Atmospheric & Oceanic Science Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2747
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Item OCEAN HEAT CONTENT CALCULATION IMPROVEMENTS FOR EARTH’S ENERGY IMBALANCE QUANTIFICATION(2024) Boyer, Tim; Carton, James; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Earth’s Energy Imbalance, the difference between incoming and outgoing radiation at the top of the atmosphere, is stored in the atmosphere, land surface, cryosphere, and ocean, but is stored overwhelmingly (~90%) in the ocean on interannual and longer time scales. This imbalance, which is reflected in ocean heat uptake, is a primary indicator of the magnitude of change in energy the Earth’s system as well as an essential variable for understanding short-term variations and their effects on long-term regional and global climate change. The primary methods for calculating ocean heat content all depend on situ measurements of ocean subsurface temperature. The ocean subsurface temperature observing system as it is currently configured, with a substantial but not exclusive contribution from autonomous Argo profiling floats, is shown here to allow estimation of annual global ocean heat uptake with an uncertainty well below that possible with earlier ocean observing systems. It is also shown that maintenance and improvement of a global best quality ocean temperature profile database will lower uncertainty, both historically and for the current observing system and compensate to some extent for areas of sparse data in both direct calculation from observation and in data assimilation models. It is also shown that improvements to the methods used for mapping the inhomogeneous and anisotropic observations onto a regular grid spanning the global ocean will reduce uncertainty historically, currently, and into the future. On shorter monthly timescales regional changes in the Earth’s Energy Imbalance requires tracking the storage within the atmosphere, land, and cryosphere, and the heat transport within the ocean especially to depths where the energy is stored on longer time scales, in addition to ocean heat uptake. Monthly heat uptake estimates discussed here can be utilized with additional terms from atmosphere/land and ocean/sea ice reanalyses to provide Earth's Energy Imbalance estimates on these shorter time-scales in the future.Item RETRIEVALS OF ANTARCTIC SEA ICE PHYSICAL PROPERTIES FROM SATELLITE RADAR ALTIMETRY(2021) Fons, Steven William; Carton, James; Kurtz, Nathan; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Satellite observations have been used in sea ice research throughout the last 40+ years and have brought to light substantial changes in the global sea ice coverage. More recently, satellite altimetry has become a valuable tool to estimate the thickness of sea ice - a parameter that plays an important role in the Earth System by moderating heat and moisture fluxes between the polar ocean and atmosphere. While radar altimetry has been effective in providing estimates of Arctic sea ice thickness, the complex snow stratigraphy and uncertain snow depth on Antarctic sea ice have precluded sea ice thickness retrievals in the Southern Ocean, leading to a decade-long gap in the thickness record spanning the lifetime of ESA’s CryoSat-2 satellite. This dissertation will address the need for Antarctic sea ice thickness estimates from CryoSat-2 through the development and assessment of new retrievals of sea ice physical properties that enable the estimation of sea ice thickness.The first part of this dissertation is aimed at developing a CryoSat-2 retrieval algorithm that is less dependent on uncertain returns from the snow-ice interface of Antarctic sea ice. This method exploits observed scattering of Ku-band radar pulses from the snow surface and snow volume atop sea ice and uses a physical waveform model and optimization approach to retrieve the air-snow interface elevation and snow freeboard. Building off the initial development, the second part of this work offers improvements to – and assessments of – the retrieval process though comparisons with coincident snow freeboard measurements from NASA’s ICESat-2 laser altimeter. The final part of this dissertation uses the retrieval process to estimate snow depth and ice freeboard, enabling first estimates of Antarctic sea ice thickness that span the CryoSat-2 mission. Potential applications for use of this method over Arctic sea ice are also explored. The studies within this dissertation represent new possibilities for CryoSat-2 data and lay a foundation for the development of a combined laser-radar altimetric record of Antarctic sea ice thickness.Item EVALUATING OCEANOGRAPHIC HYPOTHESES: THREE METHODS FOR TESTING IDEAS(2020) Johnson, Benjamin K; Kalnay, Eugenia E; Wenegrat, Jacob O; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The disciplines of meteorology and oceanography are both vital to understanding the earth system. Throughout most of the last half century, meteorology has largely been a prognostic discipline. Forecasts made by meteorologists have been widely used and scrutinized, allowing for countless opportunities to test and improve ideas about atmospheric circulation and physics. Since weather forecasts involve integrating numerical models and updating the model state via data assimilation, forecasting demands frequent use of the principles of Bayesian inference. This requirement essentially confronts the physics contained within numerical models at recurring intervals and can reveal systematic model bias. In contrast, prognostic applications have been less prevalent in oceanography. Oceanographic forecasts are much rarer than atmospheric forecasts and, perhaps as a consequence of this disparity, many ideas concerning oceanic circulation have not been tested to the same degree as ideas concerning atmospheric circulation. This dissertation presents three methods for testing oceanographic ideas: applying common methodologies to analogous regions of different ocean basins; creating synthetic time series to mimic the properties of oceanographic time series in order to construct null distributions for hypothesis testing; and using water mass census information to interpret the results of water mass transformation analysis.