Application of metaheuristic optimization algorithms to evaluate the geometric and kinematic parameters of downbursts

Strong localized downbursts generated in thunderstorms can produce surface winds very dangerous for civil structures and infrastructures. Modelling and simulating such severe wind systems is therefore extremely important for structural safety and design wind speed evaluation. This paper deals with the downburst wind field simulation by means of an optimization algorithm that uses a downburst analytical model, previously developed by the authors, and two metaheuristic algorithms, namely the Differential Evolution (DE) and the Teaching-Learning-Based Optimization (TLBO), for the downburst kinematic and geometrical parameters evaluation. The optimization problem minimizes the relative error between recorded and simulated wind speed and direction time histories. A comparison is made between the performance of two algorithms for ten thunderstorm events measured in north-western Italy between October 2011 and October 2015. Both algorithms provide solutions which are coherent with the downburst parameters values present in literature. TLBO outperforms DE since it has a faster convergence rate to the optimal solution

An advanced analytical model for simulating thunderstorm outflows

A diverging wind system known as \u201cdownburst\u201d is defined as a strong downdraft which induces an outburst of damaging winds on or near the ground. Severe wind damage in many parts of the world are often due to thunderstorm outflows and they therefore have a focal role in structural safety and design wind speed evaluation. Despite this, there is not yet a shared model for thunderstorm outflows and their action on structures. In this paper, an analytical model that simulates the horizontal mean wind velocity originated from a travelling downburst is proposed. The horizontal wind velocity is expressed as the vector summation of the stationary radial speed generated by an impinging jet, the downdraft translating velocity and the background wind velocity, where the thunderstorm is immersed. All parameters employed in the model are related to meteorological variables that are susceptible of statistical assessment. A parametric study is also developed and coupled with the analytical model in order to investigate several observed downburst events. The different parameters of the downburst such as downdraft diameter, touchdown position, translating downdraft speed and direction, intensity and decay period are estimated through the parametric study in order to reconstruct the space-time evolution of this event

Vertical profile characteristics of thunderstorm outflows

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 \u201chot-spot\u201d for the genesis of severe potentially damaging wind phenomena, such as downbursts. In the context of the European projects \u201cWind and Ports\u201d and \u201cWind, Ports and Sea\u201d, 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 \u200bm 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 show

Monitoring, cataloguing, and weather scenarios of thunderstorm outflows in the northern Mediterranean

High sampling rate (10Hz) anemometric measurements of the "Wind, Ports, and Sea" monitoring network in the northern Tyrrhenian Sea have been analysed to extract the thunderstorm-related signals and catalogue them into three families according to the different time-scale of each event, subdivided among 10min, 1, and 10h events. Their characteristics in terms of direction of motion and seasonality/daily occurrence have been analysed: The results showed that most of the selected events come from the sea and occur from 12:00 to 00:00UTC during the winter season. In terms of peak wind speed, the strongest events all belonged to the 10min family, but no systematic correlation was found between event duration and peaks. Three events, each one representative of the corresponding class of duration, have been analysed from the meteorological point of view, in order to investigate their physical nature. According to this analysis, which was mainly based on satellite images, meteorological fields obtained from GFS analyses related to convection in the atmosphere, and lightning activity, the thunderstorm-related nature of the 10min and 1h events was confirmed. The 10h event turned out to be a synoptic event, related to extra-tropical cyclone activity