PRESENT AND ONGOING RESEARCH

The University of Iowa Plasma Wave Investigation science team, including its non-Iowa Co-Investigators, are dedicated to participating in a coordinated effort with all of the ISTP spacecraft and ground-based investigators in carrying out, when possible, the scientific objectives of the GGS and ISTP programs. These objectives include the evaluation globally of effects of solar activity on the flow of energy, momentum and mass through the Sun-Earth-connected system; the understanding of how individual parts of the closely coupled, highly time-dependent geospace system work together; the determination of the control exercised by plasma processes in geospace of the energy input to the Earth's atmosphere, and the provision of a comprehensive data set for determining the accuracy and prediction capability of geospace models. The Polar PWI science team will continue to analyze plasma wave measurements in collaboration with other ISTP investigations in order to characterize wave-particle processes associated with the auroral zone, the magnetic cusp, the dayside magnetosheath, and the night side equatorial plasmasheet. Some of the specific research topics which the PWI science team intends to continue pursuing or begin studying in support of these goals and in support of furthering our understanding of plasma waves in general are summarized below:

Measurement of spectral and wave vector characteristics of electromagnetic and electrostatic plasma waves generated by ground based sources, such as lightning and VLF transmitters, and correlation with Polar CEPPAD and PIXIE data to determine the level and spatial scale of energetic particle precipitation due to resonance interactions with these waves.
First measurement of lightning-generated whistlers from mesoscale thunderstorm systems in correlation with X-Ray images from the Polar PIXIE instrument to determine the spatial extent of lightning-induced electron precipitation regions.
First ever simultaneous measurement of discrete waves (whistlers, chorus) and energetic particles (CEPPAD) with sufficient resolution in time, energy and pitch angle and sufficient sensitivity to detect bursts of electrons injected into the loss cone together with the driving waves. The complement of instruments on the Polar spacecraft will allow the first ever opportunity to measure such detailed signatures to confirm/refute theoretical models.
Measurement of lightning-generated whistlers and plasmaspheric hiss in order to determine the total whistler input energy that appears as hiss.
Measurement of electromagnetic and electrostatic waves in the plasmasphere and subauroral region to determine the characteristics of lower hybrid waves excited by electromagnetic whistler mode waves of particular importance in measurements on magnetic field lines linking mesoscale thunderstorm systems and correlation with energetic electron and ion measurements.
Measurement of electromagnetic and electrostatic waves (e.g., lower hybrid waves) in the auroral regions and correlations with ion observations to determine the acceleration mechanism of ions. The results will be used to determine whether laboratory experiments are accurate in their finding that large electrostatic waves can be generated in the auroral regions via the scattering of whistler mode hiss from field-aligned irregularities.
Measurement of whistler-mode waves on open and closed field lines to test the suggestion that the observed growth extends over large segments of paths that do not include the magnetic equator. Such data will aid in determining the properties of VLF waves and emission generation on open field lines and their potential for use as new diagnostic tools of this little understood region of the distant magnetosphere.
Investigate electromagnetic impulses of uncertain origin, with particular emphasis on the distribution in space of impulses relative to regions of open and closed field lines. Recent work indicates that these impulsive signals may be fundamentally important to very low frequency emission generation.
Analyze outer zone chorus, plasmaspheric hiss, inner zone hiss, magnetopause boundary layer waves, and polar cap/cusp waves in concert with other Polar particle and field instruments in order to characterize these regions and more precisely determine the generation mechanisms of the emissions. In connection with this is the determination of the substorm/storm dependence on these waves.
Perform collaborative studies with the energetic particle team to determine wave-particle interaction effects and predicted particle losses to the upper atmosphere/lower ionosphere.
Determine, by using PWI data and Polar UVI data, the global ionospheric energy deposition by the wave-particle interactions.
Investigate Langmuir waves, lower hybrid/ion Bernstein waves, double layers, electrostatic ion cyclotron/ion acoustic waves, spatial irregularities, and broadband noise within and above the auroral acceleration region as well as the near-earth plasma sheet using the PWI interferometry mode where spatially-separated field measurements are performed using two different modes. These modes include employing different sets of antennas as well as operating the antennas in low or high impedance to measure either density or electric field fluctuations, which depends on the Polar EFI instrument for ensuring that the antennas are put in these modes. By using the interferometry mode of PWI, wave vectors of the plasma waves can be obtained. This, along with frequency, constitutes all of the wave properties, which is essential for determining the wave origin, its propagation characteristics, and its effect on other plasma populations (wave-particle interactions).
