| 1 | subroutine calc_rayleigh |
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| 2 | |
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| 3 | !================================================================== |
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| 4 | ! |
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| 5 | ! Purpose |
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| 6 | ! ------- |
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| 7 | ! Average the Rayleigh scattering in each band, weighting the |
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| 8 | ! average by the blackbody function at temperature tstellar. |
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| 9 | ! Works for an arbitrary mix of gases (currently CO2, N2 and |
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| 10 | ! H2 are possible). |
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| 11 | ! |
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| 12 | ! Authors |
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| 13 | ! ------- |
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| 14 | ! Robin Wordsworth (2010) |
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| 15 | ! |
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| 16 | ! Called by |
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| 17 | ! --------- |
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| 18 | ! setspv.F |
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| 19 | ! |
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| 20 | ! Calls |
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| 21 | ! ----- |
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| 22 | ! none |
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| 23 | ! |
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| 24 | !================================================================== |
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| 25 | |
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| 26 | use radinc_h, only: L_NSPECTV |
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| 27 | use radcommon_h, only: WAVEV, BWNV, DWNV, tstellar, tauray, scalep |
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| 28 | use gases_h |
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| 29 | |
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| 30 | implicit none |
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| 31 | |
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| 32 | #include "comcstfi.h" |
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| 33 | #include "callkeys.h" |
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| 34 | |
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| 35 | real*8 wl |
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| 36 | integer N,Nfine,ifine,igas |
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| 37 | parameter(Nfine=500.0) |
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| 38 | real*8 :: P0 = 9.423D+6 ! Rayleigh scattering reference pressure in pascals. |
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| 39 | |
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| 40 | logical typeknown |
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| 41 | real*8 tauvar,tausum,tauwei,bwidth,bstart |
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| 42 | double precision df |
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| 43 | |
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| 44 | real*8 tauconsti(ngasmx) |
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| 45 | real*8 tauvari(ngasmx) |
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| 46 | |
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| 47 | ! tau0/p0=tau/p (Hansen 1974) |
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| 48 | ! Then calculate tau0 = (8*pi^3*p_1atm)/(3*N0^2) * 4*delta^2/(g*mugaz*lambda^4) |
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| 49 | ! where delta=n-1 and N0 is an amagat |
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| 50 | |
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| 51 | typeknown=.false. |
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| 52 | do igas=1,ngasmx |
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| 53 | if(igas.eq.vgas)then |
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| 54 | print*,'Ignoring ',gnom(igas),' in Rayleigh scattering '// & |
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| 55 | 'as it is variable.' |
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| 56 | elseif(gfrac(igas).lt.5.e-2)then |
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| 57 | print*,'Ignoring ',gnom(igas),' in Rayleigh scattering '// & |
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| 58 | 'as its mixing ratio is less than 0.05.' |
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| 59 | ! ignore variable gas in Rayleigh calculation |
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| 60 | ! ignore gases of mixing ratio < 0.05 in Rayleigh calculation |
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| 61 | tauconsti(igas) = 0.0 |
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| 62 | else |
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| 63 | if(gnom(igas).eq.'CO2')then |
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| 64 | tauconsti(igas) = (8.7/g)*1.527*scalep/P0 |
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| 65 | elseif(gnom(igas).eq.'N2_')then |
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| 66 | tauconsti(igas) = (9.81/g)*8.569E-3*scalep/(P0/93.0) |
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| 67 | elseif(gnom(igas).eq.'H2O')then |
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| 68 | tauconsti(igas) = (10.0/g)*9.22E-3*scalep/101325.0 |
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| 69 | elseif(gnom(igas).eq.'H2_')then |
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| 70 | tauconsti(igas) = (10.0/g)*0.0241*scalep/101325.0 |
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| 71 | !tauconsti(igas) = (10.0/g)*0.0487*scalep/(101325.0) |
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| 72 | ! uses n=1.000132 from Optics, Fourth Edition. |
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| 73 | ! was out by a factor 2! |
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| 74 | elseif(gnom(igas).eq.'He_')then |
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| 75 | print*,'Helium not ready yet!' |
