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

Operational Dust Prediction

Over the last few years, numerical prediction of dust aerosol concentration has become prominent at several research and operational weather centres due to growing interest from diverse stakeholders, such as solar energy plant managers, health professionals, aviation and military authorities and policymakers. Dust prediction in numerical weather prediction-type models faces a number of challenges owing to the complexity of the system. At the centre of the problem is the vast range of scales required to fully account for all of the physical processes related to dust. Another limiting factor is the paucity of suitable dust observations available for model, evaluation and assimilation. This chapter discusses in detail numerical prediction of dust with examples from systems that are currently providing dust forecasts in near real-time or are part of international efforts to establish daily provision of dust forecasts based on multi-model ensembles. The various models are introduced and described along with an overview on the importance of dust prediction activities and a historical perspective. Assimilation and evaluation aspects in dust prediction are also discussed

Morphology, lifecycles, and environmental sensitivities of tropical trimodal convection

Includes bibliographical references.2022 Fall.Convective clouds are ubiquitous in the tropics and typically follow a trimodal distribution of cumulus, congestus, and cumulonimbus clouds. Due to the crucial role each convective mode plays in tropical and global transport of heat and moisture, there has been both historical and recent interest in the characteristics, sensitivities, and lifecycles of these clouds. However, designing novel studies to further our knowledge has been challenging due to several limitations: the extensive computing resources needed to conduct modeling studies at sufficient resolution and scale to capture the trimodal distribution in detail; the lack of analysis tools which can objectively detect and track these clouds throughout their lifetime; and a need for more observational and modeling data of the tropical convective environments that produce these clouds. In this dissertation, three distinct but related studies that address these problems to advance the knowledge of our field on the morphology, lifecycles, and environmental sensitivities of tropical trimodal convection are presented. The first study examines the sensitivities of the tropical trimodal distribution and the convective environment to initial aerosol loading and low-level static stability. The Regional Atmospheric Modeling System (RAMS) configured as a Large Eddy Simulation (LES) is utilized to resolve all three modes in detail through two full diurnal cycles. Three initial static stabilities and three aerosol profiles are independently and simultaneously varied for a suite of nine simulations. This research found that (1) large aerosol loading and strong low-level static stability suppress the bulk environment and the intensity and coverage of convective clouds; (2) cloud and environmental responses to aerosol loading tend to be stronger than those from static stability; (3) the effects of aerosol and stability perturbations modulate each other substantially; (4) the deepest convection and highest dynamical intensity occur at moderate aerosol loading, rather than at low or high loading; and (5) most of the strongest feedbacks due to aerosol and stability perturbations are seen in the boundary layer (the latter being applied within the boundary layer themselves), though some are stronger above the freezing level. The second study presented seeks to further enhance an artificial intelligence analysis tool, the Tracking and Object-Based Analysis of Clouds (tobac) Python package, from both a scientific and procedural standpoint to enable a wider variety of research uses, including process-level studies of tropical trimodal convection. Scientific improvements to tobac v1.5 include an expansion of the tool from 2D to 3D analyses and the addition of a new spectral filtering tool. Procedural enhancements added include greater computational efficiency, data regridding capabilities, and treatments for processing data with singly or doubly periodic boundary conditions (PBCs). My distinct contributions to this work focused on the 2D to 3D expansion and the PBC treatment. These new capabilities are presented through figures, schematics, and discussion of the new science that tobac v1.5 facilitates, such as the analysis of large basin-scale datasets and detailed simulations of layered clouds, that would have been impossible before. Finally, the last study in this dissertation is a process-focused modeling study on the sensitivities of upscale growth of tropical trimodal convection to environmental aerosol loading. This project was enabled by the scientific and procedural improvements to tobac discussed in the second study, in particular the new abilities of tobac to detect and track objects in 3D and with model PBCs. Here, we used a subset of RAMS simulations from the first study, where only aerosol loading was changed and the upscale growth from shallow cumulus through congestus and cumulonimbus during the nighttime hours was investigated. This study revealed that moderately increasing aerosol loading enhances collision-coalescence processes in the middle of the cloud, which delays initial glaciation but promotes it later in the growth period. Greatly increasing aerosol, however, produces a cloud structure with a more extreme aspect ratio and greater entrainment aloft that rapidly loses buoyancy and vertical velocity with height, as well as exhibiting a greater amount of condensate loading towards the top of the cloud. We also found the relative timing of these processes to be especially important, with more rapid initial growth and lofting of condensate often inhibiting deeper convective growth

