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C $Header: /u/gcmpack/MITgcm/pkg/exf/exf_zenithangle.F,v 1.3 2010/04/14 23:02:18 gforget Exp $ |
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C $Name: $ |
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#include "EXF_OPTIONS.h" |
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|
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SUBROUTINE EXF_ZENITHANGLE(myTime, myIter, myThid) |
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C ================================================================== |
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C SUBROUTINE exf_zenithangle |
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C ================================================================== |
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C |
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C o compute zenith angle, derive albedo and |
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C the incoming flux at the top of the atm. |
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C |
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C ================================================================== |
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C SUBROUTINE exf_zenithangle |
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C ================================================================== |
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IMPLICIT NONE |
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C == global variables == |
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|
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#include "EEPARAMS.h" |
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#include "SIZE.h" |
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#include "PARAMS.h" |
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#include "DYNVARS.h" |
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#include "GRID.h" |
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|
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#include "EXF_PARAM.h" |
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#include "EXF_FIELDS.h" |
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#include "EXF_CONSTANTS.h" |
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# include "cal.h" |
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|
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C == routine arguments == |
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|
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_RL myTime |
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INTEGER myIter |
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INTEGER myThid |
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|
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#ifdef ALLOW_DOWNWARD_RADIATION |
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#ifdef ALLOW_ZENITHANGLE |
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C == local variables == |
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|
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INTEGER bi,bj |
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INTEGER i,j |
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|
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integer iLat1,iLat2,iTyear1,iTyear2 |
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_RL wLat1,wLat2,wTyear1,wTyear2 |
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_RL H0, dD0dDsq, CZENdaily, CZENdiurnal |
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_RL TDAY, TYEAR, ALBSEA1, ALPHA, CZEN, CZEN2 |
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_RL DECLI, ZS, ZC, SJ, CJ, TMPA, TMPB, TMPL, hlim |
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_RL SOLC, CSR1, CSR2, FLAT2, FSOL |
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integer year0,mydate(4),difftime(4) |
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integer dayStartDate(4),yearStartDate(4) |
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_RL secondsInYear, myDateSeconds |
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integer cal_IsLeap |
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external cal_IsLeap |
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C == end of interface == |
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c solar constant |
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c -------------- |
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SOLC = 1368. _d 0 |
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c note: it is fourth (342. _d 0) is called SOLC in pkg/aim_v23 |
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|
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c determine time of year/day |
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c -------------------------- |
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secondsInYear = ndaysnoleap * secondsperday |
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if ( cal_IsLeap(year0,mythid) .eq. 2) |
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& secondsInYear = ndaysleap * secondsperday |
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c |
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call cal_GetDate( myiter, mytime, mydate, mythid ) |
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year0 = int(mydate(1)/10000.) |
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yearStartDate(1) = year0 * 10000 + 101 |
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yearStartDate(2) = 0 |
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yearStartDate(3) = mydate(3) |
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yearStartDate(4) = mydate(4) |
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CALL cal_TimePassed(yearStartDate,mydate,difftime,myThid) |
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CALL cal_ToSeconds (difftime,myDateSeconds,myThid) |
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c |
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TYEAR=myDateSeconds/secondsInYear |
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c |
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dayStartDate(1) = mydate(1) |
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dayStartDate(2) = 0 |
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dayStartDate(3) = mydate(3) |
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dayStartDate(4) = mydate(4) |
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CALL cal_TimePassed(dayStartDate,mydate,difftime,myThid) |
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CALL cal_ToSeconds (difftime,myDateSeconds,myThid) |
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c |
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TDAY= myDateSeconds / ( 86400 . _d 0 ) |
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c |
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|
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IF ( useExfZenAlbedo ) THEN |
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|
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DO bj = myByLo(myThid),myByHi(myThid) |
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DO bi = myBxLo(myThid),myBxHi(myThid) |
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DO j = 1,sNy |
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DO i = 1,sNx |
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|
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if ( select_ZenAlbedo.EQ. 0) then |
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ALBSEA1=exf_albedo |
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elseif ( select_ZenAlbedo.EQ. 1) then |
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c This is the default option: daily mean albedo (i.e. without diurnal cycle) |
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c obtained from the reference table that was computed in exf_zenithangle_table.F. |
