Browsing by Author "Shi, Xueling"

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    Characteristics and Sources of Intense Geoelectric Fields in the United States: Comparative Analysis of Multiple Geomagnetic Storms
    Shi, Xueling; Hartinger, Michael D.; Baker, Joseph B. H.; Murphy, Benjamin S.; Bedrosian, Paul A.; Kelbert, Anna; Rigler, Erin Joshua (American Geophysical Union, 2022-04)
    Intense geoelectric fields during geomagnetic storms drive geomagnetically induced currents in power grids and other infrastructure, yet there are limited direct measurements of these storm-time geoelectric fields. Moreover, most previous studies examining storm-time geoelectric fields focused on single events or small geographic regions, making it difficult to determine the typical source(s) of intense geoelectric fields. We perform the first comparative analysis of (a) the sources of intense geoelectric fields over multiple geomagnetic storms, (b) using 1-s cadence geoelectric field measurements made at (c) magnetotelluric survey sites distributed widely across the United States. Temporally localized intense perturbations in measured geoelectric fields with prominences (a measure of the relative amplitude of geoelectric field enhancement above the surrounding signal) of at least 500 mV/km were detected during geomagnetic storms with Dst minima (Dst(min)) of less than -100 nT from 2006 to 2019. Most of the intense geoelectric fields were observed in resistive regions with magnetic latitudes greater than 55 degrees even though we have 167 sites located at lower latitudes during geomagnetic storms of -200 nT <= Dst(min) < -100 nT. Our study indicates intense short-lived (<1 min) and geoelectric field perturbations with periods on the order of 1-2 min are common. Most of these perturbations cannot be resolved with 1-min data because they correspond to higher frequency or impulsive phenomena that vary on timescales shorter than that sampling interval. The sources of geomagnetic perturbations inducing these intense geoelectric fields include interplanetary shocks, interplanetary magnetic field turnings, substorms, and ultralow frequency waves.
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    Effects of Subauroral Polarization Streams on the Upper Thermospheric Winds During Non-Storm Time
    Zou, Ying; Lyons, Larry R.; Shi, Xueling; Liu, Jiang; Wu, Qian; Conde, Mark; Shepherd, Simon G.; Mende, Stephen; Zhang, Yongliang; Coster, Antea (American Geophysical Union, 2022-05)
    Intense sunward (westward) plasma flows, named Subauroral Polarization Stream (SAPS), have been known to occur equatorward of the electron auroras for decades, yet their effect on the upper thermosphere has not been well understood. On the one hand, the large velocity of SAPS results in large momentum exchange upon each ion-neutral collision. On the other hand, the low plasma density associated with SAPS implies a low ion-neutral collision frequency. We investigate the SAPS effect during non-storm time by utilizing a Scanning Doppler Imager (SDI) for monitoring the upper thermosphere, SuperDARN radars for SAPS, all-sky imagers and DMSP Spectrographic Imager for the auroral oval, and GPS receivers for the total electron content. Our observations suggest that SAPS at times drives substantial (>50 m/s) westward winds at subauroral latitudes in the dusk-midnight sector, but not always. The occurrence of the westward winds varies with AE index, plasma content in the trough, and local time. The latitudinally averaged wind speed varies from 60 to 160 m/s, and is statistically 21% of the plasma. These westward winds also shift to lower latitude with increasing AE and increasing MLT. We do not observe SAPS driving poleward wind surges, neutral temperature enhancements, or acoustic-gravity waves, likely due to the somewhat weak forcing of SAPS during the non-storm time.
