Thunderstorm wind profiles are extracted from LiDAR databases.
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Signals are processed by means of the classical and directional decomposition methods.
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The nose shape of the wind profiles appears during the velocity ramp-up and peak stages.
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The wind direction is observed to be invariant with height during the outflow.
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The maximum values of turbulence intensity occur prior to those of horizontal wind speed.
Abstract
The dynamic complexity and the limited spatiotemporal structure of thunderstorms make the collection of reliable and systematic measurements of this phenomenon, which are definitely needed to evaluate its action on structures, challenging. The Northern Tyrrhenian is a “hot-spot” for the genesis of severe potentially damaging wind phenomena, such as downbursts. In the context of the European projects “Wind and Ports” and “Wind, Ports and Sea”, a large and complex wind monitoring network has been installed just in this area. Here, three LiDAR profilers provide a vertical scanning of the atmosphere up to 250 m above the ground level. From their continuous recordings, a method to extract thunderstorm events is herein proposed, based on an automated procedure involving systematic quantitative controls and specific qualitative judgments. Starting from it, this paper provides a comprehensive investigation and comparison of the main parameters ruling the outflow vertical profiles of a selected subset of thunderstorms. The nose shape of the wind profiles appears mainly during the velocity ramp-up and peak stages. During the downburst, the wind direction is systematically invariant with height. The capability of LiDAR to measure the wind speed turbulence component is also discussed and its properties along the vertical profile are shown.
