Impact of severe weather in air traffic management. Radar analysis for three convective events affecting Italian international airports.

Within the context of SINOPTICA (Satellite-borne and IN-situ Observations to Predict the Initiation of Convection for ATM, 2020-2022) project, the preliminary results of the radar analysis on different convective events affecting Italian airports are presented. Three cases of study have been selected for their relevant impact on the international airports of Milan-Malpensa, Marco Polo-Venice and Bergamo-Orio al Serio. Each one of the three cases has been characterised, identifying the best radar approach to obtain valuable information about weather hazard affecting air traffic management (ATM). This provides helpful information for forecasting and tracking convection around the airports.

The analysis is based on the mosaic radar images provided by the Italian Civil Protection, which included relevant data such as the top of the clouds, vertically integrated liquid (VIL), and VIL density products. Firstly, different zones around each affected airport were selected to monitor the different phases of the event. The proposed early warning system distinguishes four periods: non-storm alert, pre-alert, alert level 1, alert level 2. The proposed domain to be monitored would have a radius of 75 km from the airport.  The storm alert level 2 period would be considered when VIL radar echoes are above 1 mm within an area about 20 km from the airport, considering 1 km² spatial resolution and 5 min. temporal resolution (it is to say, maximum values are computed for each variable each 15 min.). The storm alert level 1 period would start two hours before the alert period, covering an area of 500 km² with a spatial resolution of 3 km² and temporal resolution of 15 min. The pre-alert period would correspond to the period between the first appearance of radar echoes on the Italian radar mosaic until the storm alert level 1 period starts. To monitor this period, the proposed spatial resolution is 5 km² and temporal resolution would be 30 min. for the whole radar mosaic.

This procedure would help to identify and track convective storm structures responsible for ATM difficulties. VIL density variable is considered the most suitable candidate to compare the different episodes since they can occur in different seasons. The application of the proposed methodology to the selected cases has shown good ability to efficiently quantify the severity of the thunderstorms. Additionally, various VIL density thresholds have been tested as severity indicators. Results show that in the three cases, storms developed at certain region past the Alps Mountain range that acts as a natural border north of Italy; then storms moved East and South-East. Maximum VIL density values in the affected region exceed 4 g/m³, however, on some occasions, they exceed 8 g/m³. VIL density showed a weak seasonal dependency with slightly higher values for summer events. A more detailed analysis comparing impacts and VIL density values is currently ongoing as part of the SINOPTICA project.