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    Geospace Plume and Its Impact on Dayside Magnetopause Reconnection Rate
    Zou, Ying; Walsh, Brian M.; Shi, Xueling; Lyons, Larry; Liu, Jiang; Angelopoulos, Vassilis; Ruohoniemi, John M.; Coster, Anthea J.; Henderson, Michael G. (2021-06)
    The role a geospace plume in influencing the efficiency of magnetopause reconnection is an open question with two contrasting theories being debated. A local-control theory suggests that a plume decreases both local and global reconnection rates, whereas a global-control theory argues that the global reconnection rate is controlled by the solar wind rather than local physics. Observationally, limited numbers of point measurements from spacecraft cannot reveal whether a local change affects the global reconnection. A distributed observatory is hence needed to assess the validity of the two theories. We use THEMIS and Los Alamos National Laboratory spacecraft to identify the occurrence of a geospace plume and its contact with the magnetopause. Global evolution and morphology of the plume is traced using GPS measurements. SuperDARN is then used to monitor the distribution and the strength of dayside reconnection. Two storm-time geospace plume events are examined and show that as the plume contacts the magnetopause, the efficiency of reconnection decreases at the contact longitude. The amount of local decrease is 81% and 68% for the two events, and both values are consistent with the mass loading effect of the plume if the plume's atomic mass is similar to 4 amu. Reconnection in the surrounding is enhanced, and when the solar wind driving is stable, little variation is seen in the cross polar cap potential. This study illuminates a pathway to resolve the role of cold dense plasma on solar wind-magnetosphere coupling, and the observations suggest that plumes redistribute magnetopause reconnection activity without changing the global strength substantially. Plain Language Summary A variety of magnetospheric plasma populations exist at the interface where the solar wind encounters the magnetosphere, and they can impact the efficiency of the energy transfer from the solar wind to the magnetosphere. One population of particular interest is geospace plumes, which are plumes of cold dense plasma of ionospheric origin drifting sunward toward the magnetopause during enhanced geomagnetic activity. Plumes often have a density much higher than the other magnetospheric populations and can therefore mass load the dayside magnetopause slowing down magnetic reconnection. However, whether reconnection is slowed at a local or global scale is under debate. Observationally, point measurements from spacecraft cannot reveal whether a local change affects the global reconnection and a distributed observatory is hence needed. In this study we strategically coordinate measurements made by THEMIS and Los Alamos National Laboratory spacecraft, GPS network, and SuperDARN to investigate the effect of plumes on reconnection. Our results suggest that plumes decrease the local reconnection rate at the plume longitude and increase the reconnection rate in regions adjacent to the plume. When the solar wind is stable, the global reconnection remains unchanged. Such observations illuminate a pathway to resolve the role of cold dense plasma on solar wind-magnetosphere coupling.
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    Listening to the Magnetosphere: How Best to Make ULF Waves Audible
    Archer, Martin O.; Cottingham, Marek; Hartinger, Michael D.; Shi, Xueling; Coyle, Shane; Hill, Ethan ''Duke''; Fox, Michael F. J.; Masongsong, Emmanuel V. (Frontiers, 2022-06-08)
    Observations across the heliosphere typically rely on in situ spacecraft observations producing time-series data. While often this data is analysed visually, it lends itself more naturally to our sense of sound. The simplest method of converting oscillatory data into audible sound is audification-a one-to-one mapping of data samples to audio samples-which has the benefit that no information is lost, thus is a true representation of the original data. However, audification can make some magnetospheric ULF waves observations pass by too quickly for someone to realistically be able to listen to effectively. For this reason, we detail various existing audio time scale modification techniques developed for music, applying these to ULF wave observations by spacecraft and exploring how they affect the properties of the resulting audio. Through a public dialogue we arrive at recommendations for ULF wave researchers on rendering these waves audible and discuss the scientific and educational possibilities of these new methods.
