05.08.2005 - 1 - COSMO General Meeting COSMO General Meeting Zürich, 20 - 23 Sept 2005 1 christoph.schraff@dwd.de Stefan Klink, Klaus Stephan and Christoph Schraff and Daniel Leuenberger [email protected][email protected][email protected][email protected]Recent developments in Latent Heat Nudging • latent heat nudging and “prognostic” precipitation ( strong overestimation of precipitation during LHN) • results of assimilation experiments
The correlation between the vertically integrated rate of latent heat release and the surface precipitation rate is significantly smaller in the simulation with prognostic precipitation
-from: R. A. Houze, Jr.: Cloud DynamicsInternational Geophysics Series Vol. 53
• main part of positive latent heat release occurs in updrafts, strong precipitation rates are often related to downdrafts
• at x < 3 km , with prognostic treatment of precipitation (model resolves large clouds): model is able to distinguish between updrafts and downdrafts inside convective systems
horizontal displacement of areas with strong latent heating resp. to surface precipitation,
modified spatial structure of latent heat release in the model
scheme will notice only with temporal delay if precipitation already activated by LHN
scores for hourly precipitation : with latent heat nudging / without latent heat nudging08 – 18 July 2004-limits : 1.7 / 0.3nested into LMBott advection
• ‘blacklist’ for radar data: avoids introduction of spurious rain at radar locations
• several adaptations to LHN to cope with prognostic precipitation; most important:use of an ‘undelayed’ reference precipitation (vertically averaged precipitation flux)
• revised LHN, assimilation mode: – simulated rain patterns in good agreement with radar observations, – overestimation of precipitation strongly reduced
• subsequent forecasts, impact on precipitation (10-day summer period):– large positive impact for 4 hours (longer than in simulations with diagnostic precip)– mixed ETS impact beyond + 6 h (interpretation yet unclear,
need verification without ‘double penalty’)
• upper-air verification (11-day summer period): – LHN cools and dries PBL, increases mid-tropospheric stability and upper-
tropospheric moisture– overall neutral impact on rmse of forecasts
• strong gravity waves induced during assimilation LHN forcing too strong
• more case studies for both summer and winter periods (up to 10 days),
(further problems ?)
• further diagnosis of LHN results,
in order to better understand some problems (e.g. performance of 0-UTC runs, decrease of forecast impact, too strong LHN forcing) and improve / tune LHN scheme
– role of gravity waves– vertical structure of precipitating cells (e.g. wind field)– vertical distribution of LHN increments– environment of precipitation cells (moisture convergence)– horizontal filtering
• introduction of PI-data (international composite) outside the German DX-area
• further use of cloud type product of Nowcasting-SAF within LHN (humidity adjustment)
• LMK test suites (periods up to three months), with comprehensive verification
• ( possibly: use of 3D reflectivity data in order to determine more precisely (both in space and time) the areas of positive latent heat release
height-dependent scaling of the latent heat rate )
