1,721,073 research outputs found
Data associated with the publication: Waugh, D.W. and Haine, T.W.N. (2020). How rapidly do the southern subtropical oceans respond to wind stress changes? Journal of Geophysical Research: Oceans
No full textModel output from a Community Climate System Model version 4 (CCSM4) simulation, described in Waugh and Haine 2020
Data associated with Yang et al., 2020, Dependence of Atmospheric Transport into the Arctic on Extent of the Hadley Cell
No full textModel output (annual-mean values for 6 years) from the GFDL dry dynamical core, see details in Yang et al. (2020), Geophysical Research Letters
Stratospheric Ices on Titan During South Polar Fall
Get PDFPolar hood clouds are a prominent feature of the polar fall and winter stratosphere on Titan, the largest moon of Saturn. Observations of north polar winter and south polar fall by NASA’s Cassini mission revealed clouds composed of organic ices, including hydrogen cyanide, benzene, and cyanoacetylene, as well as co-condensed mixtures of these species.
The appearance of a large hydrogen cyanide ice cloud during early southern fall (mid 2012) proved surprising because it formed at a significantly higher altitude than previously observed clouds, and in a region expected to be too warm for ice condensation. Through a series of simulations of hydrogen cyanide cloud using the TitanCARMA cloud microphysics model, I demonstrate that a pure hydrogen cyanide cloud consistent with the 2012 observations could only form at very cold temperatures, and that precipitation from the cloud could deplete much of the stratospheric hydrogen cyanide. However, while initial observations of the cloud only identified hydrogen cyanide ice, other species are expected to be present. Based on additional simulations of benzene and cyanoacetylene clouds as well as estimates derived from a toy model of mixed ices, I show that the presence of multiple ice species can significantly change the microphysical and macrophysical properties of the cloud, though estimating the precise effects requires additional experimental work. Finally, to better understand how the high-altitude cloud seen in 2012 relates to the polar hood previously observed in northern winter, I conducted a review of all of the imagery from Cassini from 2012 until the end of the mission in 2017. Using the images to measure the cloud top altitude, I demonstrate that the cloud gradually descended from an initial altitude of about 320 km in May 2012 to less than 230 km in June 2016, at which point it becomes obscured by atmospheric methane absorption. Over the same period, the cloud expands laterally, approximately following the terminator from an initial latitude of 80°S to 65°S by 2016. This suggests the necessity of radiative emission for maintaining the cold temperatures required to sustain the cloud, and provides important constraints for future models
Ozeanventilation und anthropogener Kohlenstoff basierend auf evaluierten Spurengasanwendungen
Get PDFThis thesis includes three manuscripts. The first describes the ventilation of the Mediterranean Sea in 2011 based on multiple transient tracer measurements. The second evaluates the application of different transient tracers and the IG-TTD model by using several data sets from the South Atlantic and Southern Ocean. The third manuscript intorduces a new theory about saturation states of transient tracers and provides a flux estimate of anthropogenic carbon through Fram Strait in 2012.Diese Dissertation besteht aus drei Manuskripten. Das erste Manuskript beschreibt die Ventilation des Mittelmeeres in 2011 basierend auf mehreren Spurengasmessungen. Das zweite Manuskript evaluiert die Anwendung von Spurengasen und dem IG-TTD Modell anahand diverser Datensätze aus dem Südatlantik und dem Südlichem Ozean, Das dritte Manuskript führt eine neue Theorie über Sättigungszustände der Spurengase ein und beeinhaltet eine Flussabschätzung von anthropogenem Kohlenstoff durch die Fram Straße in 2012
IMPROVING DECISION MAKING IN CLIMATE ADAPTATION WITH MULTIPLE OBJECTIVES UNDER UNCERTAINTY: NEW DECISION SUPPORT TOOLS AND COMPARISON OF URBAN TEMPERATURE DATA COLLECTION METHODS
Get PDFClimate change is one of the biggest challenges facing humankind. Adaptation is important and urgent but receives less attention and resources than mitigation. This motivates this dissertation to address four research questions regarding climate adaptation. The first two questions concern general methodology for adaptation planning under uncertainty, and the other two focus on urban heat adaptation specifically.
