J. D. Richardson

Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

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Publications (202)509.23 Total impact

  • L. F. Burlaga, N. F. Ness, J. D. Richardson
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    ABSTRACT: We discuss magnetic field and plasma observations from Voyager 2 (V2) during 2011, when V2 was beginning to see the effects of increasing solar activity following the solar minimum in 2009. The magnetic field strength (B) profile showed large amplitude fluctuations that can be resolved into a linear increase of B with time and a sinusoidal variation of the period of 86.2 ± 0.8 days. Voyager 2 was in a unipolar region in which the magnetic polarity was directed away from the sun along the Parker spiral 96% of the time, indicating that V2 was poleward of the heliospheric current sheet (HCS) throughout most of 2011. The distribution of B was lognormal, but a Gaussian distribution was observed when the linear variation of B was subtracted from the data. The distribution of daily increments of B was a q-Gaussian distribution with q = 1.1 ± 0.1, which is less intermittent than normally observed in the heliosheath. However, the distribution of hourly increments of B was a q-Gaussian distribution with q = 1.5 ± 0.03. The density, temperature and velocity increased linearly from the beginning of 2011 to approximately day 254. The magnetic and thermal pressure tended to increase throughout the year, but the magnetic pressure dominated most of the time. The counting rate of >70 MeV/n particles increased rapidly during the first 250 days, but it leveled out during the rest of the year when B was stronger. The empirical CR-B relationship describes this behavior.
    Journal of Geophysical Research: Space Physics. 08/2014;
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    ABSTRACT: Voyager 1(V1) and Voyager 2(V2) have observed heliosheath plasma since 2005 December and 2007 August, respectively. The observed speed profiles are very different at the two spacecrafts. Speeds at V1 decreased to zero in 2010 while the average speed at V2 is a constant 150 km s{sup -1} with the direction rotating tailward. The magnetic flux is expected to be constant in these heliosheath flows. We show that the flux is constant at V2 but decreases by an order of magnitude at V1, even after accounting for divergence of the flows and changes in the solar field. If reconnection were responsible for this decrease, the magnetic field would lose 70% of its free energy to reconnection and the energy density released would be 0.6 eV cm{sup -3}.
    The Astrophysical Journal Letters 01/2013; 762(1). · 6.35 Impact Factor
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    ABSTRACT: Jupiter magnetospheric interactions and surface composition, both important to subsurface ocean detection for the Galilean icy moons Europa, Ganymede, and Callisto, can be measured using plasma ion mass spectrometry on either an orbiting spacecraft or one designed for multiple flybys of these moons. Detection of emergent oceanic materials at the Europa surface is more likely than at Ganymede and Callisto. A key challenge is to resolve potential intrinsic Europan materials from the space weathering patina of iogenic species implanted onto the sensible surface by magnetospheric interactions. Species-resolved measurements of pickup ion currents are also critical to extraction of oceanic induced magnetic fields from magnetospheric interaction background dominated by these currents. In general the chemical astrobiological potential of Europa should be determined through the combination of surface, ionospheric, and pickup ion composition measurements. The requisite Ion Mass Spectrometer (IMS) for these measurements would need to work in the high radiation environment of Jupiter's magnetosphere between the orbits of Europa and Ganymede, and beyond. A 3D hybrid model of the moon-magnetosphere interaction is also needed to construct a global model of the electric and magnetic fields, and the plasma environment, around Europa. Europa's ionosphere is probably usually dominated by hot pickup ions with 100–1000 eV temperatures, excursions to a “classical” cold ionosphere likely being infrequent. A field aligned ionospheric wind driven by the electron polarization electric field should arise and be measurable.
