da_tpq_to_rh_lin.inc

1 subroutine da_tpq_to_rh_lin(grid)
2 
3    !---------------------------------------------------------------------------
4    !  Purpose: Convert T/pressure/q to relative humidity increments.
5    !
6    !  Method: r~ = r (q~/q - qs~/qs).
7    !
8    ! When q approaching to zero, the above formula its undefined. The
9    ! general formula below must be used:
10    ! 
11    !  Method: r~ = 100 * (q~/qs - q*(qs~/qs)/qs))
12    !             = 100 * q~/qs - (100*q/qs)*(qs~/qs)
13    !             = 100 * q~/qs - rh * (qs~/qs) 
14    !
15    !---------------------------------------------------------------------------
16 
17    implicit none
18    
19    type (domain),  intent(inout) ::grid
20    
21    real :: qs(its:ite,jts:jte,kts:kte)
22    real :: es(its:ite,jts:jte,kts:kte)
23    real :: qs_prime_over_qs(its:ite,jts:jte,kts:kte)
24 
25    if (trace_use_dull) call da_trace_entry("da_tpq_to_rh_lin")
26 
27    !---------------------------------------------------------------------------
28    ! [1.0] Calculate saturation specific humidity ratio qs~/qs:
29    !---------------------------------------------------------------------------
30  
31    call da_tp_to_qs_lin(grid, qs_prime_over_qs )
32 
33    !--------------------------------------------------------------------------
34    ! [2.0] Culcalete background saturation specific humidity qs:
35    !--------------------------------------------------------------------------
36 
37    call da_tp_to_qs1(grid, es, qs) 
38    
39    !---------------------------------------------------------------------------
40    ! [3.0] Calculate relative humidity increment:
41    !---------------------------------------------------------------------------
42 
43    grid%xa % rh(its:ite,jts:jte,kts:kte) = 100.0 * &
44                                 ( grid%xa % q(its:ite,jts:jte,kts:kte) / &
45                                       qs(its:ite,jts:jte,kts:kte) ) - &
46                                   grid%xb % rh(its:ite,jts:jte,kts:kte) * &
47                                   qs_prime_over_qs(its:ite,jts:jte,kts:kte)
48 
49    if (trace_use_dull) call da_trace_exit("da_tpq_to_rh_lin")
50 
51 end subroutine da_tpq_to_rh_lin
52 
53