subroutine asknewet (e,Tm,lambda,zwd)
c% This subroutine determines the zenith wet delay based on the
c% equation 22 by Aske and Nordius (1987)
c%
c% c Reference:
c% Askne and Nordius, Estimation of tropospheric delay for microwaves from
c% surface weather data, Radio Science, Vol 22(3): 379-386, 1987.
c%
c% input parameters:
c%
c% e: water vapor pressure in hPa
c% Tm: mean temperature in Kelvin
c% lambda: water vapor lapse rate (see definition in Askne and Nordius 1987)
c%
c% output parameters:
c%
c% zwd: zenith wet delay in meter
c%
c% Example 1 :
c%
c% e = 10.9621 hPa
c% Tm = 273.8720
c% lambda = 2.8071
c%
c% output:
c% zwd = 0.1176 m
c%
c% Johannes Boehm, 3 August 2013
C% Johannes Boehm, 24 December 2014, converted to Fortran
c% ---
implicit double precision (a-h,o-z)
double precision k1,k2,k2p,k3,lambda
!% coefficients
k1 = 77.604d0 !% K/hPa
k2 = 64.79d0 !% K/hPa
k2p = k2 - k1*18.0152d0/28.9644d0 !% K/hPa
k3 = 377600.d0 !% KK/hPa
!% mean gravity in m/s**2
gm = 9.80665d0
!% molar mass of dry air in kg/mol
dMtr = 28.965d-3
!% universal gas constant in J/K/mol
R = 8.3143d0
!% specific gas constant for dry consituents
Rd = R/dMtr
zwd = 1.0d-6*(k2p + k3/Tm)*Rd/(lambda + 1.d0)/gm*e
end subroutine