J. D. Richardson

Massachusetts Institute of Technology, Cambridge, Massachusetts, United States

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Publications (210)555.04 Total impact

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    ABSTRACT: In the heliosheath (HS), Voyager 2 has observed a flow with constant radial velocity and magnetic flux conservation. Voyager 1, however, has observed a decrease in the flow's radial velocity and an order of magnitude decrease in magnetic flux. We investigate the role of the 11 yr solar cycle variation of the magnetic field strength on the magnetic flux within the HS using a global 3D magnetohydrodynamic model of the heliosphere. We use time and latitude-dependent solar wind velocity and density inferred from Solar and Heliospheric Observatory/SWAN and interplanetary scintillations data and implemented solar cycle variations of the magnetic field derived from 27 day averages of the field magnitude average of the magnetic field at 1 AU from the OMNI database. With the inclusion of the solar cycle time-dependent magnetic field intensity, the model matches the observed intensity of the magnetic field in the HS along both Voyager 1 and 2. This is a significant improvement from the same model without magnetic field solar cycle variations, which was over a factor of two larger. The model accurately predicts the radial velocity observed by Voyager 2; however, the model predicts a flow speed ~100 km s−1 larger than that derived from LECP measurements at Voyager 1. In the model, magnetic flux is conserved along both Voyager trajectories, contrary to observations. This implies that the solar cycle variations in solar wind magnetic field observed at 1 AU does not cause the order of magnitude decrease in magnetic flux observed in the Voyager 1 data.
    04/2015; 803(1). DOI:10.1088/2041-8205/803/1/L6
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    ABSTRACT: The solar wind spectral properties are far from uniformity and evolve with the increasing distance from the sun. Most of the available spectra of solar wind turbulence were computed at 1 astronomical unit, while accurate spectra on wide frequency ranges at larger distances are still few. In this paper we consider solar wind spectra derived from the data recorded by the Voyager 2 mission during 1979 at about 5 AU from the sun. Voyager 2 data are an incomplete time series with a voids/signal ratio that typically increases as the spacecraft moves away from the sun (45% missing data in 1979), making the analysis challenging. In order to estimate the uncertainty of the spectral slopes, different methods are tested on synthetic turbulence signals with the same gap distribution as V2 data. Spectra of all variables show a power law scaling with exponents between -2.1 and -1.1, depending on frequency subranges. PDFs and correlations indicate that the flow has a significant intermittency.
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    67th APS DFD San Francisco Nov 2014; 11/2014
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    ABSTRACT: We investigate the role of the 11?yr solar cycle variations in the solar wind (SW) parameters on the flows in the heliosheath using a new three-dimensional time-dependent model of the interaction between the SW and the interstellar medium. For boundary conditions in the model we use realistic time and the latitudinal dependence of the SW parameters obtained from SOHO/SWAN and interplanetary scintillation data for the last two solar cycles (1990-2011). This data set generally agrees with the in situ Ulysses measurements from 1991 to 2009. For the first ~30 AU of the heliosheath the time-dependent model predicts constant radial flow speeds at Voyager 2 (V2), which is consistent with observations and different from the steady models that show a radial speed decrease of 30%. The model shows that V2 was immersed in SW with speeds of 500-550 km s?1 upstream of the termination shock before 2009 and in wind with upstream speeds of 450-500 km s?1 after 2009. The model also predicts that the radial velocity along the Voyager 1 (V1) trajectory is constant across the heliosheath, contrary to observations. This difference in observations implies that additional effects may be responsible for the different flows at V1 and V2. The model predicts meridional flows (VN) higher than those observed because of the strong bluntness of the heliosphere shape in the N direction in the model. The modeled tangential velocity component (VT) at V2 is smaller than observed. Both VN and VT essentially depend on the shape of the heliopause.
    The Astrophysical Journal 09/2014; 794(1):29. DOI:10.1088/0004-637X/794/1/29 · 6.28 Impact Factor