Those questions are: (1) how to select the most appropriate decision analysis for a particular adaptation problem? (2) how to rank adaptation problems based on their likelihood of being improved by comprehensive analysis? (3) what is an appropriate methodology for performing decision analyses for urban heat adaptation, and what insights can be generated? and (4) how do current intra-urban temperature monitoring approaches compare with each other and how to improve those approaches?
In this dissertation, Chapter 1 provides the background of the research and establishes the contributions of this dissertation. Chapter 2 addresses the first two questions by developing two practical tools that can assess whether uncertainty and flexibilities will affect climate adaptation decisions and help managers select the most appropriate analytical tools to use. Chapter 3 focuses on the third question and proposes a decision analysis tool, City-HEAT, that can simultaneously consider uncertainty, multi-objective, and adaptive management in generating adaptation plans. Results of a case study suggest that plans generated by City-HEAT are superior to plans based on simple rules or optimized with respect to just one scenario. Chapter 4 studies the fourth question by comparing two intra-urban temperature monitoring approaches with data collected by each approach in Baltimore, MD. It finds that measuring temperatures over various urban land covers, maximizing sensor distances, and monitoring under different weather conditions, are key criteria to improve the data quality of intra-urban temperature monitoring. Finally, Chapter 5 presents the conclusions and some future research opportunities.
Overall, the contributions of my dissertation include the development of two decision support tools for improving climate adaptation in general, the creation of an innovative decision analysis tool to support urban heat adaptation, and the generation of insights that can improve intra-urban temperature monitoring in practice
Salinity variability in the subpolar north Atlantic
No full textSalinity is a fundamental quantity which controls the density of the ocean. Fluctuations in salinity, at high latitudes along with temperature affect the global ocean circulation, especially via the Atlantic meridional overturning circulation (AMOC). Changes in salinity thus have important consequences for global climate. Variability in salinity is, however, not well understood. In this thesis, we aim to study the changes in salinity in the subpolar north Atlantic (SPNA), using a suite of modeling tools. We construct salinity budgets using the ECCO (Estimating the Circulation and Climate of the Ocean) state estimate, pre-industrial simulation of the Community Earth System Model 2 (CESM2) and 100 members of the CESM2-Large Ensemble output. Using ECCO, we find that present day anomalous salinity events are driven by distinct mechanisms, and not all salinity anomaly events are the same. We also find, using the pre-industrial simulation that anomalous salinity events in the western and eastern SPNA are driven by a combination of advective convergence and surface forcing, with a larger role of surface forcing in the western SPNA. Finally, we conclude that a major drop of nearly 2g/kg in salinity is projected to occur in the SPNA by the end of 2100. Anthropogenic signals in the vertical mixing and advective tendencies are expected to emerge in the eastern SPNA during 2020--2030 and in the west by 2040
Elucidating the relationships between surface-level ozone and meteorology
Get PDFSurface-level ozone (O3) is associated with respiratory morbidity and mortality, affects vegetation and ecosystems, and impacts the global climate. The cause of day-to-day variations in O3 remains an open question and is key in interpreting past air quality as well as the ways that future climatic changes will affect air pollution. To this end, we investigate the drivers of O3 variability on daily timescales across the Northern Hemisphere with a special emphasis on the United States. Using observations and chemical transport model simulations, we show that positive relationships between O3 and meteorological variables such as temperature and humidity persist only across continental regions in the mid-latitudes (~ 35-60˚N); elsewhere, these relationships are weak or significantly negative. The covariance of O3 with meteorology is driven by an association with transport, not a direct dependence on chemistry or emissions. We find that neither stagnation or cyclones can explain day-to-day variations in O3 or extreme events. Ultimately, we tie spatial and temporal variations in the O3-meteorology relationships to the jet stream. The jet stream regulates the surface-level mean meridional flow, which affects fluxes of O3, heat, and moisture. These results provide significant gains in understanding the dominant role of transport on O3 variability and reconcile spatial variations in the relationships among O3, temperature, humidity, and the jet stream
