E. Zesta

Air Force Research Laboratory, Washington, Washington, D.C., United States

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Publications (105)129.41 Total impact

  • Yong Shi, Eftyhia Zesta
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    ABSTRACT: We use global-scale polar cap flow vector measurements from the Super Dual Auroral Radar Network (SuperDARN) with the concurrent auroral observations from the Wideband Imaging Camera onboard Imager for Magnetopause-to-Aurora Global Exploration (IMAGE/WIC) to study the polar cap flow and auroral precursors during a substorm onset on 26 December, 2000. We show, for the first time, close connection between the dayside and night side polar cap flow enhancements (with the enhanced dayside flow preceding the night side one by several min) and the ensuing PBI/streamer and the later onset, forming a complete pre-onset sequence for a substorm onset. Our results supplement our previous study [Shi et al., 2012] by providing further evidence that the dayside polar cap flow disturbance may be the key to initiate the whole process of a certain type of substorm by triggering reconnection somewhere in the tail via applied field (or flow) perturbations on the night-side plasma sheet boundary layer (PSBL). Our results also indicate that a pre-existing double oval structure is likely a favorable precondition for a certain type of substorm to be triggered by polar cap flow disturbance and the associated PBIs/streamers. On the other hand, not all our global-scale pre-onset auroral sequences support the recent revised onset scenario proposed by Nishimura et al. [2010a] using the ASIs of the THEMIS mission. This suggests that the preceding PBI/streamer is not a sufficient condition to trigger a substorm. It may not even be a necessary condition considering the existence of various types of substorm onsets.
    Journal of Geophysical Research: Space Physics 05/2014; · 3.44 Impact Factor
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    ABSTRACT: While the formation of equatorial electrojet (EEJ) and its temporal variation is believed to be fairly well understood, the longitudinal variability at all local times is still unknown. This paper presents a case and statistical study of the longitudinal variability of dayside EEJ for all local times using ground-based observations. We found EEJ is stronger in the west American sector and decreases from west to east longitudinal sectors. We also confirm the presence of significant longitudinal difference in the dusk sector pre-reversal drift, using the ion velocity meter (IVM) instrument onboard the C/NOFS satellite, with stronger pre-reversal drift in the west American sector compared to the African sector. Previous satellite observations have shown that the African sector is home to stronger and year-round ionospheric bubbles/irregularities compared to the American and Asian sectors. This study's results raises the question if the vertical drift, which is believed to be the main cause for the enhancement of Rayleigh-Taylor (RT) instability growth rate, is stronger in the American sector and weaker in the African sector - why are the occurrence and amplitude of equatorial irregularities stronger in the African sector?
    02/2014; 32(3).
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    ABSTRACT: We investigate a rare concurrent observation of an ultra low frequency (ULF) wave event in the Earth's magnetosphere, topside ionosphere and surface employing a time-frequency analysis technique. We have examined the ULF wave activity in the Pc3 (22-100 mHz) and Pc4-5 (1-22 mHz) frequency bands within a short time interval during the Halloween 2003 magnetic storm, when the Cluster and CHAMP spacecraft were in good local time (LT) conjunction near the dayside noon-midnight meridian. A key finding of the wavelet spectral analysis of data collected from the Geotail, Cluster and CHAMP spacecraft, and the CARISMA and GIMA magnetometer networks was a remarkably clear transition of the waves' frequency into a higher regime within the Pc3 range. Our study offers insights into the energy transfer traced all the way from the solar wind through the magnetosphere and ionosphere to the ground. This work has received support from the European Community's Seventh Framework Programme under grant agreement no. 284520 for the MAARBLE (Monitoring, Analyzing and Assessing Radiation Belt Energization and Loss) collaborative research project.
