Space Weather Services for Civil Aviation—Challenges and Solutions

This paper presents a review on the PECASUS service, which provides advisories on enhanced space weather activity for civil aviation. The advisories are tailored according to the Standards and Recommended Practices of the International Civil Aviation Organization (ICAO). Advisories are disseminated in three impact areas: radiation levels at flight altitudes, GNSS-based navigation and positioning, and HF communication. The review, which is based on the experiences of the authors from two years of running pilot ICAO services, describes empirical models behind PECASUS products and lists ground- and space-based sensors, providing inputs for the models and 24/7 manual monitoring activities. As a concrete example of PECASUS performance, its products for a post-storm ionospheric F2-layer depression event are analyzed in more detail. As PECASUS models are particularly tailored to describe F2-layer thinning, they reproduce observations more accurately than the International Reference Ionosphere model (IRI(STORM)), but, on the other hand, it is recognized that the service performance is much affected by the coverage of its input data. Therefore, more efforts will be directed toward systematic measuring of the availability, timeliness and quality of the data provision in the next steps of the service development.

Analysis of the Rain Phenomenon at Fine Spatial Scale

Since 1984, the Urban Community of Lyon (CO.UR.LY.) has been setting up a network of rain gauges with a density of about 1 station per 20 km. This network is integrated in the French system of Experimental and Representative Basins. To get a better knowledge of the spatial distribution of the rainfall, a study was based on the establishment of I.D.F. relationships for each of these measuring stations. Since the study period extended only over 5 to 6 years, only return periods of 1 and 2 years were taken into account. The results show a high statistical heterogeneity of rain gauging data. These discrepancies may be due to sampling errors, to systematic measuring errors, to an excessively short observation period or to real spatial differences in rainfall. Each one of the causes of error was studied, and these 4 points all seem to play a more or less significant role in the differences observed between the stations. Thus there may be a spatial heterogeneity of the rainfall over the area of the CO.UR.LY. If confirmed, this observation may have very important consequences and may question risk assessment in urban hydrology.