Numerical Prediction of Dust

Covers the whole breadth of mineral dust research, from a scientific perspective Presents interdisciplinary work including results from field campaigns, satellite observations, laboratory studies, computer modelling and theoretical studies Explores the role of dust as a player and recorder of environmental change This volume presents state-of-the-art research about mineral dust, including results from field campaigns, satellite observations, laboratory studies, computer modelling and theoretical studies. Dust research is a new, dynamic and fast-growing area of science and due to its multiple roles in the Earth system, dust has become a fascinating topic for many scientific disciplines. Aspects of dust research covered in this book reach from timescales of minutes (as with dust devils, cloud processes, and radiation) to millennia (as with loess formation and oceanic sediments), making dust both a player and recorder of environmental change. The book is structured in four main parts that explore characteristics of dust, the global dust cycle, impacts of dust on the Earth system, and dust as a climate indicator. The chapters in these parts provide a comprehensive, detailed overview of this highly interdisciplinary subject. The contributions presented here cover dust from source to sink and describe all the processes dust particles undergo while travelling through the atmosphere. Chapters explore how dust is lifted and transported, how it affects radiation, clouds, regional circulations, precipitation and chemical processes in the atmosphere, and how it deteriorates air quality. The book explores how dust is removed from the atmosphere by gravitational settling, turbulence or precipitation, how iron contained in dust fertilizes terrestrial and marine ecosystems, and about the role that dust plays in human health. We learn how dust is observed, simulated using computer models and forecast. The book also details the role of dust deposits for climate reconstructions. Scientific observations and results are presented, along with numerous illustrations. This work has an interdisciplinary appeal and will engage scholars in geology, geography, chemistry, meteorology and physics, amongst others with an interest in the Earth system and environmental change

