Eidgenössisches Departement des Innern EDIBundesamt für Meteorologie und Klimatologie MeteoSchweiz Institut für
Physik der Atmosphäre
On the Value of
Radar-Derived Rainfall Assimilation
on High-Resolution QPF
Daniel Leuenberger1, Christian Keil2 and George Craig2
1MeteoSwiss, Zurich, Switzerland 2DLR, Oberpfaffenhofen, Germany
COSMO GM 2008, Cracow
2 Value of Radar Assimilation for QPF [email protected] COSMO GM 2008, Cracow
Introduction
• Convective-scale assimilation of radar rainfall data
• Latent Heat Nudging (LHN)
• Results of a 7 month test suite at MeteoSwiss
• What determines the impact of LHN on QPF?
3 Value of Radar Assimilation for QPF [email protected] COSMO GM 2008, Cracow
ECMWF IFS
MeteoSwiss Model Setup
COSMO-7COSMO-7•6.6km, 60 levels•Param. deep convection•Assimilation of conv. obs.
COSMO-2• 2.2km, 60 levels• Explicit deep convection• Assimilation of conv. obs.
and radar rainfall
COSMO-2
Radar
~600 km
4 Value of Radar Assimilation for QPF [email protected] COSMO GM 2008, Cracow
Setup of Experiments
• 2.2km assimilation cycle with/without LHN
• Forecasts out to +12h, initialized at 00 and 12 UTC
• 11. June 2007 – 15. January 2008 (346 forecasts)
5 Value of Radar Assimilation for QPF [email protected] COSMO GM 2008, Cracow
Examples of Improvement
6-12h Precipitation Forecast (19.06.2007) Verifying Radar
LHN NOLHN Radar
LHN NOLHN Radar
0-6h Precipitation forecast (12.06.2007) Verifying Radar
6 Value of Radar Assimilation for QPF [email protected] COSMO GM 2008, Cracow
Verification against Radar346 Forecasts, 11. June 2007 - 15. January 2008, hourly sums
7 Value of Radar Assimilation for QPF [email protected] COSMO GM 2008, Cracow
Verification against Radar (Summer)9 Forecasts, 11. June - 19. July 2007, hourly sums
8 Value of Radar Assimilation for QPF [email protected] COSMO GM 2008, Cracow
Verification of other VariablesP
a
330
325
320
335
315
Surface Pressure
12 18 00Time UTC
m/s
2.20
2.15
2.10
2.25
2.05
10m Wind speed
12 18 00Time UTC
deg
64
62
60
66
58
Wind direction
12 18 00Time UTC
RMS of 74 12UTC Forecasts (Reference: ca. 60 Swiss Sfc. Stations)
NOLHN
LHN
9 Value of Radar Assimilation for QPF [email protected] COSMO GM 2008, Cracow
Verification of other Variables
32
30
28
34
26
%
Cloud cover
12 18 00Time UTC
2.4
2.2
2.0
2.6
1.8
K
2m Temperature
12 18 00Time UTC
K
2.8
2.6
2.4
3.0
2.2
2m Dewp. Temperature
12 18 00Time UTC
RMS of 74 12UTC Forecasts (Reference: ca. 60 Swiss Sfc. Stations)
NOLHN
LHN
10 Value of Radar Assimilation for QPF [email protected] COSMO GM 2008, Cracow
What determines the impact of LHN?
• Use high-resolution NWP ensemble (2.8km mesh size)
• Driven by regional COSMO-LEPS ensemble
• 10 members with LHN, 10 members without
• Different mesoscale environment in each member
• 3 differently forced convection cases
forced frontal non-forced frontal airmass
31.July 2006 28. June 2006 12. July 2006
11 Value of Radar Assimilation for QPF [email protected] COSMO GM 2008, Cracow
Example: Airmass convection
NOLHN
0.8
0.6
0.4
1.0
0.2
0.006 09 12 15 18 21 00
Radar
NWPEnsemble
Time UTC
Timelines of observed and simulated area-averaged surface rainfall
LHN
06 09 12 15 18 21 00Time UTC
Assimilation
mm
Forecast
12 Value of Radar Assimilation for QPF [email protected] COSMO GM 2008, Cracow
Definition of Time Scales
• LHN impact factor
• LHN time scale LHN
• Convective time scale• Done et al. (QJ 2006)
)0(
)(~)(
tPP
ttPPtF
NOLHNLHN
iNOLHNLHNiLHN
5.0)( LHNLHNF
dtCAPEd
CAPEc /)(~
FLHN
time
0.5
1
LHN
13 Value of Radar Assimilation for QPF [email protected] COSMO GM 2008, Cracow
Stratification of Simulations
Results suggest 2 different regimes:
• equilibrium situation:
• short c
• precipitation only redistributed• short-lived impact of LHN
1 10 1000.1
1
10
100
LH
N [h]
c [h]
forced frontal, non-forced frontal airmass
• non-equilibrium situation:
• long c
• LHN triggers convection• long lasting impact of LHN
14 Value of Radar Assimilation for QPF [email protected] COSMO GM 2008, Cracow
Findings
• LHN improves high-resolution NWP forecasts
• QPF improvement in the first 3-12h (dependent on score and rainfall intensity)
• Other variables slightly improved, particularly in summer
• More realistic rainfall input for soil moisture
• Impact on QPF dependent on
• Precipitation forcing (equilibrium vs. non-equilibrium)
• Life time of precipitation system (predictability!)
• Mesoscale environment of convection (e.g. stability)
• Extent of NWP model domain and radar data coverage
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Thank you for your attention
