C $Header: /u/gcmpack/MITgcm/pkg/exf/exf_zenithangle.F,v 1.8 2017/03/06 22:38:03 gforget Exp $ C $Name: $ #include "EXF_OPTIONS.h" CBOP C !ROUTINE: EXF_ZENITHANGLE C !INTERFACE: SUBROUTINE EXF_ZENITHANGLE( I myTime, myIter, myThid ) C !DESCRIPTION: \bv C *==========================================================* C | SUBROUTINE EXF_ZENITHANGLE C | o compute zenith angle, derive albedo and C | the incoming flux at the top of the atm. C *==========================================================* C \ev C !USES: IMPLICIT NONE C == global variables == #include "EEPARAMS.h" #include "SIZE.h" #include "PARAMS.h" #include "GRID.h" #include "EXF_PARAM.h" #include "EXF_FIELDS.h" #include "EXF_CONSTANTS.h" #ifdef ALLOW_CAL # include "cal.h" #endif C !INPUT/OUTPUT PARAMETERS: _RL myTime INTEGER myIter INTEGER myThid #ifdef ALLOW_DOWNWARD_RADIATION #ifdef ALLOW_ZENITHANGLE C !FUNCTIONS: #ifdef ALLOW_CAL INTEGER cal_IsLeap EXTERNAL #endif C !LOCAL VARIABLES: INTEGER i, j, bi, bj INTEGER iLat1,iLat2,iTyear1,iTyear2 _RL wLat1,wLat2,wTyear1,wTyear2 _RL H0, dD0dDsq, CZENdaily, CZENdiurnal _RL TDAY, TYEAR, ALBSEA1, ALPHA, CZEN, CZEN2 _RL DECLI, ZS, ZC, SJ, CJ, TMPA, TMPB, TMPL, hlim _RL SOLC, FSOL c _RL CSR1, CSR2, FLAT2 _RL secondsInYear #ifdef ALLOW_CAL _RL myDateSeconds INTEGER year0,mydate(4),difftime(4) INTEGER dayStartDate(4),yearStartDate(4) #endif CEOP C solar constant C -------------- SOLC = 1368. _d 0 C note: it is fourth (342. _d 0) is called SOLC in pkg/aim_v23 C determine time of year/day C -------------------------- #ifdef ALLOW_CAL IF ( useCAL ) THEN CALL CAL_GETDATE( myIter, myTime, mydate, myThid ) year0 = INT(mydate(1)/10000.) secondsInYear = ndaysnoleap * secondsperday IF ( cal_IsLeap(year0,myThid) .EQ. 2) & secondsInYear = ndaysleap * secondsperday yearStartDate(1) = year0 * 10000 + 101 yearStartDate(2) = 0 yearStartDate(3) = mydate(3) yearStartDate(4) = mydate(4) CALL CAL_TIMEPASSED(yearStartDate,mydate,difftime,myThid) CALL CAL_TOSECONDS (difftime,myDateSeconds,myThid) TYEAR=myDateSeconds/secondsInYear dayStartDate(1) = mydate(1) dayStartDate(2) = 0 dayStartDate(3) = mydate(3) dayStartDate(4) = mydate(4) CALL CAL_TIMEPASSED(dayStartDate,mydate,difftime,myThid) CALL CAL_TOSECONDS (difftime,myDateSeconds,myThid) TDAY= myDateSeconds / ( 86400 . _d 0 ) ELSE #else /* ALLOW_CAL */ IF ( .TRUE. ) THEN #endif /* ALLOW_CAL */ secondsInYear = 86400. _d 0 * 365.25 _d 0 TYEAR = myTime / secondsInYear TDAY = myTime / 86400 . _d 0 TYEAR = MOD( TYEAR, oneRL ) TDAY = MOD( TDAY , oneRL ) ENDIF IF ( useExfZenAlbedo ) THEN DO bj = myByLo(myThid),myByHi(myThid) DO bi = myBxLo(myThid),myBxHi(myThid) IF ( select_ZenAlbedo.EQ.0 ) THEN DO j = 1,sNy DO i = 1,sNx zen_albedo (i,j,bi,bj) = exf_albedo ENDDO ENDDO ELSEIF ( select_ZenAlbedo.EQ.1 ) then C This is the default option: daily mean albedo (i.e. without diurnal C cycle) obtained from the reference table that was computed in C exf_zenithangle_table.F. Using either daily or 6 hourly fields, this C option yields correct values of daily upward sw flux. C This is not the case for select_ZenAlbedo.GT.1 (see comments below). iTyear1= 1 + 365.