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    Modeling geomagnetic induction in submarine cables
    Chakraborty, Shibaji; Boteler, David H.; Shi, Xueling; Murphy, Benjamin S.; Hartinger, Michael D.; Wang, Xuan; Lucas, Greg; Baker, Joseph B. H. (Frontiers, 2022-10)
    Submarine cables have become a vital component of modern infrastructure, but past submarine cable natural hazard studies have mostly focused on potential cable damage from landslides and tsunamis. A handful of studies examine the possibility of space weather effects in submarine cables. The main purpose of this study is to develop a computational model, using Python, of geomagnetic induction on submarine cables. The model is used to estimate the induced voltage in the submarine cables in response to geomagnetic disturbances. It also utilizes newly acquired knowledge from magnetotelluric studies and associated investigations of geomagnetically induced currents in power systems. We describe the Python-based software, its working principle, inputs/outputs based on synthetic geomagnetic field data, and compare its operational capabilities against analytical solutions. We present the results for different model inputs, and find: 1) the seawater layer acts as a shield in the induction process: the greater the ocean depth, the smaller the seafloor geoelectric field; and 2) the model is sensitive to the Ocean-Earth layered conductivity structure.
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    Occurrence Statistics and Driving Mechanisms of Ionospheric Ultra-Low Frequency Waves Observed by SuperDARN Radars
    Shi, Xueling (Virginia Tech, 2019-05-30)
    Ultra-low frequency (ULF; 1 mHz - 1 Hz) waves are known to play an important role in the transfer of energy from the solar wind to Earth's magnetosphere and ionosphere. The Super Dual Auroral Radar Network (SuperDARN) is an international network consisting of 35 low-power high frequency (HF: 3-30 MHz) coherent scatter radars at middle to polar latitudes that look into Earth's upper atmosphere and ionosphere. In this study, we use Doppler velocity measurements obtained by the SuperDARN radars and coordinated spacecraft observations to investigate the occurrence statistics and driving mechanisms of ionospheric ULF waves. We begin in Chapter 2 with a case study of Pi2 pulsations which are short-duration (5-15 min) damped geomagnetic field oscillations with periods of 40-150 s. Simultaneous observations of Pi2 pulsations from THEMIS spacecraft, midlatitude SuperDARN radars, and ground magnetometers, together with analysis of their longitudinal polarization pattern and azimuthal phase propagation, confirmed that they are consistent with a plasmaspheric virtual resonance excited by a longitudinally localized source near midnight. In Chapter 3, to further investigate the overall occurrence of ionospheric ULF signatures, a comprehensive statistical study was conducted using an automated detection algorithm to identify ionospheric signatures of Pc3-4 and Pc5 waves over 7 years of high time resolution SuperDARN radar data. Specifically, we have investigated their spatial occurrence, frequency characteristics, seasonal factors, and dependence on solar wind and geomagnetic conditions. We note two particular findings: (i) an internal wave-particle interaction source is most likely responsible for Pc4 waves at high latitudes in the duskside ionosphere; and, (ii) a source associated with magnetotail dynamics during active geomagnetic times is suggested for Pc3-4/Pi2 waves at midlatitudes in the nightside ionosphere. These findings are further expanded in Chapter 4 which investigates the hypothesis that internal wave-particle interactions are an important source for generation of these waves. A case study of long-lasting poloidal waves was conducted using coordinated observations with the GOES and THEMIS satellites to examine the generation and propagation of waves observed in the dayside ionosphere by multiple SuperDARN radars. The source of wave excitation is suggested to be bump-on-tail ion distributions at 1-3 keV. Collectively, these research findings provide better constraints on where and when ionospheric ULF waves occur, their source mechanisms, and how they might affect magnetospheric and ionospheric dynamics.
