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The vertical structure of the tangential wind field in tropical cyclones is investigated through observations, theory, and numerical simulations. First, a dataset of Doppler radar wind swaths obtained from NOAA/AOML/HRD is used to create azimuthal mean tangential wind fields for 7 storms on 17 different days. Three conventional wisdoms of vertical structure are reexamined: the outward slope of the Radius of Maximum Winds (RMW) decreases with increasing intensity, the slope increases with the size of the RMW, and the RMW is a surface of constant absolute angular momentum (M). The slopes of the RMW and of M surfaces are objectively determined. The slopes are found to increase linearly with the size of the low-level RMW, and to be independent of the intensity of the storm. While the RMW is approximately an M surface, M systematically decreases with height along the RMW. The steady-state analytical theory of Emanuel (1986) is shown to make specific predictions regarding the vertical structure of tropical cyclones. It is found that in this model, the slope of the RMW is a linear function of its size and is independent of intensity, and that the RMW is almost exactly an M surface. A simple time-dependent model which is governed by the same assumptions as the analytical theory yields the same results. Idealized hurricane simulations are conducted using the Weather Research and Forecasting (WRF) model. The assumptions of Emanuel's theory, slantwise moist neutrality and thermal wind balance, are both found to be violated. Nevertheless, the vertical structure of the wind field itself is generally well predicted by the theory. The percentage rate at which the winds decay with height is found to be nearly independent of both size and intensity, in agreement with observations and theory. Deviations from this decay profile are shown to be due to gradient wind imbalance. The slope of the RMW increases linearly with its size, but is systematically too large compared to observations. Also in contrast to observations, M generally increases with height along the RMW.

[pt] Nesse artigo, fornecemos evidências de que as informações sobre a infraestrutura de mitigação de riscos nos Estados Unidos (EUA) durante uma exposição indireta a ciclones tropicais e a própria exposição indireta a ciclones tropicais geram anomalias nos retornos após considerar os 5 fatores FamaFrench e momentum. Formulamos duas hipóteses possíveis para explicar essas anomalias: hipótese do investidor local e hipótese do investor geral. Ambas as hipóteses assumem que os investimentos em mitigação de riscos são inferiores ao ideal. Sua diferença é baseada em como os investidores interpretam os programas de mitigação de riscos. Na hipótese do investidor local, Nós nos concentramos nas percepções dos investidores locais sobre os programas. Investimentos mais significativos nesses programas significam que mais investidores locais irão reconhecê-los e conhecer suas falhas. Por outro lado, na hipótese do investor geral, nos concentramos nas associações que os investidores gerais fazem entre o nível de investimento em mitigação de perigos e o risco de desastres. No final, damos algumas evidências da hipótese dos investidores locais, mas não podemos garantir que essa seja a única explicação possível. A questão toda depende de quanto os investidores sabem sobre os programas de mitigação de riscos. Além disso, evidenciamos que um canal de informação é o provável caminho pelo qual as anomalias são geradas. Assim, nesta dissertação, lançamos alguma luz sobre a incerteza gerada pelos desastres naturais que precificam os ativos, um tema que recebe mais atenção em um mundo em aquecimento. / [en] In this paper, we provide evidence that information about hazard mitigation infrastructure in the United States (U.S.) during an indirect exposure to tropical cyclones and the indirect exposure to tropical cyclones per se generate anomalies in returns after considering the 5 Fama-French factors and momentum. We formulate two possible hypotheses to explain these anomalies: local investor and general market hypotheses. Both hypotheses assume that hazard mitigation investments are lower than the ideal. Their difference is based on how investors interpret the hazard mitigation programs. We focus on local investors perceptions about them in the local investor hypothesis. More significant investments in these programs mean more local investors will acknowledge them and their flaws. On the other hand, we focus on general investors associations between hazard mitigation investment level and disaster risk in the general market hypothesis. In the end, we give some evidence of the local investors hypothesis, but we cannot guarantee that this is the only possible explanation. The whole point depends on how much investors know about hazard mitigation programs. Beyond that, we give evidence that an information channel is the probable path in which the anomalies are generated. Thus, in this dissertation, we shed some light on the uncertainty generated by natural disasters that prices assets, a topic that gets more attention in a warming world.

