1 st FORALPS CONFERENCE

Transcription

1 Contributions for a wise management of water resources from meteorology and climatology TOWARDS A COMMON REPORTING SYSTEM FOR METEOROLOGICAL FORECAST VERIFICATION ACTIVITIES IN THE ALPINE SPACE: A FIRST STEP IN THE FORALPS FRAMEWORK S. Mariani (1, 2), M. Casaioli (1), I. Gallai (3), F. Stel (3), M. Ungersböck (4), G. Gregorič (5), M. Staudiger (4) (1) APAT, Rome, Italy (2) Dept. of Mathematics, University of Ferrara, Ferrara, Italy (3) OSMER, Visco (Udine), Italy (4) ZAMG-S, Salzburg, Austria (5) EARS, Ljubljana, Slovenia 1

2 THE WORK AIM (1) In the framework of the WP7 Weather and Water Resource Availability Forecasting, it was decided to conduct an annual survey on PPs forecast and verification activities. From the 1 st survey, a report about different verification methodologies employed by PPs, both in an operational and in a research activity frame, was produced. This report includes: eyeball verification; graphical summary techniques; parametric and non-parametric skill scores; spatial verification techniques, etc. Some of the PPs run limited area models at the own centres: the ALADIN model operational at ZAMG and EARS; the Quadrics BOLAM is operative at APAT; the WRF model is run, in a research configuration, at OSMER. 2

3 THE WORK AIM (2) In order to share knowledge about verification techniques, and compare and evaluate the suitability of the different methods in describing the model forecast quality, a common verification activity on selected case studies has been planned. At the moment, four selected case studies represent significant rainfall events, mainly occurred over the Italian region Friuli- Venezia Giulia (north-eastern Italy), were selected. An intercomparison study on two of these events is then started. Forecast fields modelled by ALADIN, WRF, QBOLAM and the global model of ECMWF have been verified. Rain gauge observations, ECMWF analysis, and the METEOSAT-7 water vapor channel imagery have been considered for the study. Different verification techniques, among the ones documented in the report, have been used. Preliminary results are presented here. 3

4 REPORT ON VERIFICATION TECHNIQUES EMPLOYED BY PPS (V.1) Verification techniques have been classified and described, with summary resume of their use by the different PPs. The verification activity of each PP is synthesised in a suitable, common table form. 4

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7 THE EVENT ON NOVEMBER

8 SUBJECTIVE VERIFICATION: EVOLUTION OF THE SYNOPTIC DISTURBANCE GLOBAL MODEL FORECAST QUALITY CHECK ECMWF forecasts of the same instant from different runs are compared to the analysis. Differences can be seen as a measure of forecast error, but also as a measure of the event predictability. Marked differences seems to be linked to the most complex phenomenology, i.e. the interaction with the Northern Africa orography. This may arise in significant LAM error, e.g. shift. 17 NOV 12 UTC - ECMWF analysis ECMWF +24h forecast from 16 NOV 12 UTC ECMWF +48h forecast from 15 NOV 12 UTC 8

9 SUBJECTIVE VERIFICATION: EVOLUTION OF THE SYNOPTIC DISTURBANCE 18 NOV 00 UTC - ECMWF analysis ECMWF +12h forecast from 17 NOV 12 UTC ECMWF +36h forecast from 16 NOV 12 UTC ECMWF +60h forecast from 15 NOV 12 UTC 9

10 SUBJECTIVE VERIFICATION: EVOLUTION OF THE SYNOPTIC DISTURBANCE 19 NOV 00 UTC - ECMWF analysis ECMWF +12h forecast from 18 NOV 12 UTC ECMWF +36h forecast from 17 NOV 12 UTC ECMWF +60h forecast from 16 NOV 12 UTC 10

