Spectral microphysics in weather forecast models with special emphasis on cloud droplet nucleation Verena Grützun, Oswald Knoth, Martin Simmel, Ralf Wolke.
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Spectral microphysics in Spectral microphysics in weather forecast models weather forecast models
with special emphasis on cloud with special emphasis on cloud droplet nucleationdroplet nucleation
Verena GrützunVerena Grützun, Oswald Knoth, , Oswald Knoth, Martin Simmel, Ralf WolkeMartin Simmel, Ralf Wolke
IfT LeipzigIfT Leipzig
Oct. 24Oct. 24thth 2006 2006
3 Verena Grützun, IfT, Modelling Department, Oct. 24Verena Grützun, IfT, Modelling Department, Oct. 24 thth 2006 2006
IntroductionIntroduction““Spectral microphysics in weather forecast models”Spectral microphysics in weather forecast models”
Goals:
• Introduction of a spectral microphysics into the Lokalmodell of the German Weather Service.
• Investigation of the the influence of aerosols (composition, size distribution, number concentration) on precipitation
• Improving quantitative precipitation forecast through offering new approaches to microphysical parameterizations
Status: …
4 Verena Grützun, IfT, Modelling Department, Oct. 24Verena Grützun, IfT, Modelling Department, Oct. 24 thth 2006 2006
IntroductionIntroduction
• Implementation of a SPECtral microphysicS (warm and mixed phase) into LM (“LM-SPECS“)
• Implementation of conservative advection scheme for moisture variables
• Test cases of cloud evolution (Heat bubble, 2D mountain overflow)
• Simplified description of CCN evolution in progress
• Comparison with two moment microphysical scheme
““Spectral microphysics in weather forecast models”Spectral microphysics in weather forecast models”
Work to date:
5 Verena Grützun, IfT, Modelling Department, Oct. 24Verena Grützun, IfT, Modelling Department, Oct. 24 thth 2006 2006
TheoryTheory
Model system LM-SPECS IModel system LM-SPECS I
tLM
dynamics
microphysics
tLMk tLM
k+1
m tmp
… …tmp1 tmp
mtmpi(=tLM
k) (=tLMk+1)
T,
q c,
q v
u,v,w, p, , T
T(tLMk)+itmpTdyn
p(tLMk)+itmppdyn
(tLMk)+itmpdyn
Advection u,v,w,p,T
Advection qv, nbin, qc
bin, qabin, qs
bin
6 Verena Grützun, IfT, Modelling Department, Oct. 24Verena Grützun, IfT, Modelling Department, Oct. 24 thth 2006 2006
TheoryTheory
Model system LM-SPECS IIModel system LM-SPECS II
• Combined spectrum of CCN and droplets in (currently) 66 mass-doubling bins
• Spherical ice particles in (currently) 66 bins
• Number density, total water mass, (frozen water mass,) total aerosol mass, soluble aerosol mass (binwise)
• Purely insoluble particles as ice nuclei
• Condensation, collision, break-up, contact / immersion / deposition freezing, secondary freezing processes
7 Verena Grützun, IfT, Modelling Department, Oct. 24Verena Grützun, IfT, Modelling Department, Oct. 24 thth 2006 2006
Test case: Heat bubbleTest case: Heat bubble
SetupSetup
( )( )
2
2
ln( ) ln( )exp
(ln ) 2 ln( ) 2 ln( )
gT
g g
D DNdN
d D p s s
é ù-ê ú= -ê ú
ê úê úë û
• Model domain 80 km x 80 km
• Horizontal resolution 1 km, 40 vertical layers
• Initial wind equal zero
• Temperature disturbance of up to 2 K (“Heat bubble“ at the height of 1.4 km, hor. radius 10 km)
Sensitivity study w. resp. to initial number distribution NT:
Artificial test case:
NT = 200 cm-3 (N200)
NT = 566 cm-3 (N566)
NT = 4000 cm-3 (N4000)
8 Verena Grützun, IfT, Modelling Department, Oct. 24Verena Grützun, IfT, Modelling Department, Oct. 24 thth 2006 2006
Results: Heat bubble at 24 minResults: Heat bubble at 24 minLiquid water content Liquid water content
N566