    Planetary and Space Science 01/2013; 88:26–41. · 2.11 Impact Factor
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    J. D. Richardson, C. Wang
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    ABSTRACT: Voyager 2 (V2) entered the heliosheath in 2007 August at roughly the same time solar minimum conditions were reaching the outer heliosphere. Soon after crossing the termination shock the solar wind density at Voyager decreased by a factor of two and the temperature decreased by a factor of three. At the beginning of 2011 the plasma density in the heliosheath began to increase and in mid-2012 it was up by more than a factor of two. The temperature rose by about 50% and the speed remained constant, although the flow direction continues to turn tailward. These changes may signal the end of solar minimum conditions at V2 in the heliosheath, although we do not understand why the speed did not decrease. The increased dynamic pressure has lead to an outward movement of the termination shock from its very compressed state at solar minimum.
    The Astrophysical Journal Letters 11/2012; 759(1). · 6.35 Impact Factor
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    ABSTRACT: All current global models of the heliosphere are based on the assumption that the magnetic field in the heliosheath, in the region close to the heliopause (HP), is laminar. We argue that in that region the heliospheric magnetic field is not laminar but instead consists of magnetic bubbles. We refer to it as the bubble-dominated heliosheath region. Recently, we proposed that the annihilation of the "sectored" magnetic field within the heliosheath as it is compressed on its approach to the HP produces anomalous cosmic rays and also energetic electrons. As a product of the annihilation of the sectored magnetic field, densely packed magnetic islands (which further interact to form magnetic bubbles) are produced. These magnetic islands/bubbles will be convected with ambient flows as the sector region is carried to higher latitudes filling the heliosheath. We further argue that the magnetic islands/bubbles will develop upstream within the heliosheath. As a result, the magnetic field in the heliosheath sector region will be disordered well upstream of the HP. We present a three-dimensional MHD simulation with very high numerical resolution that captures the north-south boundaries of the sector region. We show that due to the high pressure of the interstellar magnetic field a north-south asymmetry develops such that the disordered sectored region fills a large portion of the northern part of the heliosphere with a smaller extension in the southern hemisphere. We suggest that this scenario is supported by the following changes that occurred around 2008 and from 2009.16 onward: (1) the sudden decrease in the intensity of low energy electrons (0.02-1.5 MeV) detected by Voyager 2, (2) a sharp reduction in the intensity of fluctuations of the radial flow, and (3) the dramatic differences in intensity trends between galactic cosmic ray electrons (3.8-59 MeV) at Voyager 1 and 2. We argue that these observations are a consequence of Voyager 2 leaving the sector region of disordered field during these periods and crossing into a region of unipolar laminar field.
    The Astrophysical Journal 05/2011; 734(1):71. · 6.73 Impact Factor
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    J. D. Richardson, C. Wang
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    ABSTRACT: Voyager 2 (V2) has observed heliosheath (HSH) plasma since 2007 August. We describe how the plasma has evolved across the HSH. We show that the low solar wind dynamic pressure leads to an inward movement of the termination shock (TS) of about 10 AU to a minimum position of 73 AU in 2010. Near the TS large fluctuations are present in the HSH, but these fluctuations decrease as V2 moves further from the TS. The radial speed slowly decreases and the plasma flow slowly turns tailward. The temperature decreases across the HSH. The radial speed in 2011 remains above 100 km s–1, which implies that V2 is a substantial distance from the heliopause.
