Faculty: Gurnett, Howes, Mutel, Spangler
Research Staff and Postdocs: J. TenBarge, F. Duru, W. Kurth, S.-Yi Ye, D. Menietti, G. Hospodarsky, J. Pickett, I. Christopher, D. Morgan,
Graduate Students: Kevin Nielson, Kris Klein, Christene Lynch, Andrew Kopf, Catherine Whiting
The University of Iowa has a long history of exploring the space environment and the planets of our solar system dating back to the early exploration of our magnetosphere and discovery of the radiation belts by James Van Allen. Today, research into these areas remains a strong suit of the Department of Physics and Astronomy, with investigations of turbulence in the solar wind, the magnetosphere of Mars, the Saturnian Auroral Kilometric radiation, and the turbulent density fluctuations in the inner heliosphere.
Turbulence in the Solar Wind
Professors Howes, Spangler
Postdoc Jason TenBarge,
Graduate students Kevin Nielson, Kris Klein, Catherine Whiting
In the study of turbulence in magnetized plasmas, the solar wind provides a unique opportunity to characterize the nature of turbulent fluctuations by making detailed dynamical measurements through in situ satellite observations. Although astrophysical plasma turbulence has traditionally been studied using the single fluid description known as magnetohydrodynamics (MHD), the collisionless conditions in the solar wind require a more detailed kinetic description to understand the nonlinear cascade of energy and the dissipation of the turbulent fluctuations at small scales due to resonant wave-particle interactions. Professor Howes and his collaborators have lead the way with the first attempts to numerically model the kinetic evolution and dissipation of turbulence in the solar wind plasma using the Astrophysical Gyrokinetics Code, AstroGK. The collaboration has recently completed the first-of-a-kind fully electromagnetic, kinetic simulations of magnetized turbulence in a homogeneous, weakly collisional plasma at the scale of the ion Larmor radius. This numerical result, recently published in Physical Review Letters, reproduces the qualitative features found in recent solar wind turbulence observations using the Cluster spacecraft and supports the hypothesis that the frequencies of turbulent fluctuations in the solar wind remain well below the ion cyclotron frequency both above and below the ion gyroscale.
In addition to these ground-breaking computational studies of solar wind turbulence, Professor Howes also focuses on the development of simple analytical models that the describe the evolution of the turbulent cascade in the solar wind. His collaboration has recently published a cascade model for the prediction of the nonlinear turbulent energy transfer and dissipation in the solar wind plasma in the Journal of Geophysical Research.
Studies of the Ionopause at Mars
Professors Gurnett and Howes
Postdoc Firdevs Duru
Using the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on the Mars Express spacecraft, Professor Gurnett and his group explore the dynamics of the interaction between the solar wind and the Martian ionosphere. Recent studies have provided evidence for the development of Kelvin-Helmholtz instabilities at the boundary between the solar wind and the Martian ionosphere, providing a potential mechanism for the evaporation of the Martian atmosphere. Current work, recently accepted by the Journal of Geophysical Research, has shown that a sharp density gradient at the ionopause is present during only about 10% of the measurements, suggesting a transient ionopause and perhaps indicating a dynamic interaction environment.
Studies of Planetary Radio Waves
Professors Gurnett, Mutel
Research staff W. Kurth, Sheng-Yi Ye, D. Menietti, G. Hospodarsky, J. Pickett, I. Christopher, D. Morgan
Graduate students Christene Lynch, Andrew Kopf
Non-thermal planetary radio emission occurs in the magnetospheres of all planets with significant magnetic fields. The most intense radio emission is created when electron beams stream into regions of increasing magnetic field (usually near the magnetic poles), resulting in the cyclotron maser instability - CMI. This resulting radiation, which is at the local electron cyclotron frequency, is confined to a thin cone nearly perpendicular to the magnetic field. It is the most intense radiation in the solar system, and is also seen in stellar radio bursts at much higher frequencies. Understanding the physics of the CMI mechanism and the associated radio emission may also play a role in future detection of extrasolar planets, which should also radiate intensely via the CMI instability.
Mutel, R. L. et al., 2010, CMI Growth Rates for Saturnian Kilometric Radiation, Geophys. Res. Letters, in press, doi:10.1029/2010GL044398.
Lamy, L. , et al. 2010, Properties of Saturn kilometric radiation measured within its source region, Geophys. Res. Lett. 37,2,Issue 12, CiteID L12104.
Duru, F. D. A. Gurnett, R. A. Frahm, J. D. Winningham, D. D. Morgan, G. G. Howes "Steep, Transient Density Gradients in the Martian Ionopshere Similar to the Ionopause at Venus," Journal of Geophysical Research, in press 2009.
Gurnett, D. et al. 2009, Discovery of a north-south asymmetry in Saturn's radio rotation period, Geophys. Res. Lett.
Gurnett, D. and Kurth, W. 2008, Intense plasma waves at and near the solar wind termination shock, Nature.
Howes, G. G., Cowley, S. C., Dorland, W., Hammett, G. W., Quataert, E., Schekochihin, A. A. and Tatsuno, T. 2008, "Kinetic Simulations of Magnetized Turbulence in Astrophysical Plasmas," Physical Review Letters 100, 065004.
Howes, G. G., 2008, Inertial Range Turbulence in Kinetic Plasmas," Physics of Plasmas 15, 055904.
Mutel, R.L., Peterson, W., Jaeger, T. and Scudder, J. 2007, JGR, 'Dependence of cyclotron maser instability growth rates on electron velocity distributions and perturbation by solitary waves'.
Mutel, R. L., Christopher, I., and Pickett, J. 2008, "Cluster multispacecraft determination of AKR angular beaming", Geophys. Res. Letters
Spangler. S.R. 2007, A Technique for Measuring Electrical Currents in the Solar Corona, ApJ, 670, 841.
Ingleby, L. D., Spangler, S.R. and Whiting, C.A. 2007, Probing the Large Scale Plasma Structure of the Solar Corona with Faraday Rotation, ApJ, 668, 520.