + &
       real(mi,kind=dp)/1440._dp  + real(ss,kind=dp)/86400._dp

end function juldate