FUNCTION f_qv_from_rh (RH, T_K, RH0, T_K0, P_PA0) RESULT (QV_KG) 2
!!!--------------------------------------------------------------------------
!!!
!!! FUNCTION F_QV_FROM_RH
!!! **************************
!!!
!!! PURPOSE:
!!! -------
!!! TANGENT LINEAR CODE FOR
!!! COMPUTING MIXING RATIO FROM RELATIVE HUMIDITY, TEMPERATURE AND PRESSURE
!!!
!!! THE ERROR DERIVATION SHOULD USED THE TANGENT LINEAR CODE, NOT THE
!!! ORIGINAL NON-LINEAR CODE.
!!!
!! METHOD:
!! ------
!! LINEAR OR LOGARITHMIC VERTICAL INTERPOLATION
!! OUT OF BOUND LOCATIONS ARE EXTRAPOLATED
!!
!! INPUT:
!! -----
!! RH: RELAITVE HUMIDITY in %
!! P_PA: PRESSURE in Pa
!! T_K: TEMPERATURE in K
!!
!! OUTPUT:
!! ------
!! QV_KG: MIXING RATIO IN kg/kg
!!
!! COMMON: NO
!! -------
!! EXTERNAL: NO
!! --------
!!
!! REFERENCES:
!! -----------
!! R. R. ROGERS AND M. K. YAU, 1989: A SHORT COURSE IN CLOUD PHYSICS,
!! 3ND EDITION, PERGAMON PRESS, PAGE 14-19.
!!
!! VERIFICATION SET:
!! -----------------
!! T_K = 268.15 K,
!! TD_K = 262.55 K
!! RH = 65 %,
!! P_PA = 80000 Pa,
!! QV = 2.11E-03 kg/kg,
!!
!! MODIFICATIONS:
!! ------------
!! Developed by Yong-Run Guo (11/07/00)
!!----------------------------------------------------------------------------CC
IMPLICIT NONE
REAL T_K , RH , QV_KG
REAL P_PA0, T_K0, RH0
! REAL P_MB, W_KG
REAL ES , QS
REAL P_MB0, ES0, QS0, QV_KG0
!------------------------------------------------------------------------------C
!...P in mb
P_MB0 = P_PA0 / 100.
!...VAPOR PRESSURE in mb
ES = 6.112 * 17.67 * 243.5 * T_K / &
((T_K0-273.15+243.5)*(T_K0-273.15+243.5)) * &
EXP (17.67*(T_K0-273.15)/(T_K0-273.15+243.5))
ES0 = 6.112 * EXP (17.67*(T_K0-273.15)/(T_K0-273.15+243.5))
!...SATURATION MIXING RATIO in kg/kg
QS = 0.622 * (P_MB0 * ES ) / &
((P_MB0 - ES0) * (P_MB0 - ES0))
QS0 = 0.622 * ES0 /(P_MB0-ES0)
!...MIXING RATIO in kg/kg
QV_KG = 0.01 * (RH0 * QS + RH * QS0)
QV_KG0 = 0.01 * RH0 * QS0
!...Mixing ratio must be positive
IF (QV_KG0 < 0.) QV_KG = 0.
RETURN
END FUNCTION f_qv_from_rh