Joseph B.H. Baker
· Professor of Electrical and Computer EngineeringVerifiedVirginia Tech · Electrical and Computer Engineering
Active 1911–2026
About
Joseph B.H. Baker is a professor affiliated with the Bradley Department of Electrical and Computer Engineering at Virginia Tech. He holds a Ph.D. from the University of Michigan, obtained in 2001, and a B.S. from the University of New England, earned in 1992. His research interests include electromagnetics, space science, remote sensing, radar, space weather, aurora, magnetosphere-ionosphere physics, and space science. He is involved in teaching and research within these areas, contributing to the academic and scientific community at Virginia Tech.
Research topics
- Physics
- Geophysics
- Computer Science
- Geology
- Geodesy
- Remote sensing
- Astronomy
- Atmospheric sciences
- Optics
- Telecommunications
Selected publications
Geophysical Research Letters · 2026-03-12
articleOpen accessAbstract Ultra‐low‐frequency (ULF) waves cause local Thermosphere‐Ionosphere (T‐I) perturbations, but their impacts on the global T‐I system including the generation of Traveling Atmospheric Disturbances (TADs) have never been evaluated. The mechanisms responsible for the TAD generation and propagation, whether through dynamic or thermal process, are not clear either. We present a model study of ULF wave impacts on the thermosphere using the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model. The model results indicate that ULF waves can trigger globally propagating TADs at ∼810 m/s. Thermal processes are the main driver for the TAD generation and propagation, with Joule heating and adiabatic processes taking effects inside the TAD source region, and adiabatic processes and heat conduction being the dominant processes outside. Model results also show that TAD propagation is almost independent of seasonal effects. This study reveals the physical connections between magnetospheric ULF waves and thermospheric disturbances for the first time.
VTechWorks (Virginia Tech) · 2025-03-18
articleUltra low frequency (ULF; 1 mHz ‐ several Hz) waves are key to energy transport within the geospace system, yet their contribution to Joule heating in the upper atmosphere remains poorly quantified. This study statistically examines Joule heating associated with ionospheric ULF perturbations using Super Dual Auroral Radar Network (SuperDARN) data spanning middle to polar latitudes. Our analysis utilizes high‐timeresolution measurements from SuperDARN high‐frequency coherent scatter radars operating in a special mode, sampling three “camping beams” approximately every 18 s. We focus on ULF perturbations within the Pc5 frequency range (1.6–6.7 mHz), estimating Joule heating rates from ionospheric electric fields derived from SuperDARN data and height‐integrated Pedersen conductance from empirical models. The analysis includes statistical characterization of Pc5 wave occurrence, electric fields, Joule heating rates, and azimuthal wave numbers. Our results reveal enhanced electric fields and Joule heating rates in the morning and pre‐midnight sectors, even though Pc5 wave occurrences peak in the afternoon. Joule heating is more pronounced in the highlatitude morning sector during northward interplanetary magnetic field conditions, attributed to local time asymmetry in Pedersen conductance and Pc5 waves driven by Kelvin‐Helmholtz instability. Pc5 waves observed by multiple camping beams predominantly propagate westward at low azimuthal wave numbers (|m|<50), while high‐m waves propagate mainly eastward. Although Joule heating estimates may be underestimated due to assumptions about empirical conductance models and the underestimation of electric fields resulting from SuperDARN line‐of‐sight velocity measurements, these findings offer valuable insights into ULF wave‐related energy dissipation in the geospace system.
