C $Header: /u/gcmpack/MITgcm/model/src/seawater.F,v 1.11 2015/02/26 17:17:56 mlosch Exp $
C $Name:  $

#include "CPP_OPTIONS.h"

C--  File seawater.F: routines that compute quantities related to seawater.
C--   Contents
C     Seawater (SW) librabry routines
C--   o SW_PTMP: function to compute potential temperature
C--   o SW_TEMP: function to compute in-situ temperature from pot. temp.
C--   o SW_ADTG: function to compute adiabatic temperature gradient
C--              (used by both SW_PTMP & SW_TEMP)

C---+----1----+----2----+----3----+----4----+----5----+----6----+----7-|--+----|

CBOP
C     !ROUTINE: SW_PTMP
C     !INTERFACE:
      _RL FUNCTION SW_PTMP  (S,T,P,PR)

C     !DESCRIPTION: \bv
C     *=============================================================*
C     | S/R  SW_PTMP
C     | o compute potential temperature as per UNESCO 1983 report.
C     *=============================================================*
C
C     started:
C              Armin Koehl akoehl@ucsd.edu
C
C     ==================================================================
C     SUBROUTINE SW_PTMP
C     ==================================================================
C     S  :: salinity    [psu      (PSS-78) ]
C     T  :: temperature [degree C (IPTS-68)]
C     P  :: pressure    [db]
C     PR :: Reference pressure  [db]
C     \ev

C     !USES:
      IMPLICIT NONE

C     !INPUT/OUTPUT PARAMETERS:
      _RL S,T,P,PR

C     !FUNCTIONS:
      _RL sw_adtg
      EXTERNAL 

C     !LOCAL VARIABLES
      _RL del_P ,del_th, th, q
      _RL onehalf, two, three
      PARAMETER ( onehalf = 0.5 _d 0, two = 2. _d 0, three = 3. _d 0 )
CEOP

C theta1
      del_P  = PR - P
      del_th = del_P*sw_adtg(S,T,P)
      th     = T + onehalf*del_th
      q      = del_th
C theta2
      del_th = del_P*sw_adtg(S,th,P+onehalf*del_P)

      th     = th + (1 - 1/sqrt(two))*(del_th - q)
      q      = (two-sqrt(two))*del_th + (-two+three/sqrt(two))*q

C theta3
      del_th = del_P*sw_adtg(S,th,P+onehalf*del_P)
      th     = th + (1 + 1/sqrt(two))*(del_th - q)
      q      = (two + sqrt(two))*del_th + (-two-three/sqrt(two))*q

C theta4
      del_th = del_P*sw_adtg(S,th,P+del_P)
      SW_PTMP     = th + (del_th - two*q)/(two*three)

      RETURN
      END


C---+----1----+----2----+----3----+----4----+----5----+----6----+----7-|--+----| CBOP C !ROUTINE: SW_TEMP C !INTERFACE: _RL FUNCTION SW_TEMP( S, T, P, PR ) C !DESCRIPTION: \bv C *=============================================================* C | S/R SW_TEMP C | o compute in-situ temperature from potential temperature C *=============================================================* C C REFERENCES: C Fofonoff, P. and Millard, R.C. Jr C Unesco 1983. Algorithms for computation of fundamental properties of C seawater, 1983. _Unesco Tech. Pap. in Mar. Sci._, No. 44, 53 pp. C Eqn.(31) p.39 C C Bryden, H. 1973. C New Polynomials for thermal expansion, adiabatic temperature gradient C and potential temperature of sea water. C DEEP-SEA RES., 1973, Vol20,401-408. C \ev C !USES: IMPLICIT NONE C === Global variables === C !INPUT/OUTPUT PARAMETERS: C === Routine arguments === C S :: salinity C T :: potential temperature C P :: pressure C PR :: reference pressure _RL S, T, P, PR CEOP C !FUNCTIONS: _RL sw_ptmp EXTERNAL SW_temp = SW_PTMP (S,T,PR,P) RETURN END


C---+----1----+----2----+----3----+----4----+----5----+----6----+----7-|--+----| CBOP C !ROUTINE: SW_ADTG C !INTERFACE: _RL FUNCTION SW_ADTG (S,T,P) C !DESCRIPTION: \bv C *=============================================================* C | S/R SW_ADTG C | o compute adiabatic temperature gradient as per UNESCO 1983 routines. C *=============================================================* C C started: C Armin Koehl akoehl@ucsd.edu C \ev C !USES: IMPLICIT NONE C !INPUT/OUTPUT PARAMETERS: _RL S,T,P C !LOCAL VARIABLES: _RL a0,a1,a2,a3,b0,b1,c0,c1,c2,c3,d0,d1,e0,e1,e2 _RL sref CEOP sref = 35. _d 0 a0 = 3.5803 _d -5 a1 = +8.5258 _d -6 a2 = -6.836 _d -8 a3 = 6.6228 _d -10 b0 = +1.8932 _d -6 b1 = -4.2393 _d -8 c0 = +1.8741 _d -8 c1 = -6.7795 _d -10 c2 = +8.733 _d -12 c3 = -5.4481 _d -14 d0 = -1.1351 _d -10 d1 = 2.7759 _d -12 e0 = -4.6206 _d -13 e1 = +1.8676 _d -14 e2 = -2.1687 _d -16 SW_ADTG = a0 + (a1 + (a2 + a3*T)*T)*T & + (b0 + b1*T)*(S-sref) & + ( (c0 + (c1 + (c2 + c3*T)*T)*T) + (d0 + d1*T)*(S-sref) )*P & + ( e0 + (e1 + e2*T)*T )*P*P RETURN END