Plasma irregularity production in the polar cap f-region ionosphere

Thesis (Ph.D.) University of Alaska Fairbanks, 2017Plasma in the Earth's ionosphere is highly irregular on scales ranging between a few centimeters and hundreds of kilometers. Small-scale irregularities or plasma waves can scatter radio waves resulting in a loss of signal for navigation and communication networks. The polar region is particularly susceptible to strong disturbances due to its direct connection with the Sun's magnetic field and energetic particles. In this thesis, factors that contribute to the production of decameter-scale plasma irregularities in the polar F region ionosphere are investigated. Both global and local control of irregularity production are studied, i.e. we consider global solar control through solar illumination and solar wind as well as much more local control by plasma density gradients and convection electric field. In the first experimental study, solar control of irregularity production is investigated using the Super Dual Auroral Radar Network (SuperDARN) radar at McMurdo, Antarctica. The occurrence trends for irregularities are analyzed statistically and a model is developed that describes the location of radar echoes within the radar's field-of-view. The trends are explained through variations in background plasma density with solar illumination affecting radar beam propagation. However, it is found that the irregularity occurrence during the night is higher than expected from ray tracing simulations based on a standard ionospheric density model. The high occurrence at night implies an additional source of plasma density and it is proposed that large-scale density enhancements called polar patches may be the source of this density. Additionally, occurrence maximizes around the terminator due to different competing irregularity production processes that favor a more or less sunlit ionosphere. The second study is concerned with modeling irregularity characterics near a largescale density gradient reversal, such as those expected near polar patches, with a particular focus on the asymmetry of the irregularity growth rate across the gradient reversal. Directional dependencies on the plasma density gradient, plasma drift, and wavevector are analyzed in the context of the recently developed general fluid theory of the gradient-drift instability. In the ionospheric F region, the strongest asymmetry is found when an elongated structure is oriented along the radar's boresight and moving perpendicular to its direction of elongation. These results have important implications for finding optimal configurations for oblique-scanning ionospheric radars such as SuperDARN to observe gradient reversals. To test the predictions of the developed model and the general theory of the gradient-drift instability, an experimental investigation is presented focusing on decameter-scale irregularities near a polar patch and the previously uninvestigated directional dependence of irregularity characteristics. Backscatter power and occurrence of irregularities are analyzed using measurements from the SuperDARN radar at Rankin Inlet, Canada, while background density gradients and convection electric fields are found from the north face of the Resolute Bay Incoherent Scatter Radar. It is shown that irregularity occurrence tends to follow the expected trends better than irregularity power, suggesting that while the gradient-drift instability may be a dominant process in generating small-scale irregularities, other mechanisms such as a shear-driven instability or nonlinear process may exert greater control over their intensity. It is concluded from this body of work that the production of small-scale plasma irregularities in the polar F-region ionosphere is controlled both by global factors such as solar illumination as well as local plasma density gradients and electric fields. In general, linear gradient-drift instability theory describes small-scale irregularity production well, particularly for low-amplitude perturbations. The production of irregularities is complex, and while ground-based radars are invaluable tools to study the ionosphere, care must be taken to interpret results correctly

Observations and Modeling of Scintillation in the Vicinity of a Polar Cap Patch

Small-scale ionospheric plasma structures can cause scintillation in radio signals passing through the ionosphere. The relationship between the scintillated signal and how plasma structuring develops is complex. We model the development of small-scale plasma structuring in and around an idealized polar cap patch observed by the Resolute Bay Incoherent Scatter Radars (RISR) with the Geospace Environment Model for Ion-Neutral Interactions (GEMINI). Then, we simulate a signal passing through the resulting small-scale structuring with the Satellite-beacon Ionospheric scintillation Global Model of the upper Atmosphere (SIGMA) to predict the scintillation characteristics that will be observed by a ground receiver at different stages of instability development. Finally, we compare the predicted signal characteristics with actual observations of scintillation from ground receivers in the vicinity of Resolute Bay. We interpret the results in terms of the nature of the small-scale plasma structuring in the ionosphere and how it impacts signals of different frequencies, and attempt to infer information about the ionospheric plasma irregularity spectrum

Infrastructure needs on latitudinal and longitudinal chains of co-located ground-based observations

The generation, propagation, and dissipation of atmospheric planetary waves (PW), tides, and gravity waves (GW) constitute the primary mechanism that transfers energy and momentum from the atmosphere to space. While single-location ground-based observations have been making successful measurements of such waves over the past decades, NSF funded ground-based observations are not yet systematically distributed at the same latitude or the same longitude, despite the importance of latitudinal and longitudinal dependence of dynamical processes like large scale wave propagation, interaction, and dissipation. This white paper discusses the significance and potential of coordinating a chain of ground-based instruments with the current large facilities to extend the latitudinal and longitudinal observational coverage in the American sector (both South and North America). We further discuss the benefits of co-locating heterogeneous instruments with different techniques and different temporal/spatial resolution/coverage, for instance, radio instruments (e.g., ISR, HF radar, meteor radar), optical instruments (e.g., FPI, lidar, airglow imager), magnetometers, ionosondes, sounding rockets and so on