    The Astrophysical Journal Letters 05/2011; 734(1):L21. · 6.35 Impact Factor
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    ABSTRACT: All the current global models of the heliosphere are based on the assumption that the magnetic field in the heliosheath, in the region close to the heliopause is laminar. We argue that in that region the heliospheric magnetic field is not laminar but instead consists of magnetic bubbles. Recently, we proposed that the annihilation of the "sectored" magnetic field within the heliosheath as it is compressed on its approach to the heliopause produces the anomalous cosmic rays and also energetic electrons. As a product of the annihilation of the sectored magnetic field, densely-packed magnetic islands/bubbles are produced. These magnetic islands/bubbles will be convected with the ambient flows as the sector region is carried to higher latitudes filling the heliosheath. We further argue that the magnetic islands/bubbles will develop upstream within the heliosheath. As a result, the magnetic field in the heliosheath sector region will be disordered well upstream of the heliopause. We present a 3D MHD simulation with very high numerical resolution that captures the north-south boundaries of the sector region. We show that due to the high pressure of the interstellar magnetic field a north-south asymmetry develops such that the disordered sectored region fills a large portion of the northern part of the heliosphere with a smaller extension in the southern hemisphere. We suggest that this scenario is supported by the following changes that occur around 2008 and from 2009.16 onward: a) the sudden decrease in the intensity of low energy electrons detected by Voyager 2; b) a sharp reduction in the intensity of fluctuations of the radial flow; and c) the dramatic differences in intensity trends between GCRs at V1 and 2. We argue that these observations are a consequence of V2 leaving the sector region of disordered field during these periods and crossing into a region of unipolar laminar field.
    03/2011;
  • A. Lynnyk, J. Safránková, Z. Nemecek, J. D. Richardson
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    ABSTRACT: Interplanetary coronal mass ejections (ICMEs) and their subset, magnetic clouds (MCs), are important manifestations of solar activity which have substantial impact on the geomagnetic field. We re-analyze events already identified in Wind and Voyager 2 data and estimate changes of their geometry along the path from the Sun. The analysis is based on the thickness of the sheath between a shock and a particular ICME or MC which is proportional to the apparent curvature radius of ICMEs/MCs. We have found that this apparent radius of curvature increases with the Mach number and this effect is attributed to the larger deformation of the fast ICME/MC. Further, the relative sheath thickness that is proportional to the flux rope oblateness decreases with the magnetic field intensity inside the ICME/MC and increases with the heliospheric distance.
    Planetary and Space Science 01/2011; 59:840-847. · 2.11 Impact Factor
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    J. D. Richardson, L. F. Burlaga
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    ABSTRACT: The solar wind environment has a large influence on the transport of cosmic rays. This chapter discusses the observations of the solar wind plasma and magnetic field in the outer heliosphere and the heliosheath. In the supersonic solar wind, interaction regions with large magnetic fields form barriers to cosmic ray transport. This effect, the “CR-B” relationship, has been quantified and is shown to be valid everywhere inside the termination shock (TS). In the heliosheath, this relationship breaks down, perhaps because of a change in the nature of the turbulence. Turbulence is compressive in the heliosheath, whereas it was non-compressive in the solar wind. The plasma pressure in the outer heliosphere is dominated by the pickup ions which gain most of the flow energy at the TS. The heliosheath plasma and magnetic field are highly variable on scales as small as ten minutes. The plasma flow turns away from the nose roughly as predicted, but the radial speeds at Voyager 1 are much less than those at Voyager 2, which is not understood. Despite predictions to the contrary, magnetic reconnection is not an important process in the inner heliosheath with only one observed occurrence to date. KeywordsSolar wind–Termination shock–Heliosheath–Heliopause–Pickup ions–Interstellar neutral atoms–Anomalous cosmic rays
    Space Science Reviews 01/2011; · 5.52 Impact Factor
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    ABSTRACT: The combination of the Interstellar Boundary Explorer (IBEX) all‐sky maps of the energetic neutral atom fluxes with the Voyager in situ measurements gives us a unique opportunity to learn more about the physics governing the solar wind (SW) interaction with the local interstellar medium (LISM). Moreover, since the position of the ribbon of an enhanced ENA flux in the sky strongly depends on the LISM properties, we are able to constrain those by comparing numerical simulations with the IBEX observations. In this paper, we discuss the current status of the Huntsville model of the SW‐LISM interaction, compare numerical results with the IBEX and Voyager observations, and discuss the importance of taking into account time‐dependent phenomena, particularly the solar cycle effects.
    AIP Conference Proceedings. 12/2010; 1302(1):3-12.