    09/2013;
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    ABSTRACT: ULF waves with frequencies of a few millihertz (mHz) have been associated with changes in the flux levels among relativistic electrons comprising the outer zone of the radiation belts. In particular, the fluxes of electrons with energies > 1 MeV in the outer radiation belt increase and decrease during geospace magnetic storms. For all storms studied by Reeves et al. [2003], only about half of them led to increased electron fluxes, one quarter led to decreased the fluxes, and one quarter produced little or no change in the fluxes. We focus on the increase of relativistic electrons observed during a number of magnetic storms by GOES satellites at geosynchronous orbit. To minimise the effects caused by the Earth's magnetic field asymmetries, we apply a statistical reconstruction of the fluxes to a common local time, which is chosen to be noon, a technique proposed by O’Brien et al. [2001]. Next, we look into multipoint observations from ground-based magnetometer arrays and the characteristics of Pc 4-5 waves during the different phases of the magnetic storms with particular emphasis on the distribution of Pc 4-5 wave power over the L shells that correspond to the radiation belts. With these observations as a starting point, we investigate whether Pc 4-5 wave power penetrates to lower L shells during periods of enhanced relativistic electron fluxes. We discuss, lastly, the implications to wave-particle interaction. The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7–SPACE–2011–1) under grant agreement n. 284520 for the MAARBLE (Monitoring, Analyzing and Assessing Radiation Belt Energization and Loss) collaborative research project.
    09/2013;
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    ABSTRACT: We have found a specific time interval during the Halloween 2003 magnetic storm, when the Cluster and CHAMP spacecraft were in good local time (LT) conjunction, and have examined the Pc3 (22-100 mHz) and Pc4-5 (1-22 mHz) ULF wave activity using data from Cluster, CHAMP and the CARISMA magnetometer network. We provide evidence for the first simultaneous observation of a Pc3 ULF wave event in the magnetosphere, in the topside ionosphere and on the ground, by Cluster, CHAMP and the Dawson (DAWS) magnetic station respectively at ~ 13:00 LT. Moreover, we show the remarkably clear transition of the wave's frequency into a higher regime within the Pc3 range, simultaneously detected in the magnetosphere and topside ionosphere and on the Earth's surface. The commonly observed wave parameters (i.e., onset, duration and frequency content) at Cluster, CHAMP and DAWS provide evidence that we are, indeed, observing manifestation of the same phenomenon. This work has received support from the European Space Agency under contract ESTEC 4000103770/11/NL/JA/ef and from the European Community's Seventh Framework Programme under grant agreement no. 284520 for the MAARBLE (Monitoring, Analyzing and Assessing Radiation Belt Energization and Loss) collaborative research project.
    04/2013;
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    ABSTRACT: Focused on the exceptional 2003 Halloween geospace magnetic storm, when Dst reached a minimum of -383 nT, we examine data from topside ionosphere and two magnetospheric missions (CHAMP, Cluster, and Geotail) for signatures of ULF waves. We present the overall ULF wave activity through the six-day interval from 27 October to 1 November 2003 as observed by the three spacecraft and by the Andenes ground magnetic station of the IMAGE magnetometerer array in terms of time variations of the ULF wave power. The ULF wave activity is divided upon Pc3 and Pc5 wave power. Thus, we provide different ULF wave activity indices according to the wave frequency (Pc3 and Pc5) and location of observation (Earth's magnetosphere, topside ionosphere and surface). We also look at three specific intervals during different phases of the storm when at least two of the satellites are in good local time (LT) conjunction and examine separately Pc3 and Pc4-5 ULF wave activity and its concurrence in the different regions of the magnetosphere and down to the topside ionosphere and on the ground. This work has received support from the European Community's Seventh Framework Programme under grant agreement no. 284520 for the MAARBLE (Monitoring, Analyzing and Assessing Radiation Belt Energization and Loss) collaborative research project.
