Proceedings - C-SRNWP Project

efficiently and does not have severe drawbacks for the convective scale in the short and mid
term provided that retrievals can be made available, accordant development should be done.
4. Some ongoing and planned activities
Fig 3: Equitable threat scores for
hourly precipitation (threshold: 0.1
mm/h) of LM-K forecasts (00- and
12-UTC runs) from 16 June to 15
August 2006 against radar-derived
precipitation as a function of forecast
time (in hours; the vertical pink
dashed line indicates the start of the
forecasts, in which data are still
assimilated during the first 30 min.).
Green solid line: forecasts starting
from the assimilation cycle with
LHN; blue dashed line: forecasts
starting from the assimilation cycle
without LHN. The red bars indicate
number of rainy radar pixels.
This section lists and details the main activities on the further developments of the nudging
and in particular of the retrieval schemes.
• Assimilation of radar-derived precipitation rates by latent heat nudging (LHN):
Surface precipitation rates are derived from radar reflectivity and assimilated by means of
LHN (and an adjustment of humidity). The main task has been to adapt the original LHN
scheme (similar to that of Jones and Macpherson, 1997) such that it works well (see Fig.3)
with the prognostic treatment of precipitation in the high-resolution LM (Schraff et al.,
2006). Since August 2006, it has been running as part of the pre-operational LM-K at
DWD. The work continues on a better understanding of the convection in the model and
of LHN itself and on further refining the scheme. A special contribution dedicated to LHN
in LM is included in this volume.
• Simple adjoint retrieval (SAR) of 3-dimensional wind from radar Doppler velocity and
reflectivity:
3-dimensional wind fields are retrieved from three consecutive scans of 3-d reflectivity
and radial velocity from single radars by means of a simple adjoint method (Gao et al.,
2001). A cost function is set up which consists of a background term, a mass continuity
term, a smoothing term, an observation term in the usual form for radial velocity, and a
second observation term for a tracer, typically reflectivity. For this term, the tracer
observed in the first scan is advected with the retrieved velocity and compared to the
tracer observations from the second and third scan. The simplified advection model
includes eddy viscosity. First tests with data from Polish radars have revealed problems
with the quality of the radial velocity input data. After implementing high-frequency noise
removal and a revised interpolation to Cartesian coordinates, the method works now for
single radar data. Assimilation tests with nudging of the wind retrievals are planned.
• Use of ground-based GPS data and GPS tomography:
Past attempts to use ground-based GPS data in COSMO have been based on assimilating
integrated water vapour derived from zenith total delay data by scaling the model’s
humidity profiles within the nudging scheme. Besides improving upper-air humidity and
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