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    ABSTRACT: The Rankine‐Hugoniot (R‐H) jump conditions at the heliospheric termination shock provide a means of knitting together the in situ measurements from Voyager 2 (VGR2) with the remote sensing of the heliosheath plasma via energetic neutral atom (ENA) imaging by IBEX and Cassini∕INCA. The VGR2 instrument suite has a gap (∼1–30 keV) in the ion measurements. While the ENA images (0.2–6 keV and 5–55 keV) fill the VGR2 gap in the pixel containing the VGR2 spacecraft, they do so only in the sense that they provide the ion intensity integrated along the radial line of sight throughout the entire heliosheath. The synthesis we attempt is further complicated by the observational results from all three spacecraft that the non‐thermal component of the ion pressure dominates that of the thermal component. We therefore have developed (and applied) a generalized formulation of the R‐H conditions that does not invoke an equation of state, but rather can directly ingest the instrumentally‐measured non‐thermal spectrum. The result is an estimate that the ratio (upstream∕downstream) of the non‐thermal pressure is ∼43%, confirming anew that the termination shock (at least at VGR2) is strongly mediated by non‐thermal ions.
    AIP Conference Proceedings. 12/2010; 1302(1):133-141.
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    ABSTRACT: We analyzed high-resolution observations of the magnetic field strength measured by Voyager 1 and Voyager 2 on their path through the Jupiter' magnetosheath and Voyager 2 in the heliosheath prior to and after the crossing of the termination shock and compared them with those fluctuations measured by Cluster and THEMIS in the different places of the Earth's magnetosheath and with magnetic field variations in the sheaths of ICMEs and CMEs registered by Wind as well as Voyager 1 and 2 on their path. To characterize the type of fluctuations, we investigate their spectral slopes and correlation properties, mainly the correlations between the magnetic field and ion density. Finally, we discuss similarities and differences of the fluctuations in different regions on various time scales (from several hours to tens of days).
    AGU Fall Meeting Abstracts. 12/2010;
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    ABSTRACT: The diversity of albedos and surface colors on observed Kuiper Belt and Inner Oort Cloud objects remains to be explained in terms of competition between primordial intrinsic versus exogenic drivers of surface and near-surface evolution. Earlier models have attempted without success to attribute this diversity to the relations between surface radiolysis from cosmic ray irradiation and gardening by meteoritic impacts. A more flexible approach considers the different depth-dependent radiation profiles produced by low-energy plasma, suprathermal, and maximally penetrating charged particles of the heliospheric and local interstellar radiation environments. Generally red objects of the dynamically cold (low inclination, circular orbit) Classical Kuiper Belt might be accounted for from erosive effects of plasma ions and reddening effects of high energy cosmic ray ions, while suprathermal keV-MeV ions could alternatively produce more color neutral surfaces. The deepest layer of more pristine ice can be brought to the surface from meter to kilometer depths by larger impact events and potentially by cryovolcanic activity. The bright surfaces of some larger objects, e.g. Eris, suggest ongoing resurfacing activity. Interactions of surface irradiation, resultant chemical oxidation, and near-surface cryogenic fluid reservoirs have been proposed to account for Enceladus cryovolcanism (Cooper et al., Plan. Sp. Sci., 2009) and may have further applications to other icy irradiated bodies. The diversity of causative processes must be understood to account for observationally apparent diversities of the object surfaces.
    10/2010;
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    J. D. Richardson, C. Wang
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    ABSTRACT: Voyager 2 (V2) has observed heliosheath plasma since 2007 August. The plasma flux decreases by 25% before the termination shock (TS), then, as V2 moved into the heliosheath, the plasma density, temperature, and flux all decreased by an additional factor of 2. We suggest three effects combine to cause these decreases. (1) V2 moved into the lower-flux transition region between the low- and high-speed solar wind. This hypothesis is consistent with Ulysses observations of the transition location, explains the 25% decrease in solar wind flux observed before the TS crossing, and can reconcile discrepancies between the V2 and Voyager 1 heliosheath speeds and between the V2 speeds and model results. (2) The weaker source at the Sun. (3) The heliosheath plasma turning and flowing toward the heliotail.