11 SUBJECTIVE VERIFICATION: SPACE-TIME SHIFT IN RAINFALL PATTERN WRF total precipitation 06 UTC 17 NOV WRF total precipitation 12 UTC 17 NOV ALADIN total precipitation 12 UTC 17 NOV ALADIN total precipitation 18 UTC 17 NOV Comparison of different models rainfall forecast pattern can evidence some shifting. One can try to link these findings with the large-scale analysis displayed previously. The example shown here is interesting, since evidences a space-time shifting. On 17 Nov, during the morning, both WRF and ALADIN show a precipitation plume which starts on the Liguria Apennine and propagates to north-east. In the ALADIN forecast, rain starts 6h later than in the WRF one, and is shifted about 100 km towards south-east (perpendicular to the propagation direction). Note that the space and time scales of the shift are comparable: if U ~ 10 m/s, L ~ 100 km, T ~ L/U = s ~ 6h. Verification against observed rainfall should be performed. 11

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13 SPATIAL DISTRIBUTION OF RAIN GAUGES AVAILABLE FOR THE 2002 EVENT Rain gauge observation from EARS, OSMER, ZAMG and the former Italian National Hydrographic and Marigraphic Service (SIMN), but only over the Alpine regions, were initially considered for the study. Starting from this analysis, rain gauge observations over Liguria and surrounding areas seem to be important to understand the event evolution check availability. Observations accumulated every 3h should be also useful for the forecast 13 analysis, in particular for assessing the forecasts misplacements.

14 SUB-SYNOPTIC VERIFICATION: METEOSAT-7 WATER VAPOR CHANNEL A powerful tool for model verification on sub-synoptic scale is provided by the METEOSAT-7 water vapor channel imagery. From model output, a comparable field (in cloud-free zones) can be calculated: the temperature on the specific humidity isosurface at 75 mg/kg. It is possible to verify the predicted evolution of the cyclone through its structural elements (for instance, high potential vorticity bands, visible as dark stripes). This is particularly useful in order to verify mesoscale details, especially when they have an impact on the evolution of the disturbance. In particular, one can try to find the origin of shifting error and to link it to the forecast misplacement of determined physical processing, occurring earlier in the forecast. 14

15 SUB-SYNOPTIC VERIFICATION: METEOSAT-7 WATER VAPOR CHANNEL 00 UTC 18 Nov QBOLAM forecast +12h 00 UTC 19 Nov QBOLAM forecast +12h 00 UTC 18 Nov METEOSAT 7 WV channel 00 UTC 19 Nov METEOSAT 7 WV channel 15

16 THE EVENT ON 9 SEPTEMBER

17 Standard Verification Methods for dichotomous (yes/no) forecasts vs Scientific or diagnostic verification methods for spatial forecasts Contiguous Rain Area analysis (CRA; Ebert and McBride 2000) is an object-oriented technique based on a pattern-matching of two contiguous areas, observed and forecast, delimited by a chosen isohyet. From E. Example Ebert website of contiguous areas to ( be compared VOLTAIRE case study over Cyprus. 17

18 RAIN GAUGE OBSERVATIONS Rain gauge observation from EARS, OSMER, ZAMG and Italian regional Services of the north-eastern Italy (former Veneto compartment of SIMN), were initially considered for the study. Rain gauge observations over Lombardia region should be also useful check availability at ARPA Lombardia. Observations accumulated every 3h should be also useful for the forecast 18 analysis.

19 SKILL SCORES OVER A COMMON 0.1 VERIFICATION DOMAIN 19

20 SKILL SCORES OVER A COMMON 0.1 VERIFICATION DOMAIN 20

21 VERIFICATION DOMAINS 0.1 DOMAIN 0.5 DOMAIN 21

22 CONCLUSIONS In the frame of a common forecast verification activities over the Alpine Space, two events, which mainly occurred over the north-eastern part of Italy, have been firstly investigated. Forecast fields from three LAMs (ALADIN-Slovenia, QBOLAM, and WFR) and from the ECMWF model have been studied. Rain gauge data from Austria, Italy and Slovenia, ECMWF analysis, METEOSAT-7 WV channel imagery and blitze have been considered for the verification. Several verification techniques have been considered (from subj. to obj., from standard to scientific/diagnostic). Some evidences of forecast misplacements have been found, further investigations are needed by including in the observational analysis also rain gauges over Liguria (2002 event) and Lombardia (2005 event). Standard and diagnostic verifications will be performed considering data (for. and obs.) accumulated at 3, 6 and 12 h. 22

23 That s s all! Thank you for your attention. 23