Proceedings - C-SRNWP Project

temperature forecasts, this had a significant positive impact on precipitation on occasions,
however the positive cases
outnumbered the negative ones
only slightly. The main
problem was identified to be
related to the vertical distribution
of the vertically integrated
humidity information.
Information on the vertical
distribution is required and can
be provided by GPS tomography
in the form of vertical
humidity profiles. This has
been developed at the ETH
(Federal Institute of Technology,
Zurich) by Troller et al.
(2006), and sets of 18 hourly
Fig 4: Location of the Swiss GPS gound receivers and of
the voxels for which hourly humidity profiles are
retrieved quasi-operationally.
humidity profiles are produced quasi-operationally over Switzerland where there is a
dense network of GPS ground receivers (Fig 4). Although the method is found to work
well in some cases provided that surface synoptic data are included in the tomographic
reconstruction, preliminary statistical comparisons of tomography profiles with Payerne
radiosonde and model analysis and forecast data have revealed shortcomings in the overall
quality. Further work focuses on improving the tomography technique and on monitoring
and eventually assimilating the resulting profiles.
• Cloud analysis
It is planned to derive vertical profiles of cloudiness from radiosonde humidity, surface
synoptic and ceilometer data, using Meteosat IR brightness temperature and model fields
as background. These profiles will then be spread horizontally using the cloud type
product of the MSG Nowcasting SAF as a cluster analysis. Each profile will be assigned a
class and spread only to pixels with the same class. The cloud analysis will be used to
adjust humidity and possibly condensate.
• Use of satellite radiances by 1DVAR
A 1DVAR minimisation is being implemented in LM. This is to derive temperature and
humidity profiles from radiances of polar orbiting as well as geostationary satellites
(ATOVS, AIRS / IASI, SEVIRI). The resulting profiles will be assimilated like
conventional data with the nudging scheme. Currently, the focus lies on clear-sky
radiances, and the work is carried out as a COSMO priority project. In the mid-term, it is
planned to extend the methodology to cloudy radiances by retrieving profiles of cloud
cover, liquid water content and ice content, and converting them to temperature and
humidity profiles by employing the diagnostic cloud scheme of LM and its adjoint.
• Use of screen-level observations and PBL initialisation
Work is about to start on advancing the use of in-situ screen-level observations in order to
improve the initialisation of the planetary boundary layer (PBL), in particular with regard
to moisture convergence in convective situations. The selection and screening of
representative land stations, the meteorological pre-processing to extrapolate the
observational information to the lowest model level, and the vertical and horizontal
structure functions will be re-considered.
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