Federal Department of Home Affairs FDHAFederal Office of Meteorology and Climatology MeteoSwiss

COSMO Priority Project ’Tackle deficiencies in quantitative

precipitation forecasts’

COSMO General Meeting, 19 September 2007, Athens

S. Dierer1, M. Arpagaus1, U. Damrath2, A. Seifert2, J. Achimowicz8, E. Avgoustoglou7, M. Baldauf2, R. Dumitrache9, V. Fragkouli7, F. Grazzini3, P. Louka7, P. Mercogliano6, P. Mezzasalma3, M. Milelli4, D. Mironov2, A. Morgillo3, E. Oberto4, A. Parodi5, I.V. Pescaru9, U. Pflüger2, A. Sanna4, F. Schubiger1, K. Starosta8, M. S. Tesini3

1MeteoSwiss (CH), 2DWD (D), 3ARPA-ER (IT), 4ARPA-P (IT), 5Uni Genova

(IT), 6CIRA-CMCC (IT), 7HNMS (GR), 8IMGW (PO), 9NMA (RO)

2 PP QPF

Aim of PP QPF

The aim of PP QPF is improved knowledge about • most suitable namelist settings or • parts of the model that need to be reformulated

to obtain a better QPF at 7 km horizontal grid size

Good quantitative precipitation forecast is a challenging task – also for the COSMO model:

The project has a focus on model deficiencies – not on errors from e.g. initial and large scale conditions

3 PP QPF

Overview of PP QPF

• Task 1: Selection of test cases representative for „typical“ QPF deficiencies of COSMO model

• Task 2: Definition of sensitivity studies

• Task 3: Run sensitivity studies and draw conclusions

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List of test cases from all countries

DATE INSITUTION Overestimation (+)/underestimation (-)

Stratiform (strat)/convective(con)

06.12.2004 DWD + strat warm sector

18.03.2005 DWD + strat cold front+orography

03.05.2005 DWD + Strat+conv warm front

21.06.2005 DWD - conv cold front

02.02.2005 MeteoSwiss + strat occluded front+orogr.

22.03.2005 MeteoSwiss + strat warm front

12.07.2005 MeteoSwiss + conv -

17.12.2005 MeteoSwiss + strat orography

24.09.2004 ARPA-P - conv cold front+orography

10.04.2005 ARPA-ER + strat occluded front+orogr.

17.08.2006 CIRA-CMCC - conv cold front+orography

09.09.2005 CIRA-CMCC - conv -

01.12.2005 NMA - strat cold front

03.12.2005 NMA - strat cold front+orography

17.12.2005 NMA - Strat+conv cold front

15.09.2005 HNMS - conv -

23.11.2005 HNMS - Strat+conv warm front

26.11.2005 HNMS - strat orography

03.05.2005 IMGW - strat cold front

04.05.2005 IMGW 0 strat cold front

09.06.2005 IMGW + strat -

09.08.2005 IMGW + strat -

23.06.2005 NMA + strat+conv cold front

02.07.2005 NMA + strat cold front

12.07.2005 NMA - strat cold front

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Forecast errors

• 10 cases of stratiform overestimation (8 from D, CH and PO)• 4 cases of stratiform underestimation• 3 cases of convective overestimation• 7 cases of convective underestimation (6 from I and GR)

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Sensitivity studies

• 1. Changes of initial conditions• 2. Changes of numerical methods• 3.1 Changes of microphysics• 3.2 Changes of convection schemes• 3.3 Changes of PBL schemes

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Sensitivity studies: initial conditions

• Soil moisture increased/decreased by 20%• Initial humidity increased/decreased by 10%

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Sensitivity studies: numerical methods

• Halved time step• Leapfrog, tri-cubic semi-Lagrange advection of QR

and QS• Runge-Kutta, tri-cubic semi-Lagrange advection of

QV, QC, QI, QR and QS • Runge-Kutta, flux-form advection of QV, QC, QI, QR

and QS • Runge-Kutta, flux form advection and T’-p’ dynamics • increased orography filtering

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Sensitivity studies: physics 1 - microphysics

