Capabilities of Detecting Aerosol Layers with Coherent Doppler LIDARs for Enhancing Forecasting and Warning Systems

The accurate localization and the characterization of aerosol and cloud layers is crucial for climate studies (aerosol indirect effect), meteorology (Planetary Boundary Layer PBL height), site monitoring (industrial emissions, mining,…) and to better mitigate natural hazards (thunderstorms, volcanic eruptions). For this latest hazard, an international advisory network composed of nine VAAC – Volcanic Ash Advisory Centers has been built in order to keep air traffic controllers, airlines informed about the dangerousness of ash layers. These layers given their altitues but also their mass concentrations can affect in—depth an area of thousand kilometers and block like in 2011 the majority of the air traffic above the Atlantic Ocean. Strong progresses have been performed in the modelisation of ash layers through the resolution of numerical weather forecast models. Still, observations of localization, altitudes and density of ash layers are mandatory to provide to models accurate initial conditions that play a major role to better forecast the dispersion of ash layers and thus better mitigate them. Coherent LIDARS are nowadays well-recognized for their accurate measurements of wind speed profiles based on the Doppler shift effect on atmospheric particles and clouds. The signal reflectivity (CNR for Carrier-to-Noise Ratio) profiles can also be retrieved from the signal strength of the detected Doppler peak. Based on the CNR and wind information, specific aerosol and cloud functionalities were developed on WINDCUBE long range scanning Doppler lidar at 1.54 microns. They consist in 5 aerosol/cloud features: 1) Aerosol/cloud detection 2) Aerosol/cloud discrimination 3) Attenuated backscatter coefficient 4) Planetary Boundary Layers height detection 5) Speciation of atmospheric structures The general flowchart of the aerosol/cloud measurements is given on figure 1. The study will present the applications of these features to several kinds of aerosol / cloud layers in order to demonstrate their capabilities to detect the bottom and top of these layers. The study will also demonstrate on a practical case that given the local aerosol environment and with the combination of other sensors the possibility to classify the layers. The figure 2 shows an example of one day of measurements of cirrus layers in Iceland with a Coherent Doppler LIDAR. The study will highlight the capabilities of future networks of Coherent Doppler LIDARs for better mitigating aerosol hazards by the combination of wind and aerosol measurements and with all the other observations. Figure 1: General flowchart of the aerosol/cloud measurements on WINDCUBE LIDARs Figure 2: Cirrus clouds detected in Iceland by a Scanning Coherent Doppler LIDAR