1 | !================================================================================================ |
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2 | ! This is the "toy" chemistry module. |
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3 | !================================================================================================ |
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4 | |
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5 | MODULE Terminator |
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6 | |
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7 | implicit none |
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8 | private |
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9 | save |
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10 | |
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11 | public :: initial_value_Terminator ! initialize cl and cl2 |
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12 | public :: tendency_Terminator ! interface to tendency computation |
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13 | |
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14 | !integer, parameter :: 8 = selected_real_kind (12) |
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15 | |
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16 | real(8), parameter :: cly_constant = 4.e-6_8 |
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17 | real(8), parameter :: pi = 3.1415926535897932384626433832795028841971693993751058209749445923078164_8 |
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18 | real(8), parameter :: half_pi = pi*0.5_8 |
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19 | real(8), parameter :: degrees_to_radians = pi/180.0_8 |
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20 | real(8), parameter :: k1_lat_center = 20.d0*degrees_to_radians |
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21 | real(8), parameter :: k1_lon_center = 300.d0*degrees_to_radians |
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22 | |
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23 | contains |
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24 | |
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25 | !=============================================================================== |
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26 | ! Solar photolysis rate and recombination rate |
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27 | !=============================================================================== |
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28 | |
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29 | subroutine k_vals( lat, lon, k1, k2 ) |
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30 | |
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31 | !----------------------------------------------------------------------- |
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32 | ! Arguments: |
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33 | !----------------------------------------------------------------------- |
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34 | real(8), intent(in) :: lat, lon ! latitude and longitude, radians |
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35 | real(8), intent(out) :: k1, k2 ! reaction rates |
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36 | |
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37 | k1 = 1.0_8*max(0.d0,sin(lat)*sin(k1_lat_center) + cos(lat)*cos(k1_lat_center)*cos(lon-k1_lon_center)) |
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38 | k2 = 1._8 |
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39 | |
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40 | return |
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41 | |
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42 | end subroutine k_vals |
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43 | |
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44 | !=============================================================================== |
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45 | ! Tendencies of cl and cl2 |
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46 | !=============================================================================== |
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47 | |
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48 | subroutine tendency_Terminator( lat, lon, cl, cl2, dt, cl_f, cl2_f ) |
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49 | |
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50 | !----------------------------------------------------------------------- |
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51 | ! Arguments: |
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52 | !----------------------------------------------------------------------- |
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53 | |
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54 | real(8), intent(in) :: lat, lon ! latitude and longitude, degrees |
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55 | real(8), intent(in) :: cl, cl2 ! molar mixing ratio of cl and cl2 |
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56 | real(8), intent(in) :: dt ! size of physics time step |
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57 | |
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58 | real(8), intent(out) :: cl_f, cl2_f ! time rate of change of cl and cl2 |
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59 | |
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60 | !----------------------------------------------------------------------- |
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61 | ! Local variables |
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62 | !----------------------------------------------------------------------- |
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63 | |
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64 | real(8) :: r, det, expdt, el ! useful algebaic quantities used in the computation |
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65 | real(8) :: k1, k2 ! reaction rates |
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66 | real(8) :: cly ! quantity that should be conseved |
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67 | |
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68 | call k_vals( lat, lon, k1, k2 ) |
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69 | |
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70 | r = k1 / (4._8*k2) |
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71 | cly = cl + 2._8* cl2 |
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72 | |
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73 | det = sqrt( r*r + 2._8*r*cly ) |
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74 | expdt = exp( -4._8*k2*det*dt ) |
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75 | |
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76 | if ( abs(det * k2 * dt) .gt. 1e-16 ) then |
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77 | el = (1._8 - expdt) /det /dt |
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78 | else |
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79 | el = 4._8*k2 |
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80 | endif |
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81 | |
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82 | cl_f = -el * (cl - det + r)*(cl + det + r) / (1._8 + expdt + dt*el*(cl + r)) |
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83 | cl2_f = -cl_f / 2._8 |
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84 | |
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85 | return |
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86 | |
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87 | end subroutine tendency_Terminator |
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88 | |
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89 | !=============================================================================== |
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90 | ! Compute initial values |
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91 | !=============================================================================== |
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92 | |
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93 | subroutine initial_value_Terminator( lat, lon, cl, cl2 ) |
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94 | |
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95 | !----------------------------------------------------------------------- |
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96 | ! Arguments: |
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97 | !----------------------------------------------------------------------- |
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98 | |
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99 | real(8), intent(in) :: lat, lon ! latitude and longitude, degrees |
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100 | real(8), intent(out) :: cl, cl2 ! molar mixing ratio of cl and cl2 |
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101 | |
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102 | !----------------------------------------------------------------------- |
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103 | ! Local variables |
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104 | !----------------------------------------------------------------------- |
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105 | |
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106 | real(8) :: r, det ! useful algebraic forms |
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107 | real(8) :: k1, k2 ! reaction rates |
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108 | |
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109 | call k_vals( lat, lon, k1, k2 ) |
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110 | |
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111 | r = k1 / (4._8*k2) |
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112 | det = sqrt(r*r + 2._8*cly_constant*r) |
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113 | |
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114 | cl = (det-r) |
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115 | cl2 = cly_constant/2._8 - (det-r)/2._8 |
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116 | |
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117 | return |
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118 | |
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119 | end subroutine initial_value_Terminator |
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120 | |
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121 | end module Terminator |
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122 | |
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123 | |
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124 | |
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