Tropical cyclones (TCs) often change intensity as they move over mesoscale oceanic features, as a function of the oceanic mixed layer (OML) thermal response (cooling) to the storm's wind stress. For example, observational evidence indicates that TCs in the Gulf of Mexico rapidly weaken over cyclonic cold core eddies (CCEs) where the cooling response is enhanced, and they rapidly intensify over anticyclonic warm features such as the Loop Current (LC) and Warm Core Eddies (WCEs) where OML cooling is reduced. Understanding this contrasting thermal response has important implications for oceanic feedback to TCs' intensity in forecasting models. Based on numerical experimentation and data acquired during hurricanes Katrina and Rita, this dissertation delineates the contrasting velocity and thermal response to TCs in mesoscale oceanic eddies. Observational evidence and model results indicate that, during the forced stage, the wind-driven horizontal current divergence under the storm's eye is affected by the underlying geostrophic circulation. Upwelling (downwelling) regimes develop when the wind stress vector is with (against) the geostrophic OML velocity vector. During the relaxation stage, background geostrophic circulations modulate vertical dispersion of OML near-inertial energy. The near-inertial velocity response is subsequently shifted toward more sub-inertial frequencies inside WCEs, where rapid vertical dispersion prevents accumulation of kinetic energy in the OML that reduces vertical shears and layer cooling. By contrast, near-inertial oscillations are vertically trapped in OMLs inside CCEs that increases vertical shears and entrainment. Estimates of downward vertical radiation of near-inertial wave energies were significantly stronger in the LC bulge (12.1X10 super -2 W m super -2) compared to that in CCEs (1.8X10 super -2 W m super -2). The rotational and translation properties of the geostrophic eddies have an important impact on the internal wave wake produced by TCs. More near-inertial kinetic energy is horizontally trapped in more rapidly rotating eddies. This response enhances vertical shear development and mixing. Moreover, the upper ocean temperature anomaly and near-inertial oscillations induced by TCs are transported by the westward-propagating geostrophic eddies. From a broader perspective, coupled models must capture oceanic features to reproduce the differentiated TC-induced OML cooling to improve intensity forecasting.

Depuis une vingtaine d'années, la qualité de la prévision de la trajectoire des cyclones tropicaux a fortement progressé mais peu d'améliorations ont été apportées à la prévision de l'intensité. Cette thèse s'intéresse aux changements d'intensité des cyclones tropicaux du sud-ouest de l'océan Indien sous l'angle original de l'activité électrique.Une première étude climatologique s'appuyant sur les données du réseau de détection d'éclairs World Wide Lightning Location Network (WWLLN) a permis de valider la qualité de ces données et de montrer que les cyclones tropicaux pouvaient être une source importante de production d'éclairs à l'échelle du bassin. À partir de ce résultat, une étude ciblée a été menée en considérant la spécificité du bassin et trois régions ont été définis (océan ouvert, région à proximité de la côte est de Madagascar et Canal du Mozambique). L'activité électrique des cyclones tropicaux dépend de la région où ils se trouvent ainsi que de leur stade d'intensité. Les éclairs semblent être un marqueur des phases d'intensification et d'affaiblissement dans certains situations. La troisième étape de cette thèse a consisté à simuler de manière idéalisée un cyclone tropical mature et a tenté d'expliquer les processus physiques à l'origine de l'activité électrique. Le modèle reproduit bien le comportement sporadique des éclairs habituellement observé. Des bilans montrent que ce cyclone présente trois phases caractéristiques, chacune associée à un comportement dynamique, microphysique et électrique différent. Enfin, une deuxième étude purement numérique a tenté d'identifier des estimateurs de l'activité électrique. Pourcelà deux approches ont été adoptées : une étude globale et une étude par cellule. Dans les deux cas, les meilleurs estimateurs sont la masse totale de graupel, le volume d'updraft et le produit des flux des masses de glace précipitante et non précipitante. / Tropical cyclone track forecast has improved over the past two decades but little improvement have been done in intensity changes forecast. This thesis focuses on the intensity changes of tropical cyclones in the southwest Indian ocean through the original aspect of lightning activity. A climatology of lightning activity in the southwest Indian ocean using data from the World Wide Lightning Location Network (WWLLN) is first proposed. Results showed that the WWLLN was able to locate and capture the lightning activity in the basin and that tropical cyclones can be considered as a major source of lightning flashes in some oceanic parts of this region. From this result, study of lightning activity in tropical cyclones of the southwest Indian ocean has been done considering the basin configuration. Thus, three regions were defined: open ocean, region near the eastern coast of Madagascar and the Mozambique Channel. The location and intensity of lightning activity depend on the region and the intensity stage. Lightning flashes seem to be a proxy of intensification or weakening under some conditions. The third step of this thesis was to simulate in an idealized framework a mature tropical cyclone. The model was first able to reproduce the sporadic behavior of lightning activity as observed. Budgets have shown that the presence of three distinctive phases characterized by different dynamical, microphysical and electrical behaviors. Finally, another purely numerical work tried to identify some proxies of lightning activity according two approaches : a global analysis anda per-cell analysis. In both cases, the best proxies are the total graupel mass, the updraft volume and the product of precipitating and non-precipitating ice mass fluxes.

