Evaluation of convective parameters derived from pressure level and native ERA5 data and different resolution WRF climate simulations over Central Europe

The mean climatological distribution of convective environmental parameters from the ERA5 reanalysis and WRF regional climate simulations is evaluated using radiosonde observations. The investigation area covers parts of Central and Eastern Europe. Severe weather proxies are calculated from daily 1200 UTC sounding measurements and collocated ERA5 and WRF pseudo-profiles in the 1985-2010 period. The pressure level and the native ERA5 reanalysis, and two WRF runs with grid spacings of 50 and 10 km are verified. ERA5 represents convective parameters remarkably well with correlation coefficients higher than 0.9 for multiple variables and mean errors close to zero for precipitable water and mid-tropospheric lapse rate. Monthly mean mixed-layer CAPE biases are reduced in the full hybrid-sigma ERA5 dataset by 20-30 J/kg compared to its pressure level version. The WRF model can reproduce the annual cycle of thunderstorm predictors but with considerably lower correlations and higher errors than ERA5. Surface elevation differences between the stations and the corresponding grid points in the 50-km WRF run lead to biases and false error compensations in the convective indices. The 10-km grid spacing is sufficient to avoid such discrepancies. The evaluation of convection-related parameters contributes to a better understanding of regional climate model behavior. For example, a strong suppression of convective activity might explain precipitation underestimation in summer. A decreasing correlation of WRF-derived wind shear away from the western domain boundaries indicates a deterioration of the large-scale circulation as the constraining effect of the driving reanalysis weakens

An analysis of environmental influences on morphologies and tornadogenesis within quasi-linear convective systems

A Thesis presented to the Faculty of the Graduate School at the University of Missouri In Partial Fulfillment of the Requirements for the Degree Master of Science.Thesis supervisor: Dr. Patrick Market.Includes bibliographical references (pages 144-148).The entire text is included in the research.pdf file; the abstract appears in the short.pdf file; a non-technical general description appears in the public.pdf file.Mesoscale convective systems (MCSs) often take the form of quasi-linear convective systems (QLCSs) within the mid-latitudes of the United States. QLCSs have a quasi-linear convective precipitation structure either followed or led by stratiform precipitation, and often produce strong winds, hail, and tornadoes. Quasi-linear convective systems have been the subject of research for more than a half-century. Early work was performed to classify different morphologies and structures, whereas more recent work has been focused heavily on the dynamics associated with QLCS structures, and investigating forecasting problems that QLCSs pose, in particular the 3-12 hour time period. Thirty-two cases were selected for this investigation, comprised of 8 "tornado" events, 8 "hybrid" events, 8 "wind" events, and 8 "marginal" events. These thirty-two events were selected based on a general geographic location in the central United States. The purpose of this investigation was to better understand the atmospheric conditions resulting in the variety of observed event "types," to improve event predictability, and therefore forecasting, especially with regards to tornadic QLCS cases

The effects of climate change on hailstorms

Hailstorms are dangerous and costly phenomena that are expected to change in response to a warming climate. In this Review, we summarize current knowledge of climate change effects on hailstorms. As a result of anthropogenic warming, it is generally anticipated that low-level moisture and convective instability will increase, raising hailstorm likelihood and enabling the formation of larger hailstones; the melting height will rise, enhancing hail melt and increasing the average size of surviving hailstones; and vertical wind shear will decrease overall, with limited influence on the overall hailstorm activity, owing to a predominance of other factors. Given geographic differences and offsetting interactions in these projected environmental changes, there is spatial heterogeneity in hailstorm responses. Observations and modelling lead to the general expectation that hailstorm frequency will increase in Australia and Europe, but decrease in East Asia and North America, while hail severity will increase in most regions. However, these projected changes show marked spatial and temporal variability. Owing to a dearth of long-term observations, as well as incomplete process understanding and limited convection-permitting modelling studies, current and future climate change effects on hailstorms remain highly uncertain. Future studies should focus on detailed processes and account for non-stationarities in proxy relationships