Use wave vectors obtained through PWI interferometry mode, phase velocities and times of flight to develop quantitative tests for theories of wave-particle interactions and plasma wave origin.
Perform numerical test particle calculations that predict the electron spectra that would be expected given various kinds of waves and compare these predictions or make further calculations if necessary and then compare the results of these calculations with both the Polar wave and particle data. This study is applicable to the acceleration of electrons and ions in the aurora by waves and is relevant to the ISTP program because auroral acceleration and the creation of the outer electron radiation belt are two sinks of energy for magnetospheric processes, all of which is applicable to finding out how energy is transferred within the magnetosphere.
Determine the wave normal angle and frequency spectrum of chorus emissions or other waves in regions coincident with the outer radiation belt. These outer zone electrons have a practical importance since they can lead to the degradation of spacecraft through radiation damage and deep dielectric charging.
Analyze the multi-component wave data by the method of wave distribution function (WDF) analysis, a form of generalized direction-finding crucial for determining the modes of origin of natural wave emissions, since the growth rate of an unstable wave depends on the angle between the wave normal and the magnetic field, other things being equal.
Study electrostatic electron cyclotron harmonic bands which are long thought to be responsible for diffuse aurora via pitch-angle scattering of ~keV electrons. This work will be carried out in concert with the Polar HYDRA instrument team, which will measure electron distribution, in order to determine source of free energy and to assess extent of pitch angle diffusion.
Build on IMP, Hawkeye, ISEE, and DE studies of nonthermal continuum radiation by studying the conversion of electromagnetic waves from electrostatic upper hybrid ECH bands. Capture of the waveform will be used to investigate electromagnetic and electrostatic wave vectors in order to support or refute Jone's radio window hypothesis which suggests wave-wave interaction conditions of nonlinear conversion.
Perform a general study of broadband electrostatic noise (BEN) in conjunction with the Polar VIS, EFI, MAG, and HYDRA instruments for the following reasons: likely tracer for auroral field lines to establish mapping from auroral zones to low latitude boundary layer or plasma sheet; link between BEN and electrostatic solitary waves; possible mechanism for field-aligned electric fields (integration of small double layers along field lines); occurrence and characteristics of BEN with electron/ion distribution functions; and possible connection between BEN and parallel electric fields.
Use Auroral Kilometric Radiation (AKR) in the following studies: integrate over AKR band when in emission cone to establish proxy for AE index (perhaps with the WIND/WAVES instrument to subtract type III solar bursts); determine under what circumstances Type III Solar Radio Bursts trigger AKR; demonstrate that the onset of AKR is a temporal marker of substorm activity and correlate with the WIND spacecraft upstream conditions and response of the magnetosphere to changes such as rotations of the interplanetary field to southward Bz and with GEOTAIL and ground-based observations ; investigate the cause of AKR fine structure in relation to density perturbations in the source region; study AKR snaking to identify the source with global imaging data; map source region, especially as function of R, by search for fmin(AKR) ~ fce.; and investigate source distribution function (trapped electrons or loss cone) with the Polar HYDRA instrument.
Study auroral myriametric radiation, which appears to have a continuum type spectrum and frequently coincident with AKR, in order to determine whether it is a general or propagation phenomenon.
Investigate auroral hiss with the goal of identifying sources for the hiss with the aid of other instruments (plasma, energetic particles, magnetometers), of determining its propagation characteristics and what regions of geospace it populates.
Characterization of the structure and dynamics of the cold plasma throughout the POLAR orbit using measurements of the electron number density.
Investigate what phenomena are observed by POLAR when plasmoids and flux-ropes are detected in the geomagnetic tail by GEOTAIL.
Study Continuum Storms with the goal of determining under what circumstances they can or will be observed by POLAR, what are the source regions and source mechanisms, what is responsible for the time delays between substorm onset and their detection; and why does their spectral form frequently have an aerodynamic shape.