    The Astrophysical Journal Letters 02/2010; 711(1):L44. · 6.35 Impact Factor
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    ABSTRACT: 1] The density and temperature profiles of the plasma measured by Voyager 2 (V2) behind the termination shock changed abruptly near 2008.6 from relatively large average values and large fluctuations during 2007.7 to 2008.6 (interval A) to relatively low average values and very small‐amplitude fluctuations during 2008.6 to 2009.4 (interval B). This paper shows that the change in the magnetic field strength B(t) was less abrupt than the plasma changes, and the fluctuations of the magnetic field strength in interval B were of moderate amplitude, with indications of a quasiperiodic structure in part of the interval. The magnetic field was directed away from the sun (positive polarity) ∼ 78% ± 5% of the time in both interval A and interval B, changing in an irregular way from positive to negative polarities throughout the interval. The polarity distribution indicates that the minimum latitudinal extent of the heliospheric current sheet (HCS) was near V2 throughout the interval, consistent with the extrapolated minimum latitudes of the HCS computed from solar magnetic field observations. Thus, V2 was observing magnetic fields from the southern polar coronal hole most of the time. The distribution of B was lognormal in interval A and Gaussian interval B.
    Journal of Geophysical Research 01/2010; 74(115). · 3.17 Impact Factor
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    C. Wang, T. R. Sun, X. C. Guo, J. D. Richardson
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    ABSTRACT: Observations show that the geosynchronous magnetic field in midnight sector sometimes decreases when an interplanetary (IP) fast forward shock (FFS) passes Earth, even though the magnetosphere is always compressed. We perform case studies of the response observed by the GOES spacecraft at geosynchronous orbit near midnight to two IP shocks passing Earth. One shock produces a decrease in BZ (a negative response) and the other an increase in BZ (a positive response). A global 3D MHD code is run to reproduce the responses at geosynchronous orbit, and to further provide information on the initiation and development of BZ variations in the entire magnetosphere. The model reveals that when a FFS sweeps over the magnetosphere, there exist mainly two regions, a positive response region caused by the compressive effect of the shock and a negative response region which is probably associated with the temporary enhancement of earthward convection in the nightside magnetosphere. The spacecraft may observe an increase or decrease of the magnetic field depending on which region it is in. The numerical results reproduce the main characters of the geosynchronous magnetic field response to IP shocks for these two typical cases.
    Journal of Geophysical Research 01/2010; 115. · 3.17 Impact Factor
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    C. Wang, H. Li, J. D. Richardson, J. R. Kan
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    ABSTRACT: Interplanetary (IP) shocks disturb the magnetosphere-ionosphere system resulting in geosynchronous magnetic field changes and sudden impulses observed by ground-based magnetometers. We extend the implications of a previous statistical study and show that sudden impulses (SIs) can be used to estimate some parameters at the L1 point and geosynchronous orbit, including the change of the square root of solar wind dynamic pressure across the shock and the associated geosynchronous magnetic field changes near the subsolar region. It should be pointed out that the relationship between magnetospheric field change and SIs amplitude and the solar wind dynamic pressure is not a single valued one, but a statistical relationship is useful in cases when interplanetary data are not available. Empirical formulae deduced from observations can be used to estimate certain IP shock characteristics and geosynchronous magnetic field changes from sudden impulse data observed on the ground, with the prediction efficiency as high as 90% and 86%, respectively. These estimates are useful for studying historic, pre-space era data or if the L1 and geosynchronous data are not available at some future time.
