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C Copyright 1981-2007 ECMWF
C
C Licensed under the GNU Lesser General Public License which
C incorporates the terms and conditions of version 3 of the GNU
C General Public License.
C See LICENSE and gpl-3.0.txt for details.
C
SUBROUTINE STRLAT( OLDLAT, STRETCH, KFLAG, NEWLAT, MFACTOR)
C
C---->
C**** STRLAT
C
C PURPOSE
C _______
C
C This routine transforms between stretched and real latitudes
C and calculates the map factor.
C
C INTERFACE
C _________
C
C CALL STRLAT( OLDLAT, STRETCH, KFLAG, NEWLAT, MFACTOR)
C
C Input parameters
C ________________
C
C OLDLAT - Input latitude
C STRETCH - Stretching factor
C KFLAG - Flag to show direction of transform (real <-> stretched)
C 0 = transform from real latitudes to stretched latitudes
C 1 = transform from stretched latitudes to real latitudes
C
C Output parameters
C ________________
C
C NEWLAT - Input latitude
C MFACTOR - Map factor
C
C
C Common block usage
C __________________
C
C None
C
C Method
C ______
C
C Stretching factor S
C
C Map factor, m = S**2 + 1 + (S**2 -1)*mu
C -----------------------
C 2*S
C
C where mu = sin(lat) on the real sphere
C
C mu = (S**2+1)*md + (S**2-1)
C ----------------------
C (S**2+1) + (S**2-1)*md
C
C where md = sin(lat) on the stretched sphere.
C
C By rearrangement:
C
C md = (S**2+1)*mu - (S**2-1)
C ----------------------
C (S**2+1) - (S**2-1)*mu
C
C Wind U and V components are transformed as
C
C vreal = m * vtransformed
C
C Vorticity and divergence fields are transformed as
C
C vreal = (m*m) * vtransformed
C
C
C Externals
C _________
C
C None
C
C
C Reference
C _________
C
C None
C
C
C Comments
C ________
C
C None.
C
C
C AUTHOR
C ______
C
C J.D.Chambers ECMWF July 1999
C
C
C MODIFICATIONS
C _____________
C
C None
C
C----<
C _______________________________________________________
C
C
IMPLICIT NONE
C
C Subroutine arguments
C
REAL OLDLAT, STRETCH, NEWLAT, MFACTOR, MSCALE
INTEGER KFLAG
C
C Parameters
C
INTEGER JPRL2TR
PARAMETER (JPRL2TR = 0)
REAL PPI, DEG2RAD, RAD2DEG
PARAMETER ( PPI = 3.14159265358979 )
PARAMETER (DEG2RAD = PPI / 180.0)
PARAMETER (RAD2DEG = 180.0 / PPI)
C
C Local variables
C
REAL A, B, ANGLE, MU, MUPRIME
C _______________________________________________________
C
C* Section 1. Initialization.
C _______________________________________________________
C
100 CONTINUE
C
A = STRETCH * STRETCH + 1
B = A - 2
ANGLE = OLDLAT * DEG2RAD
C
C _______________________________________________________
C
C* Section 2. Work out geometry
C _______________________________________________________
C
200 CONTINUE
C
C Transform from real latitudes to stretched latitudes
C
IF( KFLAG.EQ.JPRL2TR ) THEN
MUPRIME = SIN(ANGLE)
MU = (A*MUPRIME + B) / (A + B*MUPRIME)
NEWLAT = ASIN(MU) * RAD2DEG
C
C Transform from stretched latitudes to real latitudes
C
ELSE
MU = SIN(ANGLE)
MUPRIME = (A*MU - B) / (A - B*MU)
NEWLAT = ASIN(MUPRIME) * RAD2DEG
ENDIF
C
C Calculate the map factor
C
MFACTOR = (A + B*MU) / (2*STRETCH)
C
C _______________________________________________________
C
C* Section 9. Return to calling routine.
C _______________________________________________________
C
RETURN
END
|