*TYEAR wTyear1= iTyear1 - 365.*TYEAR iTyear2= iTyear1 + 1 wTyear2= 1.0 _d 0 - wTyear1 DO j = 1,sNy DO i = 1,sNx IF ( zen_albedo_pointer(i,j,bi,bj).EQ. 181. _d 0 ) THEN iLat1=181 wLat1=0.5 _d 0 iLat2=181 wLat2=0.5 _d 0 ELSE iLat1= INT(zen_albedo_pointer(i,j,bi,bj)) wLat1= 1. _d 0 + iLat1 - zen_albedo_pointer(i,j,bi,bj) iLat2= iLat1 + 1 wLat2= 1. _d 0 - wLat1 ENDIF ALBSEA1 = & wTyear1*wLat1*zen_albedo_table(iTyear1,iLat1) & + wTyear1*wLat2*zen_albedo_table(iTyear1,iLat2) & + wTyear2*wLat1*zen_albedo_table(iTyear2,iLat1) & + wTyear2*wLat2*zen_albedo_table(iTyear2,iLat2) C determine overall albedo: approximation: half direct and half diffus zen_albedo (i,j,bi,bj) = & 0.5 _d 0 * exf_albedo + 0.5 _d 0 * ALBSEA1 ENDDO ENDDO C if select_ZenAlbedo = 0, = 1, else ELSE C determine solar declination C --------------------------- C (formula from Hartmann textbook, after Spencer 1971) ALPHA= 2. _d 0*PI*TYEAR DECLI = 0.006918 _d 0 & - 0.399912 _d 0 * COS ( 1. _d 0 * ALPHA ) & + 0.070257 _d 0 * SIN ( 1. _d 0 * ALPHA ) & - 0.006758 _d 0 * COS ( 2. _d 0 * ALPHA ) & + 0.000907 _d 0 * SIN ( 2. _d 0 * ALPHA ) & - 0.002697 _d 0 * COS ( 3. _d 0 * ALPHA ) & + 0.001480 _d 0 * SIN ( 3. _d 0 * ALPHA ) C note: alternative formulas include C 1) formula from aim_surf_bc.F, neglecting eccentricity: C ALPHA= 2. _d 0*PI*(TYEAR+10. _d 0/365. _d 0) C DECLI = COS(ALPHA) * ( -23.45 _d 0 * deg2rad) C 2) formulas that accounts for minor astronomic effects, e.g. C Yallop, B. D., Position of the sun to 1 minute of arc precision, C H. M. Nautical Almanac Office, Royal Greenwich Observatory, C Herstmonceux Castle, Hailsham, Sussex BN27 1RP, 1977. ZC = COS(DECLI) ZS = SIN(DECLI) DO j = 1,sNy DO i = 1,sNx SJ = SIN(yC(i,j,bi,bj) * deg2rad) CJ = COS(yC(i,j,bi,bj) * deg2rad) TMPA = SJ*ZS TMPB = CJ*ZC IF ( select_ZenAlbedo.EQ.3 ) THEN C determine DAILY VARYING cos of solar zenith angle CZEN C ------------------------------------------------------ C (formula from Hartmann textbook, classic trigo) CZENdiurnal = TMPA + TMPB * & COS( 2. _d 0 *PI* TDAY + xC(i,j,bi,bj) * deg2rad ) C note: a more complicated hour angle formula is given by Yallop 1977 IF ( CZENdiurnal .LE.0 ) CZENdiurnal = 0. _d 0 CZEN = CZENdiurnal ELSEIF ( select_ZenAlbedo.EQ.2 ) THEN C determine DAILY MEAN cos of solar zenith angle CZEN C --------------------------------------------------- C ( formula from aim_surf_bc.F <--> mean(CZEN*CZEN)/mean(CZEN) ) TMPL = -TMPA/TMPB IF (TMPL .GE. 1.0 _d 0) THEN CZEN = 0.0 _d 0 ELSEIF (TMPL .LE. -1.0 _d 0) THEN CZEN = (2.0 _d 0)*TMPA*PI CZEN2= PI*((2.0 _d 0)*TMPA*TMPA + TMPB*TMPB) CZEN = CZEN2/CZEN ELSE hlim = ACOS(TMPL) CZEN = 2.0 _d 0*(TMPA*hlim + TMPB*SIN(hlim)) CZEN2= 2.0 _d 0*TMPA*TMPA*hlim & + 4.0 _d 0*TMPA*TMPB*SIN(hlim) & + TMPB*TMPB*( hlim + 0.5 _d 0*SIN(2.0 _d 0*hlim) ) CZEN = CZEN2/CZEN ENDIF CZENdaily = CZEN c CZEN = CZENdaily ELSE print *, 'select_ZenAlbedo is out of range' STOP 'ABNORMAL END: S/R EXF_ZENITHANGLE' ENDIF C determine direct ocean albedo C ----------------------------- C (formula from Briegleb, Minnis, et al 1986) C comments on select_ZenAlbedo.GT.1 methods: C - CZENdaily