DUST AND DROUGHT IN THE SAHEL: DYNAMICS, VARIABILITY, AND FEEDBACKS IN EARTH SYSTEM MODELS
Get PDFMineral dust aerosols, tiny soil particles suspended in the atmosphere, play a key role in climate. North Africa is the largest contributor to the total global dust burden, where sources of dust emission are both the Sahara Desert and neighboring Sahel. As a semi-arid region with high impact inter-annual and decadal rainfall variability, the Sahel represents one of the most sensitive regions to changes in climate. Though data records show that dust and climate covary, characterization of this covariability is still actively debated in recent scientific literature. The use of models to better understand the role of North African dust in modulating Sahelian climate has been inconclusive, with diverging results on whether dust increases or decreases rainfall over the Sahel. These models are highly parameterized and many do not account for the deeply coupled processes between soil, vegetation, dust, rainfall and the neighboring ocean. Insufficient understanding of dust feedbacks in the Sahel has significant implications for our ability to simulate past Sahel climate variability and to predict future climatic and environmental change. In order to better understand the dust-climate relationship over the Sahel, this dissertation uses a global climate model (GCM) and regional modeling system – along with observational and reanalysis data – to investigate the mechanisms involved during the Sahel rainy season.
First, the impact of ocean coupling on the atmospheric response to dust is explored in a GCM. Comparisons between coupled (atmosphere-ocean) and uncoupled (atmosphere only) versions of the model are used to quantify the role of evolving sea surface temperatures (SSTs) in mediating the impacts of dust on rainfall. Results show the role of prescribed SSTs (i.e. an uncoupled ocean model) in the GCM is to exaggerate the magnitude of rainfall change due to dust. Second, improved dust modeling is implemented within a regional model that resolves mesoscale dynamics and captures the vital couplings between land, atmosphere, ocean, and aerosols. The strength of dust-atmosphere coupling is evaluated by assessing the influence of land surface conditions and near-surface meteorology on dust emissions, and the impact of simulated dust on monsoon circulation. The general spatial and temporal variability of dust distributions are captured in the model, though the feedback between dust and Sahelian climate on inter-annual timescales is not strong. Third, this dissertation explores the direct and indirect effects of dust on atmospheric stability and monsoon-relevant circulation patterns that are drivers of rainfall in the Sahel. The rainfall response to dust within the regional modeling system is moderate, yet significant, and the impact of coupling dust is to increase the contrast between simulated rainfall amounts during the phases of ENSO
Salinity variability in the subpolar north Atlantic
No full textSalinity is a fundamental quantity which controls the density of the ocean. Fluctuations in salinity, at high latitudes along with temperature affect the global ocean circulation, especially via the Atlantic meridional overturning circulation (AMOC). Changes in salinity thus have important consequences for global climate. Variability in salinity is, however, not well understood. In this thesis, we aim to study the changes in salinity in the subpolar north Atlantic (SPNA), using a suite of modeling tools. We construct salinity budgets using the ECCO (Estimating the Circulation and Climate of the Ocean) state estimate, pre-industrial simulation of the Community Earth System Model 2 (CESM2) and 100 members of the CESM2-Large Ensemble output. Using ECCO, we find that present day anomalous salinity events are driven by distinct mechanisms, and not all salinity anomaly events are the same. We also find, using the pre-industrial simulation that anomalous salinity events in the western and eastern SPNA are driven by a combination of advective convergence and surface forcing, with a larger role of surface forcing in the western SPNA. Finally, we conclude that a major drop of nearly 2g/kg in salinity is projected to occur in the SPNA by the end of 2100. Anthropogenic signals in the vertical mixing and advective tendencies are expected to emerge in the eastern SPNA during 2020--2030 and in the west by 2040
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