Using Scanning Doppler Wind Lidars to Understand and Forecast Extreme Wind Flows and Wind Shears over Airports

At airports, common wind sensors are cup anemometers and wind vanes or sonic anemometers to provide standard wind information to observers, forecasters, air traffic controllers, and pilots. The information consists in the wind speed and direction at a 10m height usually located at three points along the runways and averaged over 10 minutes to one hour. These measurements are not well representative of the wind aloft that directly affects the aircrafts during the landing and takeoff phases. The wind can vary a lot between the ground and the boundary layer especially in case of convective weather, thunderstorm and when airports are located close to the shore and to complex orography (mountains, valleys). In case of extreme wind conditions, like wind shears, dedicated ground-based equipment like Doppler Radar and/or Doppler Lidar shall be used to understand, alert and forecast wind shears as mentioned by ICAO and WMO standards. If Doppler Radars started to be widely used at airports in late 90’s, Doppler Lidars remain confidential with less than 20 airports equipped permanently worldwide.

In this study, the use of Doppler LIDAR for better understanding wind flows and for improving their mitigation by the end users at Dubrovnik airports will be described. At Dubrovnik airport, which handles more than 2 Million passengers per year, extreme crosswind conditions due to Bora wind occur regularly with more than 10 to 20 events. Such event can last several hours and crosswinds can reach 70 kts (35m/s). The MET Division of Croatia Control, which is national air navigation service provider, is therefore preparing a project called Bora Dubrovnik to better characterize the Bora wind and to improve forecasts at Dubrovnik airport. As a first step of this project, a measurement campaign has been achieved in winter 2017 and 2018 with a long range scanning Doppler Lidars a WINDCUBE400S. 14 Bora events occurred with crosswinds up to 60 kts. They have been measured in using a sequence of azimuthal scans at different elevations, of vertical scans perpendicular to the mountains, a profiling mode and a vertical line of sight to characterize the vertical structure of the wind. The presentation will show the measurements performed by the Lidar showing the high complexity of the wind flows in 3D due to the proximity with mountains and the sea. These results allow to better understand Bora events and should be used to support the forecasters to anticipate such events.