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subroutine da_ref_height(pres, ref_height) 1,2
!---------------------------------------------------------------------------
! Purpose: To calculate the height from the reference pressure
!---------------------------------------------------------------------------
implicit none
real, intent(in) :: pres
real, intent(out) :: ref_height
real :: aa, bb, cc
real :: p0iso, ziso
real, parameter :: rovg = gas_constant/gravity
if (trace_use) call da_trace_entry
("da_ref_height")
aa = 0.5 * rovg * base_lapse
bb = rovg * t0
cc = log(pres/base_pres)
ref_height = -(bb + aa * cc) * cc
if (base_temp > 0.0) then
p0iso=base_pres*exp((base_temp-t0)/base_lapse)
cc=log(p0iso/base_pres)
ziso=-(aa*cc+bb)*cc
if (ref_height > ziso) then
ref_height=ziso+rovg*base_temp*log(p0iso/pres)
end if
end if
if (trace_use) call da_trace_exit("da_ref_height")
end subroutine da_ref_height