9 Verena Grützun, IfT, Modelling Department, Oct. 24Verena Grützun, IfT, Modelling Department, Oct. 24 thth 2006 2006
Results: Heat bubble at 24 minResults: Heat bubble at 24 minParticles and relative humidity Particles and relative humidity
10 Verena Grützun, IfT, Modelling Department, Oct. 24Verena Grützun, IfT, Modelling Department, Oct. 24 thth 2006 2006
Results: Heat bubble at 24 minResults: Heat bubble at 24 min
Particle spectra Particle spectra
6.4 km
3.7 km
2.9 km
11 Verena Grützun, IfT, Modelling Department, Oct. 24Verena Grützun, IfT, Modelling Department, Oct. 24 thth 2006 2006
Results: Results: Heat bubble at 24 minHeat bubble at 24 min Accumulated rain Accumulated rain
13 Verena Grützun, IfT, Modelling Department, Oct. 24Verena Grützun, IfT, Modelling Department, Oct. 24 thth 2006 2006
Test case: 2D MountainTest case: 2D Mountain
SetupSetup
• 2-dimensional mountain overflow, 400 gridpoints in x-direction
• Horizontal resolution 2.8 km, 38 vertical layers
• Horizontal wind at start:15 m/s
• Idealized vertical sounding (Thompson et al., 2004)
• Warm-phase microphysics
Sensitivity study w. resp. to mountain height, comparison with 2-moment bulk microphysics scheme
Artificial test case:
14 Verena Grützun, IfT, Modelling Department, Oct. 24Verena Grützun, IfT, Modelling Department, Oct. 24 thth 2006 2006
Results: 2D mountain at 6hResults: 2D mountain at 6h
Liquid water contentLiquid water content
Height: 500 m
polluted
clean
15 Verena Grützun, IfT, Modelling Department, Oct. 24Verena Grützun, IfT, Modelling Department, Oct. 24 thth 2006 2006
Results: 2D mountain at 6hResults: 2D mountain at 6h
Liquid water contentLiquid water content
Clean case
1000m
500m
16 Verena Grützun, IfT, Modelling Department, Oct. 24Verena Grützun, IfT, Modelling Department, Oct. 24 thth 2006 2006
Results: 2D mountain at 6hResults: 2D mountain at 6h
Liquid water contentLiquid water content
Clean case
A. Mühlbauer et al., 2006
500m
comparison with 2-mom. scheme
18 Verena Grützun, IfT, Modelling Department, Oct. 24Verena Grützun, IfT, Modelling Department, Oct. 24 thth 2006 2006
Results: 2D mountain at 6hResults: 2D mountain at 6h
Precipitation – spatialPrecipitation – spatialdistributiondistribution
A. Mühlbauer et al., 2006
Spectral microphysics
comparison with 2-mom. scheme
19 Verena Grützun, IfT, Modelling Department, Oct. 24Verena Grützun, IfT, Modelling Department, Oct. 24 thth 2006 2006
SummarySummary
• The model system LM-SPECS has been developed, coupling the LM with a spectral microphysics scheme
• Sensitivity studies on an artificial heat bubble were done to test the model performance, results:
• Spectral information about the development from humid aerosol particles to rain drops; depletion, supersaturation
• Strong influence of particle number on accumulated rain: more particles less & later rain
• 2D Mountain test case: Sensitivity study on mountain height, comparison with 2-moment-bulk scheme.
• Quantitatively similar results, but differences in cloud structure and resulting distribution of rain
20 Verena Grützun, IfT, Modelling Department, Oct. 24Verena Grützun, IfT, Modelling Department, Oct. 24 thth 2006 2006
OutlookOutlook
OutlookOutlook
Second project phase
• Improving the mixed phase microphysics
• Aiming for realistic episodes, e.g.
- Boundary conditions, model nesting
• Further comparison with two-moment microphysics, esp. mixed phase microphysics
• Improving the numerics & further improvement of realistic runs
Perspective:
• Case studies with the help of COPS data
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