Maitrayee Bordikar

Observations and theory of ion gyro-harmonic structures in the stimulated radiation spectrum during second electron gyro-harmonic heating

Recent observations of Stimulated Electromagnetic Emissions SEE for ionospheric heating near the second electron gyro-harmonic frequency at the HAARP facility are provided. These observations show previously unobserved structures ordered by harmonics of the ion gyro-frequency. An analytical model is presented for three-wave coupling between the pump wave, upper hybrid/electron Bernstein waves, and electrostatic ion cyclotron harmonic waves. It is shown that for pump wave frequencies near the second electron gyro-harmonic, a band of upper hybrid/electron Bernstein waves separated by harmonics of the ion gyro-frequency can be destabilized. A new 2-D computational model using the Particle-In-Cell PIC method is used to more thoroughly investigate the nonlinear processes involved in producing these spectral features and provide results reasonably in line with predictions of the simplified analytical model.

Irregularities Associated With Creation of Dusty Plasmas in the Near-Earth Space Environment

Plasma irregularities associated with the creation of an artificial dust layer in the Earths ionosphere are investigated with a 2-D plasma simulation model. The scenario considered in this investigation is the production of electron irregularities due to growth of a plasma instability driven by inhomogeneities in the boundary between the background plasma and the expanding charged dust layer. The mechanism is shown to effectively generate irregularities for early times after a localized release of dust for the parameter regimes of upcoming space experiments.

Impact of active geomagnetic conditions on stimulated radiation during ionospheric second electron gyroharmonic heating

Recently, narrowband emissions ordered near the H+ (proton) gyrofrequency (fcH) were reported in the stimulated electromagnetic emission (SEE) spectrum during active geomagnetic conditions. This work presents new observations and theoretical analysis of these recently discovered emissions. These emission lines are observed in the stimulated electromagnetic emission (SEE) spectrum when the transmitter is tuned near the second electron gyroharmonic frequency (2fce) during recent ionospheric modification experiments at the High Frequency Active Auroral Research (HAARP) facility near Gakona, Alaska. The spectral lines are typically shifted below and above the pump wave frequency by harmonics of a frequency roughly 10% less than fcH (≈ 800 Hz) with a narrow emission bandwidth less than the O+ gyrofrequency (≈ 50 Hz). However, new observations and analysis of emission lines ordered by a frequency approximately 10% greater than fcH are presented here for the first time as well. The interaction altitude for the heating for all the observations is in the range of 160 km up to 200 km. As described previously, proton precipitation due to active geomagnetic conditions is considered as the reason for the presence of H+ ions known to be a minor background constituent in this altitude region. DMSP satellite observations over HAARP during the heating experiments and ground-based magnetometer and riometer data validate active geomagnetic conditions. The theory of parametric decay instability in multi-ion component plasma including H+ ions as a minority species described in previous work is expanded in light of simultaneously observed preexisting SEE features to interpret the newly reported observations. Impact of active geomagnetic conditions on the SEE spectrum as a diagnostic tool for proton precipitation event characterization is discussed.

Lower Hybrid Turbulence Associated With Creation of Dusty Plasmas in the Near-Earth Space Environment

Plasma turbulence associated with the creation of an artificial dust layer in the Earths ionosphere is investigated. Two scenarios are considered for plasma irregularity generation as dust is injected at an oblique angle across the magnetic field. The first is a shear-driven plasma instability due to inhomogeneities in the boundary layer between the injected charged dust layer and the background plasma. This begins to appear at very early times relative to the release of the dust into the plasma, which is on the order of or less than the dust charging time period. The second mechanism is free streaming of the dust relative to the background plasma, which produces irregularities at times much longer than the dust charging period and also longer than the dust plasma period. Although both mechanisms are shown to produce turbulence in the lower hybrid frequency range, the resulting irregularities have important differences in their physical characteristics. A comparison between the processes is made to determine the consequences for upcoming observations. Both processes are shown to have the possibility to generate turbulence after the release of dust for the regimes of upcoming space experiments over a range of timescales.

Narrowband stimulated electromagnetic emissions (SEE) spectra: A new ionospheric diagnostic technique

Use of high frequency (HF) heating experiments has been extended in recent years as a useful methodology for plasma physicists wishing to remotely study the properties and behavior of the ionosphere as well as nonlinear plasma processes. Our recent work using high latitude heating experiments has lead to several important discoveries that have enabled assessment of active geomagnetic conditions, determination of minor ion species and their densities, ion mass spectrometry, electron temperature measurements in the heating ionosphere, as well a deeper understanding of physical processes associated with electron acceleration and formation of field aligned irregularities. All of these diagnostic capabilities have been made possible for the first time by utilizing the narrowband Stimulated Electromagnetic Emission SEE spectrum. Narrowband SEE spectra from the High Frequency Active Auroral Research Program (HAARP) facility are presented with theoretical models to demonstrate these new capabilities along with other supporting diagnostic measurements including, range-time-intensity of FAIs (field aligned irregularities) using SuperDARN HF radar, enhanced ion lines detected by MUIR radar, DMSP satellite observations over HAARP, and coordinated observations of pump induced optical emissions.