Spectral microphysics in weather forecast models with special emphasis on cloud droplet nucleation Verena Grützun, Oswald Knoth, Martin Simmel, Ralf Wolke.

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: …


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:


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


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


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)


Results: Heat bubble at 24 minResults: Heat bubble at 24 minLiquid water content Liquid water content

N566


Results: Heat bubble at 24 minResults: Heat bubble at 24 minParticles and relative humidity Particles and relative humidity


Results: Heat bubble at 24 minResults: Heat bubble at 24 min

Particle spectra Particle spectra

6.4 km

3.7 km

2.9 km


Results: Results: Heat bubble at 24 minHeat bubble at 24 min Accumulated rain Accumulated rain


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:


Results: 2D mountain at 6hResults: 2D mountain at 6h

Liquid water contentLiquid water content

Height: 500 m

polluted

clean




Clean case

1000m

500m




Clean case

A. Mühlbauer et al., 2006

500m

comparison with 2-mom. scheme



Precipitation – spatialPrecipitation – spatialdistributiondistribution

A. Mühlbauer et al., 2006

Spectral microphysics

comparison with 2-mom. scheme


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


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

Spectral microphysics in weather forecast models with special emphasis on cloud droplet nucleation Verena Grützun, Oswald Knoth, Martin Simmel, Ralf Wolke.

Documents

t mp t mp

t tt lm

i t mp p dyn t lm

i t mp t dyn pt lm

modelling department

n566 n t

n200 n t

t advection q v