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    pyDARN: A Python software for visualizing SuperDARN radar data
    Shi, Xueling; Schmidt, Marina; Martin, Carley J.; Billett, Daniel D.; Bland, Emma; Tholley, Francis H.; Frissell, Nathaniel A.; Khanal, Krishna; Coyle, Shane; Chakraborty, Shibaji; Detwiller, Marci; Kunduri, Bharat; McWilliams, Kathryn (Frontiers, 2022-12)
    The Super Dual Auroral Radar Network (SuperDARN) is an international network of high frequency coherent scatter radars that are used for monitoring the electrodynamics of the Earth's upper atmosphere at middle, high, and polar latitudes in both hemispheres. pyDARN is an open-source Python-based library developed specifically for visualizing SuperDARN radar data products. It provides various plotting functions of different types of SuperDARN data, including time series plot, range-time parameter plot, fields of view, full scan, and global convection map plots. In this paper, we review the different types of SuperDARN data products, pyDARN's development history and goals, the current implementation of pyDARN, and various plotting and analysis functionalities. We also discuss applications of pyDARN, how it can be combined with other existing Python software for scientific analysis, challenges for pyDARN development and future plans. Examples showing how to read, visualize, and interpret different SuperDARN data products using pyDARN are provided as a Jupyter notebook.
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    ULF Wave Modeling, Effects, and Applications: Accomplishments, Recent Advances, and Future
    Hartinger, Michael D.; Takahashi, Kazue; Drozdov, Alexander Y.; Shi, Xueling; Usanova, Maria E.; Kress, Brian (Frontiers, 2022-04-14)
    Ultra Low Frequency (ULF) waves play important roles in magnetosphere-ionosphere coupling, ring current and radiation belt dynamics, and modulation of higher frequency wave modes and energetic particle precipitation. The "ULF wave modeling, effects, and applications" (UMEA) focus group - part of the Geospace Environment Modeling effort from 2016 to 2021 - sought to improve understanding of the physics of ULF waves and their specification in geospace models. Through a series of in person and virtual meetings the UMEA focus group brought modelers and experimentalists together to compare ULF wave outputs in different models, plan observation campaigns focused on ULF waves, discuss recent advances in ULF wave research, and identify unresolved ULF wave science questions. This article summarizes major discussion points and accomplishments in the UMEA focus group over the last 6 years, recent advances and their connection to Richard Thorne and Peter Gary's significant contributions to ULF wave research, and the future of ULF wave research.
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    Understanding Strong Neutral Vertical Winds and Ionospheric Responses to the 2015 St. Patrick's Day Storm Using TIEGCM Driven by Data-Assimilated Aurora and Electric Fields
    Lu, Xian; Wu, Haonan; Kaeppler, Stephen; Meriwether, John; Nishimura, Yukitoshi; Wang, Wenbin; Li, Jintai; Shi, Xueling (American Geophysical Union, 2023-02)
    As one of the strongest geomagnetic storms in Solar Cycle 24, the 2015 St. Patrick's Day storm has attracted significant attention. We revisit this event by taking advantage of simultaneous observations of high-latitude forcings (aurora and electric fields) and ionosphere-thermosphere (I-T) responses. The forcing terms are assimilated to drive the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) using a newly adopted Lattice Kriging method (Wu & Lu, 2022, https://doi. org/10.1029/2021SW002880; Wu et al., 2022, https://doi.org/10.1029/2022SW003146). Compared to the default run, the TIEGCM simulation with assimilation captures: (a) secondary E-region electron density peak due to aurora intensification; (b) strongly elevated ion temperatures (up to similar to 3000 K) accompanied by a strong northward electric field (similar to 80 mV/m) and associated ion frictional heating; (c) elevation of electron temperatures; and (d) substantially enhanced neutral vertical winds (order of 50 m/s). Root-mean-square errors decrease by 30%-50%. The strong neutral upwelling is caused by large Joule heating down to similar to 120 km resulting from enhanced aurora and electric field. Data assimilation increases the height-integrated Joule heating at Poker Flat to a level of 50-100 mW/m2 while globally, its maximum value is comparable with the default run: the location of energy deposition becomes guided by data. Traveling atmospheric disturbances in the assimilation run show stronger magnitudes and larger extension leading to an increase of vertical wind variability by a factor of similar to 1.5-3. Our work demonstrates that data assimilation of model drivers helps produce realistic storm-time I-T responses, which show richer dynamic range, scales, and variability than what has been simulated before.