    Journal of Geophysical Research 01/2010; 115. · 3.17 Impact Factor
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    ABSTRACT: Magnetic fields play an important (sometimes dominant) role in the evolution of gas clouds in the Galaxy, but the strength and orientation of the field in the interstellar medium near the heliosphere has been poorly constrained. Previous estimates of the field strength range from 1.8-2.5 microG and the field was thought to be parallel to the Galactic plane or inclined by 38-60 degrees (ref. 2) or 60-90 degrees (ref. 3) to this plane. These estimates relied either on indirect observational inferences or modelling in which the interstellar neutral hydrogen was not taken into account. Here we report measurements of the deflection of the solar wind plasma flows in the heliosheath to determine the magnetic field strength and orientation in the interstellar medium. We find that the field strength in the local interstellar medium is 3.7-5.5 microG. The field is tilted approximately 20-30 degrees from the interstellar medium flow direction (resulting from the peculiar motion of the Sun in the Galaxy) and is at an angle of about 30 degrees from the Galactic plane. We conclude that the interstellar medium field is turbulent or has a distortion in the solar vicinity.
    Nature 12/2009; 462(7276):1036-8. · 38.60 Impact Factor
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    ABSTRACT: We show that the heliosheath flows can be used as a new and highly important data set to determine the interstellar magnetic field orientation and magnitude. We use a new three-dimensional model that includes both the plasma and the neutral H atoms as well as the interplanetary and interstellar magnetic fields. The field orientation and magnitude that we derive differ substantially from the those previously reported (Opher et al. 2006, 2007). We comment on the consequences of this result on the heliospheric global asymmetries (such as the field-aligned streaming of low energy particles, the distance of the termination shock, and the shape of the heliopause). We comments as well on the inference on the conditions on the local interstellar medium. We study the effect of numerical resolution and non-stationary on the model shock and find them to be negligible. We also comment on the possible effects of the tilt of current sheet, not included currently in the model (which at the time of the termination shock crossings of Voyager 1 and 2 was about 30 degrees). We present a simulation with a scaled down heliosphere which includes a dynamic time dependent current sheet.
    AGU Fall Meeting Abstracts. 12/2009;
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    C. Wang, H. Li, J. D. Richardson, J. R. Kan
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    ABSTRACT: Interplanetary (IP) shocks disturb the magnetosphere-ionosphere system resulting in geosynchronous magnetic field changes and sudden impulses observed by ground-based magnetometers. We extend the implications of a previous statistical study and show that sudden impulses (SIs) can be used to estimate key parameters at L1 point and geosynchronous orbit, including the arrival time of an IP shock at L1 point, the change of the solar wind dynamic pressure across the shock, and the associated geosynchronous magnetic field changes near the subsolar region. Empirical formulae deduced from observations can be used to estimate certain IP shock characteristics and geosynchronous magnetic field changes from observed sudden impulse data observed on the ground with prediction efficiency as high as 89%. These estimates are useful for studying historic, pre-space era data, or if L1 and geosynchronous data are not available at some future time.
    AGU Fall Meeting Abstracts. 12/2009;

Publication Stats

2k Citations
509.23 Total Impact Points

Institutions

  • 1205–2013
    • Massachusetts Institute of Technology
      • • Kavli Institute for Astrophysics and Space Research
      • • Department of Physics
      Cambridge, Massachusetts, United States
  • 2009
    • Cambridge Healthtech Institute
      Needham, Massachusetts, United States
    • George Mason University
      Fairfax, Virginia, United States
  • 2008
    • NASA
      Washington, West Virginia, United States
  • 2002–2007
    • Chinese Academy of Sciences
      • Center for Space Science and Applied Research
      Peping, Beijing, China
  • 2005
    • Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of Russian Academy of Sciences
      Moskva, Moscow, Russia
  • 2004
    • Northeast Institute of Geography and Agroecology
      • Center for Space Science and Applied Research
      Beijing, Beijing Shi, China
  • 1999
    • Tel Aviv University
      Tell Afif, Tel Aviv, Israel
  • 1305–1996
    • University of Delaware
      • Bartol Research Institute
      Newark, DE, United States