Identification, Representation, and Analysis of Convective Storms

Large amount of time series of spatial snapshot data have been collected or generated for the monitoring and modeling of environmental systems. Those data provide an opportunity to study the movement and dynamics of natural phenomena. While the snapshot organization is conceptually simple and straightforward, it does not directly capture or represent the dynamic characteristics of the phenomena. This study presents computational methods to identify dynamic events from time series of spatial snapshots. Events are represented as directed spatiotemporal graphs to characterize their initiation, development, movement, and cessation. Graph-based algorithms are then used to analyze the dynamics of the events. The method is demonstrated using the time series radar reflectivity images during one of the deadliest storm outbreaks that impacted 15 states of southeastern U.S. between April 23 and 29, 2011. As shown in this case study, convective storm events identified using our methods are consistent with previous studies and our analysis indicates that the left split/merger occurs more than right split/merger in those convective storm events, which confirms theory, numerical simulations, and other observed case studies. This study also examines the spatial and temporal characteristics of thunderstorm life cycles in central United States mainly covering Kansas, Oklahoma, and northern Texas during the warm seasons from 2010 to 2014. Radar reflectivity and cloud-to-ground lightning data were used to identify thunderstorms. The thunderstorms were stored in a GIS database with a number of additional thunderstorm attributes. The spatial and temporal characteristics of thunderstorm occurrence, duration, initiation time, termination time, movement speed, and direction were analyzed. Results revealed that thunderstorms were most frequent in the eastern part of the study area, especially at the borders among Kansas, Missouri, Oklahoma, and Arkansas. We also linked thunderstorm features to land cover types and compared thunderstorm characteristics between urban and surrounding rural areas. Our results indicated that thunderstorms favor forests and urban areas. This research demonstrates that advanced GIS representations and analyses for spatiotemporal events provide insights in thunderstorm climatology study

Examining the impacts of convective environments on storms using observations and numerical models

2022 Summer.Includes bibliographical references.Convective clouds are significant contributors to both weather and climate. While the basic environments supporting convective clouds are broadly known, there is currently no unifying theory on how joint variations in different environmental properties impact convective cloud properties. The overaching goal of this research is to assess the response of convective clouds to changes in the dynamic, thermodynamic and aerosol properties of the local environment. To achieve our goal, two tools for examining convective cloud properties and their environments are first described, developed and enhanced. This is followed by an examination of the response of convective clouds to changes in the dynamic, thermodynamic and aerosol properties using these enhanced tools. In the first study comprising this dissertation, we assess the performance of small temperature, pressure, and humidity sensors onboard drones used to sample convective environments and convective cloud outflows by comparing them to measurements made from a tethersonde platform suspended at the same height. Using 82 total drone flights, including nine at night, the following determinations about sensor accuracy are made. First, when examining temperature, the nighttime flight temperature errors are found to have a smaller range than the daytime temperature errors, indicating that much of the daytime error arises from exposure to solar radiation. The pressure errors demonstrate a strong dependence on horizontal wind speed with all of the error distributions being multimodal in high wind conditions. Finally, dewpoint temperature errors are found to be larger than temperature errors. We conclude that measurements in field campaigns are more accurate when sensors are placed away from the drone's main body and associated propeller wash and are sufficiently aspirated and shielded from incoming solar radiation. The Tracking and Object-Based Analysis of Clouds (tobac) tracking package is a commonly used tracking package in atmospheric science that allows for tracking of atmospheric phenomena on any variable and on any grid. We have enhanced the tobac tracking package to enable it to be used on more atmospheric phenomena, with a wider variety of atmospheric data and across more diverse platforms than before. New scientific improvements (three spatial dimensions and an internal spectral filtering tool) and procedural improvements (enhanced computational efficiency, internal re-gridding of data, and treatments for periodic boundary conditions) comprising this new version of tobac (v1.5) are described in the second study of this dissertation. These improvements have made tobac one of the most robust, powerful, and flexible identification and tracking tools in our field and expanded its potential use in other fields. In the third study of this dissertation, we examine the relationship between the thermodynamic and dynamic environmental properties and deep convective clouds forming in the tropical atmosphere. To elucidate this relationship, we employ a high-resolution, long-duration, large-area numerical model simulation alongside tobac to build a database of convective clouds and their environments. With this database, we examine differences in the initial environment associated with individual storm strength, organization, and morphology. We find that storm strength, defined here as maximum midlevel updraft velocity, is controlled primarily by Convective Available Potential Energy (CAPE) and Precipitable Water (PW); high CAPE (>2500 J kg-1) and high PW (approximately 63 mm) are both required for midlevel CCC updraft velocities to reach at least 10 m s-1. Of the CCCs with the most vigorous updrafts, 80.9% are in the upper tercile of precipitation rates, with the strongest precipitation rates requiring even higher PW. Furthermore, vertical wind shear is the primary differentiator between organized and isolated convective storms. Within the set of organized storms, we also find that linearly-oriented CCC systems have significantly weaker vertical wind shear than nonlinear CCCs in low- (0-1 km, 0-3 km) and mid-levels (0-5 km, 2-7 km). Overall, these results provide new insights into the joint environmental conditions determining the CCC properties in the tropical atmosphere. Finally, in the fourth study of this dissertation, we build upon the third study by examining the relationship between the aerosol environment and convective precipitation using the same simulations and tracking approaches as in the third study. As the environmental aerosol concentrations are increased, the total domain-wide precipitation decreases (-3.4%). Despite the overall decrease in precipitation, the number of tracked terminal congestus clouds increases (+8%), while the number of tracked cumulonimbus clouds is decreased (-1.26%). This increase in the number of congestus clouds is accompanied by an overall weakening in their rainfall as aerosol concentration increases, with a decrease in overall rain rates and an increase in the number of clouds that do not precipitate (+10.7%). As aerosol particles increase, overall cloud droplet size gets smaller, suppressing the initial generation of rain and leading to clouds evaporating due to entrainment before they are able to precipitate

CIRA annual report FY 2016/2017

Reporting period April 1, 2016-March 31, 2017

CIRA annual report FY 2017/2018

Reporting period April 1, 2017-March 31, 2018

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

Assessing similarity of dynamic geographic phenomena in spatiotemporal databases.

The growing availability of routine observations from satellite imagery and other remote sensors holds great promise for improved understanding of processes that act in the landscape. However, geographers' ability to effectively use such spatiotemporal data is challenged by large data volume and limitations of conventional data models in geographic information systems (GIS), which provide limited support for querying and exploration of spatiotemporal data other than simple comparisons of temporally referenced snapshots. Current GIS representations allow measurement of change but do not address coherent patterns of change that reflects the working of geographic events and processes. This dissertation presents a representational and query framework to overcome the limitations and enable assessing similarity of dynamic phenomena. The research includes three self contained but related studies: (1) development of a representational framework that incorporates spatiotemporal properties of geographic phenomena, (2) development of a framework to characterize events and processes that can be inferred from GIS databases, and (3) development of a method to assess similarity of events and processes based on the temporal sequences of spatiotemporal properties. Collectively the studies contribute to scientific understanding of spatiotemporal components of geographic processes and technological advances in representation and analysis