CIRA annual report FY 2016/2017

Reporting period April 1, 2016-March 31, 2017

Identification and characterization of natural aerosols over the Arctic

Le réchauffement climatique est l'un des défis les plus graves auxquels nous sommes confrontés aujourd'hui. L'Arctique est particulièrement vulnérable à ses effets. Les aérosols jouent un rôle clé en termes d'effets de forçage radiatif (à la fois directement et indirectement en termes d'influence sur les nuages). Par conséquent, ils sont l'une des plus grandes sources d'incertitude dans la modélisation du climat dans la mesure où leurs caractéristiques microphysiques, chimiques et optiques ne sont pas bien comprises. Les aérosols arctiques peuvent être classés selon deux catégories: les aérosols anthropiques et les aérosols naturels. Les aérosols naturels comprennent le carbone noir et le carbone brun (BC et BrC), la poussière, le sel de mer, les sulfates volcaniques et les cendres ainsi que les nuages stratosphériques polaires de niveau Ib (PSC). Le but ultime du projet de recherche était de caractériser les propriétés optiques et microphysiques des aérosols naturels dans les contraintes de pouvoir capturer des événements d'opportunité spécifiques. Bien que nous ayons enquêté sur de nombreux événements d'aérosols naturels dans l'Arctique, nous nous sommes finalement concentrés sur deux événements extraordinaires. Dans le premier article, nous avons utilisé la photométrie solaire au sol, les récupérations au sol FTIR (Fourier Transform IR), les profils lidar, la télédétection par satellite et la modélisation des aérosols pour analyser un événement de fumée extrême en août 2017 sur Eureka, entraîné par le incendies pyrocb (convection extrême) près de Prince George, en Colombie-Britannique. Selon nous, cet article a été une contribution innovante et originale à divers égards: d'abord en termes d'événements d’aérosols ainsi que l'infrastructure instrumentale et l'expertise que nous avons développées et apportées au fil des années sur Eureka. L’article était également original en termes de production d'une climatologie des fumées f (profondeur optique en mode fin) sur 10 ans qui excluait les événements confondants tels que les intrusions stratosphériques de sulfates en mode fin de Kasatochi et Sarychev de 2008 et 2009. Une contrainte originale sur l'étiquetage des événements f en tant qu'événements de fumée était la corrélation entre f et l'abondance de CO récupérée par FTIR (le CO étant un produit de fumée classique). Pour démontrer la nature extrême de l'événement, nous avons utilisé une analyse ‘‘pic au-dessus du seuil’’ (Peak Over Threshold, POT) des pics f individuels au cours de notre période d'échantillonnage de 10 ans. Le deuxième article était sans doute la contribution la plus importante et la plus originale de ce projet. Elle impliquait la réussite de l’application de techniques de télédétection pour détecter un panache de poussière à basse altitude et dans l'Extrême-Arctique (81 °N) au-dessus du lac Hazen (Ellesmere Island) en utilisant plusieurs techniques de télédétection passives et actives par satellite. Nous n'avons connaissance d'aucune publication traitant de la télédétection de la poussière locale de l'Arctique effectuée sur la surface complexe de neige, de glace et de poussière telle que présente au lac Hazen. Nous avons exploité les capacités d'imagerie multiangles et multispectrales (imagerie MISR et MODIS) ainsi que les capacités de profilage dépendantes de la taille des particules des capteurs actifs (le CALIOP lidar et le radar CloudSat) pour identifier et caractériser les propriétés physiques et optiques clés du panache de poussière. Cela a été accompli malgré le fait que les algorithmes de télédétection de tous ces capteurs n'étaient pas adaptés aux conditions arctiques. Nous avons réussi à caractériser l'épaisseur du panache supérieur (la région du signal comportant le bruit le plus élevé) en termes d’épaisseur optique à 532 nm (~ 0.7) et le rayon effectif des particules du panache (entre 18 et 25 µm de rayon; ce que les spécialistes du domaine qualifient de particules de poussière ‘‘géantes’’).Abstract: Global warming is one of the most serious challenges that we face today. The Arctic is particularly vulnerable to its effects. Aerosols play a key role in terms of their radiative forcing effects (both directly and indirectly in terms of their influence on clouds). They are, accordingly, one of the greatest uncertainty sources in climate modelling inasmuch as their microphysical, chemical and optical characteristics are not well understood. Arctic aerosols can be categorized into anthropogenic and natural aerosols. Natural aerosols include black and brown carbon (BC and BrC), dust, sea-salt, volcanic sulphates and ash as well as level Ib polar stratospheric clouds (PSCs). The ultimate goal of the research project was to characterize the optical and microphysical properties of natural aerosols within the constraints of being able to capture specific events of opportunity. While we investigated numerous natural aerosol events over the Arctic, we eventually focussed on two extraordinary events. In Paper 1, we employed ground-based sunphotometry, ground-based FTIR (Fourier Transform IR) retrievals, lidar profiles, satellite remote sensing and aerosol modelling to analyze an extreme, August-2017 smoke event over Eureka that was driven by pyrocb (extreme convection) fires near Prince George, BC. This paper was, we believe, an innovative and original contribution on various levels: first and foremost, in terms of the event as well as the instrumental infrastructure and expertise that we developed and brought to bear over many years at Eureka. It was also original in terms of the production of a 10-year f (fine mode optical depth) smoke climatology that excluded confounding events such as the 2008 and 2009 Kasatochi and Sarychev stratospheric intrusions of fine mode sulphates. An original constraint on the labelling of f events as smoke events was the correlation between f and FTIR-retrieved CO abundance (CO being a classical smoke product). To demonstrate the extreme nature of the event we employed a "peak over threshold" (POT) analysis of individual f peaks during our 10-year sampling period. Paper 2 was arguably the most significant and original contribution. It involved the successful application of remote sensing techniques to detect a low-altitude, high-Arctic (81 °N) dust plume over Lake Hazen (Ellesmere Island) using a diverse array of passive and active, satellite-based remote sensing techniques. We are not aware of any published remote sensing investigations of local Arctic dust carried out over the complex surface of snow, ice and dust that was encountered in the Lake Hazen case. We exploited multi-angle and multi-spectral imaging capabilities (MISR and MODIS imagery) as well as the particle size dependant profiling capabilities of active sensors (the CALIOP lidar and the CloudSat radar) to identify and characterize the key physical and optical properties of the dust plume. This was accomplished in spite of the fact that the remote sensing algorithms of all these sensors were not adapted to Arctic conditions. We succeeded in characterizing the upper plume thickness (the region of highest signal-to-noise) in terms of 532 nm optical depth (~ 0.7) and the effective radius of the plume particles (between 18 and 25 µm in radius; what the dust community characterize as “giant” dust particles)