Indiana University-Purdue University Indianapolis (IUPUI)

The Philippines is considered one of the most vulnerable countries in the world to climate disasters due to a combination of its geospatial, political, economic, and social attributes. The nation gets hit with an average of 20 annual tropical cyclones, also known as typhoons, and through the process of climate change, these events are only growing in both frequency and magnitude. In the coastal capital city of Metro Manila, climate change coupled with rapid and unplanned urbanization has led to increased vulnerabilities of populations, infrastructures, and increased inequalities.  This thesis aims to assess the current disaster risk reduction and management (DRRM) frameworks present within the nation and National Capital Region (NCR), through a case study approach of the 2020 typhoons: Quinta, Rolly, and Ulysses. It presents findings through four thematic pillars of disaster prevention and mitigation, preparedness, response and early- recovery, and recovery and rehabilitation. It uses the perspectives of three key informants from the Office of Civil Defense (OCD), the Philippine Disaster Resilience Foundation (PDRF), and the Asian Development Bank (ADB), as well as additional diversified perspectives.  Findings suggest that DRRM has evolved since the implementation of the Republic Act No 10121 (RA 10121), or the Philippine Disaster Reduction and Management Act of 2010, however, can still be improved to tackle root causes of vulnerabilities. I use Roberts and Pelling’s (2020) transformation as liberation model as a theoretical framework to generate recommendations to policymakers that can help address vulnerabilities to typhoons. These recommendations include increasing participation and inclusivity within policy and decision making, creating a formal mechanism to measure vulnerabilities and inform future DRRM policies, and finally to reframe climate change and disaster risks as a socio-ecological issue rather than just an environmental one. / Filippinerna anses vara ett av de mest sårbara länderna i världen för klimatkatastrofer på grund av en kombination av dess geospatiala, politiska, ekonomiska och sociala egenskaper. Nationen drabbas av i genomsnitt 20 årliga tropiska cykloner, även kända som tyfoner, och genom klimatförändringsprocessen växer dessa händelser bara i både frekvens och omfattning. I kusthuvudstaden Metro Manila har klimatförändringar i kombination med snabb och oplanerad urbanisering lett till ökad sårbarhet hos befolkningar, infrastrukturer och ökade ojämlikheter.  Denna avhandling syftar till att bedöma de nuvarande ramverken för katastrofriskminskning och -hantering (DRRM) som finns i landet och i National Capital Region (NCR), i fallet med tyfonerna 2020: Quinta, Rolly och Ulysses. Avhandlingen illustrerar resultaten genom fyra tematiska pelare: förebyggande och begränsning av katastrofer, beredskap, insatser och tidig återhämtning samt återhämtning och rehabilitering. Detta görs utifrån tre nyckelinformanters perspektiv, från Office of Civil Defense (OCD), Philippine Disaster Resilience Foundation (PDRF) och Asian Development Bank (ADB).  Resultaten tyder på att nuvarande DRRM-policyer vidmakthåller orättvisa mönster i nationen och det borde tillämpas en förändring som befrielsemodell, baserad på Roberts och Pelling (2020), för att främja en mer rättvis och hållbar hantering av tyfoner i landet. Därför rekommenderas det att DRRM-policyer ökar deltagande och inkludering inom policy- och beslutsfattande, skapa en formell mekanism för att mäta sårbarheter och informera framtida DRRM-policyer, och slutligen att omformulera klimatförändringar och katastrofrisker som socioekologiska frågor snarare än bara miljömässiga sådana.