True volumes of slope failure estimated from a Quaternary mass-transport deposit in the northern South China Sea

Submarine slope failure can mobilize large amounts of seafloor sediment, as shown in varied offshore locations around the world. Submarine landslide volumes are usually estimated by mapping their tops and bases on seismic data. However, two essential components of the total volume of failed sediments are overlooked in most estimates: a) the volume of sub-seismic turbidites generated during slope failure and b) the volume of shear compaction occurring during the emplacement of failed sediment. In this study, the true volume of a large submarine landslide in the northern South China Sea is estimated using seismic, multibeam bathymetry and ODP/IODP well data. The submarine landslide was evacuated on the continental slope and deposited in an ocean basin connected to the slope through a narrow moat. This particular character of the sea floor provides an opportunity to estimate the amount of strata remobilized by slope instability. The imaged volume of the studied landslide is ~1035±64 km3, ~406±28 km3 on the slope and ~629±36 km3 in the ocean basin. The volume of sub-seismic turbidites is ~86 km3 (median value) and the volume of shear compaction is ~100 km3, which are ~8.6% and ~9.7% of the landslide volume imaged on seismic data, respectively. This study highlights that the original volume of the failed sediments is significantly larger than that estimated using seismic and bathymetric data. Volume loss related to the generation of landslide-related turbidites and shear compaction must be considered when estimating the total volume of failed strata in the submarine realm

Polar Cap Patches Detected with RISR-N

<p>Database of Polar Cap Patches detected with the North face of the Resolute Bay Incoherent Scatter Radar (RISR-N)</p> <p>This dataset was generated by applying two polar cap patch detection algorithm described to the full RISR-N database</p> <p>The Ren2018 algorithm was first described in <a href="http://https//doi.org/10.1029/2018JA025621">Ren et al., 2018 (doi:10.1029/2018JA025621)</a>.  It includes the time, peak, and prominence of all detected patches, asd well as the average electron and ion temperature and electron density within each patch.</p> <p>The Perry2018 algorithm was first described in <a href="https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018RS006600">Perry & St. Maurice, 2018 (doi:10.1029/2018RS006600)</a>.  Instead of a list of patches, this algorithm generates a patch index for each time in the database which corresponds to the percentage of the F-region FoV filled with patches.</p> <p>The script that generates this database in available on GitHub: <a href="https://github.com/Polar-Cap-Scintillation/polar_cap_patch_detection">Polar-Cap-Scintillation/polar_cap_patch_detection</a></p&gt

Polar Cap Patches Detected with RISR-N

Database of Polar Cap Patches detected with the North face of the Resolute Bay Incoherent Scatter Radar (RISR-N) This dataset was generated by applying the polar cap patch detection algorithm described in Ren et al., 2018 (doi:10.1029/2018JA025621) to the full RISR-N database. It includes the time, peak, and prominence of all detected patches

Observations and modeling of scintillation in the vicinity of a polar cap patch

Small-scale ionospheric plasma structures can cause scintillation in radio signals passing through the ionosphere. The relationship between the scintillated signal and how plasma structuring develops is complex. We model the development of small-scale plasma structuring in and around an idealized polar cap patch observed by the Resolute Bay Incoherent Scatter Radars (RISR) with the Geospace Environment Model for Ion-Neutral Interactions (GEMINI). Then, we simulate a signal passing through the resulting small-scale structuring with the Satellite-beacon Ionospheric-scintillation Global Model of the upper Atmosphere (SIGMA) to predict the scintillation characteristics that will be observed by a ground receiver at different stages of instability development. Finally, we compare the predicted signal characteristics with actual observations of scintillation from ground receivers in the vicinity of Resolute Bay. We interpret the results in terms of the nature of the small-scale plasma structuring in the ionosphere and how it impacts signals of different frequencies and attempt to infer information about the ionospheric plasma irregularity spectrum

Reproducible Software Environment: a tool enabling computational reproducibility in geospace sciences and facilitating collaboration

The Reproducible Software Environment (Resen) is an open-source software tool enabling computationally reproducible scientific results in the geospace science community. Resen was developed as part of a larger project called the Integrated Geoscience Observatory (InGeO), which aims to help geospace researchers bring together diverse datasets from disparate instruments and data repositories, with software tools contributed by instrument providers and community members. The main goals of InGeO are to remove barriers in accessing, processing, and visualizing geospatially resolved data from multiple sources using methodologies and tools that are reproducible. The architecture of Resen combines two mainstream open source software tools, Docker and JupyterHub, to produce a software environment that not only facilitates computationally reproducible research results, but also facilitates effective collaboration among researchers. In this technical paper, we discuss some challenges for performing reproducible science and a potential solution via Resen, which is demonstrated using a case study of a geospace event. Finally we discuss how the usage of mainstream, open-source technologies seems to provide a sustainable path towards enabling reproducible science compared to proprietary and closed-source software