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subroutine da_tp_to_qs( t, p, es, qs) 34,2
!---------------------------------------------------------------------------
! Purpose: Convert T/p to saturation specific humidity.
!
! Method: qs = es_alpha * es / ( p - ( 1 - rd_over_rv ) * es ).
! use Rogers & Yau (1989) formula: es = a exp( bTc / (T_c + c) )
!--------------------------------------------------------------------------
implicit none
real, intent(in) :: t, p
real, intent(out) :: es, qs
real :: t_c ! T in degreesC.
if (trace_use_dull) call da_trace_entry
("da_tp_to_qs")
!---------------------------------------------------------------------------
! [1.0] initialise:
!---------------------------------------------------------------------------
t_c = t - t_kelvin
!---------------------------------------------------------------------------
! [2.0] Calculate saturation vapour pressure:
!---------------------------------------------------------------------------
es = es_alpha * exp( es_beta * t_c / ( t_c + es_gamma ) )
!---------------------------------------------------------------------------
! [3.0] Calculate saturation specific humidity:
!---------------------------------------------------------------------------
qs = rd_over_rv * es / ( p - rd_over_rv1 * es )
if (trace_use_dull) call da_trace_exit("da_tp_to_qs")
end subroutine da_tp_to_qs