Song-You Hong (Yonsei Univ) Jimy Dudhia (NCAR) Shu-Hua Chen (U.C. Davis)

Numerical Modeling Laboratory


Yonsei UniversityYonsei University

A new ice microphysical processes for a commonly used bulk parameterization of

cloud and precipitation

Song-You Hong (Yonsei Univ)

Jimy Dudhia (NCAR)

Shu-Hua Chen (U.C. Davis)




List of presentation

• Background • A revised cloud scheme• Idealized case experiment• Heavy rainfall case experiment• Ice cloud – radiation interaction• Conclusion

A tip for the MRFPBL




The highest level for the PBL is the half of the total number of vertical layersKLPBL = KL/2 (currently in WRF & MM5)

The PBL mixing is ill-posed with many layers near the surface as done for the air pollution application

Correction : In the “mrfpbl.F”, change

KLPBL = 1 (modified one)




WRF (Weather and Research Forecasting Model) http://wrf-model.org

• Community model: NCAR, NCEP, FSL, AFWA, NSSL, and University communities

• Real time fcsts : NCAR (22km, 10km), NSSL(34km), AWFA(45km), Italy (20km)

MRF PBL, Kain-Fritsch cumulusRRTM, Dudhia RadiationLin or NCEP simple ice microphysics




NCEP Cloud Microphysics

- Hong et al. (1998), NCEP RSM cloud physics

- NCEP cloud microphysics v1.0

(Hong et al. 1998, with some modifications)


(Jimy’s bug fix in computing Vr, Vs)

- > solves the too much precip.


(Hong et al. 2002, the new scheme)




NCEP (Hong) Cloud schemes

NCEP CLOUD 3 (simple ice) and CLOUD 5 (mixed phase) (qci,qrs) (qc,qi,qr,qs)qv

Modifications after Dudhia (1989) and Rutledge and Hobbs (1983)




Background

• Lin et al. (1983) and Rutledge and Hobbs (1983) -> core part of microphyscs

• A typical problem -> too much cirrus due to Ni from Fletcher

• Different assumptions in microphysics ( Meyers et al. 1992, Kruger et al. 1995, Reisner et al. 1998, Rotstayn et al. 2000, Ryan 2001 )

• Sedimentation of ice crystals (Manning and Davis, 1997, Wang 2001)




Ice crystal property

(Mass, Diameter, Mixing ratio, Ice number)

1 0 . 1 6( ) 3 . 2 9 ( )I IV m s q : H e y m s f i e l d a n d D o n n e r ( 1 9 9 0 ) ( H D 1 9 9 0 )

,yIV x D m D : H e y m s f i e l d a n d I a q u i n t a ( 2 0 0 0 ) ( H I 2 0 0 0 )

ii qmN

( ) di iN c q

1 4 1.31

0.5

3 7 0.75

1.333 11

( ) 1.49 10 ,

( ) 11.9

( ) 5.38 10 ( )

( ) 4.92 10

I

I i

I I

V ms D

D m m

N m q

q kgm N




Ryan 1996 Rotstayn 2000

Ryan 2000

Observed and formulated Ni




- I c e n u m b e r c o n c e n t r a t i o n ( IN ) :

3 20( ) 1 0 e x p [ 0 . 6 ( ) ]IN m T T : F l e t c h e r

3 7 0 . 7 5( ) 5 . 3 8 1 0 ( )I IN m q

- I n i t i a t i o n o f c l o u d i c e c r y s t a l ( P g e n )

0m i n ( ) / , ( ) /I I v S IP g e n q q t q q t

N i 0 : F l e t c h e r

3

0 01 0 e x p [ 0 . 1 ( ) ]IN T T




- I n t e r c e p t p a r a m e t e r f o r s n o w :

SN 0 , a c o n s t a n t ( = 7102 4m )

4 6 80 0( ) m i n { 2 1 0 e x p { 0 . 1 2 ( ) } , 2 1 0 }SN m T T

T e m p e r a t u r e (C )

-6 0 -5 0 -4 0 -3 0 -2 0 -1 0 0

No

s (m

-4)

0

5 e + 7

1 e + 8

2 e + 8

2 e + 8

F ig . 1 . T he c o m pute d c o ns tant N 0 s (m - 4 ) as a func tio n o f te m pe r atur e in e q . (1 ).