VTechWorks (Virginia Tech) · 2025-10-23
articleSolar flares are a rapid increase in solar irradiance, specifically in X‐ray and Extreme Ultraviolet spectra, which enhances the ionization in the dayside ionosphere and creates Sudden Ionospheric Disturbances (SIDs). SIDs are known to create space weather impacts on traveling high frequency (HF: 3–30 MHz) radio waves, by disrupting the communication channels. In this study, we examine ionospheric scatters at dawn terminator, which stems from a severe X9.3 flare on 6 September 2017 peaked at 12:02 UT, utilizing SuperDARN HF coherent scatter radars and Global Navigation Satellite System (GNSS) Total Electron Content (TEC) observations. Specifically, we are interested in the transients in the ionospheric electrodynamics at the sub‐auroral latitude near the terminator stemming from the flare effect. Observations suggest that flare‐induced density gradient likely favors the formation of gradient‐drift instability near the dawn terminator, leading to the irregularities observed by the SuperDARN radars with line‐of‐sight (LoS) Doppler velocity reaching nearly 300 m/s. The flare amplifies the eastward TEC gradient near the dawn terminator by approximately 2–3 times compared to a geomagnetically quiet and non‐flare day. The observed irregularities, attributed to flare‐driven instabilities, exhibit a velocity consistent with the equatorial return flow of ionospheric Hall convection. In contrast to prior studies indicating decreased cross‐polar‐cap potential and associated ionospheric convection flow, our findings show the flare is followed by an increase in localized electric field near the dawn terminator, as depicted in radar LoS velocity.
Journal of Geophysical Research Space Physics · 2025-03-01 · 3 citations
articleOpen accessAbstract Ultra low frequency (ULF; 1 mHz ‐ several Hz) waves are key to energy transport within the geospace system, yet their contribution to Joule heating in the upper atmosphere remains poorly quantified. This study statistically examines Joule heating associated with ionospheric ULF perturbations using Super Dual Auroral Radar Network (SuperDARN) data spanning middle to polar latitudes. Our analysis utilizes high‐time‐resolution measurements from SuperDARN high‐frequency coherent scatter radars operating in a special mode, sampling three “camping beams” approximately every 18 s. We focus on ULF perturbations within the Pc5 frequency range (1.6–6.7 mHz), estimating Joule heating rates from ionospheric electric fields derived from SuperDARN data and height‐integrated Pedersen conductance from empirical models. The analysis includes statistical characterization of Pc5 wave occurrence, electric fields, Joule heating rates, and azimuthal wave numbers. Our results reveal enhanced electric fields and Joule heating rates in the morning and pre‐midnight sectors, even though Pc5 wave occurrences peak in the afternoon. Joule heating is more pronounced in the high‐latitude morning sector during northward interplanetary magnetic field conditions, attributed to local time asymmetry in Pedersen conductance and Pc5 waves driven by Kelvin‐Helmholtz instability. Pc5 waves observed by multiple camping beams predominantly propagate westward at low azimuthal wave numbers , while high‐m waves propagate mainly eastward. Although Joule heating estimates may be underestimated due to assumptions about empirical conductance models and the underestimation of electric fields resulting from SuperDARN line‐of‐sight velocity measurements, these findings offer valuable insights into ULF wave‐related energy dissipation in the geospace system.
2025-03-14
preprintOpen accessGeomagnetic field variations related to magnetospheric Ultra Low Frequency (ULF) waves are frequently observed during geomagnetically active conditions, and they induce geoelectric fields that ultimately drive geomagnetically induced currents (GIC) in power systems. The properties of these waves &#8211; including frequency, amplitude, and polarization &#8211; vary widely due to many factors including local time, latitude, phase of geomagnetic storm, state of magnetosphere-ionosphere system, and type of solar wind driving condition. Additionally, measurements of geomagnetic fields, geoelectric fields, and GIC with sampling intervals needed to detect many ULF waves (~1s) are sparse during major historical storms. For these reasons, it is challenging to quantitatively assess extreme ULF wave amplitudes and determine which conditions lead to the largest wave fields and GIC. In this research, we use recently improved ground conductivity constraints and an expanded catalog of 1s measurements during past geomagnetic storms to estimate moderate, large, and extreme ULF wave geoelectric field amplitudes, primarily focusing on mid- and low-latitude regions and comparing with direct GIC measurements in several cases. We further describe the conditions that lead to the largest amplitude ULF wave geoelectric fields and GIC.