    04/2013;
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    ABSTRACT: Energetic particle fluxes in the outer radiation belt can vary over orders of magnitude on time scales ranging from minutes, to days and years. Geospace magnetic storms when sufficiently strong to exceed key thresholds of the Dst index may either increase or decrease the fluxes of energetic electrons. We examine the responses of energetic electrons to nine moderate, intense and weak magnetic storms, which occurred at different phases of the solar cycle, and compare these with concurrent variations of ULF wave power. Pc 4-5 waves with frequencies in the range of a few mHz may be generated internally in the magnetosphere by low frequency instabilities of ring current ions and externally by shear instabilities at the magnetopause flanks, or compressive variations in the solar wind. Here, we present multipoint observations from ground-based magnetometer arrays collocated with electron drift orbits, which are complemented and measurements by conjugate multi-point satellites, such as CHAMP, Cluster, GOES and THEMIS. We discuss the excitation, growth and decay characteristics of Pc 4-5 waves during the different phases of the magnetic storms with particular emphasis on the distribution of Pc 4-5 wave power over a variety of L shells. We investigate whether Pc 4-5 wave power penetrates to lower L shell values during periods of relatively intense geomagnetic activity as compared to weak magnetic storms. Structural changes of the magnetosphere during intense geomagnetic storms can play an important role in the generation and penetration of Pc 4-5 waves deep into the inner magnetosphere, which in turn is of significance for the wave-particle interactions contributing to the acceleration, transport and loss of electrons in the outer radiation belt. We present preliminary statistics of Pc 4-5 waves observed during magnetic storms of varying intensity, which occurred over the course of the previous solar cycle. This work is supported by the European Community's Seventh Framework Programme under grant agreement no. 284520 for the MAARBLE (Monitoring, Analyzing and Assessing Radiation Belt Energization and Loss) collaborative research project.
    04/2013;
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    ABSTRACT: We examine data from a topside ionosphere and two magnetospheric missions (CHAMP, Cluster and Geotail) for signatures of ultra low frequency (ULF) waves during the exceptional 2003 Halloween geospace magnetic storm, when Dst reached ~-380 nT. We use a suite of wavelet-based algorithms, which are a subset of a tool that is being developed for the analysis of multi-instrument multi-satellite and ground-based observations to identify ULF waves and investigate their properties. Starting from the region of topside ionosphere, we first present three clear and strong signatures of Pc3 ULF wave activity (frequency 15-100 mHz) in CHAMP tracks. We then expand these three time intervals for purposes of comparison between CHAMP, Cluster and Geotail Pc3 observations but also to be able to search for Pc4-5 wave signatures (frequency 1-10 mHz) into Cluster and Geotail measurements in order to have a more complete picture of the ULF wave occurrence during the storm. Due to the fast motion through field lines in a low Earth orbit (LEO) we are able to reliably detect Pc3 (but not Pc4-5) waves from CHAMP. This is the first time, to our knowledge, that ULF wave observations from a topside ionosphere mission are compared to ULF wave observations from magnetospheric missions. Our study provides evidence for the occurrence of a number of prominent ULF wave events in the Pc3 and Pc4-5 bands during the storm and offers a platform to study the wave evolution from high altitudes to LEO. The ULF wave analysis methods presented here can be applied to observations from the upcoming Swarm multi-satellite mission of ESA, which is anticipated to enable joint studies with the Cluster mission.
    Annales Geophysicae 12/2012; 30(12):1751-1768. · 1.52 Impact Factor
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    ABSTRACT: In this paper, we use a rare and close longitudinal conjunction of the THEMIS spacecraft with the Sondrestrom radar to present multipoint observations of important features of the time sequence of substorm pre-onset plasma flows in the ionosphere and magnetotail on March 5, 2008. We found that the onset was preceded sequentially by enhanced polar cap flows heading equatorward near the polar cap boundary, and then by tail fast flows from the mid-tail to the near-Earth region. We also observed in situ fluctuations in short-period Pi2 band (˜30-50 s) in both the magnetic field and plasma pressure during the initial couple of min of the fast flows, occurring nearly simultaneously with the dipolarization and the fast flows and propagating earthward. Our results suggest that these fluctuations may be triggered by the fast flows, and may play an important role in the substorm onset process. Our event suggests that localized tail reconnection may be triggered by the enhanced polar cap flows, though the reconnection location cannot be unambiguously determined. Earthward fast flows are generated as a result of the tail reconnection and reach the inner magnetosphere to initiate the substorm onset. The presented case is consistent with that predicted by the Nishimura et al. (2010a) scenario.
