da_tpq_to_rh_lin1.inc

1 subroutine da_tpq_to_rh_lin1( t, p, es, rh, &
2                               t_prime, p_prime, q_prime, rh_prime )
3 
4    !---------------------------------------------------------------------------
5    !  Purpose: Convert T/pressure/q to relative humidity increments.
6    !
7    !  Method: r~ = r (q~/q - qs~/qs).
8    !
9    !  When q approaching to zero, the above formula is undefined. The
10    !  general formula below must be used:
11    ! 
12    !  Method: r~ = 100 * (q~/qs) - rh*(qs~/qs)
13    !---------------------------------------------------------------------------
14 
15    implicit none
16 
17    real, intent(in)              :: t        ! Temperature.
18    real, intent(in)              :: p        ! Pressure.
19    real, intent(in)              :: es       ! Saturation vapour pressure.
20    real, intent(in)              :: rh       ! Relative Humidity.
21    real, intent(in)              :: t_prime  ! Temperature increment.
22    real, intent(in)              :: p_prime  ! Pressure increment.
23    real, intent(in)              :: q_prime  ! Pressure increment.
24    real, intent(out)             :: rh_prime ! Pressure increment.
25    
26    real                          :: es1, qs  ! Saturation specific humidity.
27    real                          :: qs_prime_over_qs ! qs~/qs.
28 
29    !---------------------------------------------------------------------------
30    ! [1.0] Calculate saturation specific humidity ratio qs~/qs:
31    !---------------------------------------------------------------------------
32 
33    call da_tp_to_qs_lin1( t, p, es, t_prime, p_prime, qs_prime_over_qs )
34    
35    !--------------------------------------------------------------------------
36    ! [2.0] Culcalete background saturation specific humidity qs:
37    !--------------------------------------------------------------------------
38 
39    call da_tp_to_qs( t, p, es1, qs) 
40    
41    !---------------------------------------------------------------------------
42    ! [3.0] Calculate relative humidity increment:
43    !---------------------------------------------------------------------------
44 
45    rh_prime = 100. * (q_prime / qs) - rh * qs_prime_over_qs
46 
47 end subroutine da_tpq_to_rh_lin1
48 
49