!-------------------------------------- LICENCE BEGIN ------------------------------------
!Environment Canada - Atmospheric Science and Technology License/Disclaimer, 
!                     version 3; Last Modified: May 7, 2008.
!This is free but copyrighted software; you can use/redistribute/modify it under the terms 
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***FONCTION SHUAES  -  PASSAGE DE HU A ES
*

      FUNCTION SHUAES(HU,TX,PX,LNPS,MODP,SWTT,SWPH) 1,1
#include "impnone.cdk"
      REAL SHUAES, HU, TX, PX, LNPS
      INTEGER MODP
      LOGICAL SWTT, SWPH
*
*Author
*          N. Brunet  (Jan91)
*
*Object
*          to return dew point depression (Celsius) calculated from
*          specific humidity, temperature and pressure
*
*Arguments
*
*          - Input -
* HU       specific humidity in kg/kg
* TX       temperature or virtual temperature in Kelvins
* PX       see MODP
* LNPS     see MODP
* MODP     pressure mode(SI units only):
*          =0; pressure level in PX
*          =1; sigma level in PX and PS(surface pressure) in LNPS
*          =2; sigma level in PX and logarithm of sigma level in
*          LNPS
*          =3; all points of pressure in LNPS(NI,*) in Pascals
*          =4; sigma level in PX and logarithm of sigma level in
*          LNPS(in millibars unless using SI units)
*          =5; logarithm of pressure level in PX(in millibars unless
*          using SI units)
* SWTT     .TRUE. to pass TT for argument
*          .FALSE. to pass TV for argument
* SWPH     .TRUE. to consider water and ice phase
*          .FALSE. to consider water phase only
*
*Notes
*     If HU <=0, we don't change the value of HU, but we take
*     the maximum value of: MAX(HU,0.0000000001).
*     to avoid the occurence of taking the log of a negative
*     number
*
*IMPLICITES
#include "consphy.cdk"
*MODULES
      EXTERNAL INCTPHY
*
*
**
*--------------------------------------------------------------------
      REAL E, CTE, TD, PETIT, TP, PN
*
#include "dintern.cdk"
#include "fintern.cdk"
*--------------------------------------------------------------------
#include "initcph.cdk"
*
      PETIT = 0.0000000001
*
#include "modpr1.cdk"
#include "modtp1.cdk"
      E = FOEFQ(MAX(PETIT,HU),PN)
      CTE = ALOG(E/610.78)
      TD = (35.86*CTE - 17.269*TRPL)/(CTE - 17.269)
      IF(TD.LT.TRPL.AND.SWPH)THEN
         TD = (7.66*CTE - 21.875*TRPL)/(CTE - 21.875)
      END IF
*
      SHUAES = TP-TD
*
      RETURN
      CONTAINS
#include "fintern90.cdk"
      END