    Journal of Geophysical Research Atmospheres 09/2012; 117(A9):9203-. · 3.44 Impact Factor
  • 07/2012;
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    ABSTRACT: Accurate estimation of global vertical distribution of ionospheric and plasmaspheric density as a function of local time, season, and magnetic activity is required to improve the operation of space-based navigation and communication systems. The vertical density distribution, especially at low and equatorial latitudes, is governed by the equatorial electrodynamics that produces a vertical driving force. The vertical structure of the equatorial density distribution can be observed by using tomographic reconstruction techniques on ground-based global positioning system (GPS) total electron content (TEC). Similarly, the vertical drift, which is one of the driving mechanisms that govern equatorial electrodynamics and strongly affect the structure and dynamics of the ionosphere in the low/midlatitude region, can be estimated using ground magnetometer observations. We present tomographically reconstructed density distribution and the corresponding vertical drifts at two different longitudes: the East African and west South American sectors. Chains of GPS stations in the east African and west South American longitudinal sectors, covering the equatorial anomaly region of meridian ˜37°E and 290°E, respectively, are used to reconstruct the vertical density distribution. Similarly, magnetometer sites of African Meridian B-field Education and Research (AMBER) and INTERMAGNET for the east African sector and South American Meridional B-field Array (SAMBA) and Low Latitude Ionospheric Sensor Network (LISN) are used to estimate the vertical drift velocity at two distinct longitudes. The comparison between the reconstructed and Jicamarca Incoherent Scatter Radar (ISR) measured density profiles shows excellent agreement, demonstrating the usefulness of tomographic reconstruction technique in providing the vertical density distribution at different longitudes. Similarly, the comparison between magnetometer estimated vertical drift and other independent drift observation, such as from VEFI onboard Communication/Navigation Outage Forecasting System (C/NOFS) satellite and JULIA radar, is equally promising. The observations at different longitudes suggest that the vertical drift velocities and the vertical density distribution have significant longitudinal differences; especially the equatorial anomaly peaks expand to higher latitudes more in American sector than the African sector, indicating that the vertical drift in the American sector is stronger than the African sector.
    Journal of Geophysical Research Atmospheres 07/2012; 117(A7):7312-. · 3.44 Impact Factor
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    ABSTRACT: Field Line Resonances (FLR) have been shown to be an effective method for remote sensing of the plasmaspheric mass density. A power law solution models the mass density well in the outer plasmasphere, and solutions have been tabulated that allow direct conversion between resonance frequency and mass density. The plasma density in the inner plasmasphere, L < 3, is not modeled well by a power law, and thus must be modeled by a realistic plasma mass density distribution in order to create a similar inverse problem relating FLR frequency observations to plasma mass density. We use the time-dependent Field Line Interhemispheric Plasma (FLIP) model for the density distribution and solve the FLR equation with a finite element method. We compare the solutions with FLR measurements from magnetometer chains in the northern and southern hemisphere in the American sector, South American Meridional B-field Array (SAMBA), magnetometers along the Eastern Atlantic Seaboard for Undergraduate Research and Education (MEASURE), and Mid-continent Magnetoseismic Chain (McMAC). We find good agreement in comparison between the FLIP model and observations during quiet times. During a large storm, we find significant differences between the FLIP model and observations. The agreement can be improved by including the effects of flux tube depletion and electric convection. By comparing with observations, we can infer the importance of these drivers in the inner magnetosphere during large storms.