Solar Flare‐Induced Gradient Drift Instability Observed by SuperDARN HF Radars
Journal of Geophysical Research Space Physics · 2025-10-01 · 1 citations
articleOpen accessAbstract Solar flares are a rapid increase in solar irradiance, specifically in X‐ray and Extreme Ultraviolet spectra, which enhances the ionization in the dayside ionosphere and creates Sudden Ionospheric Disturbances (SIDs). SIDs are known to create space weather impacts on traveling high frequency (HF: 3–30 MHz) radio waves, by disrupting the communication channels. In this study, we examine ionospheric scatters at dawn terminator, which stems from a severe X9.3 flare on 6 September 2017 peaked at 12:02 UT, utilizing SuperDARN HF coherent scatter radars and Global Navigation Satellite System (GNSS) Total Electron Content (TEC) observations. Specifically, we are interested in the transients in the ionospheric electrodynamics at the sub‐auroral latitude near the terminator stemming from the flare effect. Observations suggest that flare‐induced density gradient likely favors the formation of gradient‐drift instability near the dawn terminator, leading to the irregularities observed by the SuperDARN radars with line‐of‐sight (LoS) Doppler velocity reaching nearly 300 m/s. The flare amplifies the eastward TEC gradient near the dawn terminator by approximately 2–3 times compared to a geomagnetically quiet and non‐flare day. The observed irregularities, attributed to flare‐driven instabilities, exhibit a velocity consistent with the equatorial return flow of ionospheric Hall convection. In contrast to prior studies indicating decreased cross‐polar‐cap potential and associated ionospheric convection flow, our findings show the flare is followed by an increase in localized electric field near the dawn terminator, as depicted in radar LoS velocity.
Space Weather · 2025-02-01 · 4 citations
articleOpen accessAbstract Intense geoelectric fields during geomagnetic storms generate geomagnetically induced currents in power grids and other infrastructure, necessitating an understanding of their causes, for example, through coordinated space and ground observations. This study investigates localized intense geoelectric ( E ) and geomagnetic ( B ) field perturbations following an Interplanetary Magnetic Field (IMF) turning during a geomagnetic storm on 25 October 2011. Observations from EarthScope magnetotelluric sites in the upper Midwest United States revealed shorter period (1 min) ultra‐low‐frequency (ULF) waves superimposed on longer period (10 min) perturbations in both E and B fields. These sites, located at 19 hr magnetic local time and magnetic latitude, recorded large amplitude E and B perturbations. Ground‐based all‐sky imagers showed auroral brightening with sunward and poleward propagation, while upstream spacecraft linked the perturbations to an IMF turning and solar wind dynamic pressure impulse. The longer‐period E and B field perturbations likely stem from localized ionospheric currents tied to substorm auroral activity post‐IMF turning. The combination of ionospheric currents, ULF waves, and the Earth's varying conductivity produces intense geoelectric fields of 2 V/km in the upper Midwest. A comparison using input data and software compatible with the NOAA/USGS geoelectric field nowcast model revealed its limitations in capturing such events due to the temporal and spatial resolution of the underlying data. Using 1‐s geomagnetic field data can improve geoelectric field models by capturing short‐period and large spatial scale waves, although localized magnetic perturbations remain underestimated due to insufficient ground magnetometer density.
2025-10-12
preprintOpen accessUltra-Low-Frequency (ULF) waves cause local Thermosphere-Ionosphere (T-I) perturbations, but their impacts on the global T-I system including the generation of Travelling Atmospheric Disturbances (TADs) have never been evaluated. The main mechanisms responsible for the TAD generation and propagation, whether through dynamic or thermal process, are not clear either. We present a model study of ULF wave impacts on the thermosphere using the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM). The model results indicate that ULF waves can trigger globally propagating TADs. Thermal processes are the main driver for the TAD generation and propagation, with Joule heating and adiabatic processes taking effects inside the TAD source region, and adiabatic processes and heat conduction being the dominant processes outside. Model results also show that TAD propagation is almost symmetric in two hemispheres and independent of seasonal effects. This study reveals the physical connections between magnetospheric ULF waves and thermospheric disturbances for the first time.
