eucos observing system experiments with the cosmo ......• eucos stands for “eumetnet composite...

EUCOS observing system experimentswith the COSMO Local Model

Jean-Marie BettemsSwiss Federal Office for Meteorology and Climatology3hd COSMO General Meeting, Athens, October 2001

• EUCOS stands for “EUMETNET Composite Observing System”

• The main goal of the EUCOS program is to define the optimumground based observing sytem for short range NWP

• Two scenarios have been proposed, both associated with a drasticreduction of the number of radiosonde stations over continentalEurope and an increased number of AMDAR platforms

• A special observation campaign took place from 20 September to14 November 1999 to support observing system experiments

• Observing system experiments with both global and limited areamodels are made to evaluate the impact of the proposed scenarios

• OSE studies have been done with the ECMWF global model (T319),with the DMI-HIRLAM-G (50km) model and with the high resolutionCOSMO Local Model (7km)

3hd COSMO general meeting, Athens octobre 2001 [email protected]

Experimental set-up (1)

• A 27 days period was chosen, from 19th October 1999 to 15th November 1999;

this period includes seven MAP heavy precipitation events and was also chosen by

DMI

• Three observing systems have been considered:

S1 is the standard observing systembefore EUCOS field experiment

S2 has 37 radiosonde stations less, but 13 upgraded stations (-50% bulletins)

S3 is S2 complemented by 121 more AMDAR platforms (+400% bulletins)

• For each observing system: a 27 days continuous assimilation and a daily 24h

forecast have been calculated with the non-hydrostatic COSMO Local Model

• All experiments were based on the operational configuration of the Local Model

installed at MeteoSwiss:

1. 385x325 mesh, about 7km horizontal resolution, 45 layers in the vertical

2. data assimilation based on the nudging scheme, with use of all conventional

observing systems (SYNOP, SHIP, DRIBU, AIREP, AMDAR, TEMP, PILOT)

3. aicraft data grouped in multi-level reports before assimilation

4. boundary conditions from the ECMWF operational deterministic forecast

(forecast) and from the operational 4d var stream (assimilation)

5. soil model updated once a day from the driving model

• Results have been evaluated with two verification packages:

1. verification of the vertical structure of the atmosphere against a set of 28

radiosondes regularly distributed over the whole LM domain

2. verification of near-surface weather parameters over Switzerland


Experimental set-up (2)

a. all observations influencing the model flow during the considered 24h period.

TEMP PILOT AIRCRAFT SYNOP

S1active stations 55 12 135 1078

active reportsa 202 24 4671 18542


active reports 110 24 4671 18542


active reports 110 24 21261 18542

Local Model domain

60˚N

50˚N

40˚N

0˚ 20˚E20˚W

Typical daily coverage of AMDAR platforms in S3

Typical number of observations assimilated in 24h

4th SRNWP Workshop, Bad Orb septembre 2001 [email protected]

Impact of radiosonde network modification

Number of active radiosondes over LM domain reduced from 55 to 25

From the remaining stations 12 have been upgraded to measure every 6hours

• Significant degradation of model quality at analysis time

both dynamical and thermodynamical fields are affected

mainly visible in the distribution of model fields (meso-β structures)

consistent with the results of an earlier OSSE study [Bettems, 1999]

• Negative impact in the very short range forecast

after 12hour most differences have disappeared


Relative humidity +00h (12UTC) All stations

Bias Standard deviation

Vertical structure of the atmosphere

S1S2S3


Wind speed +00h (12UTC) All stations



S1S2S3

4th SRNWP Workshop, Bad Orb octobre 2001 [email protected]

Wind speed +00h (12UTC) Innsbruck (not part of S1/S2/S3)



S1S2S3


Total precipitation, mean over 5 grid points All active ANETZ stations

Near-surface weather parameters over Switzerland

S1S2S3

(Obs. frequence of Payerne RS is double in S2/S3)


Impact of additional AMDAR platforms

Number of active AMDAR platforms in LM domain increased from ~135 to ~216

Number of AMDAR reports increased by a factor 4

• Over the whole model domain the impact is positive but very small

• Clear local improvement, in regions well covered by AMDAR platforms

humidity field is also improved

does not compensate quality loss brought by the radiosonde network degradation


Wind speed +00h (12UTC) Stuttgart (many AMDARs around that location)

S1S2S3




Wind direction All representative ANETZ stations below 800m

Near-surface weather parameters over Switzerland

S1S2S3


46ON

48ON

4OE

4OE

6OE

6OE

8OE

8OE

10OE

10OE

12OE

12OE

6h Sum of total rain and snow in mmLM Forecast 06.11.1999 12 UTC +6h VT: Sat 6 Nov 1999 18 UTC

Copyright MeteoSwiss

0.1 0.5 1 5 10 20 50 100 121.8

.5 rosa - bettems Tue May 8 10:52:37 2001 S3a

Exper

imen

t S3

46ON

48ON

4OE

4OE

6OE

6OE

8OE

8OE

10OE

10OE

12OE

12OE



0.1 0.5 1 5 10 20 50 79.5

5.5 rosa - bettems Fri May 11 01:03:54 2001 S1a

Exper

imen

t S1

46ON

48ON

4OE

4OE

6OE

6OE

8OE

8OE

10OE

10OE

12OE

12OE



0.1 0.5 1 5 10 20 50 100 122.8

.5 rosa - bettems Sun May 6 18:21:45 2001 S2a

Exper

imen

t S2

Heavy precipitation case – 6th November 1999

6h precipitation sum from LM

MAP Alpine radar composite

(12UTC - 18UTC)


Conclusion

• The results obtained at a higher horizontal resolution with theLocal Model (~7km) differ substantially from those obtainedwith the global ECMWF model (~60km) or the DMI-HIRLAM-Glimited area model (~50km).

• ECMWF and DMI studies have shown that a reduction of thenumber of active radiosonde stations had a very small negativeimpact, and that the additional AMDAR data slightly degradethe forecast quality.

• This study suggests a significative degradation of the shortrange forecast quality associated with the introduction of theproposed EUCOS scenario, if no compensatory action are taken.

AMDAR observations have a clear potential, and an improvedhorizontal coverage would mitigate the expected quality loss.

However, additional information about local structures in thehumidity field are needed (e.g. GPS).

• EUCOS stands for “EUMETNET Composite Observing S...• The main goal of the EUCOS program is to define ...• Two scenarios have been proposed, both associate...• A special observation campaign took place from 2...• Observing system experiments with both global an...• OSE studies have been done with the ECMWF global...EUCOS observing system experiments with the COSMO ...Jean-Marie Bettems Swiss Federal Office for Meteor...• A 27 days period was chosen, from 19th October 1...• Three observing systems have been considered: S1...• For each observing system: a 27 days continuous ...• All experiments were based on the operational co...• Results have been evaluated with two verificatio...• The results obtained at a higher horizontal reso...• ECMWF and DMI studies have shown that a reductio...• This study suggests a significative degradation ...

eucos observing system experiments with the cosmo ......• eucos stands for “eumetnet composite...

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