| 1 | real function zenithangle(ylat,xlon,jul) |
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| 2 | |
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| 3 | !********************************************************************* |
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| 4 | ! * |
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| 5 | ! Author: G. WOTAWA * |
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| 6 | ! Date: 1993-11-17 * |
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| 7 | ! Project: POP-M * |
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| 8 | ! Last update: * |
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| 9 | ! * |
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| 10 | !********************************************************************* |
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| 11 | ! * |
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| 12 | ! DESCRIPTION: This function returns the sinus of solar * |
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| 13 | ! elevation as a function of geographic longitude, * |
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| 14 | ! latitude and GMT-Time. * |
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| 15 | ! * |
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| 16 | !********************************************************************* |
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| 17 | ! * |
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| 18 | ! INPUT: * |
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| 19 | ! * |
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| 20 | ! ylat geographical latitude [DEG] * |
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| 21 | ! xlon geographical longitude [DEG] * |
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| 22 | ! jjjj Year * |
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| 23 | ! mm Month * |
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| 24 | ! dd Day * |
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| 25 | ! hh Hour * |
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| 26 | ! minute Minute * |
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| 27 | ! * |
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| 28 | !********************************************************************* |
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| 29 | |
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| 30 | use par_mod, only: dp |
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| 31 | |
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| 32 | implicit none |
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| 33 | |
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| 34 | integer :: jjjj,mm,id,iu,minute,yyyymmdd,hhmmss |
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| 35 | integer :: ndaynum |
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| 36 | real :: sinsol,solelev,ylat,xlon |
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| 37 | real :: rnum,rylat,ttime,dekl,rdekl,eq |
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| 38 | real,parameter :: pi=3.1415927 |
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| 39 | real(kind=dp) :: jul |
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| 40 | |
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| 41 | call caldate(jul,yyyymmdd,hhmmss) |
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| 42 | jjjj=yyyymmdd/10000 |
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| 43 | mm=yyyymmdd/100-jjjj*100 |
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| 44 | id=yyyymmdd-jjjj*10000-mm*100 |
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| 45 | iu=hhmmss/10000 |
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| 46 | minute=hhmmss/100-100*iu |
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| 47 | |
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| 48 | ndaynum=31*(mm-1)+id |
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| 49 | if(mm.gt.2) ndaynum=ndaynum-int(0.4*mm+2.3) |
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| 50 | if((mm.gt.2).and.(jjjj/4*4.eq.jjjj)) ndaynum=ndaynum+1 |
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| 51 | |
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| 52 | rnum=2.*pi*ndaynum/365. |
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| 53 | rylat=pi*ylat/180. |
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| 54 | ttime=real(iu)+real(minute)/60. |
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| 55 | |
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| 56 | dekl=0.396+3.631*sin(rnum)+0.038*sin(2.*rnum)+0.077*sin(3.*rnum)- & |
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| 57 | 22.97*cos(rnum)-0.389*cos(2.*rnum)-0.158*cos(3.*rnum) |
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| 58 | rdekl=pi*dekl/180. |
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| 59 | |
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| 60 | eq=(0.003-7.343*sin(rnum)-9.47*sin(2.*rnum)- & |
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| 61 | 0.329*sin(3.*rnum)-0.196*sin(4.*rnum)+ & |
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| 62 | 0.552*cos(rnum)-3.020*cos(2.*rnum)- & |
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| 63 | 0.076*cos(3.*rnum)-0.125*cos(4.*rnum))/60. |
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| 64 | |
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| 65 | sinsol=sin(rylat)*sin(rdekl)+cos(rylat)*cos(rdekl)* & |
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| 66 | cos((ttime-12.+xlon/15.+eq)*pi/12.) |
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| 67 | ! Calculate the maximum solar elevation on that day |
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| 68 | !sinsol=sin(rylat)*sin(rdekl)+cos(rylat)*cos(rdekl)* |
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| 69 | ! & cos((eq)*pi/12.) |
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| 70 | solelev=asin(sinsol)*180./pi |
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| 71 | zenithangle=90.-solelev |
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| 72 | |
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| 73 | return |
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| 74 | end function zenithangle |
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