Study of thunderstorm wind outflows and proposition of mean wind profiles

The impact of thunderstorm (TS) winds on the built environment has been extensively reported in recent years showing that current wind standards do not properly represent all types of extreme wind events. This document discusses the characteristics of TS winds in depth, focusing on existing vertical full-scale measurements, modeling approaches and their occurrence worldwide. Firstly, the development of the downburst research worldwide is reviewed and, due to Brazil’s vulnerability to this type of event, reported cases in national news and scientific literature are investigated. This study showed that most of Brazil is vulnerable to downbursts, having the Amazon region the larger amount of occurrences and the Southern states the most susceptible for extreme winds generated by TS outflows or simply downbursts. The Southeastern states are also prone to extreme downburst occurrence. Northeast and central north states present downburst events with lower intensity, which are caused mostly by isolated thunderstorms. Modeling techniques are commonly adopted to study the effects of these events on the built environment. A systematic review of 122 publications on downburst modeling identified four main clusters of alternative approaches to simulating these events: analytical modeling, experimental laboratory simulations, computer fluid dynamics (CFD) and data-driven models. An analytical method is proposed to describe the mean wind speed profiles at their maximum stage based on full-scale measurements considering the storm organization, time averaging and terrain categories. The proposed fitted curve profile functions are valid only for the original measured average intervals. Results showed that most of the proposed fitted curve profile functions had a "nose-like" shape, highly defined by the terrain roughness, with peak velocities typically observed at lower levels in TS winds – between 50 and 250 meters – allowing the profile fitting by a third‐degree polynomial function, instead of the traditional power law function as adopted for synoptic winds. Seventeen profiles originated from full-scale measurements were selected and carefully analyzed. However, in order to propose a practical application that can be coupled with a general extreme wind climatology, only seven fitted curve profile functions were taken for further analysis. Six out of seven fitted curve profiles demonstrated good adherence to Ponte Junior (2005) model and the TS wind profile proposed by the international code ISO 4354. These proposed profiles were further analyzed along with the typical NBR-6123 boundary layer velocity profiles. For Terrain Category II, the fitted curve profile function based on the maximum profile of Gunter and Schroeder (2015) "PEP Event" for 1-min time averaging presented the most conservative case at all elevations. For Terrain Category III, results were mixed, but the fitted curve profile function based on the maximum profile measured by Lombardo et al. (2014) "03-Aug-2010 Event" presented maximum values at lower levels for 3-s time averaging and is therefore considered the maximum profile for this terrain category. Finally, for Category IV, it is suggested to use as reference the fitted curve profile based on the maximum profile of Zhang *et al.* (2019) "15:01 Meas.", since this is a more realistic TS wind profile dataset for 30-s time averaging due to the particular effects of the terrain on that specific measurement.O impacto dos ventos gerados por tempestades (TS) no ambiente construído tem sido amplamente relatado nos últimos anos, revelando que as normas de vento atuais não representam adequadamente todos os tipos de ventos extremos. Neste documento se discute em profundidade as características dos ventos TS, com foco em medições verticais de escala real, abordagens de modelagem e sua ocorrência no mundo. Primeiramente, é revisado o desenvolvimento mundial das pesquisas sobre downbursts e, devido à vulnerabilidade do Brasil a esse tipo de evento, é feita uma investigação de casos relatados em notícias e literatura científica. Este estudo mostrou que a maior parte do Brasil é extremamente vulnerável a downbursts, tendo a região Amazônica o maior número de ocorrências e os estados da região Sul os mais suscetíveis a ventos extremos gerados por tormentas TS ou simplesmente downbursts. Os estados do Sudeste são também propensos à ocorrência de downbursts severos. Os estados do Nordeste e Centro-Norte apresentam eventos de menor intensidade, causados principalmente por tempestades isoladas. Técnicas de modelagem são comumente adotadas para estudar os efeitos desses eventos no ambiente construído. Uma revisão sistemática de 122 publicações sobre modelagem de downbursts identificou quatro grupos principais de abordagens para simular esses eventos: modelos analíticos, simulações experimentais em laboratório, dinâmica de fluidos computacional (CFD) e modelos baseados em dados. Um método analítico é proposto para descrever os perfis médios de velocidade de vento em seu estágio máximo com base em medições em escala real, considerando-se organização da tempestade, intervalo de tempo e categorias de terreno. As funções de perfil de curva ajustada propostas são válidas apenas para os intervalos de tempo medidos originais. Os resultados mostraram que a maioria das funções propostas de perfis de curvas ajustadas tinham forma de "nariz", fortemente definida pela rugosidade do terreno e com velocidades de pico tipicamente observadas em níveis mais baixos em ventos TS – entre 50 e 250 metros – permitindo o ajuste do perfil por uma função polinomial de terceiro grau, em vez da função de potência tradicional, como utilizado para ventos sinóticos. Dezessete perfis oriundos de medições reais foram selecionados e analisados minuciosamente. Porém, para possibilitar a proposição de uma aplicação prática capaz de incorporar resultados de climatologias gerais de ventos extremos TS, somente sete curvas ajustadas foram levadas adiante para análise. Seis dos sete perfis ajustados demonstraram boa aderência ao modelo de Ponte Junior (2005) e ao perfil de vento TS proposto pelo código internacional ISO 4354. Esses perfis propostos foram posteriormente analisados juntamente com os perfis de velocidade de camada limite típicos da NBR-6123. Para a categoria de terreno II, a função do perfil ajustada com base nos valores máximos obtidos por Gunter e Schroeder (2015) no "PEP Event" para intervalo de tempo de 1-min apresentou o caso mais conservador em todas as elevações. Para a categoria de terreno III, os resultados foram mistos, mas considerou-se como evento extremo o perfil ajustado baseado no evento extremo de “03-ago-2010" de Lombardo et al. (2014) para o intervalo de média de tempo de 3-s. Finalmente, para a Categoria IV, sugere-se utilizar como referência o perfil de curva ajustado ao evento extremo registrado por Zhang et al. (2019) "15:01 Meas.", uma vez que o perfil de vento TS resultante é mais realista para média de tempo de 30-s devido aos efeitos do terreno específicos deste caso

