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chgres_cube: New function to convert from RH to SPFH for GFS GRIB2 da…
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…ta (#566)

New function 'rh2spfh_gfs' to convert from relative humidity to 
specific humidity using a formula consistent with the 
GFS v15/v16 GRIB2 files.

New unit test for function 'rh2spfh_gfs'.

Fixes #565.
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@JiliDong-NOAA
JiliDong-NOAA authored Sep 1, 2021
1 parent f7cbbb5 commit 2ad0033
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146 changes: 146 additions & 0 deletions sorc/chgres_cube.fd/grib2_util.F90
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Original file line number Diff line number Diff line change
Expand Up @@ -17,9 +17,16 @@ module grib2_util

implicit none

public :: rh2spfh_gfs
public :: fpvsnew


contains

!> Convert relative humidity to specific humidity.
!> Calculation of saturation water vapor pressure is based on
!> Brock and Richardson 2001 (Meterological Measurement
!> Systems, p. 86, equation 5.1)
!!
!! @param[inout] rh_sphum rel humidity on input. spec hum on output.
!! @param[in] p pressure in Pa
Expand Down Expand Up @@ -57,6 +64,145 @@ subroutine rh2spfh(rh_sphum,p,t)

end subroutine RH2SPFH

!> Convert relative humidity to specific humidity (GFS formula)
!> Calculation of saturation water vapor pressure is based on
!> GFS function fvpsnew (Phillips 1982). The model does account for the variation of the
!> latent heat of condensation with temperature. A linear interpolation is done
!> between values in a calculated lookup table. Ice and water are considered
!> separately. This option provides a consistent conversion for GFS grib2 data
!> to be ingested.
!!
!! @param[inout] rh_sphum rel humidity on input. spec hum on output.
!! @param[in] p pressure in Pa
!! @param[in] t temperature
!! @author Jili Dong NCEP/EMC
subroutine rh2spfh_gfs(rh_sphum,p,t)

implicit none

integer kind_phys

parameter (kind_phys = selected_real_kind(13,60)) ! the '60' maps to 64-bit real


real(kind=kind_phys),parameter:: con_rd =2.8705e+2 ! gas constant air (J/kg/K)
real(kind=kind_phys),parameter:: con_rv =4.6150e+2 ! gas constant H2O (J/kg/K)

real(kind=kind_phys),parameter:: con_eps =con_rd/con_rv
real(kind=kind_phys),parameter:: con_epsm1 =con_rd/con_rv-1.




real(esmf_kind_r4), intent(inout), dimension(i_input,j_input) ::rh_sphum
real(esmf_kind_r8), intent(in) :: p, t(i_input,j_input)

real, dimension(i_input,j_input) :: QC, rh
real :: ES
integer :: i,j

print*,"- CONVERT RH TO SPFH AT LEVEL ", p

rh = rh_sphum

do j=1,j_input
do i=1,i_input
ES = MIN(FPVSNEW(T(I,J)),P)
QC(i,j) = CON_EPS*ES/(P+CON_EPSM1*ES)
rh_sphum(i,j) = rh(i,j)*QC(i,j)/100.0
end do
end do


!print *, 'T = ', T, ' RH = ', RH, ' P = ', P
!print *, 'q = ', sphum


end subroutine RH2SPFH_GFS


!> Compute saturation vapor pressure
!!
!! @param[in] t temperature in Kelvin
!! @return fpvsnew Saturation vapor pressure
!! @author N Phillips w/NMC2X2
!! @date 30 dec 82