    07/2012;
  • 07/2012;
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    ABSTRACT: The solar wind dynamic pressure, both through its steady state value and through its variations, plays an important role in the determination of the state of the terrestrial magnetosphere and ionosphere, its effects being only secondary to those of the Interplanetary Magnetic Field (IMF). Recent studies have demonstrated the significant effect solar wind dynamic pressure enhancements have on ionospheric convection and the transpolar potential. Further studies have shown a strong response of the polar cap boundary and thus the open flux content of the magnetosphere. These studies clearly illustrate the strong coupling of solar wind dynamic pressure fronts to the terrestrial magnetosphere-ionosphere system. We present statistical studies of the response of Super Dual Auroral Radar Network (SuperDARN) flows, and Assimilative Mapping of Ionospheric Electrodynamics (AMIE) transpolar potentials to sudden enhancements in solar wind dynamic pressure. The SuperDARN results show that the convection is enhanced within both the dayside and nightside ionosphere. The dayside response is more clear and immediate, while the response on the nightside is slower and more evident for low IMF By values. AMIE results show that the overall convection, represented by the transpolar potential, has a strong response immediately after an increase in pressure, with magnitude and duration modulated by the background IMF Bz conditions. We compare the location of the SuperDARN convection enhancements with the location and motion of the polar cap boundary, as determined by POLAR Ultra-Violet Imager (UVI) images and runs of the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic model for specific events. We find that the boundary exhibits a poleward motion after the increase in dynamic pressure. The enhanced ionospheric flows and the poleward motion of the boundary on the nightside are both signatures of enhanced tail reconnection, a conclusion that is reinforced by the observation of the enhanced flows crossing the polar cap boundary in selected case studies when simultaneous measurements are available.
    EGU General Assembly 2012, Vienna; 04/2012
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    ABSTRACT: Magnetospheric ULF waves influence radiation belt dynamics and are therefore of particular relevance for space weather nowcasting and forecasting efforts. We have used novel algorithms based on wavelet spectral methods to analyze multipoint observations of ULF wave activity by the Cluster and THEMIS missions and by ground-based magnetometers. Wavelet analysis is becoming a common tool for analyzing localized variations of power within a time series. By decomposing a time series into time-frequency space, we are able to determine both the dominant modes of variability and how these modes vary in time. The advantage of analyzing a signal with wavelets as the analyzing kernel is that it enables us to study features of the signal locally with a detail matched to their scale. Owing to its unique time-frequency localization, wavelet analysis is especially useful for signals that are non-stationary, have short-lived transient components, have features at different scales, or have singularities. The results are rather promising for the development of automatic identification tools, which will allow the detection and classification of various categories of ULF waves from multipoint magnetospheric observations according to well-defined criteria.
    10th Hellenic Astronomical Conference, Proceedings of the conference held at Ioannina, Greece, 5-8 September 2011. Edited by Iossif Papadakis and Anastasios Anastasiadis., pp. 9-9; 01/2012
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    ABSTRACT: VLF and magnetometer observations can be used to remotely sense the plasmasphere. VLF whistler waves can be used to measure the electron density and magnetic Field Line Resonance (FLR) measurements can be used to measure the mass density. In principle it is then possible to remotely map the plasmasphere with a network of ground-based stations which are also less expensive and more permanent than satellites. The PLASMON project, funded by the EU FP-7 program, is in the process of doing just this. A large number of ground-based observations will be input into a data assimilative framework which models the plasmasphere structure and dynamics. The data assimilation framework combines the Ensemble Kalman Filter with the Dynamic Global Core Plasma Model. Here we simulate the observations from these networks, with appropriate uncertainties, and use them to drive the data assimilation framework to recover the plasmaspheric configuration. We will discuss the level of accuracy that can be achieved.