The physics of wind-blown sand and dust

The transport of sand and dust by wind is a potent erosional force, creates sand dunes and ripples, and loads the atmosphere with suspended dust aerosols. This article presents an extensive review of the physics of wind-blown sand and dust on Earth and Mars. Specifically, we review the physics of aeolian saltation, the formation and development of sand dunes and ripples, the physics of dust aerosol emission, the weather phenomena that trigger dust storms, and the lifting of dust by dust devils and other small-scale vortices. We also discuss the physics of wind-blown sand and dune formation on Venus and Titan.Comment: 72 journal pagers, 49 figure

Gazing at the Solar System: Capturing the Evolution of Dunes, Faults, Volcanoes, and Ice from Space

Gazing imaging holds promise for improved understanding of surface characteristics and processes of Earth and solar system bodies. Evolution of earthquake fault zones, migration of sand dunes, and retreat of ice masses can be understood by observing changing features over time. To gaze or stare means to look steadily, intently, and with fixed attention, offering the ability to probe the characteristics of a target deeply, allowing retrieval of 3D structure and changes on fine and coarse scales. Observing surface reflectance and 3D structure from multiple perspectives allows for a more complete view of a surface than conventional remote imaging. A gaze from low Earth orbit (LEO) could last several minutes allowing for video capture of dynamic processes. Repeat passes enable monitoring time scales of days to years. Numerous vantage points are available during a gaze (Figure 1). Features in the scene are projected into each image frame enabling the recovery of dense 3D structure. The recovery is robust to errors in the spacecraft position and attitude knowledge, because features are from different perspectives. The combination of a varying look angle and the solar illumination allows recovering texture and reflectance properties and permits the separation of atmospheric effects. Applications are numerous and diverse, including, for example, glacier and ice sheet flux, sand dune migration, geohazards from earthquakes, volcanoes, landslides, rivers and floods, animal migrations, ecosystem changes, geysers on Enceladus, or ice structure on Europa. The Keck Institute for Space Studies (KISS) hosted a workshop in June of 2014 to explore opportunities and challenges of gazing imaging. The goals of the workshop were to develop and discuss the broad scientific questions that can be addressed using spaceborne gazing, specific types of targets and applications, the resolution and spectral bands needed to achieve the science objectives, and possible instrument configurations for future missions. The workshop participants found that gazing imaging offers the ability to measure morphology, composition, and reflectance simultaneously and to measure their variability over time. Gazing imaging can be applied to better understand the consequences of climate change and natural hazards processes, through the study of continuous and episodic processes in both domains

CIRA annual report FY 2017/2018

Reporting period April 1, 2017-March 31, 2018

Review article: A European perspective on wind and storm damage – from the meteorological background to index-based approaches to assess impacts

Wind and windstorms cause severe damage to natural and human-made environments. Thus, wind-related risk assessment is vital for the preparation and mitigation of calamities. However, the cascade of events leading to damage depends on many factors that are environment-specific and the available methods to address wind-related damage often require sophisticated analysis and specialization. Fortunately, simple indices and thresholds are as effective as complex mechanistic models for many applications. Nonetheless, the multitude of indices and thresholds available requires a careful selection process according to the target sector. Here, we first provide a basic background on wind and storm formation and characteristics, followed by a comprehensive collection of both indices and thresholds that can be used to predict the occurrence and magnitude of wind and storm damage. We focused on five key sectors: forests, urban areas, transport, agriculture and wind-based energy production. For each sector we described indices and thresholds relating to physical properties such as topography and land cover but also to economic aspects (e.g. disruptions in transportation or energy production). In the face of increased climatic variability, the promotion of more effective analysis of wind and storm damage could reduce the impact on society and the environment