!
!-------------------------------------------------------------------------------------
!
elemental function fpvsnew(t)
!
implicit none
integer,parameter:: nxpvs=7501
real,parameter:: con_ttp =2.7316e+2 ! temp at H2O 3pt
real,parameter:: con_psat =6.1078e+2 ! pres at H2O 3pt
real,parameter:: con_cvap =1.8460e+3 ! spec heat H2O gas (J/kg/K)
real,parameter:: con_cliq =4.1855e+3 ! spec heat H2O liq
real,parameter:: con_hvap =2.5000e+6 ! lat heat H2O cond
real,parameter:: con_rv =4.6150e+2 ! gas constant H2O
real,parameter:: con_csol =2.1060e+3 ! spec heat H2O ice
real,parameter:: con_hfus =3.3358e+5 ! lat heat H2O fusion
real,parameter:: tliq=con_ttp
real,parameter:: tice=con_ttp-20.0
real,parameter:: dldtl=con_cvap-con_cliq
real,parameter:: heatl=con_hvap
real,parameter:: xponal=-dldtl/con_rv
real,parameter:: xponbl=-dldtl/con_rv+heatl/(con_rv*con_ttp)
real,parameter:: dldti=con_cvap-con_csol
real,parameter:: heati=con_hvap+con_hfus
real,parameter:: xponai=-dldti/con_rv
real,parameter:: xponbi=-dldti/con_rv+heati/(con_rv*con_ttp)
real tr,w,pvl,pvi
real fpvsnew
real(esmf_kind_r8),intent(in):: t
integer jx
real xj,x,tbpvs(nxpvs),xp1
real xmin,xmax,xinc,c2xpvs,c1xpvs
! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
xmin=180.0
xmax=330.0
xinc=(xmax-xmin)/(nxpvs-1)
! c1xpvs=1.-xmin/xinc
c2xpvs=1./xinc
c1xpvs=1.-xmin*c2xpvs
! xj=min(max(c1xpvs+c2xpvs*t,1.0),real(nxpvs,krealfp))
xj=min(max(c1xpvs+c2xpvs*t,1.0),float(nxpvs))
jx=min(xj,float(nxpvs)-1.0)
x=xmin+(jx-1)*xinc

tr=con_ttp/x
if(x>=tliq) then
tbpvs(jx)=con_psat*(tr**xponal)*exp(xponbl*(1.-tr))
elseif(x<tice) then
tbpvs(jx)=con_psat*(tr**xponai)*exp(xponbi*(1.-tr))
else
w=(t-tice)/(tliq-tice)
pvl=con_psat*(tr**xponal)*exp(xponbl*(1.-tr))
pvi=con_psat*(tr**xponai)*exp(xponbi*(1.-tr))
tbpvs(jx)=w*pvl+(1.-w)*pvi
endif

xp1=xmin+(jx-1+1)*xinc

tr=con_ttp/xp1
if(xp1>=tliq) then
tbpvs(jx+1)=con_psat*(tr**xponal)*exp(xponbl*(1.-tr))
elseif(xp1<tice) then
tbpvs(jx+1)=con_psat*(tr**xponai)*exp(xponbi*(1.-tr))
else
w=(t-tice)/(tliq-tice)
pvl=con_psat*(tr**xponal)*exp(xponbl*(1.-tr))
pvi=con_psat*(tr**xponai)*exp(xponbi*(1.-tr))
tbpvs(jx+1)=w*pvl+(1.-w)*pvi
endif

fpvsnew=tbpvs(jx)+(xj-jx)*(tbpvs(jx+1)-tbpvs(jx))
! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
end function fpvsnew



!> Convert omega to vertical velocity.
!!
!! @param[inout] omega on input, vertical velocity on output
Expand Down
28 changes: 24 additions & 4 deletions sorc/chgres_cube.fd/input_data.F90
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Original file line number Diff line number Diff line change
Expand Up @@ -2459,7 +2459,7 @@ subroutine read_input_atm_grib2_file(localpet)

use wgrib2api

use grib2_util, only : rh2spfh, convert_omega
use grib2_util, only : rh2spfh, rh2spfh_gfs, convert_omega

implicit none

Expand Down Expand Up @@ -2490,7 +2490,9 @@ subroutine read_input_atm_grib2_file(localpet)
logical :: lret
logical :: conv_omega=.false., &
hasspfh=.true., &
isnative=.false.
isnative=.false., &
use_rh=.false.


real(esmf_kind_r8), allocatable :: rlevs(:)
real(esmf_kind_r4), allocatable :: dummy2d(:,:)
Expand Down Expand Up @@ -2603,11 +2605,23 @@ subroutine read_input_atm_grib2_file(localpet)
if (localpet==0) print*, "- LEVEL AFTER SORT = ",slevs(i)
enddo
endif

