An investigation of the nature of Pc5 pulsations using SuperDARN and magnetometer data.

Ph. D. University of KwaZulu-Natal, Durban 2014.Pc5 pulsations are global magnetohydrodynamic events in the magnetosphere. We employed an Automated Pulsation Finder program to identify significant Pc5 pulsation events in SuperDARN data. Those events for which a resonance of similar frequency band was observed in more than one HF radar were selected. The three events presented here are such that a similar resonance was observed in Goose Bay, Saskatoon and Pykkvibaer HF radars, located in the northern polar region. One event was isolated in which the resonance was observed at the conjugate hemisphere at Sanae, Antarctica. Those events have a good data from magnetometer chains within the field of view of HF radars are chosen for analysis. These two instruments complement each other. We combined these two instruments to investigate the nature of the pulsation, determining its qualitative polarization characteristics. Observations of a resonance that extend over a large fraction of the polar region are rarely reported. A complex demodulation technique was employed to determine the amplitude and phase relationship between field components observed by the radars and magnetometer chains, this in turn, affords resolution of other characteristics of pulsations such as wave number and phase velocity. We present results in a graphical form and discuss them in the context of MHD theory of magnetic pulsations, speculating on their generation mechanism

Relative occurrence rates and connection of discrete frequency oscillations in the solar wind density and dayside magnetosphere

[1] We present an analysis of the occurrence distributions of statistically significant apparent frequencies of periodic solar wind number density structures and dayside magnetospheric oscillations in the f = 0.5–5.0 mHz range. Using 11 years (1995–2005) of solar wind data, we identified all spectral peaks that passed both an amplitude test and a harmonic F test at the 95% confidence level in 6-hour data segments. We find that certain discrete frequencies, specifically f = 0.7, 1.4, 2.0, and 4.8 mHz, occur more often than do other frequencies over those 11 years. We repeat the analysis on discrete oscillations observed in 10 years (1996–2005) of dayside magnetospheric data. We find that certain frequencies, specifically f = 1.0, 1.5, 1.9, 2.8, 3.3, and 4.4 mHz, occur more often than do other frequencies over those 10 years. Many of the enhancements found in the magnetospheric occurrence distributions are similar to those found in the solar wind. Lastly, we counted the number of times the same discrete frequencies were identified as statistically significant using our two spectral tests on corresponding solar wind and magnetospheric 6-hour time series. We find that in 54% of the solar wind data segments in which we identified a spectral peak, at least one of the same discrete frequencies was statistically significant in the corresponding magnetospheric data segment. Our results argue for the existence of inherent apparent frequencies in the solar wind number density that directly drive global magnetospheric oscillations at the same discrete frequencies, although the magnetosphere also oscillates through other physical mechanisms

An investigation of traveling ionospheric disturbances (TIDs) in the SANAE HF radar data

This thesis aims to study the characteristics of traveling ionospheric disturbances (TIDs) as identified in the radar data of the South African National Antarctic Expedition (SANAE) Super Dual Auroral Radar Network (SuperDARN) radar located in Antarctica. For this project, 22 TIDs were identified from visual inspection of range time-intensity (RTI) plots of backscattered power and Doppler velocity parameters of the SANAE radar between 2005âAS2015. These events were studied to determine their characteristics and driving mechanisms. Where good quality data were available, the SANAE HF radar data were supplemented by Halley radar data, which has large area of overlapping field of view (FOV) with the SANAE radar, and also by GPS TEC data. This provided a multi-instrument data analysis of some TID events. Different spectral analysis methods, namely the multitaper method (MTM), Fast Fourier transform (FFT) and the Lomb-Scargle periodogram were used to obtain spectral information of the observed waves. The advantage of using multiple windowing in MTM over the traditional windowing method was illustrated using one of the TID events. In addition, the analytic signal of the wave from the MTM method was used to estimate the instantaneous phase velocity and propagation azimuth of the wave, which was able to track the change in the characteristics of the medium-scale TID (MSTID) efficiently throughout the duration of the event. This is a clear advantage over other windowing techniques. The energy contribution by this MSTID through Joule heating was estimated over the region where spectral analysis of both SANAE and Halley data showed it to be present. The majority of the TIDs (65.4%) could be classified as MSTIDs with periods of 20–60 minutes, velocities of 50–333 ms1 and wavelengths of 129–833 km. The TID occurrence rate was high around the March equinox with 12 out of the 16 event days being during March–May. March had a particularly high number of occurrences of TIDs (46%). The majority of the TIDs observed during this month propagated northward or southeastward. In terms of prevailing geomagnetic conditions, 6 out of 16 event days were geomagnetically quiet, while 10 occurred during geomagnetic storms and substorms. During quiet conditions, TIDs could be linked to Es and polarised electric fields in 2 of these events. The other quiet time events could not be related to Es instability and polarised electric field either because their exact propagation direction could not be determined or data quality from the Es region scatter was too poor to perform spectral analysis. The storm-/substorm-related TIDs are possibly generated through Joule heating, the Lorentz force and energetic particle precipitation.Thesis (PhD) -- Faculty of Science, Physics and Electronics, 202

