| 1 | function qv_sat(TTK,ss,pstar,pt,lsf) |
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| 2 | |
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| 3 | !--------------------------------------------------------------------------+ |
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| 4 | ! MAR PHYSICS Mc 30-05-2007 MAR | |
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| 5 | ! Function qv_sat computes the Saturation Specific Humidity (kg/kg) | |
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| 6 | ! | |
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| 7 | !--------------------------------------------------------------------------+ |
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| 8 | ! | |
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| 9 | ! INPUT : TTK : Air Temperature (K) | |
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| 10 | ! ^^^^^^^ pstar * ss + pt: Pressure of sigma level ss (kPa) | |
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| 11 | ! | |
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| 12 | ! OUTPUT : e__sat: Saturation Vapor Pressure (hPa) | |
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| 13 | ! ^^^^^^^ qv_sat: Saturation Specific Humidity (kg/kg) | |
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| 14 | ! | |
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| 15 | !--------------------------------------------------------------------------+ |
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| 16 | |
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| 17 | |
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| 18 | IMPLICIT NONE |
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| 19 | |
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| 20 | |
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| 21 | ! Global Variables |
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| 22 | ! ================ |
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| 23 | |
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| 24 | real :: qv_sat |
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| 25 | real :: TTK |
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| 26 | real :: ss |
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| 27 | real :: pstar |
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| 28 | real :: pt |
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| 29 | integer :: lsf |
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| 30 | |
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| 31 | |
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| 32 | ! Local Variables |
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| 33 | ! ================ |
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| 34 | |
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| 35 | real :: pr |
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| 36 | real :: e__sat |
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| 37 | real :: r273p1 = 273.16 |
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| 38 | real :: zer0 = 1.00 |
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| 39 | real :: un_1 = 1.00 |
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| 40 | real :: eps9 = 1.e-9 |
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| 41 | real :: pr__75 = 75.00 |
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| 42 | real :: pr_b75 |
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| 43 | |
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| 44 | |
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| 45 | ! Saturation Vapor Pressure |
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| 46 | ! ============================ |
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| 47 | |
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| 48 | |
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| 49 | pr = 10.d0 *(pstar *ss + pt) ! pressure (hPa) |
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| 50 | |
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| 51 | IF (TTK.ge.273.16d0.or.lsf.eq.0) THEN |
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| 52 | |
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| 53 | e__sat = 6.1078d0 * exp (5.138d0*log( r273p1 /TTK)) &! saturated vapor pressure with respect to water |
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| 54 | & * exp (6827.d0*(un_1/r273p1-un_1/TTK)) ! Dudhia (1989) JAS, (B1) and (B2) p.3103 |
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| 55 | ! See also Pielke (1984), p.234 and Stull (1988), p.276 |
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| 56 | |
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| 57 | ELSE |
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| 58 | e__sat = 6.107d0 * exp (6150.d0*(un_1/r273p1-un_1/TTK)) ! saturated vapor pressure with respect to ice |
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| 59 | ! Dudhia (1989) JAS, (B1) and (B2) p.3103 |
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| 60 | END IF |
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| 61 | |
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| 62 | pr_b75 = max(zer0 , sign(un_1,pr - pr__75)) |
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| 63 | |
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| 64 | |
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| 65 | |
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| 66 | ! ****** |
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| 67 | qv_sat = pr_b75*max(eps9 , .622d0*e__sat/(pr-.378d0*e__sat)) &! |
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| 68 | & + (1.0-pr_b75) * 1.e-3 ! |
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| 69 | ! ****** |
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| 70 | |
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| 71 | |
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| 72 | |
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| 73 | return |
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| 74 | end |
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