Cyclones are complex weather phenomena, affected by multiple variables such as pressure, wind, temperature and more. Therefore, how cyclones are formed, what affects them and how they can be tracked is still actively researched today. Cyclones can have multiple centers (eyes), which can split and merge during its lifetime, which make them even more complex to define mathematically. In this thesis, how multi-center cyclones can be meaningfully visualized for domain scientists using multivariate visualization is investigated. An important aspect of the visualization is how a cyclone’s spread and boundary can be defined. The result is a visualization where the cyclonic region is defined by segmenting a pressure volume, and then a surface is extracted to get the cyclone’s boundary. Temperature is visualized using color mapping onto surfaces, while the wind velocity is shown using particles. The framework allows domain scientists to affect the visualization by picking criteria for segmenting the volume, color maps, and more. In conclusion, an improved cyclonic region could be defined by using multiple fields instead of only pressure, and the visualization would be improved with a greater detail put into the wind part. / <p>Examensarbetet är utfört vid Institutionen för teknik och naturvetenskap (ITN) vid Tekniska högskolan, Linköpings universitet</p>

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Forests are crucial for mitigating the effects of climate change and providing ecosystem services. Global deforestation trends coupled with changes in climate and disturbance regimes threaten the ability of forests to sequester carbon, provide timber, and regulate other ecosystem processes. My dissertation draws from principles in ecology, hydrology, and geography to identify the effects of forest disturbance from extreme events (i.e., hurricanes and droughts) on carbon sequestration and streamflow in Puerto Rico. In Chapter 1, I utilized hydroclimatic time series, geospatial analysis, and statistical techniques to evaluate the relationships between forest cover and rainfall variability on streamflow regimes. I determined that (i) watersheds with high forest cover had consistently greater streamflow than deforested ones and (ii) during dry antecedent rainfall conditions, highly forested watersheds had higher streamflow than deforested ones, suggesting that increased hillslope infiltration and storage afforded by well-developed forest soils outweigh higher vegetation water demand in forests compared to other land cover types. In Chapter 2, I combined field data from permanent forest plots with geospatial attributes, satellite imagery, and lidar point clouds to estimate forest damage extent and a loss in carbon sequestration across Puerto Rican forests after Hurricane María (2017). I also developed a random forest model to identify the biophysical and climatic drivers of spatial variation in forest damage from the hurricane. I found (i) a strong relationship between field-based estimates of aboveground biomass (AGB) loss after Hurricane María and the remotely sensed estimate of damage, (ii) 23% (10.44 ±2.33 Tg) of pre-hurricane forest AGB was lost, and (iii) storm-related rainfall was a strong predictor of forest damage, in addition to canopy height, maximum wind speeds, and soil moisture and water storage variables. Finally, in Chapter 3, I quantified changes to streamflow in Puerto Rico in the months following Hurricane María and tested whether estimates of storm-related forest damage account for these differences. I found that (i) “fast” (i.e. quickflow) and “slow” (i.e., baseflow) streamflow components reacted differently to Hurricane María, (ii) magnitude of change in quickflow was positively correlated to the magnitude of forest damage from the storm, while changes to baseflow were unrelated to forest cover or damage, and (iii) under the same level of relative damage, watersheds with low forest cover had greater quickflow increases than deforested ones, suggesting that interactions between forest cover and forest damage modulate the effects of disturbance on quickflow in highly forested watersheds and exacerbate effects of disturbance in less forested watersheds. Overall, the results from my dissertation inform management practices by quantifying vulnerability to changing climate and disturbance regimes, and highlight the importance of forests for regulating water provision and other ecosystem services.

La complexité du climat repose en grande partie sur le cycle de l'eau. Dans les tropiques,l'eau atmosphérique est un paramètre clef,60% des précipitations globales ont lieu dans lestropiques. La compréhension du cycle de l'eau atmosphérique à l'échelle globale passe par l'utilisation d'observations satellites. Le satellite franco indien Megha-Tropiques, lancé en 2011, permet d'étudier pour la première fois des observations simultanées de l'humidité et de la pluie. La première partie de la thèse consiste en l'étude de l'impact d'un cyclone sur son environnement. Pour cela, un cas d'étude a été sélectionné (typhon Bopha) et undiagnostique a été réalisé pour étudier la production/ consommation d'humidité et de chaleur dans le typhon. La seconde partie de la thèse consiste en l'étude des relations entre les nuages et l'humidité dans la haute troposphère. Cette étude est réalisée au-dessus de l'océan Indien (entre 2011 et 2014) et au-dessus du Sahel (entre 2012 et 2015). / The complexity of the climate depends largely on the water cycle. In the tropics, atmosphericwater is a key parameter, 60% of global rainfall occurs in the tropics. The understandingof the atmospheric water cycle on a global scale need to use satellite observations. The Indo-French satellite Megha-Tropiques, launched in 2011, allows to study for the _rst time simultaneous observations from moisture and rain. The _rst part of the thesis is the study of the impact of a hurricane on its environment. For this, a case study was selected (Typhoon Bopha) and a diagnosis was performed to study the production / consumption of moisture and heat in the typhoon. The second part of the thesis is the study of the relationshipbetween clouds and humidity in the upper troposphere. This study was conducted over the Indian Ocean (between 2011 and 2014) and over the Sahel (between 2012 and 2015).

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology and Physical Oceanography, 1981. / Microfiche copy available in Archives and Science. / Bibliography: leaves 98-99. / by Ronald Francis Fournier. / M.S.