  • J. D. Richardson, R. B. Decker
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    ABSTRACT: Voyager 2 has crossed through 20 AU of the heliosheath; assuming the same heliosheath thickness as at Voyager 1, it is now two-thirds of the way to the heliopause. The plasma data are generally of good quality, although the increasing flow angle of the plasma makes analysis more difficult. The average plasma speed has remained constant but the flow angles have increased to almost 60° in the RT plane and to almost 30° in the RN plane. The average density and thermal speed have been constant since a density increase observed in 2011. Comparison of V2 plasma flows derived from plasma science experiment (PLS) data and Low Energy Charged Particle (LECP) proton anisotropies give good agreement except when heavy ion contributions or non-convective proton anisotropies are observed in the LECP data.
    The Astrophysical Journal 08/2014; 792(2):126. DOI:10.1088/0004-637X/792/2/126 · 6.28 Impact Factor
  • 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; 119(8). DOI:10.1002/2014JA020297 · 3.44 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 11/2013; 88:26–41. DOI:10.1016/j.pss.2013.01.013 · 1.63 Impact Factor
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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). DOI:10.1088/2041-8205/762/1/L14 · 5.60 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). DOI:10.1088/2041-8205/759/1/L19 · 5.60 Impact Factor
  • F. Bagenal, R. J. Wilson, J. D. Richardson, W. R. Paterson
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    ABSTRACT: We have collated and, in some cases, re-analyzed the plasma data obtained by the Voyager 1 & 2 and Galileo spacecraft in the magnetosphere of Jupiter. We present the derived spatial and temporal variations in plasma density, temperature and velocity throughout the plasmasheet. We also use a simple model for density distribution with latitude to produce 3-D maps of plasmasheet properties and derive the flow of mass and energy in the magnetosphere.
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    J. D. Richardson
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    ABSTRACT: The heliosheath is the shocked solar wind between the termination shock and the heliopause. Plasma properties are highly variable in this region, with factor-of-two variations of density and thermal speed on timescales from tens of minutes to hours to days. Gaussian distributions fit all the heliosheath plasma data well and are used to quantify these variations. We show that these fits can be used to compensate for data lost due to cutoffs in the instrument response and show that the flow angle in the RT plane is about 50% larger than previous determinations. The turbulent component of the flow has about 25% of the flow energy in the heliosheath, but this energy is not a significant percentage of the upstream solar wind flow energy.
    The Astrophysical Journal 10/2011; 740. DOI:10.1088/0004-637X/740/2/113 · 6.28 Impact Factor
  • 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 07/2011; 59:840-847. DOI:10.1016/j.pss.2011.03.016 · 1.63 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 06/2011; 176(1-4):1-19. DOI:10.1007/s11214-011-9825-5 · 5.87 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. DOI:10.1088/0004-637X/734/1/71 · 6.28 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. DOI:10.1088/2041-8205/734/1/L21 · 5.60 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.
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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.
    12/2010; 1302(1):3-12. DOI:10.1063/1.3529988
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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.
    12/2010; 1302(1):133-141. DOI:10.1063/1.3529960
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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).

Publication Stats

3k Citations
555.04 Total Impact Points

Institutions

  • 1205–2015
    • Massachusetts Institute of Technology
      • • Kavli Institute for Astrophysics and Space Research
      • • Department of Physics
      Cambridge, Massachusetts, United States
  • 2014
    • Boston University
      • Department of Astronomy
      Boston, Massachusetts, United States
  • 2009
    • George Mason University
      Fairfax, Virginia, United States
  • 2004–2007
    • Chinese Academy of Sciences
      • Center for Space Science and Applied Research
      Peping, Beijing, China
  • 2003
    • Charles University in Prague
      • Faculty of Mathematics and Physics
      Praha, Praha, Czech Republic
  • 1999
    • Tel Aviv University
      Tell Afif, Tel Aviv, Israel