EURO4M 4th GA, Norrköping, 17-19 April 2013 Overview of the new MESCAN precipitation analysis...

EURO4M 4th GA, Norrköping, 17-19 April 2013

Overview of the new MESCAN precipitation analysis system

C. Soci, E. Bazile, J-F. Mahfouf

with contributions from

F. Besson and M. Lafaysse


Analysis of precipitation

Validation

Issues

Further plans

Outline


Principle:- Based on the OI code used also for the analysis of T2m and RH2m

- Background field: accumulated precipitation forecasted by a numerical model (ARPEGE, AROME, ALADIN, HIRLAM).

- Observations: cumulated precipitation from raingauge measurements (at this stage)

- Possibility of producing 24-h, 12-h, 6-h, 3-h or 1-h accumulated precipitation analysis, the only limiting factor is that the background and the observations must span the same period.

- The analysis is performed at the background horizontal resolution

Analysis of accumulated precipitation in MESCAN


Correlation function:

Analysis of accumulated precipitation in MESCAN (2)

L

r

)L

r1()(

erCor

Two options are available:

1. MESCAN-Log: analysis in log-space on a transformed variable ln(RR+1) RR ~ LN (0, 1

2) ln(RR) ~ N (0, 22)

Preliminary error statistics: o=0.6 et b =0.71, L=43km [after Mahfouf et al., 2007 for CAnadian Precipitation Analysis Project (CAPA)]

2. MESCAN-RR: analysis in physical space on RR ~ N (0, 2)

Preliminary error statistics: o =5 et b =13, L=35km (as in SAFRAN)


Test period : October 2009 – June 2010

First guess: ALADIN operational downscaled with fullpos

Indirect validation of the MESCAN analysis system by forcing with its output (analyses of T2m, RH2m, RR24) the surface scheme ISBA and the hydrological module MODCOU.

Evaluation of the impact of changing the surface forcing variables (T2m, RH2m, RR24, 10-m wind speed, downward SW and LW radiation) on:

• River flow, and

• Snow Depth

The reference system used for validation is the operational system called SIM (SAFRAN-ISBA-MODCOU)

Preliminary validation over France at 5.5 km grid


Validation of MESCAN precipitation analysis vs SAFRAN over France

~ 4200 obs for computing scores~ 1700 obs for analyses

Heidke Skill ScoreMar 2010Jun 2010

Heidke Skill ScoreNov 2009Jun 2010

• MESCAN-RR compared to SAFRAN and MESCAN-Log for spring (Mar-Jun):

- improves the HSS for RR > 5mm/day, but- deteriorates HSS for RR < 2mm/day

Heidke Skill ScoreNov 2009Feb 2010

Bias Absolute error

FG 0.40 1.87

MESCAN-RR -0.08 0.87

MESCAN-Log -0.27 0.96

SAFRAN -0.06 0.93


OBS MAX=397mm

ALADIN RR24 MAX=77mm

SAFRAN MAX=309mm

MESCAN-Log MAX=277mm

Validation on extreme event: Var, 2010 (Grid 0.1°, RR24h)


OBS MAX=397mm

MESCAN-RR MAX=265mm

SAFRAN MAX=309mm

MESCAN-Log

MAX=277mm

Validation on extreme event: Var, 2010 (Grid 0.1°, RR24h)


Validation of MESCAN precipitation analysis vs SAFRAN over France

Accumulated daily RR for 1/10/2009 to 31/07/2010

over France [mm]

~50mm

• Bias correction needed for MESCAN-log

Obs (~4200)MESCAN-RRMESCAN-LogSAFRAN


2D Analysis at ~5 km:T2m, Rh2m, RR

SURFEX (V7): Surface Externalized(www.cnrm.meteo.fr/surfex) with a sophisticated snow scheme (Vionet et al. submitted) and the lake model: Flake (Mironov, 2008)

SH, LH, snow depth, snow cover, soil moisture, Ts_lake

Forecast model:SW, LW, Wind, Ps

Hydrological Model

Coupling the 2D surface analysis and a Surface Scheme for Indirect Validation and Hydrological purposes


• MESCAN-RR (physical space) and SAFRAN are of equal quality with regard to Nash criterion.

• SAFRAN is better over the western part of France, i.e. flat terrain!

Map based on Nash scores

Indirect validation of MESCAN precipitation analysis using the MODCOU hydrological model (F. Besson)


Forcing by ALADIN precipitation

• The forcing provided by the MESCAN-RR precipitation analysis is significantly improved in comparison to the one generated by the ALADIN precipitation.

Impact of different types of forcing on the river flow (Oct09-Jun10)

Forcing by MESCAN-RR

Daily river discharge for the Seine river at Paris

Plots provided by F. Besson


Impact of precipitation on the river flow (Oct09-Jun10)

- in June, the different behaviour of the river flow forced by MESCAN-RR is probably due to a lower accumulation of snowfall during the winter throughout the Rhone watershed.

- Compared with SAFRAN, this underestimation is very likely due to the misleading information provided by the non-heated rain gauges in the mountains during the winter season.

Daily river discharge for the Rhone river at Beaucaire

Provided by F. Besson


– Observations

– SAFRAN

– ALADIN-forecast

– MESCAN v0

– MESCAN v1

– MESCAN v2

Validation of snow depth at observation location (M. Lafaysse)

Bellecote Nivose (3000 m)FLAINE (1640m)

• Generally, the underestimation of the snow depth forcing by MESCAN RR is probably due to the misleading information provided by the non-heated rain gauges or to the under catch due to wind.


Issues

Observations:– high level of uncertainty in using precipitation data particularly in winter

(heated/ non-heated rain gauges, ‘Zero’ precip reports when it snows etc)

– rain gauge measurements not corrected for the wind

Background (downscaled HIRLAM fields from 22km to 5.5km):– What guess to use: fc00+30-fc00+06, fc06+24, fc00+18-fc00+06 + fc12+18 - fc12+06?The quality of the background fields is still under investigation.

revised statistics for background and observation errors


Further plans

At ECMWF for the 2007-2010 (2011 ??) period:

– running and monitoring the production of the background files for both the precipitation and screen-level (T2m/RH2m) analyses;

– running and monitoring the production of the reanalysis:• T2m/RH2m every 6 hours (4 analysis per day)• RR24 (one analysis per day)

Validation of re-analyses– monthly mean, RMSE of 6-hourly T2m– computation of some categorical scores for RR24


Thank you for your attention!

AcknowledgementsThe research leading to these results has received funding from the European Union,

Seventh Framework Programme (FP/2007-2013) under grant agreement no 242093.

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EURO4M 4th GA, Norrköping, 17-19 April 2013 Overview of the new MESCAN precipitation analysis...

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