- C o n v e r s i o n o f i c e c r y s t a l s t o s n o w ( IP a u t ) ,

m a x ( ) / , 0I I c r i tP a u t q q t ,

I c r i tq = I m a x IM N w h e r e kgM ax10

Im 104.9

axD Im ( = 5 0 0 m ) I c r i tq = 0 . 0 8 1 /g k g

- qicrit has small range of T : 0.1 and 1 gkg-1 for –27 and –32C

Fletcher : D89, RH83

- qicrit=0.18gkg-1, at T=-40C, P=300 mb

This study




- V a p o r d e p o s i t i o n o f a s m a l l i c e c r y s t a l ( P i s d ) : 0 . 54 ( 1 ) ( )4 ( 1 ) I c o n I II I I

I I

I

I I

D S qD S NP i s d

A B

N

A B

- S u b l i m a t i o n o f s n o w a n d d e p o s i t i o n a l g r o w t h o f s n o w ( P r e s ) :

1 / 2 1 / 41 / 3 0

2 ( 5 ) / 20

( 5 ) / 24 ( 1 ) 0 . 6 5P r 0 . 4 4

( ) S

SI Sc b

I I SS

SbS a

e sN

SA B




Comparison of deposition rate of water vapor onto ice as a function of cloud temperature, with the assumption that cloud ice mixing ratio is 0.

1 gkg-1 and the air is supersaturated with respect to ice by 10 %.

T (C)

-60 -40 -20 0

Pis

d (g

kg-1

s-1)

0.0001

0.001

0.01

0.1

1

10

FletcherThis study

RH83,D89

This study




• LW radiation : RRTM • SW radiation : Dudhia• Vertical diffusion : MRF• Cumulus scheme : Kain-Fritsch• Microphysics : NCEP (HONG) simple ice• Grid size : 45 km, 15 km• Time step : 120 s, 60 s• Initial time : 1200 UTC 23 June 1997• Integration : 48 hrs• Initial and BDY : NCEP GDAS

WRF version 1.1-beta




Sensitivity Experiments

• Exp1 : Dudhia microphysics (OLD)

• Exp2 : Dudhia + sedimentation of qi

• Exp3 : New microphysics

• Exp4 : New + sedimentation of qi (NEW)




Cloud and Precipitation after 30 min.

qci

qrs

HDC3 Lin




Fig. 3. Profiles of domain-averaged (a) cloud/ice water and (b) snow/rain water mixing ratio (gkg-1) for the Exp1 (thin solid line), Exp2 (dotted line), Exp3 (dashed line), and Exp4 (thick solid line) experiments.

Exp1Exp3 Exp2Exp4

qci

Exp1, 2Exp3,4

qrs




A heavy rainfall case : 1997.6.25

(a) (b)

A




45-km experiment : 24-hr precipitation (mm)

EXP1

EXP3 EXP4

OBSEXP2

> 90 mm




Cloudiness at 36-h fcst (0000UTC 25 June)

Exp1

Exp4




Exp1

Exp2

Exp3

Exp4

Exp1

Exp2 Exp3

Exp4

ANAL

Volume-averaged qci Domain averaged 300 hPa T




• Exp1 : Dudhia microphysics (too much cloud ice -> warm bias)

• NORA : Exp1 but without radiation feedback due to ice cloud)

• NOLW : Exp1 but without LW radiation feedback due to ice cloud)

• NOSW : Exp1 but without SW radiation feedback due to ice cloud)

Ice cloud - radiation feedback




Volume-averaged qci Domain averaged 300 hPa T

EXP1

NORANOLW

NOSW

NORANOLW

ANAL

NOSW

EXP1




Ice cloud - radiation feedback

More cloud ice

Less SW heating More LW heating

Tropospheric cooling

Less SFC buoyancy

Upper level heating

Less cloud ice

Less explicit rainLess implicit rain

Less Precipitation, Warmer Troposphere




Concluding Remarks

• New scheme produces better cloudiness (remove high cloud bias)

• New scheme alleviates the discontinuity problem of small and large ice particles

• Reduction of ice clouds induces more surface precipitation

• Combined effects of improved microphysics and the inclusion of sedimentation of ice crystals are attributed to the improvement of precipitation, cloudiness, and large-scale features

• Sedimentation of HD1990 dominates the effects of detailed ice-microphysical processes




V

k V P

Df

Dt

Severe weather

Regional climate

Seasonal prediction

Climate mechanismNWP

Song-You Hong (Yonsei Univ) Jimy Dudhia (NCAR) Shu-Hua Chen (U.C. Davis)

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