Thesis: S.M., Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2016 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 119-123). / Most traditional theories regarding upper oceanic response due to passing tropical cyclones involve an initial and predominant upwelling based on storms' strong cyclonic flow and resulting positive wind stress curl imparted on the sea surface. In August 2015, Air-Launched Autonomous Micro Observer float 9077 was intercepted by Hurricane Ignacio and its temperature measurements revealed a 40 m depression of the 26°C isotherm ahead of the device's closest point of approach with the storm and usual upwelling response. This unique finding motivated attempting to replicate the apparent downwelling ahead of Hurricane Ignacio and three others-Irma, Florence and Michael, using the Price-Weller-Pinkel 1/2 order closure model, via comparisons of the depth of the 26°C isotherm, tropical cyclone heat potential and vertical velocity. When modeling the total stress, two other traditional ideas were challenged. / First, many legacy drag coefficients linearly increase with wind speed, while the modem variety maximize near tropical cyclone strength, with varying asymptotic and/or decreasing end behavior. Second, it is believed that sea spray droplets are sheared off the largest wave crests, quickly accelerate in the high winds, but upon reentry, dampen the smaller waves and flux substantial amounts of momentum to the sea. Taken together, many traditional atmosphere-ocean models bulk parameterize air-sea interaction processes and employ a legacy drag coefficient and omit or crudely formulate sea spray. Therefore, this study aimed to simulate the aforementioned downwelling using 14 total forcing parameterizations, including seven different legacy or modem drag coefficients, with and without spray stress. / A combination of qualitative and statistical analyses illustrated downwelling was present in Hurricane Ignacio and every other storm by a large majority of variable indices, legacy drag coefficients were statistically significantly over-estimating outliers and should not be employed in tropical cyclone models, and while the explicit addition of sea spray to interfacial stress reduced model accuracy, this phenomenon remains paramount through modem drag coefficient selection. The confirmation of downwelling is physically founded in Ekman dynamics and may be significant in storm surge enhancement due to the accompanying surface height anomaly and near-shore depth limitations forcing water, with a negative vertical velocity, ashore. / Office of Naval ResearchN00014-15-12293 / Office of Naval ResearcN00014-18-12819 / U. S. Navy Civilian Institution Program / by Stephan D. Gallagher. / S.M. / S.M. Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution)

Decades of research have fostered a greater understanding of the environmental controls that drive tropical cyclone (TC) intensity change, yet the community has achieved only small improvements in intensity forecasting. Numerous environmental factors impact TC intensity, such as vertical wind shear and sea surface temperatures (SSTs), but little research has focused on establishing if SST change under the TC, or SST gradients, influence these intensity changes. This study investigated three methods to compute SST gradients. The first method calculated the SST change within fixed distances along the track. In the second and third methods, the SST was calculated over the distance traversed by the TC in two separate six-hour periods. By examining 455 24-hour weakening episodes in the eastern North Pacific, this study revealed that the first SST gradient method explained the highest 24-hour weakening variance for TCs located within SSTs at or lower than 26.5 degrees C.

African easterly waves (AEWs) are known precursors to tropical cyclone (TC) formation, although it is not always clear which AEWs will develop and which AEWs will not. To investigate AEW evolution, this study examines novel observations from the geostationary Advanced Baseline Imager (ABI) during July-September 2019. Case studies are conducted for two AEWs: one that became Hurricane Dorian, the strongest and most devastating hurricane of the 2019 Atlantic hurricane season, and a long-lived September AEW that did not become a TC. Lower-level moisture and flow, and the strength and spatial distribution of convective activity, differed between these two waves. By then exploring these characteristics for additional developing and non-developing AEWs, ABI observations show that developing AEWs are associated with low-level moist air ahead of the wave combined with enhanced convective activity, while non-developing AEWs tend to encounter drier air and exhibit a persistently broader structure with less-organized convection.

Tropical cyclone (TC) intensity and structure are affected by their environments, including sea surface temperature, vertical wind shear, and atmospheric moisture. Analyses of TC environments often rely on area-averaged quantities, yet the spatial variability of these fields can affect TC behavior, such as moisture distribution impacting where and how much rain falls. This study identifies spatial patterns of environmental moisture surrounding mature North Atlantic TCs during 2000-2021 in shear of less than 20 knots. Empirical orthogonal function analysis of total column water vapor reveals six dominant patterns. These patterns account for nearly 67% of the variance in the dataset and are affected by geographic location and large-scale atmospheric phenomena. Mid-level ventilation appears more likely in certain patterns. Future work will explore radar and passive microwave observations for cases in each pattern to quantify the physical impacts of these moisture patterns on mature TCs.

Polar mesoscale cyclones (PMCs) are low-pressure systems that form in polar regions. Their small size and short lifespan pose challenges for coarse resolution models in capturing PMCs and their associated air-sea mass and energy transfer. To address the influence of resolution on PMCs, a comparison between a higher resolution dataset (CARRA with 2.5 km resolution) and a lower resolution reanalysis dataset (ERA5 with 30km resolution) over a 10-year period in the North Atlantic is conducted by employing an automatic algorithm. The results revealed that CARRA detected a greater number of PMC activities, highlighting the benefits of higher resolution data in reducing uncertainties during tracking. PMCs identified using CARRA exhibited smaller vortex sizes, but higher relative vorticity and faster movement speeds compared to ERA5 results. Notably, the typical vortex diameters derived from ERA5 and CARRA were 80 km and 120 km, respectively. Furthermore, the climatology of PMCs in the North Atlantic is presented. Monthly variations indicated that the majority of PMCs occurred during winter, with only a few cases developing in summer. The spatial distribution exhibits that the highest density of PMCs was observed in the Irminger Sea and the Norwegian Sea. It also shows that the presence of sea ice can influence the PMC density, as a significant number of cases formed near the sea ice edge. The comparison results indicate that the current coarse climate simulation may underestimate the influence of PMCs in the Arctic due to the misrepresentation of them, thus introducing uncertainties in the climate prediction.