Ashanthi Maxworth

Effect of finite electron and ion temperature on magnetospheric whistler mode raytracing

Numerical raytracing is an important technique that is being used to determine the trajectory of whistler mode waves in the magnetosphere. Previous whistler mode raytracing techniques were developed by assuming cold magnetospheric plasma. In this work we analyze the effect of finite electron and ion temperature on the whistler mode wave trajectories.

Power distribution of magnetospheric whistler mode waves with finite electron and ion temperature

Whistler mode waves play an important role in energy dynamics of Earths magnetosphere. A majority of the previous work on whistler mode raytracing in the Earths magnetosphere was done assuming a cold background plasma (0 k) even though the temperature of electrons and ions is around 1eV In this work we present our recent results on power distribution and lifetime of whistler mode waves with the inclusion of finite electron and ion temperature. The simulated power distribution results with finite temperature effects show a better agreement with the Van-Allen Probe space craft observations than the simulated results under cold plasma assumptions.

Warm plasma raytracing of whistler mode waves in the Earth's magnetosphere

Whistler mode waves play a major role in the energy dynamics of the Earths upper atmosphere. Previous studies show that inclusion of finite electron and ion temperature can modify the refractive index surface significantly for frequencies near the lower hybrid resonance and hence modify the ray trajectories. In this work we further study the properties of whistler mode waves originating around L = 4, with and without finite temperature effects. According to our ray tracing results inclusion of finite temperature increases the number of magnetospheric reflections. It also confines the wave energy inside the plasmasphere. Agreement of the ray tracing results and the Van Allen Probes observations are also presented.

Non-causal filtering applied to numerical whistler mode raytracing

Non causal filtering or smoothing is an important signal processing technique. In this work we implement a new non causal filter and apply it to whistler mode ray tracing platform. This smoothing technique is highly resistant to outliers; hence it helps on increasing the accuracy of the numerical results.

Multi-station observations of frequency dependence of amplitude and polarization of the ELF waves generated via ionospheric modification

Summary form only given. Generation of Extremely Low Frequency (ELF) and Very Low Frequency (VLF) signals through ionospheric modification has been practiced for many years. In ionospheric heating with high power HF waves, the electron temperature of the lower ionosphere is increased thereby changing the particle collision frequency and conductivity of the medium. Modulating the conductivity allows modulation of natural current systems.Our experiments were carried out at the High Frequency Active Auroral Research Program (HAARP) facility in Alaska, USA. In this experiment, the ionosphere was heated with a vertical amplitude modulating signal and the modulation frequency was changed sequentially within an array of 40 frequencies. The observed magnetic field amplitude and polarization of the generated ELF/VLF signals were analyzed for multiple sites and as a function of modulation frequency. Our three observation sites: Chistochina, Paxon and Paradise are located within 36km (azimuth 47.7°), 50.2km (azimuth -20°) and 99km (azimuth 80.3°) respectively. Based on the experimental results, we can show that the highest magnetic field strength was observed at 2.1 kHz which is the resonance frequency of the ionosphere, and the next highest peaks are observed at 4.1 kHz, 6.1 kHz respectively for all three sites. Out of the three sites Paxon shows the highest circularity in the magnetic field polarization, compared to Chistochina and Paradise which show highly linear polarizations. The experimental results were compared with a theoretical simulation model results and it was clear that in both cases, Hall current dominates in Chistochina and Paradise sites and Paxon is dominated by the Pedersen current. The Chistochina site shows the highest magnetic fieldfield amplitudes in both experimental and simulation environments. Depending upon the experimental and simulation observations at the three sites, a radiation pattern for the HAARP ionospheric heater can be mapped.