William Lotko

Efficiency of Electromagnetic Energy Transfer from Solar Wind to Ionosphere through Magnetospheric Ultra-Low Frequency Waves

whawkins — Wed, 13 Aug 2025 20:10:55 +0000

Efficiency of Electromagnetic Energy Transfer from Solar Wind to Ionosphere through Magnetospheric Ultra-Low Frequency Waves whawkins Wed, 08/13/2025 - 14:10

Author:

whawkins

Aug 13, 2025

(a) 5-200 s bandpassed $S_{A//}$ mapped to the ionospheric altitude and averaged over the four-hour interval. (b) 5-200s bandpassed $S_{A//}$ in the 7 MLT plane. (c) 4.5-5.5 mHz root-integrated power (RIP) of radial electric field $E_r$ in the equatorial plane. (d) 4.5-5.5 mHz RIP of azimuthal magnetic field $B_\phi$ in the meridional plane of 7 MLT. (e-f) Field-aligned keograms of $E_{mrd}$ and $B_\phi$ along the green field line with the largest $S_{A//}$. The green curve in (b) and (d) is a magnetic field line in the 7 MLT plane connecting to the green cross in (a) which marks the location with the peak $S_{A//}$. This field line crosses the equatorial plane at the green cross in (c).

Geophysical Research Letter: Scientists have long been interested in how energy from the Sun is transferred into Earth’s space environment. The Earth's magnetosphere is an important intermediate environment between the solar wind and the upper atmosphere. Consisting of plasma and magnetic field, the magnetosphere is full of intrinsic plasma waves that are capable of energy transport, particularly a group in the frequency range of a few to a few tens Millihertz that are especially efficient in connecting the magnetosphere and the ionosphere. However, due to the global presence and propagation features of those waves, it has been very challenging with measurements from a limited number of locations to understand the efficiency of the wave based energy transfer mechanism. This study uses a first-principles computational model that can resolve the fundamental physics related to the low frequency plasma waves, to carry out idealized numerical experiments to investigate the electromagnetic energy flow in response to undulating solar wind. The theoretical study provides new understanding of the significance of the electromagnetic energy flow and its dependence on different parameters.

Thermospheric Impact on the Magnetosphere through Ionospheric Outflow

whawkins — Wed, 12 Oct 2022 20:32:56 +0000

Thermospheric Impact on the Magnetosphere through Ionospheric Outflow whawkins Wed, 10/12/2022 - 14:32

Author:

whawkins

Oct 12, 2022

Latest coupled model of thermosphere-ionosphere-magnetosphere system that includes realistic and causal ion outflow.

Kevin Pham, William Lotko, Roger Varney, Binzheng Zhang, Jing Liu have taken a key step in evaluating the importance of ionospheric outflows relative to electrodynamic coupling in the thermosphere’s impact on geospace dynamics. We isolated the thermosphere’s material influence and suppressed electrodynamic feedback in whole geospace simulations by imposing a time-constant ionospheric conductance in the ionospheric Ohm’s law in a coupled model that combines the multi-fluid Lyon-Fedder-Mobarry magnetosphere model with the Thermosphere Ionosphere Electrodynamic General Circulation Model and the Ionosphere Polar Wind Model that includes both polar wind and transversely accelerated ion species. Numerical experiments were conducted for different thermospheric states parameterized by F10.7 for interplanetary driving representative of the stream interaction region that swept past Earth on 27 March 2003. We demonstrate that thermosphere through its regulation of ionospheric outflows influences magnetosphere-ionosphere (MI) convection and the ion composition, symmetries, x-line perimeter and magnetic merging of the magnetosphere. Feedback to the ionosphere-thermosphere from evolving MI convection, and Alfvénic Poynting fluxes and soft (~ few 100 eV) electron precipitation originating in the magnetosphere, in turn, modify the evolving O+ outflow properties. The simulation results identify a variety of observed magnetospheric features that are attributable directly to the thermosphere’s material influence: Asymmetries in O+ outflow fluxes and velocities in the pre/postnoon low-altitude magnetosphere, dawn/duskside lobes and pre/postmidnight plasmasheet; O+ distribution of the plasmasheet; magnetic x-line location and reconnection rate along it. O+ outflows during solar maximum conditions (high F10.7) tend to counteract the plasmasheet’s pre/postmidnight asymmetries caused by the night-to-day gradient in ionospheric Hall conductance.