Radial Diffusion Models of Earth’s Outer Radiation Belt using Stochastic Parameterizations

Earth’s outer radiation belt is very dynamic and contains high-energy particles which are hazardous to spacecraft. Radial diffusion is the process by which energetic electrons undergo bulk transport and energization, driven by interactions with ultralow frequency (ULF) waves. Modelled by a Fokker-Planck equation, all of the physics to describe the strength of radial diffusion is contained in the radial diffusion coefficient, DLL, typically modelled proportionally to ULF wave power as a function of electron drift-shell (L ∗ ) and geomagnetic activity. A number of parameterizations for DLL exist but can vary by orders of magnitude. State of the art radial diffusion coefficient models therefore carry great uncertainty. All modern DLL parameterizations are deterministic and based on median ULF wave power spectral density. In this Thesis we investigate the impact on radial diffusion when DLL is modelled as an ensemble which encompasses the probabilistic distribution of ULF wave power. The underlying factors which contribute to variability in ULF wave power distributions are extensive and we concentrate on three of the largest: the variability of L ∗ with an observation’s location when mapping ULF wave power to adiabatic space, the shape of ULF wave power distributions as measured on board spacecraft as a function of L ∗ , local time and ULF wave frequency, and finally the mapping of ground-based magnetic wave power to space-based electric field power to infer a key component of DLL. We find that L ∗ varies in physical space significantly as a function of magnetic field model and geomagnetic activity, with uncertainties between magnetic field models unable to be completely mitigated. Further, shapes of space-based power approximations are either log-symmetric or log-skewed when separated into L ∗ and wave frequency, although there are characteristic differences across local time. Finally, we find that while mapping ground-based power with a stochastic ULF wave resonance width better aligns with space-based power distributions compared to the state-of-the-art analytic mapping, stochastic parameterizations of other key wave parameters are necessary to recover the full distribution. Combining the sources of variability which quantify the ULF wave power distributions into a stochastically parameterized DLL, we model an ensemble of radial diffusion and compare with a number of deterministic radial diffusion coefficients. In most cases a stochastic DLL results in more diffusion, with the spread of resulting phase space densities in the ensemble rarely enclosing those from the deterministic parameterizations. In addition, ensembles are collectively more diffusive when DLL is sampled more frequently in time and on shorter scale-lengths in L∗. Overall, this thesis demonstrates the importance of variability for impacting rates of radial transport. Future work could extend the stochastic approaches used to here to account for yet to be determined spatio-temporal ULF wave power variability

Spectral and polarization analysis of geomagnetic pulsations data using a multitaper method

Made available in DSpace on 2019-09-12T16:53:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2004Spectral and polarization parameters of geomagnetic pulsations are computed from geomagnetic data recorded at ground station, using multitaper and singular value decomposition (SVD) analysis. These techniques were adapted to provide appropriate polarization parameters of pulsations. The spectra are comparable to those obtained from classical methods, but the dynamic spectra of degree of polarization present more localized spectral information, allowing easier identification of polarized pulsation events mixed to noise, which are associated by coherent sources of MHD waves. The time-frequency polarization parameters of polarized pulsations show different signatures to regular and irregular pulsation events, and the multiwavelet polarization method is used to compare with multitaper. The regular pulsation events showed to be more continuous on time with a narrow spectral frequency band, while the irregular events showed to be more localized on time with a wide spectral frequency band. The dynamic analysis of multitaper method is indicated to characterize regular pulsations and the time-frequency analysis of multiwavelet method efficiently detects irregular pulsations. The continuous multiwavelet analysis of ellipticity and azimuth is useful in progressively monitoring the propagations of MHD waves in the magnetosphere, mainly in the irregular pulsations as observed on the magnetic storm of March 24, 1991. (C) 2004 Elsevier Ltd. All rights reserved.Natl Inst Space Res, ITA, Elect Engn Div, IEE, BR-12228900 Sao Jose Dos Campos, SP, Brazil; Natl Inst Space Res, DGE, Dept Geophys, BR-12201970 Sao Jose Dos Campos, SP, Brazil; Universidade de Taubaté (Unitau), Dept Math & Phys, BR-12020270 Taubate, SP, Brazil; Natl Inst Space Res, LAC, Lab Comp & Appl Math, BR-12201970 Sao Jose Dos Campos, SP, Brazi