Impact of May 2024 Geomagnetic Superstorm on the Submarine Cables
2025-01-07
articleSenior authorDuring the first half of May 2024, solar active regions (ARs) 3663 and 3664 produced numerous solar flares, SEPs, and associated CMEs, which created major geospace disturbances. Specifically, the CME associated with the aforementioned ARs caused G5 geomagnetic storms, pushing Kp beyond 9 and Dst below -400 nT, creating a superstorm. During the storm, we observed large fluctuations in the magnetospheric and ionospheric current systems, recorded by space-borne and ground-based instruments such as magnetometers, coherent radars, and ISRs. Previous studies reported possible hazards of storm induced ground electric fields (GEF) and associated geomagnetically induced currents (GICs). While magnetic superstorms are known to be known to permanently damage ground-based transformers and lead to blackouts [1], we have not had a clear vision of the impact of these superstorms on underwater electrical equipment such as submarine cables, due to the low accessibility of underwater measurements. The March 1989 storm, the largest superstorm of the last century, caused widespread effects on power systems, including a blackout of the Hydro-Quebec system, and created rapid fluctuations on submarine cables [2, and references therein]. Due to the lack of underwater measurements, the general understanding of submarine cable risk and vulnerability during superstorms is limited. We have recently developed a capability to model (SCUBAS) the impact of storm-driven GICs on underwater cables [3]. In this study, we will leverage this capability to estimate the voltage fluctuations during the May 2024 superstorm and compare them with the March 1989 superstorm. We will also include the variability in the model parameters and uncertainties in the inputs to create ensemble outputs from SCUBAS to quantify the uncertainties. This study will be the steppingstone towards validating the SCUBAS estimates during extreme space weather events and will provide insight into the health of the underwater electronics during these types of space weather hazards.
Unusual SuperDARN Backscatter During the 11 May 2024 Geomagnetic Storm
Space Weather · 2025-12-01 · 1 citations
articleOpen accessAbstract A geomagnetic storm, one of the largest in this solar cycle, was launched on 10 May 2024, producing spectacular auroral displays that could be observed across the continental United States (US) at middle and low latitudes. In this study, we focus on a brief 20‐min interval during the peak of the storm when the Sym‐H index dropped to −500 nT, and the auroral activity specified by the AL and AU indices was elevated. During this interval, the Blackstone (BKS) Super Dual Auroral Radar Network (SuperDARN) radar, observed strong ionospheric backscatter blanketing the near‐ranges across its field‐of‐view. Upon analyzing the elevation and virtual height characteristics of this backscatter we find that: (a) the BKS radar observed F‐region backscatter at unusually close ranges (750 km), and (b) this backscatter was observed over a broad range of elevation angles, including unusual very high ones. It is not physically realistic that all the radio waves, launched over a broad range of elevation angles, refract to become perpendicular to the B‐field. We therefore interpret that a sizable portion of this backscatter is produced by irregularities that are not field‐aligned. These observations show that plasma irregularities generated during strong geomagnetic storms can produce strong and unusual High Frequency (HF) radar backscatter, and significantly impact their operations. Finally, we suggest that the high‐aspect angle backscatter was most likely associated with the non‐linear decay of gradient‐drift modes that had been excited unusually strongly during the event.
Recent grants
CAREER: Inter-Hemispheric Magnetic Conjugacy of Ionospheric Convection
NSF · $488k · 2012–2017
NSF · $195k · 2009–2011
NSF · $794k · 2020–2026
Collaborative Research: Inferring High Latitude Convection Patterns Using SuperDARN, DMSP and ACE
NSF · $150k · 2014–2018
Frequent coauthors
- 188 shared
J. M. Ruohoniemi
Virginia Tech
- 55 shared
R. A. Greenwald
Virginia Tech
- 50 shared
A. J. Coster
Northeast Radio Observatory Corporation
- 49 shared
P. J. Erickson
Northeast Radio Observatory Corporation
- 37 shared
M. Hartinger
Space Science Institute
- 37 shared
B. Kunduri
Virginia Tech
- 37 shared
Xueling Shi
Virginia Tech
- 35 shared
E. G. Thomas
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