subroutine gffgch(t ,es ,itype ) 2,5
!-----------------------------------------------------------------------
!
! Purpose:
! Computes saturation vapor pressure over water and/or over ice using
! Goff & Gratch (1946) relationships.
! <Say what the routine does>
!
! Method:
! T (temperature), and itype are input parameters, while es (saturation
! vapor pressure) is an output parameter. The input parameter itype
! serves two purposes: a value of zero indicates that saturation vapor
! pressures over water are to be returned (regardless of temperature),
! while a value of one indicates that saturation vapor pressures over
! ice should be returned when t is less than freezing degrees. If itype
! is negative, its absolute value is interpreted to define a temperature
! transition region below freezing in which the returned
! saturation vapor pressure is a weighted average of the respective ice
! and water value. That is, in the temperature range 0 => -itype
! degrees c, the saturation vapor pressures are assumed to be a weighted
! average of the vapor pressure over supercooled water and ice (all
! water at 0 c; all ice at -itype c). Maximum transition range => 40 c
!
! Author: J. Hack
!
!-----------------------------------------------------------------------
use shr_kind_mod
, only: r8 => shr_kind_r8
use physconst, only: tmelt
use abortutils, only: endrun
use cam_logfile, only: iulog
implicit none
!------------------------------Arguments--------------------------------
!
! Input arguments
!
real(r8), intent(in) :: t ! Temperature
!
! Output arguments
!
integer, intent(inout) :: itype ! Flag for ice phase and associated transition
real(r8), intent(out) :: es ! Saturation vapor pressure
!
!---------------------------Local variables-----------------------------
!
real(r8) e1 ! Intermediate scratch variable for es over water
real(r8) e2 ! Intermediate scratch variable for es over water
real(r8) eswtr ! Saturation vapor pressure over water
real(r8) f ! Intermediate scratch variable for es over water
real(r8) f1 ! Intermediate scratch variable for es over water
real(r8) f2 ! Intermediate scratch variable for es over water
real(r8) f3 ! Intermediate scratch variable for es over water
real(r8) f4 ! Intermediate scratch variable for es over water
real(r8) f5 ! Intermediate scratch variable for es over water
real(r8) ps ! Reference pressure (mb)
real(r8) t0 ! Reference temperature (freezing point of water)
real(r8) term1 ! Intermediate scratch variable for es over ice
real(r8) term2 ! Intermediate scratch variable for es over ice
real(r8) term3 ! Intermediate scratch variable for es over ice
real(r8) tr ! Transition range for es over water to es over ice
real(r8) ts ! Reference temperature (boiling point of water)
real(r8) weight ! Intermediate scratch variable for es transition
integer itypo ! Intermediate scratch variable for holding itype
!
!-----------------------------------------------------------------------
!
! Check on whether there is to be a transition region for es
!
if (itype < 0) then
tr = abs(real(itype,r8))
itypo = itype
itype = 1
else
tr = 0.0_r8
itypo = itype
end if
if (tr > 40.0_r8) then
write(iulog,900) tr
call endrun ('GFFGCH') ! Abnormal termination
end if
!
if(t < (tmelt - tr) .and. itype == 1) go to 10
!
! Water
!
ps = 1013.246_r8
ts = 373.16_r8
e1 = 11.344_r8*(1.0_r8 - t/ts)
e2 = -3.49149_r8*(ts/t - 1.0_r8)
f1 = -7.90298_r8*(ts/t - 1.0_r8)
f2 = 5.02808_r8*log10(ts/t)
f3 = -1.3816_r8*(10.0_r8**e1 - 1.0_r8)/10000000.0_r8
f4 = 8.1328_r8*(10.0_r8**e2 - 1.0_r8)/1000.0_r8
f5 = log10(ps)
f = f1 + f2 + f3 + f4 + f5
es = (10.0_r8**f)*100.0_r8
eswtr = es
!
if(t >= tmelt .or. itype == 0) go to 20
!
! Ice
!
10 continue
t0 = tmelt
term1 = 2.01889049_r8/(t0/t)
term2 = 3.56654_r8*log(t0/t)
term3 = 20.947031_r8*(t0/t)
es = 575.185606e10_r8*exp(-(term1 + term2 + term3))
!
if (t < (tmelt - tr)) go to 20
!
! Weighted transition between water and ice
!
weight = min((tmelt - t)/tr,1.0_r8)
es = weight*es + (1.0_r8 - weight)*eswtr
!
20 continue
itype = itypo
return
!
900 format('GFFGCH: FATAL ERROR ******************************',/, &
'TRANSITION RANGE FOR WATER TO ICE SATURATION VAPOR', &
' PRESSURE, TR, EXCEEDS MAXIMUM ALLOWABLE VALUE OF', &
' 40.0 DEGREES C',/, ' TR = ',f7.2)
!
end subroutine gffgch