as computed in aim was found to imply sizable biases in C daily upward sw fluxes. It is not advised to use it, but it is kept C in connection to pkg/aim_v23. C - CZENdiurnal should never be used with daily mean input fields. C Furthermore, at this point, it is not advised to use it even with 6 C hourly swdown input fields. This is because we simply time interpolate C between 6 hourly swdown fields, so each day there will be times when C CZENdiurnal correctly reflects that it is night time, but swdown.NE.0. C does not. CZENdiurnal may actually be rather harmful in this context, C since an inconsistency of phase between CZENdiurnal and swdown will C yield biases in daily mean upward sw fluxes. So ... ALBSEA1 = & ( ( 2.6 _d 0 / (CZEN**(1.7 _d 0) + 0.065 _d 0) ) & + ( 15. _d 0 * (CZEN-0.1 _d 0) * (CZEN-0.5 _d 0) & * (CZEN-1.0 _d 0) ) ) / 100.0 _d 0 C determine overall albedo C ------------------------ C (approximation: half direct and half diffu.) zen_albedo (i,j,bi,bj) = & 0.5 _d 0 * exf_albedo + 0.5 _d 0 * ALBSEA1 ENDDO ENDDO C end if select_ZenAlbedo = 0, = 1, else ENDIF C end bi,bj loops ENDDO ENDDO C end if ( useExfZenAlbedo ) ENDIF C---+----1----+----2----+----3----+----4----+----5----+----6----+----7-|--+----| IF ( useExfZenIncoming ) THEN DO bj = myByLo(myThid),myByHi(myThid) DO bi = myBxLo(myThid),myBxHi(myThid) C compute incoming flux at the top of the atm.: C --------------------------------------------- C (formula from Hartmann textbook, after Spencer 1971) ALPHA= 2. _d 0*PI*TYEAR DECLI = 0.006918 _d 0 & - 0.399912 _d 0 * COS ( 1. _d 0 * ALPHA ) & + 0.070257 _d 0 * SIN ( 1. _d 0 * ALPHA ) & - 0.006758 _d 0 * COS ( 2. _d 0 * ALPHA ) & + 0.000907 _d 0 * SIN ( 2. _d 0 * ALPHA ) & - 0.002697 _d 0 * COS ( 3. _d 0 * ALPHA ) & + 0.001480 _d 0 * SIN ( 3. _d 0 * ALPHA ) dD0dDsq = 1.000110 _d 0 & + 0.034221 _d 0 * COS ( 1. _d 0 * ALPHA ) & + 0.001280 _d 0 * SIN ( 1. _d 0 * ALPHA ) & + 0.000719 _d 0 * COS ( 2. _d 0 * ALPHA ) & + 0.000077 _d 0 * SIN ( 2. _d 0 * ALPHA ) ZC = COS(DECLI) ZS = SIN(DECLI) DO j = 1,sNy DO i = 1,sNx SJ = SIN(yC(i,j,bi,bj) * deg2rad) CJ = COS(yC(i,j,bi,bj) * deg2rad) TMPA = SJ*ZS TMPB = CJ*ZC C DAILY VARYING value: CZEN = TMPA + TMPB * & COS( 2. _d 0 *PI*TDAY + xC(i,j,bi,bj)*deg2rad ) IF ( CZEN .LE.0 ) CZEN = 0. _d 0 FSOL = SOLC * dD0dDsq * MAX( 0. _d 0, CZEN ) zen_fsol_diurnal(i,j,bi,bj) = FSOL C DAILY MEAN value: H0 = -TAN( yC(i,j,bi,bj) *deg2rad ) * TAN( DECLI ) IF ( H0.LT.-1. _d 0 ) H0 = -1. _d 0 IF ( H0.GT. 1. _d 0 ) H0 = 1. _d 0 H0 = ACOS( H0 ) FSOL = SOLC * dD0dDsq / PI & * ( H0 * TMPA + SIN(H0) * TMPB ) zen_fsol_daily(i,j,bi,bj) = FSOL C note: an alternative for the DAILY MEAN is, as done in pkg/aim_v23, C ALPHA= 2. _d 0*PI*(TYEAR+10. _d 0/365. _d 0) C CSR1=-0.796 _d 0*COS(ALPHA) C CSR2= 0.147 _d 0*COS(2. _d 0*ALPHA)-0.477 _d 0 C FLAT2 = 1.5 _d 0*SJ**2 - 0.5 _d 0 C FSOL = 0.25 _d 0 * SOLC C & * MAX( 0. _d 0, 1. _d 0+CSR1*SJ+CSR2*FLAT2 ) C zen_fsol_daily (i,j,bi,bj) = FSOL ENDDO ENDDO C end bi,bj loops ENDDO ENDDO C end if ( useExfZenIncoming ) ENDIF #endif /* ALLOW_ZENITHANGLE */ #endif /* ALLOW_DOWNWARD_RADIATION */ RETURN END