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c |
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c Using either daily or 6 hourly fields, this option yields correct values of daily upward sw flux. |
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c |
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c This is not the case for select_ZenAlbedo.GT.1 (see comments below). |
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|
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iTyear1= 1 + 365.*TYEAR |
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wTyear1= iTyear1 - 365.*TYEAR |
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iTyear2= iTyear1 + 1 |
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wTyear2= 1.0 _d 0 - wTyear1 |
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if ( zen_albedo_pointer(i,j,bi,bj).EQ. 181. _d 0 ) then |
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iLat1=181 |
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wLat1=0.5 _d 0 |
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iLat2=181 |
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wLat2=0.5 _d 0 |
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else |
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iLat1= zen_albedo_pointer(i,j,bi,bj) |
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wLat1= 1. _d 0 + iLat1 - zen_albedo_pointer(i,j,bi,bj) |
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iLat2= iLat1 + 1 |
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wLat2= 1. _d 0 - wLat1 |
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endif |
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ALBSEA1= |
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& wTyear1*wLat1*zen_albedo_table(iTyear1,iLat1)+ |
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& wTyear1*wLat2*zen_albedo_table(iTyear1,iLat2)+ |
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& wTyear2*wLat1*zen_albedo_table(iTyear2,iLat1)+ |
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& wTyear2*wLat2*zen_albedo_table(iTyear2,iLat2) |
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|
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else!if ( select_ZenAlbedo.GT. 1) then |
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c determine solar declination |
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c --------------------------- |
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c (formula from Hartmann textbook, after Spencer 1971) |
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ALPHA= 2. _d 0*PI*TYEAR |
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DECLI = 0.006918 _d 0 |
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& - 0.399912 _d 0 * cos ( 1. _d 0 * ALPHA ) |
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& + 0.070257 _d 0 * sin ( 1. _d 0 * ALPHA ) |
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& - 0.006758 _d 0 * cos ( 2. _d 0 * ALPHA ) |
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& + 0.000907 _d 0 * sin ( 2. _d 0 * ALPHA ) |
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& - 0.002697 _d 0 * cos ( 3. _d 0 * ALPHA ) |
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& + 0.001480 _d 0 * sin ( 3. _d 0 * ALPHA ) |
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|
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c note: alternative formulas include |
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c 1) formula from aim_surf_bc.F, neglecting eccentricity: |
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c ALPHA= 2. _d 0*PI*(TYEAR+10. _d 0/365. _d 0) |
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c DECLI = COS(ALPHA) * ( -23.45 _d 0 * deg2rad) |
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c 2) formulas that accounts for minor astronomic effects, e.g. |
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c Yallop, B. D., Position of the sun to 1 minute of arc precision, H. M. Nautical Almanac Office, |
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c Royal Greenwich Observatory, Herstmonceux Castle, Hailsham, Sussex BN27 1RP, 1977. |
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ZC = COS(DECLI) |
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ZS = SIN(DECLI) |
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SJ = SIN(yC(i,j,bi,bj) * deg2rad) |
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CJ = COS(yC(i,j,bi,bj) * deg2rad) |
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TMPA = SJ*ZS |
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TMPB = CJ*ZC |
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c determine DAILY VARYING cos of solar zenith angle CZEN |
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c ------------------------------------------------------ |
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c (formula from Hartmann textbook, classic trigo) |
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CZENdiurnal = TMPA + TMPB * |
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& cos( 2. _d 0 *PI* TDAY + xC(i,j,bi,bj) * deg2rad ) |
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c note: a more complicated hour angle formula is given by Yallop 1977 |
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if ( CZENdiurnal .LE.0 ) CZENdiurnal = 0. _d 0 |
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c determine DAILY MEAN cos of solar zenith angle CZEN |
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c --------------------------------------------------- |
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c ( formula from aim_surf_bc.F <--> mean(CZEN*CZEN)/mean(CZEN) ) |
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TMPL = -TMPA/TMPB |
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IF (TMPL .GE. 1.0 _d 0) THEN |
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CZEN = 0.0 _d 0 |
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ELSEIF (TMPL .LE. -1.0 _d 0) THEN |
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CZEN = (2.0 _d 0)*TMPA*PI |
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CZEN2= PI*((2.0 _d 0)*TMPA*TMPA + TMPB*TMPB) |
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CZEN = CZEN2/CZEN |
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ELSE |
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hlim = ACOS(TMPL) |
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CZEN = 2.0 _d 0*(TMPA*hlim + TMPB*SIN(hlim)) |
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CZEN2= 2.0 _d 0*TMPA*TMPA*hlim |
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& + 4.0 _d 0*TMPA*TMPB*SIN(hlim) |
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& + TMPB*TMPB*( hlim + 0.5 _d 0*SIN(2.0 _d 0*hlim) ) |
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CZEN = CZEN2/CZEN |
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ENDIF |
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CZENdaily=CZEN |
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c determine direct ocean albedo |
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c ----------------------------- |
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c (formula from Briegleb, Minnis, et al 1986) |
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c |
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c comments on select_ZenAlbedo.GT.1 methods: |
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c - CZENdaily as computed in aim was found to imply sizable biases in daily upward sw fluxes. |
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c It is not advised to use it, but it is kept in connection to pkg/aim_v23. |
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c - CZENdiurnal should never be used with daily mean input fields. |
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c Furthermore, at this point, it is not advised to use it even with 6 hourly swdown input fields. |
