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Stefan Klink, Klaus Stephan and Christoph Schraff and Daniel Leuenberger
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Transcript of Stefan Klink, Klaus Stephan and Christoph Schraff and Daniel Leuenberger
05.08.2005 - 1 -COSMO General Meeting
COSMO General MeetingZürich, 20 - 23 Sept 2005 [email protected]
Stefan Klink, Klaus Stephan and Christoph Schraff
and Daniel [email protected]
Recent developments in Latent Heat Nudging
• latent heat nudging and “prognostic” precipitation
( strong overestimation of precipitation during LHN)
• results of assimilation experiments
05.08.2005 - 2 -COSMO General Meeting
COSMO General MeetingZürich, 20 - 23 Sept 2005 [email protected]
Latent heat nudging and “prognostic” precipitation
LHN-Assumption: vertically integrated latent heat release precipitation rate
55km
yx
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
05.08.2005 - 3 -COSMO General Meeting
COSMO General MeetingZürich, 20 - 23 Sept 2005 [email protected]
+
-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
05.08.2005 - 4 -COSMO General Meeting
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possible adaptations I
• horizontal displacement of vertically integrated latent heating and surface precip.:
strong horizontal smoothing applied to 2D fields of observed and modelled surface precipitation rate and to 3D field of latent heat release,
in order to get higher correlation of precipitation and latent heating
(is found to have limited impact, tends to decrease precipitation amounts)
05.08.2005 - 5 -COSMO General Meeting
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possible adaptations II
• change of the spatial structure of latent heat release in the model:
– updraft regions (at the leading edge of a convective cell): very high values of latent heat release TLHmo, little precipitation RRmo
higher values of the scaling factor and of LHN increments often occur
mo
obsLHmoLHN RR
RRTT , 1
reduce upper limit of the scaling factor
adapt grid point search routine
– downdraft regions (further upstream): high precipitation rate, weak latent heat release (often negative in most vertical layers)
LHN increments are inserted only in the vertical layers where the model latent heating rates are positive (approx. in cloudy layers)
(to avoid e.g. negative LHN increments and cooling where the precipitation rate should be
increased)
05.08.2005 - 6 -COSMO General Meeting
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possible adaptations III:
• temporal delay effect (generated precipitation reaches the ground with some delay):
an immediate reference information, on how much precipitation the temperature increment has initialised already, is required within each time step
use of a ’reference precipitation’ RRref: refRR
RR
RR
RR obs
mo
obs
• diagnostically calculated precipitation rate (by additional call of diagnostic precipitation scheme without any feedback on other model variables)
• vertically averaged precipitation flux (more consistent, however it does not eliminate the temporal delay completely)
for LHN: temporal delay effect found to be much more important than spatial displacement
05.08.2005 - 7 -COSMO General Meeting
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Hourly accumulated precipitation height
continuous assimilation cycle for 07 – 18 July 2004, 3 daily forecasts LMK configurations (x = 2.8 km, SL advection), adapted LHN (-limits : 2.0 / 0.5)
nested into GME nested into LM
05.08.2005 - 8 -COSMO General Meeting
COSMO General MeetingZürich, 20 - 23 Sept 2005 [email protected]
Hourly accumulated precipitation height
continuous assimilation cycle for 07 – 18 July 2004, 3 daily forecasts LMK configurations (x = 2.8 km, SL advection), adapted LHN (-limits : 2.0 / 0.5)
nested into GME nested into LM
05.08.2005 - 9 -COSMO General Meeting
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assimilation
2.0 mm
FBI
ETS
0.1 mm threshold values
scores for hourly precipitation : with latent heat nudging / without latent heat nudging08 – 18 July 2004-limits : 1.7 / 0.3nested into LMBott advection
05.08.2005 - 10 -COSMO General Meeting
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12-UTC forecasts
2.0 mm
FBI
ETS
0.1 mm threshold values
scores for hourly precipitation : with latent heat nudging / without latent heat nudging
… and similar results for 18-UTC forecasts
05.08.2005 - 11 -COSMO General Meeting
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0-UTC forecasts
2.0 mm
FBI
ETS
0.1 mm threshold values
scores for hourly precipitation : with latent heat nudging / without latent heat nudging
05.08.2005 - 12 -COSMO General Meeting
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verification against German radiosondes, 11-day period (8 – 18 July 2004): dashed: with latent heat nudging / solid: without latent heat nudging
bias
temperature
relativehumidity
+ 0 h + 6 h + 12 h + 18 h
more stable
colder
drier
moister
05.08.2005 - 13 -COSMO General Meeting
COSMO General MeetingZürich, 20 - 23 Sept 2005 [email protected]
verification against German radiosondes, 11-day period (8 – 18 July 2004): dashed: with latent heat nudging / solid: without latent heat nudging
r m s e
t e m p e r a t u r e
r e l a t I v e h u m I d I t y
+ 0 h + 6 h + 12 h + 18 h
worse
better
05.08.2005 - 14 -COSMO General Meeting
COSMO General MeetingZürich, 20 - 23 Sept 2005 [email protected]
Role of low-level Environment
OBS
CTRL from aLMo ANA 12UTC
LHN from aLMo ANA 12UTC
LHN from aLMo ANA 15UTC
05.08.2005 - 15 -COSMO General Meeting
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3h sum of precipitation21 - 24 UTC(+1 to +4 h free forecast)
Additional three hours of conventional aLMo assimilation improve environment and thus precip forecast started from LHN!
LHN12 - 20 UTC(starting fromaLMo ANA)
Nudging12 - 15 UTC,LHN15 - 20 UTC
05.08.2005 - 16 -COSMO General Meeting
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Response of model dynamics to forcing
OBS CTRL
05.08.2005 - 17 -COSMO General Meeting
COSMO General MeetingZürich, 20 - 23 Sept 2005 [email protected]
• ‘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
Summary of Results
05.08.2005 - 18 -COSMO General Meeting
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• 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 )
Aspects of Further Work
05.08.2005 - 19 -COSMO General Meeting
COSMO General MeetingZürich, 20 - 23 Sept 2005 [email protected]
05.08.2005 - 20 -COSMO General Meeting
COSMO General MeetingZürich, 20 - 23 Sept 2005 [email protected]
Hourly accumulated precipitation height
test case with “prognostic” precipitation