• New warm rain scheme (Seifert and Beheng; 2001)• Strong changes of ice microphysics and new warm

rain scheme • Moderate changes of ice microphysics and new warm

rain scheme

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Sensitivity studies: physics 2 –convection

• Modified Tiedtke scheme • Kain-Fritsch/Bechtold scheme • No parameterization of deep convection

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Sensitivity studies: physics 3 – PBL

• Decreased/increased scaling factor of height of laminar boundary layer for heat

• Decreased/increased stomatal resistance• Decreased/increased laminar scaling factor for heat

over sea

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Relative change of 24h area average precipitation, first forecast day (06 – 30)

Initial humidityRunge-Kutta Snow microphysicsConvection scheme

Vertical heat/moisture exchange

German{

Swiss{

Ital. (LAMI){Ital.(EuroLM){

Greek {

Polish{Romanian {

Cases

ws80

ws120qv

90

qv11

0dt20

LFsl RKsl

RKbottRKtp

orom

icro1

micro2

micro3

conm

od

kfbco

noffrlam01

rlam50st

o50

sto25

0sea0

1

sea4

0

Δrr > +30%+10% < Δrr <+30%0% < Δrr < +10%Δrr = 0%0% > Δrr > -10%-10% > Δrr > -30%Δrr < -30%

Δrel = (rrexp–rrref)/rrref

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Change of bias between simulated and measured area average precipitation

stratiform

convective

overestimation underestimation

Initial humidity Runge-Kuttasnow microphysics convection

bias > 200%100% < bias <200%bias = 100%100% > bias > 50%bias < 50%

15 PP QPF

Conclusions until now …• Strongest effect (5-40%) on area average precipitation by:

• Initial humidity • Runge-Kutta• microphysics • convection scheme

• Strong effect for Roman and Greek cases • Vertical heat/moisture exchange (extreme change of RLAM)

• Runge-Kutta • reduces mean precipitation in most of the cases• and has an overall positive effect on the results

• None of the studies completely solves a QPF problem, but some give a significant improvement for single cases like • changes of snow microphysics for a case with overestimation

of stratiform precipitation • Kain-Fritsch/Bechtold for underestimated convective

precipitation

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Cross experiments

No. Sensitivity study

23 COSMO 4.0

24 COSMO 4.0 + 90% initial humidity + Runge-Kutta

25 COSMO 4.0 + Kain-Fritsch/Bechtold

26 COSMO 4.0 + 90% initial humidity + Runge-Kutta + Kain-Fritsch/Bechtold

27 COSMO 4.0 + modified Tiedtke scheme

28 COSMO 4.0 + 90% initial humidity + Runge-Kutta + modified Tiedtke scheme

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Relative change of area average precipitation in cross experiments compared to control simulation

Δrr > +30%+10% < Δrr <+30%0% < Δrr < +10%Δrr = 0%0% > Δrr > -10%-10% > Δrr > -30%Δrr < -30%

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Bias of reference run and cross experimentsDWD M-Swiss Italy HNMS IMGW NMA

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Relative bias of cross experimentsDWD M-Swiss Italy HNMS IMGW NMA

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Improvement of area average precipitation in numbers…

• 17 cases improved by one of the studies: COSMO4.0+• KFB: 5 cases (3C- / 2S+)• QV90+RK+Tiedtkemod : 3 cases • QV90+RK+KFB : 3 cases• -/Tiedtkemod/RK+QV90: 2 cases

• 7 cases hardly affected or worse (5C-)

} 8S+/3S-

23 PP QPF

Conclusions• COSMO4.0+

• reduced initial humidity• modified convection• Runge-Kutta

• has a positive impact on stratiform overestimation• little or negative impact on convective underestimation• Few cases are “solved”• COSMO Version 4.0 is a step forward!• Further improvements expected from Runge-Kutta.• We should have a closer look at the (initial) humidity fields. – Any

improvements in data assimilation expected?• Convection schemes are the next thing to look at.

• Draft of a final report has been written and will be revised based on the discussion of PP QPF sessions in Athens and will be available in the next weeks

• publication of results planned until end of the year