# OPERA the Radar Project
## 3 Results
### Data for Users  
OPERA produces three different composites [15], which are updated every quarter of an hour (on the hour, and at 15, 30, and 45 min past the hour), issued approximately 15 min after the start of data acquisition. The OPERA composites, covering large parts of Europe with a spatial resolution of 2 km \(\times\) 2 km (Lambert Azimuthal Equal Area projection), are distributed in the ODIM HDF5 format. The maximum reflectivity product is also shown as an animation on the EUMETNET website.  
Odyssey was developed with four user groups in mind: Forecasting and nowcasting, numerical weather prediction (assimilation and verification), civil and military aviation, and hydrology and water management.  
For the weather forecasters of national weather services, the products from their national radar network are always the priority. A radar is a mesoscale tool, and, while its strength is superior resolution in time and space, it is most suitable for the observation and analysis of short-lived, quickly-developing mesoscale weather phenomena, such as thunderstorms. For such an analysis, the unavoidable delay of creating a continent-wide composite is too long. However, the composites can be useful for synoptic scale analysis; see Figure 8.  
For nowcasting, several systems are in use in Europe. [16] showed that assimilation in rapid-update cycle models outperforms observations-based extrapolation after 2 h. However, there are user groups which are most interested in the first 2 h, especially in the aviation community.  
For the assimilation of radar data in numerical weather prediction models, several approaches are used around Europe. Most of the limited area models use radar data in their original radial coordinates in order to take full benefit of the three-dimensional structure of the precipitating system. Global models have used two-dimensional composites. In the European Centre of Medium-Range Weather forecasting (ECMWF), [PERSON] et al. [17] have used 6-hourly precipitation sums in 4 DVAR. They have implemented the use of NCEP Stage IV data from the contiguous United States operationally. This data is a combination of radar and rain gauges. A similar product for Europe is not available, and the quality of OPERA composites alone have not yet been sufficient for such use. The COSMO consortium has tried  
Figure 8: OPERA composite at 12 UTC on 12 November 2018 (**left**) and the corresponding weather map (**right**, courtesy of the Finnish Meteorological Institute).  
to use the rainrate composite for Latent Heat Nudging [18] and experimented with the assimilation of 3-dimensional radar reflectivities with an ensemble Kalman filter [19]. The HARMONIE consortium has used an indirect 3 DVAR approach for single-site radar data [20]. Meteo France has assimilated radars in AROME, combining 1-dimensional and 3-dimensional variational assimilation [21; 22], where 30 French radars have been operationally used (Meteo France in-house-product) and 62 radars from OPERA data are planned to be introduced. The LACE consortium has used over 150 radars.  
The OPERA composites are also available for commercial use under the rules of ECOMET. This is not a cheap option--the price is the same as it would be to buy all the national data sets used as input--but the ease of obtaining the composite from one place has been indicated as satisfying by a few customers.  
[PERSON] et al. [23] have used the OPERA composites to assess flash flood hazard induced by heavy rainfalls in European scales, together with the European Flood Awareness System (EFAS). So far, the quantitative accuracy of the OPERA composites alone has not been high enough for their needs, but they have combined the point accuracy of gauge data and the superior resolution of the radar data.  
The data collected for weather service purposes has also been used by animal migration researchers [11]. It has been shown that the OPERA network can be used effectively to map continental-scale bird migration events [24].