Browsing by Author "Lysak, Robert L"

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    Fortran code for modeling the propagation of ULF waves in a 3-dimensional dipole magnetosphere
    (2020-04-13) Lysak, Robert L; Waters, Colin; Sciffer, Murray; lysak001@umn.edu; Lysak, Robert L; University of Minnesota Space Physics Group
    This code allows for the modeling of Ultra-Low-Frequency (ULF) waves in the Earth's magnetosphere. It has been used in a number of publications and presentations at conferences. It takes a prescribed driver in the form of a compression at the outer boundary and follows the propagation of the waves through the magnetosphere and to the ground. The output consists of files each containing snapshots of one component of the electromagnetic field at all points in the simulation volume at an instant of time, in addition to files containing background information such as the Alfven speed profile throughout the simulation.
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    A Numerical Model for Alfven Waves in Jupiter's Magnetosphere
    (2021-08-18) Lysak, Robert L; lysak001@umn.edu; Lysak, Robert L; University of Minnesota Space Physics Group
    The ionospheric Alfvén resonator (IAR) is a structure formed by the rapid decrease in the plasma density above a planetary ionosphere. This results in a corresponding increase in the Alfvén speed that can provide partial reflection of Alfvén waves. At Earth, the IAR on auroral field lines is associated with the broadband acceleration of auroral particles, sometimes termed the Alfvenic aurora. This arises since phase mixing in the IAR reduces the perpendicular wavelength of the Alfvén waves, which enhances the parallel electric field due to electron inertia. This parallel electric field fluctuates at frequencies of 0.1-20.0 Hz, comparable to the electron transit time through the region, leading to the broadband acceleration. The prevalence of such broadband acceleration at Jupiter suggests that a similar process can occur in the Jovian IAR. A numerical model of Alfvén wave propagation in the Jovian IAR has been developed to investigate these interactions. This model describes the evolution of the electric and magnetic fields in the low-altitude region close to Jupiter that is sampled during Juno’s perijove passes. In particular, the model relates measurement of magnetic fields below the ion cyclotron frequency from the MAG and Waves instruments on Juno and electric fields from Waves to the associated parallel electric fields that can accelerate auroral particles.
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    Numerical Model for the propagation of Alfven Waves produced by Jupiter's moon Io
    (2022-11-28) Lysak, Robert L; lysak001@umn.edu; Lysak, Robert L; Minnesota Institute for Astrophysics Space Physics Group
    We present first results from a new numerical model to describe the propagation of these Alfvén waves in the Io-Jupiter system. The model is cast in magnetic dipole coordinates and includes a dense plasma torus that is centered around the centrifugal equator. Results are presented for two density models, showing the dependence of the interaction on the magnetospheric density. The effect of the conductance of Jupiter’s ionosphere is considered. A model for the development of parallel electric fields is introduced, indicating that the main auroral footprints of Io can generated parallel potentials of up to 100 kV.
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    A numerical model to calculated field line resonances in Jupiter's magnetosphere
    (2020-08-07) Lysak, Robert L; Song, Yan; lysak001@umn.edu; Lysak, Robert L; Minnesota Institute for Astrophysics
    The arrival of the Juno satellite at Jupiter has led to an increased interest in the dynamics of the Jovian magnetosphere. Jupiter’s auroral emissions often exhibit quasi-periodic oscillations with periods of tens of minutes. Magnetic observations indicate that ultra-low-frequency (ULF) waves with similar periods are often seen in data from Galileo and other satellites traversing the Jovian magnetosphere. Such waves can be associated with field line resonances, which are standing shear Alfvén waves on the field lines. Using model magnetic fields and plasma distributions, the frequencies of field line resonances and their harmonics on field lines connecting to the main auroral oval have been determined. Time domain simulations of Alfvén wave propagation have illustrated the evolution of such resonances. These studies indicate that harmonics of the field line resonances are common in the 10-40 minute band.
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    Updated Fortran program for modeling ULF waves in a three-dimensional magnetosphere
    (2022-05-19) Lysak, Robert L; lysak001@umn.edu; Lysak, Robert L; University of Minnesota School of Physics and Astronomy Space Physics Group
    This is the update of a three-dimensional code in dipole geometry for modeling Ultra-Low-Frequency (ULF) waves. The previous version is at https://doi.org/10.13020/d1g7-c676. This code has been used in a study of so-called Pi2 pulsations in the magnetosphere, which are waves with a period of 1-2 minutes that are commonly observed during substorms. This code has been used in conjunction with analysis of data from the Van Allen Probes mission.