Dans un contexte international, la prévision d'intensité des cyclones tropicaux connaît encore de graves déficiences tandis que la prévision de trajectoire de ces phénomènes météorologiques extrêmes s'est grandement améliorée ces dernières décennies. Une source d'erreur pour la prévision d'intensité est le manque de connaissance des processus physiques qui régissent l'évolution de la structure et de l'intensité des cyclones. Cette thèse, proposée dans le cadre des responsabilités du Centre Météorologique Régional Spécialisé (CMRS) de la Réunion et des axes de recherche du LACy et du CNRM, a pour but d'améliorer la prévision numérique et la compréhension des mécanismes de changement de structure et d'intensité des cyclones dans le sud-ouest de l'océan Indien. On observe statistiquement dans le bassin de fréquents déferlements d'ondes de Rossby qui correspondent à une intrusion des talwegs d'altitude depuis les moyennes latitudes vers les régions où évoluent les cyclones. Ces déferlements advectent dans la troposphère tropicale de l'air d'origine stratosphérique à fort tourbillon potentiel (PV). Le cœur d'un cyclone tropical étant caractérisé par un vortex cyclonique de fort PV, il est donc légitime de se demander si de tels talwegs sont capables de « nourrir » un cyclone en déferlant jusqu'à lui, et l'intensifier par superposition de PV. D'un autre côté, l'approche d'un talweg est associée à d'autres facteurs pouvant jouer en défaveur d'une intensification, comme un fort cisaillement vertical de vent. L'étude de processus est réalisée sur le cyclone Dora (2007) avec le modèle opérationnel du CMRS sur le bassin, Aladin-Réunion. Ce modèle hydrostatique à aire limitée bénéficie d'une résolution horizontale de 8 km et de son propre schéma d'assimilation 3Dvar avec bogus de vent. Un tel bogus permet d'affiner la structure du cyclone à l'instant initial en ajoutant des observations de vent déduites d'un profil analytique et des paramètres de structure du cyclone estimés par les images satellites. Des diagnostiques sur les variables thermodynamiques en sortie de modèle montrent que la phase d'intensification rapide de Dora est bien associée à l'advection de tourbillon potentiel (PV) en provenance du talweg. Bien que fortement cisaillé, le système parvient à s'intensifier grâce à la forte inclinaison du talweg qui advecte du PV au cœur du cyclone en 2 temps et à 2 niveaux (haute et moyenne troposphère). Lorsque le talweg est au plus proche du cyclone, il force un processus dynamique interne appelé « cycle de remplacement du mur de l'œil ». On observe une inclinaison et un renforcement des vitesses verticales à l'extérieur du mur de l'œil principal, associé à une accélération de la circulation cyclonique tangentielle par advection de moment angulaire sur toute l'épaisseur de la troposphère dans cette zone annulaire (mis en évidence par les flux d'Eliassen-Palm). Un second maximum de vent relatif apparaît alors et une deuxième phase d'intensification rapide s'ensuit avec la contraction du mur secondaire. Le forçage de processus internes par une influence externe (un talweg) semble donc être le moteur de l'intensification rapide de Dora dans un environnement cisaillé, et potentiellement celui d'autres cyclones dans le bassin qui sont approchés par des talwegs d'altitude. Les prévisionnistes du CMRS sont invités à surveiller les champs de PV de tels systèmes, en attendant que de plus amples diagnostiques soient réalisés avec l'outil d'inversion du tourbillon potentiel développé sur le modèle global Arpège. / Despite significant improvements in Tropical Cyclone (TC) track forecasts over the past few decades, anticipating the sudden intensity changes of TCs remains a major operational issue. The main purpose of this thesis is to analyze TC rapid intensification processes in relation with external forcing induced by upper-level troughs originating from the mid-latitudes. The impact of initial storm structure on storm evolution and prediction is also documented. An objective definition for rapid intensification in the southwest Indian Ocean is first proposed. The location and frequency of TC-trough interactions are identified, as well as TC-trough arrangements conducive to TC intensification. An interesting study case, TC Dora (2007), is chosen to run numerical simulations initialized with synthetic TC observations blended in a global analysis. The simulated TC-trough interaction is intricate with potential vorticity (PV) advection from the trough into the TC core at mid and upper levels. Vortex intensification first occurs inside the eyewall and results from PV superposition. Further intensification is associated with a subsequent secondary eyewall formation triggered by external forcing from the trough. The numerical model is able to reproduce the main features associated with outer eyewall spin-up, inner eyewall spin-down, and their effects on vortex intensity changes. Another numerical study examines typhoons in the northwest Pacific and demonstrates the critical role played by initial vortex structure in TC track and intensity prediction. Upgrading the initial specification of a TC inner-core structure in numerical models is recommended for future TC prediction improvements.