Alfvénic thermospheric upwelling in a global geospace model

kolinski — Tue, 16 Nov 2021 21:47:34 +0000

Alfvénic thermospheric upwelling in a global geospace model kolinski Tue, 11/16/2021 - 14:47

Publication: Journal of Geophysical Research: Space Physics; Authors: Benjamin Hogan, William Lotko, Kevin Pham

Author:

kolinski

Nov 16, 2021

First author, William Lotko, reveals that the CHAMP satellite orbiting near 400 km altitude near the magnetic cusp routinely traversed thermospheric density enhancements (up to 50%) that are not predicted by empirical models. The density enhancements are well-correlated with kilometer-scale field-aligned currents interpreted as ionospheric Alfvén resonator modes.

Air density in the northern hemisphere on 27 March 2003 when CHAMP passes through the edge of a high-latitude density enhancement. A: Simulated air density (color) at the CHAMP altitude vs MLT and MLAT at the UT corresponding to “CHAMP Location” in panel B. B: Comparison of instantaneously observed, simulated and MSIS empirical air density vs. UT. C: % difference in CMIT air density with and without Alfvénic heating.

With this motivation, we investigated the effects of Alfvén wave energy deposition on thermospheric upwelling and density. A subgrid model for the altitude dependence of the Alfvén wave electric field, constrained by CHAMP data, was developed and embedded in the Joule heating module of the National Center for Atmospheric Research (NCAR) Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model. The CMIT model was then used to simulate the geospace response to an interplanetary stream interaction region (SIR) that swept past Earth on 26-27 March 2003. Simulation results show that 1) inclusion of Alfvénic Joule heating in CMIT improves its instantaneous density prediction (up to 15%) along the CHAMP orbit near the cusp heating region; and 2) Thermospheric density changes of 20-30% caused by the cusp-region Alfvénic heating sporadically populate the polar region through the action of co-rotation and neutral winds.

Geospace response to an extreme solar flare

kolinski — Mon, 15 Nov 2021 21:58:00 +0000

Geospace response to an extreme solar flare kolinski Mon, 11/15/2021 - 14:58

Publication Name: AGU Advances; HAO Author: Jing Liu; Authors names as listed: Jing Liu, Wenbin Wang, Liying Qian, William Lotko, Alan G. Burns, Kevin Pham, Gang Lu, Stanley C. Solomon, et al.

Author:

kolinski

Nov 15, 2021

Solar flares—a sudden eruption of electromagnetic radiation at the Sun—are known to have significant impacts on Earth’s upper atmosphere and ionosphere, but their collective effects on geospace as an integrated system have never been examined. We use a newly developed whole geospace model, combined with key observational data, to study the effects of the 6 September 2017 X9.3 flare on the geospace system.

Solar flare effects on magnetospheric convection and ionospheric potential. Comparison of 50-minute averages (12:02-12:51 UT) from LTR simulations of magnetospheric and ionospheric states on September 6, 2017 with and without solar flare effects. Bottom row: LTR-simulated magnetospheric convection velocity in equatorial plane (ZGSM = 0) with (A) and without (B) solar flare effects and their difference (C). Arrows indicate direction and magnitude (also in color) of the convection velocity projected onto the plane. Top row: High-latitude electric potential, essentially convection streamlines in the ionosphere with (D) and without (E) solar flare effects and their difference (F). The minimum and maximum potentials are labeled below panels (D-F).

The analysis shows that the solar wind-magnetosphere interaction, magnetotail, field-aligned current distribution, auroral precipitation and high-latitude ionospheric convection respond to atmospheric absorption of solar flare radiation. This study, for the first time, demonstrates that a rapid and large increase in the iono-spheric E-region photoionization due to a solar transient event globally modifies the electrodynamic cou-pling of the geospace system.

William Lotko

Efficiency of Electromagnetic Energy Transfer from Solar Wind to Ionosphere through Magnetospheric Ultra-Low Frequency Waves

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Thermospheric Impact on the Magnetosphere through Ionospheric Outflow

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Alfvénic thermospheric upwelling in a global geospace model

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Geospace response to an extreme solar flare

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