Version 1.0: 9th June 2014
This software and documentation was developed
within the context of the EUMETSAT satellite Application
Facility (NWP SAF). The partners in the NWP SAF are the Met
Office, ECMWF, KNMI, and Météo-France.
If the parameter Cloud_Liquid_Water is
requested to be retrieved in the
Retrievals.NL namelist, the 1DVar code retrieves either
Liquid Water Path or Qtotal depending on the value for Lqtotal
given through the ControlData.NL.
The retrieval code follows the one implemented in the deprecated
SSMIS 1D-Var package but the minimisation routines which are used came
from the Met Office 1D-Var. In this case the internal logical variable
MwClwRetreival is set to .TRUE. If Lqtotal is set to
0, LWP is retrieved and if Lqtotal is set to 1, Qtotal will be
retrieved.
The differences in processing when cloudy retrievals are used
are:
- Background Profile should contain cloud liquid water profile
in kg/kg.
- Bmatrix element is diagonal with no correlation to any other
variables, and is hence set to a fixed value of 0.2, which is
hardcoded.
- For LWP retrievals, the first guess is set to a fixed value
0.1 kgm-2, which is also hardcoded.
(Both these values
are inherited from the SSMIS 1Dvar)
For LWP retrieval, during the minimization process, LWP is allowed
to vary while a cloud structure S(i) remains fixed
S(i)=clw(i)/LWP, where i stands for pressure levels
and clw for cloud liquid
water profile.
Qtotal is defined as the sum of the water vapor content (q) and
cloud liquid water content (clw). Instead of ln(q),
ln(qtotal) is retrieved.
The dependence of q and clw on qtotal is such that, below a
threshold value of relative humidity of 95% q=qtotal. Between
RH values of 95% and 105%, qtotal is split half way between q and
clw. Above 105%, q is fixed and any excess water is clw.
It is recommended that Marquardt-Levenberg minimisation is used
for cloudy retrievals.
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