    AGU Fall Meeting; 01/2012
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    ABSTRACT: We will present the results of data assimilation of density measurements into the Dynamic Global Core Plasma Model (DGCPM) using a Kalman filter approach. Being able to produce accurate maps of plasmaspheric density is important because plasma density gradients are sites of waves which contribute to acceleration or loss of radiation belt particles. The plasmasphere is largely described in terms of plasma flow out of and into the ionosphere, as well as a convection electric field, with the electric field being primarily responsible for the dynamics. Although these dynamics appear to be reasonably well understood, modeling the plasma density distribution accurately requires accurate knowledge of the electric field history. A way around that is data assimilation in which we adjust the electric field to make the model agree with observations. In this presentation we will compare several different electric field models. We will run the plasmasphere model with these electric field models both with and without data assimilation and compare with in-situ, FLR, and VLF whistler observations.
    39th COSPAR Scientific Assembly; 01/2012
  • Washington DC American Geophysical Union Geophysical Monograph Series. 01/2012;
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    ABSTRACT: The SAMBA (South American Meridional B-field Array) chain is a Southern Hemisphere meridional chain of 12 magnetometers, 11 of them at L=1.1 to L=2.5 along the coast of Chile and in the Antarctica peninsula, and one auroral station along the same meridian. SAMBA is ideal for low and mid-latitude studies of geophysical events and ULF waves. The MEASURE (Magnetometers along the Eastern Atlantic Seaboard for Undergraduate Research and Education) and McMAC (Mid-continent Magnetoseismic Chain) chains are Northern Hemisphere meridional chains in the same local time as SAMBA, but cover low to sub-auroral latitudes. SAMBA is partly conjugate to MEASURE and McMAC chains, offering unique opportunities for inter-hemispheric studies. We use 5 of the SAMBA stations and an even larger number of conjugate stations from the Northern hemisphere to determine the field line resonance (FLR) frequency of closely spaced flux tubes in the inner magnetosphere. Standard inversion techniques are used to derive the equatorial mass density of these flux tubes from the FLRs. We thus yield the mass density distribution of the plasmasphere for specific events and compare our results with results from the FLIP thermosphere-ionosphere model model. We find that for moderate activity the model determined FLR radial distribution is in excellent agreement with the observed distribution. During storm time observations indicate stronger depletion than predicted by the model initial runs.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: Field Line Resonances (FLRs) have been shown to be an effective way to remote sense plasmaspheric mass density. In the outer plasmasphere the mass density is modeled well by a power-law distribution and solutions have been tabulated that allow the direct conversion between resonance frequency and mass density. In the inner plasmasphere, for L<3, plasma density is not modeled by a power law and the resonance equation must be solved directly using a model plasma density. We use the time-dependent Field Line Interhemispheric Plasma (FLIP) model and solve the resonance equation with a finite element method. We compare the solutions with FLR measurements from several magnetometer chains in both the northern and southern hemisphere in the American sector, South American Meridional B-field Array (SAMBA), Magnetometers along the Eastern Atlantic Seaboard for Undergraduate Research and Education (MEASURE), and Mid-continent Magnetoseismic Chain (McMAC). During quiet periods the FLIP model and the observations are in good agreement. During a large storm we find significant differences between the FLIP model and observations. We attribute this difference to the fact that the FLIP model does not automatically incorporate the effects of strong convection, such as a change in flux tube volume (and location), nor the depletion of plasma from the flux tube. In the present study we incorporate these effects realistically and use comparison with observations to estimate their importance in driving the inner plasmasphere during large storms.
    AGU Fall Meeting Abstracts. 12/2011;

Publication Stats

826 Citations
129.41 Total Impact Points

Institutions

  • 2011–2012
    • Air Force Research Laboratory
      Washington, Washington, D.C., United States
  • 2000–2008
    • University of California, Los Angeles
      • Department of Atmospheric and Oceanic Sciences (AOS)
      Los Angeles, California, United States
  • 2005–2007
    • University of Southern California
      Los Angeles, California, United States