| 1 | !################################################################## |
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| 2 | !################################################################## |
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| 3 | !###### ###### |
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| 4 | !###### Developed by ###### |
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| 5 | !###### Center for Analysis and Prediction of Storms ###### |
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| 6 | !###### University of Oklahoma ###### |
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| 7 | !###### ###### |
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| 8 | !################################################################## |
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| 9 | !################################################################## |
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| 10 | |
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| 11 | function f_qvsat( p, t ) |
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| 12 | |
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| 13 | !PURPOSE: |
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| 14 | ! |
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| 15 | !Calculate the saturation specific humidity using enhanced Teten's |
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| 16 | !formula. |
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| 17 | ! |
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| 18 | !AUTHOR: Yuhe Liu |
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| 19 | !01/08/1998 |
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| 20 | ! |
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| 21 | !MODIFICATION HISTORY: |
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| 22 | ! |
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| 23 | !INPUT : |
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| 24 | ! p Pressure (Pascal) |
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| 25 | ! t Temperature (K) |
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| 26 | !OUTPUT: |
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| 27 | ! f_qvsat Saturation water vapor specific humidity (kg/kg). |
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| 28 | ! |
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| 29 | !Variable Declarations. |
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| 30 | ! |
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| 31 | |
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| 32 | implicit none |
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| 33 | |
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| 34 | real :: p ! Pressure (Pascal) |
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| 35 | real :: t ! Temperature (K) |
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| 36 | real :: f_qvsat ! Saturation water vapor specific humidity (kg/kg) |
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| 37 | real :: f_esl,f_esi,fespt |
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| 38 | |
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| 39 | real,parameter :: rd = 287.0 ! Gas constant for dry air (m**2/(s**2*K)) |
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| 40 | real,parameter :: rv = 461.0 ! Gas constant for water vapor (m**2/(s**2*K)). |
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| 41 | real,parameter :: rddrv = rd/rv |
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| 42 | |
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| 43 | |
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| 44 | ! Change by A. Stohl to save computation time: |
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| 45 | ! IF ( t.ge.273.15 ) THEN ! for water |
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| 46 | if ( t.ge.253.15 ) then ! modification Petra Seibert |
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| 47 | ! (supercooled water may be present) |
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| 48 | fespt=f_esl(p,t) |
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| 49 | else |
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| 50 | fespt=f_esi(p,t) |
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| 51 | endif |
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| 52 | |
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| 53 | !!$ f_qvsat = rddrv * fespt / (p-(1.0-rddrv)*fespt) !old |
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| 54 | if (p-(1.0-rddrv)*fespt == 0.) then !bugfix |
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| 55 | f_qvsat = 1. |
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| 56 | else |
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| 57 | f_qvsat = rddrv * fespt / (p-(1.0-rddrv)*fespt) |
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| 58 | end if |
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| 59 | |
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| 60 | return |
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| 61 | end function f_qvsat |
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| 62 | |
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| 63 | |
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| 64 | function f_esl( p, t ) |
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| 65 | |
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| 66 | implicit none |
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| 67 | |
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| 68 | real :: p ! Pressure (Pascal) |
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| 69 | real :: t ! Temperature (K) |
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| 70 | real :: f_esl ! Saturation water vapor pressure over liquid water |
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| 71 | |
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| 72 | real :: f |
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| 73 | |
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| 74 | !####################################################################### |
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| 75 | ! |
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| 76 | !Saturation specific humidity parameters used in enhanced Teten's |
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| 77 | !formula. (See A. Buck, JAM 1981) |
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| 78 | ! |
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| 79 | !####################################################################### |
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| 80 | |
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| 81 | real,parameter :: satfwa = 1.0007 |
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| 82 | real,parameter :: satfwb = 3.46e-8 ! for p in Pa |
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| 83 | |
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| 84 | real,parameter :: satewa = 611.21 ! es in Pa |
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| 85 | real,parameter :: satewb = 17.502 |
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| 86 | real,parameter :: satewc = 32.18 |
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| 87 | |
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| 88 | real,parameter :: satfia = 1.0003 |
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| 89 | real,parameter :: satfib = 4.18e-8 ! for p in Pa |
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| 90 | |
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| 91 | real,parameter :: sateia = 611.15 ! es in Pa |
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| 92 | real,parameter :: sateib = 22.452 |
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| 93 | real,parameter :: sateic = 0.6 |
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| 94 | |
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| 95 | f = satfwa + satfwb * p |
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| 96 | f_esl = f * satewa * exp( satewb*(t-273.15)/(t-satewc) ) |
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| 97 | |
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| 98 | return |
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| 99 | end function f_esl |
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| 100 | |
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| 101 | function f_esi( p, t ) |
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| 102 | |
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| 103 | implicit none |
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| 104 | |
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| 105 | real :: p ! Pressure (Pascal) |
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| 106 | real :: t ! Temperature (K) |
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| 107 | real :: f_esi ! Saturation water vapor pressure over ice (Pa) |
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| 108 | |
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| 109 | real :: f |
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| 110 | |
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| 111 | !####################################################################### |
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| 112 | ! |
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| 113 | !Saturation specific humidity parameters used in enhanced Teten's |
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| 114 | !formula. (See A. Buck, JAM 1981) |
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| 115 | ! |
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| 116 | !####################################################################### |
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| 117 | ! |
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| 118 | real,parameter :: satfwa = 1.0007 |
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| 119 | real,parameter :: satfwb = 3.46e-8 ! for p in Pa |
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| 120 | |
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| 121 | real,parameter :: satewa = 611.21 ! es in Pa |
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| 122 | real,parameter :: satewb = 17.502 |
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| 123 | real,parameter :: satewc = 32.18 |
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| 124 | |
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| 125 | real,parameter :: satfia = 1.0003 |
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| 126 | real,parameter :: satfib = 4.18e-8 ! for p in Pa |
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| 127 | |
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| 128 | real,parameter :: sateia = 611.15 ! es in Pa |
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| 129 | real,parameter :: sateib = 22.452 |
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| 130 | real,parameter :: sateic = 0.6 |
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| 131 | |
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| 132 | f = satfia + satfib * p |
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| 133 | f_esi = f * sateia * exp( sateib*(t-273.15)/(t-sateic) ) |
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| 134 | |
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| 135 | return |
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| 136 | end function f_esi |
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