NASA/MSFC FY-85 Atmospheric Processes Research Review

The two main areas of focus for the research program are global scale processes and mesoscale processes. Geophysical fluid processes, satellite doppler lidar, satellite data analysis, atmospheric electricity, doppler lidar wind research, and mesoscale modeling are among the topics covered

Severe Storms Branch research report (April 1984 April 1985)

The Mesoscale Atmospheric Processes Research Program is a program of integrated studies which are to achieve an improved understanding of the basic behavior of the atmosphere through the use of remotely sensed data and space technology. The program consist of four elements: (1) special observations and analysis of mesoscale systems; (20 the development of quanitative algorithms to use remotely sensed observations; (3) the development of new observing systems; and (4) numerical modeling. The Severe Storms Branch objectives are the improvement of the understanding, diagnosis, and prediction of a wide range of atmospheric storms, which includes severe thunderstorms, tornadoes, flash floods, tropical cyclones, and winter snowstorms. The research often shed light upon various aspects of local weather, such as fog, sea breezes, air pollution, showers, and other products of nonsevere cumulus cloud clusters. The part of the program devoted to boundary layer processes, gust front interactions, and soil moisture detection from satellites gives insights into storm growth and behavior

NASA/MSFC FY-82 atmospheric processes research review

The NASA/MSFC FY-82 Atmospheric Processes Research Program was reviewed. The review covered research tasks in the areas of upper atmosphere, global weather, and severe storms and local weather. Also included was research on aviation safety environmental hazards. The research project summaries, in narrative outline form, supplied by the individual investigators together with the agenda and other information about the review are presented

Numerical simulation of intense multi-scale vortices generated by supercell thunderstorms

December 19, 1997.Bibliography: pages 276-287.Sponsored by National Science Foundation ATM-9306754.Sponsored by National Science Foundation ATM-9420045