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| 76 | tauconsti(igas) = 0.0 |
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| 77 | call abort |
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| 78 | else |
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| 79 | print*,'Error in calc_rayleigh: Gas species not recognised!' |
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| 80 | call abort |
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| 81 | endif |
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| 82 | |
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| 83 | if(gfrac(igas).eq.1.0)then |
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| 84 | print*,'Rayleigh scattering is for a pure ',gnom(igas),' atmosphere.' |
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| 85 | typeknown=.true. |
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| 86 | endif |
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| 87 | |
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| 88 | endif |
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| 89 | enddo |
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| 90 | |
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| 91 | if(.not.typeknown)then |
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| 92 | print*,'Rayleigh scattering is for a mixed gas atmosphere.' |
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| 93 | typeknown=.true. |
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| 94 | endif |
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| 95 | |
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| 96 | |
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| 97 | do N=1,L_NSPECTV |
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| 98 | |
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| 99 | tausum = 0.0 |
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| 100 | tauwei = 0.0 |
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| 101 | bstart = 10000.0/BWNV(N+1) |
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| 102 | bwidth = (10000.0/BWNV(N)) - (10000.0/BWNV(N+1)) |
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| 103 | do ifine=1,Nfine |
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| 104 | wl=bstart+dble(ifine)*bwidth/Nfine |
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| 105 | |
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| 106 | tauvar=0.0 |
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| 107 | do igas=1,ngasmx |
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| 108 | if((igas.eq.vgas).or.(gfrac(igas).lt.5.e-2))then |
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| 109 | ! ignore variable gas in Rayleigh calculation |
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| 110 | ! ignore gases of mixing ratio < 0.05 in Rayleigh calculation |
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| 111 | tauvari(igas) = 0.0 |
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| 112 | else |
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| 113 | if(gnom(igas).eq.'CO2')then |
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| 114 | tauvari(igas) = (1.0+0.013/wl**2)/wl**4 |
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| 115 | elseif(gnom(igas).eq.'N2_')then |
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| 116 | tauvari(igas) = (1.0+0.0113/wl**2+0.00013/wl**4)/wl**4 |
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| 117 | elseif(gnom(igas).eq.'H2O')then |
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| 118 | tauvari(igas) = 1.0/wl**4 ! to be improved... |
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| 119 | elseif(gnom(igas).eq.'H2_')then |
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| 120 | tauvari(igas) = 1.0/wl**4 |
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| 121 | elseif(gnom(igas).eq.'He_')then |
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| 122 | print*,'Helium not ready yet!' |
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| 123 | tauvari(igas) = 0.0 |
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| 124 | else |
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| 125 | print*,'Error in calc_rayleigh: Gas species not recognised!' |
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| 126 | call abort |
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| 127 | endif |
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| 128 | endif |
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| 129 | |
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| 130 | tauvar=tauvar+tauconsti(igas)*tauvari(igas)*gfrac(igas) |
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| 131 | |
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| 132 | enddo |
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| 133 | |
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| 134 | call blackl(dble(wl*1e-6),dble(tstellar),df) |
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| 135 | df=df*bwidth/Nfine |
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| 136 | tauwei=tauwei+df |
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| 137 | tausum=tausum+tauvar*df |
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| 138 | |
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| 139 | enddo |
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| 140 | TAURAY(N)=tausum/tauwei |
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| 141 | ! we multiply by scalep here (100) because plev, which is used in optcv, |
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| 142 | ! is in units of mBar, so we need to convert. |
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| 143 | |
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| 144 | end do |
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| 145 | |
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| 146 | print*,'At 1 atm and lambda = ',WAVEV(L_NSPECTV-6),' um' |
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| 147 | print*,'tau_R = ',TAURAY(L_NSPECTV-6)*1013.25 |
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| 148 | print*,'sig_R = ',TAURAY(L_NSPECTV-6)*g*mugaz*1.67e-27*100, & |
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| 149 | 'cm^2 molecule^-1' |
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| 150 | |
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| 151 | end subroutine calc_rayleigh |
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