! Is SPFH on full levels Jili Dong
do vlev = 1, lev_input
iret = grb2_inq(the_file,inv_file,':SPFH:',slevs(vlev))
if (iret <= 0) then
use_rh = .TRUE.
if (localpet == 0) print*, ':SPFH on level '//trim(slevs(vlev))//' does not exist. &
Will read in RH and convert to SPFH instead.'
exit
end if
end do


if (localpet == 0) print*,"- FIND SPFH OR RH IN FILE"
iret = grb2_inq(the_file,inv_file,trim(trac_names_grib_1(1)),trac_names_grib_2(1),lvl_str_space)

if (iret <= 0) then
if (iret <= 0 .or. use_rh) then
iret = grb2_inq(the_file,inv_file, ':var0_2','_1_1:',lvl_str_space)
if (iret <= 0) call error_handler("READING ATMOSPHERIC WATER VAPOR VARIABLE.", iret)
hasspfh = .false.
Expand Down Expand Up @@ -2782,7 +2796,13 @@ subroutine read_input_atm_grib2_file(localpet)
endif !iret<=0

if (n==1 .and. .not. hasspfh) then
call rh2spfh(dummy2d,rlevs(vlev),dummy3d(:,:,vlev))
if (trim(external_model) .eq. 'GFS') then
print *,'CALRH GFS'
call rh2spfh_gfs(dummy2d,rlevs(vlev),dummy3d(:,:,vlev))
else
print *,'CALRH non-GFS'
call rh2spfh(dummy2d,rlevs(vlev),dummy3d(:,:,vlev))
end if
endif

print*,'tracer ',vlev, maxval(dummy2d),minval(dummy2d)
Expand Down
7 changes: 7 additions & 0 deletions tests/chgres_cube/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -83,6 +83,13 @@ target_link_libraries(ftst_dint2p

add_test(NAME chgres_cube-ftst_dint2p COMMAND ftst_dint2p)

add_executable(ftst_rh2spfh_gfs ftst_rh2spfh_gfs.F90)
target_link_libraries(ftst_rh2spfh_gfs
chgres_cube_lib)

add_test(NAME chgres_cube-ftst_rh2spfh_gfs COMMAND ftst_rh2spfh_gfs)


add_executable(ftst_quicksort ftst_quicksort.F90)
target_link_libraries(ftst_quicksort
chgres_cube_lib)
Expand Down
42 changes: 42 additions & 0 deletions tests/chgres_cube/ftst_rh2spfh_gfs.F90
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Original file line number Diff line number Diff line change
@@ -0,0 +1,42 @@
program ftst_rh2spfh_gfs

use grib2_util

implicit none

real, parameter :: eps=1E-4

real*4, dimension(3,2) :: rh_500hpa, rh_900hpa, rh_tmp
real*4, dimension(3,2) :: spfh_gfs_900hpa_expected, spfh_gfs_500hpa_expected
real*8, dimension(3,2) :: temp_500hpa, temp_900hpa
real*8 :: pres

data temp_900hpa /280.9, 282.6, 281.4, 289.9, 286.5, 288.7/
data rh_900hpa /17.6, 75.2, 99.9, 95.4, 86.6, 89.1/

data temp_500hpa /254.1, 259.7, 259.7, 267.2, 262.0, 269.5/
data rh_500hpa /10.7, 9.1, 0.5, 10.1, 4.2, 0.9/

data spfh_gfs_900hpa_expected /1.286259, 6.169457, 7.554718, 12.64650, 9.210890, 10.93505/
data spfh_gfs_500hpa_expected /0.1519615, 0.2257435, 1.2403490E-02, 0.4856212, 0.1288972, 5.2061662E-02/

i_input = 3
j_input = 2

! rh to spfh at 500 hPa with GFSv15/16 conversion
rh_tmp=rh_500hpa
pres=50000.0
call rh2spfh_gfs(rh_tmp,pres,temp_500hpa)
if (any((abs(rh_tmp*1000.0-spfh_gfs_500hpa_expected)) .gt. eps)) stop 500

! rh to spfh at 900 hPa with GFSv15/16 conversion
rh_tmp=rh_900hpa
pres=90000.0
call rh2spfh_gfs(rh_tmp,pres,temp_900hpa)
if (any((abs(rh_tmp*1000.0-spfh_gfs_900hpa_expected)) .gt. eps)) stop 900

print*, "OK"
print*, "SUCCESS!"

end program ftst_rh2spfh_gfs

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