Atmospheric Hazards

Natural and environmental hazards research comprises a diverse set of subjects and methodologies and this book is no exception - offering the reader only a small glimpse into the physical and social processes that threaten human interests. Atmospheric Hazards-Case Studies in Modeling, Communication, and Societal Impacts explores atmospheric-based hazards through focused investigations ranging from a local to global perspective. Within this short compendium, the major scales of atmospheric motion are well represented with topics on microscale turbulent transport of pollutants, mesoscale events stemming from thunderstorm complexes, and synoptic scale extreme precipitation episodes. Chapters include discussions on modeling aspects for investigating hazards (pollution, regional climate models) and the forecasting and structure of high wind events (derechos), whereas others delve into hazard communication, preparedness, and social vulnerability issues (tornadoes, hurricanes, and lightning). Although the chapters are quite disparate upon first inspection, the topics are united through their interweaving of both the physical and societal mechanisms that create the atmospheric hazard and eventual disaster

Data Assimilation in high resolution Numerical Weather Prediction models to improve forecast skill of extreme hydrometeorological events.

The complex orography typical of the Mediterranean area supports the formation, mainly during the fall season, of the so-called back-building Mesoscale Convective Systems (MCS) producing torrential rainfall often resulting into flash floods. These events are hardly predictable from a hydrometeorological standpoint and may cause significant amount of fatalities and socio-economic damages. Liguria region is characterized by small catchments with very short hydrological response time, and it has been proven to be very exposed to back-building MCSs occurrence. Indeed this region between 2011 and 2014 has been hit by three intense back-building MCSs causing a total death toll of 20 people and several hundred million of euros of damages. Building on the existing relationship between significant lightning activity and deep convection and precipitation, the first part of this work assesses the performance of the Lightning Potential Index, as a measure of the potential for charge generation and separation that leads to lightning occurrence in clouds, for the back-building Mesoscale Convective System which hit Genoa city (Italy) in 2014. An ensemble of Weather Research and Forecasting simulations at cloud-permitting grid spacing (1 km) with different microphysical parameterizations is performed and compared to the available observational radar and lightning data. The results allow gaining a deeper understanding of the role of lightning phenomena in the predictability of back-building Mesoscale Convective Systems often producing flash flood over western Mediterranean complex topography areas. Despite these positive and promising outcomes for the understanding highly-impacting MCS, the main forecasting issue, namely the uncertainty in the correct reproduction of the convective field (location, timing, and intensity) for this kind of events still remains open. Thus, the second part of the work assesses the predictive capability, for a set of back-building Liguria MCS episodes (including Genoa 2014), of a hydro-meteorological forecasting chain composed by a km-scale cloud resolving WRF model, including a 6 hour cycling 3DVAR assimilation of radar reflectivity and conventional ground sensors data, by the Rainfall Filtered Autoregressive Model (RainFARM) and the fully distributed hydrological model Continuum. A rich portfolio of WRF 3DVAR direct and indirect reflectivity operators, has been explored to drive the meteorological component of the proposed forecasting chain. The results confirm the importance of rapidly refreshing and data intensive 3DVAR for improving first quantitative precipitation forecast, and, subsequently flash-floods occurrence prediction in case of back-building MCSs events. The third part of this work devoted the improvement of severe hydrometeorological events prediction has been undertaken in the framework of the European Space Agency (ESA) STEAM (SaTellite Earth observation for Atmospheric Modelling) project aiming at investigating, new areas of synergy between high-resolution numerical atmosphere models and data from spaceborne remote sensing sensors, with focus on Copernicus Sentinels 1, 2 and 3 satellites and Global Positioning System stations. In this context, the Copernicus Sentinel satellites represent an important source of data, because they provide a set of high-resolution observations of physical variables (e.g. soil moisture, land/sea surface temperature, wind speed, columnar water vapor) to be used in NWP models runs operated at cloud resolving grid spacing . For this project two different use cases are analyzed: the Livorno flash flood of 9 Sept 2017, with a death tool of 9 people, and the Silvi Marina flood of 15 November 2017. Overall the results show an improvement of the forecast accuracy by assimilating the Sentinel-1 derived wind and soil moisture products as well as the Zenith Total Delay assimilation both from GPS stations and SAR Interferometry technique applied to Sentinel-1 data