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c This is because we simply time interpolate between 6 hourly swdown fields, so each day there |
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c will be times when CZENdiurnal correctly reflects that it is night time, but swdown.NE.0. does not. |
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c CZENdiurnal may actually be rather harmful in this context, since an inconsistency of phase between |
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c CZENdiurnal and swdown will yield biases in daily mean upward sw fluxes. So ... |
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|
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if ( select_ZenAlbedo.EQ. 2) then |
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CZEN=CZENdaily |
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elseif ( select_ZenAlbedo.EQ. 3) then |
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CZEN=CZENdiurnal |
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else |
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print *, 'select_ZenAlbedo is out of range' |
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STOP 'ABNORMAL END: S/R EXF_ZENITHANGLE' |
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endif |
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ALBSEA1 = ( ( 2.6 _d 0 / (CZEN**(1.7 _d 0) + 0.065 _d 0) ) |
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& + ( 15. _d 0 * (CZEN-0.1 _d 0) * (CZEN-0.5 _d 0) |
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& * (CZEN-1.0 _d 0) ) ) / 100.0 _d 0 |
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c |
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|
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endif!if ( select_ZenAlbedo.EQ. 0) then |
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c determine overall albedo |
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c ------------------------ |
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c (approximation: half direct and half diffu.) |
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zen_albedo (i,j,bi,bj) = |
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& 0.5 _d 0 * exf_albedo + 0.5 _d 0 * ALBSEA1 |
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|
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ENDDO |
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ENDDO |
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ENDDO |
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ENDDO |
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endif! IF ( useExfZenAlbedo ) THEN |
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IF ( useExfZenIncoming ) THEN |
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DO bj = myByLo(myThid),myByHi(myThid) |
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DO bi = myBxLo(myThid),myBxHi(myThid) |
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DO j = 1,sNy |
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DO i = 1,sNx |
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|
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c compute incoming flux at the top of the atm.: |
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c --------------------------------------------- |
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c (formula from Hartmann textbook, after Spencer 1971) |
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ALPHA= 2. _d 0*PI*TYEAR |
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ALPHA= 2. _d 0*PI*TYEAR |
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DECLI = 0.006918 _d 0 |
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& - 0.399912 _d 0 * cos ( 1. _d 0 * ALPHA ) |
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& + 0.070257 _d 0 * sin ( 1. _d 0 * ALPHA ) |
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& - 0.006758 _d 0 * cos ( 2. _d 0 * ALPHA ) |
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& + 0.000907 _d 0 * sin ( 2. _d 0 * ALPHA ) |
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& - 0.002697 _d 0 * cos ( 3. _d 0 * ALPHA ) |
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& + 0.001480 _d 0 * sin ( 3. _d 0 * ALPHA ) |
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dD0dDsq = 1.000110 _d 0 |
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& + 0.034221 _d 0 * cos ( 1. _d 0 * ALPHA ) |
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& + 0.001280 _d 0 * sin ( 1. _d 0 * ALPHA ) |
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& + 0.000719 _d 0 * cos ( 2. _d 0 * ALPHA ) |
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& + 0.000077 _d 0 * sin ( 2. _d 0 * ALPHA ) |
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c DAILY VARYING value: |
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ZC = COS(DECLI) |
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ZS = SIN(DECLI) |
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SJ = SIN(yC(i,j,bi,bj) * deg2rad) |
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CJ = COS(yC(i,j,bi,bj) * deg2rad) |
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TMPA = SJ*ZS |
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TMPB = CJ*ZC |
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CZEN = TMPA + TMPB * |
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& cos( 2. _d 0 *PI* TDAY + xC(i,j,bi,bj) * deg2rad ) |
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if ( CZEN .LE.0 ) CZEN = 0. _d 0 |
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FSOL = SOLC * dD0dDsq * MAX( 0. _d 0, CZEN ) |
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zen_fsol_diurnal (i,j,bi,bj) = FSOL |
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c DAILY MEAN value: |
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H0 = -tan( yC(i,j,bi,bj) *deg2rad ) * tan( DECLI ) |
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if ( H0.LT.-1. _d 0 ) H0 = -1. _d 0 |
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if ( H0.GT.1. _d 0 ) H0 = 1. _d 0 |
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H0 = acos( H0 ) |
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FSOL= SOLC * dD0dDsq / pi * |
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& ( H0 * TMPA + sin(H0) * TMPB ) |
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zen_fsol_daily (i,j,bi,bj) = FSOL |
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|
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c note: an alternative for the DAILY MEAN is, as done in pkg/aim_v23, |
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c ALPHA= 2. _d 0*PI*(TYEAR+10. _d 0/365. _d 0) |
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c CSR1=-0.796 _d 0*COS(ALPHA) |
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c CSR2= 0.147 _d 0*COS(2. _d 0*ALPHA)-0.477 _d 0 |
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c FLAT2 = 1.5 _d 0*SJ**2 - 0.5 _d 0 |
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c FSOL = 0.25 _d 0 * SOLC * MAX( 0. _d 0, 1. _d 0+CSR1*SJ+CSR2*FLAT2 ) |
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c zen_fsol_daily (i,j,bi,bj) = FSOL |
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|
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ENDDO |
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ENDDO |
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ENDDO |
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ENDDO |
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|
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endif! IF ( useExfZenIncoming ) THEN |
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|
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#endif /* ALLOW_ZENITHANGLE */ |
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#endif /* ALLOW_DOWNWARD_RADIATION */ |
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|
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RETURN |
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END |
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