摘要:

In late 2003 as Voyager 1 moves beyond 90 AU in the recovery phase of solar cycle 23, the effects of the termination shock (TS) and the heliosheath on particle transport are becoming more evident. There are now detectable fluxes of 2.5 – 70 MeV electrons but at low intensity levels that suggest they are heavily modulated in the heliosheath. The modulation of galactic and anomalous cosmic rays is significant but much smaller than observed at 1 AU. At V1 a large increase of MeV ions was observed with a flat energy spectra which persisted over a period of 6.5 months. A second event has now been in progress for some eight months. These ions appear to originate at the TS. At V2, 17 AU behind V1, there are a series of 8 increases of low energy ions that occur approximately every 140 days starting in late 2000. Many of these increases can be related to specific periods of high solar activity that occurred some 6 months earlier. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809511

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We combined daily averages of magnetic field vector data and 0.6–1.8 MeV proton angular intensity data to construct 32 pitch angle distributions (PADs) for measurements made by Voyager 1 (V1) at 85–87 AU. The PADs were observed during the period 2002.6–2003.1, when energetic particle instruments on V1 measured unusually high intensities. The angular data show large, mainly unidirectional beaming of protons most often in the −T⁁direction, i.e., away from the sun in the sense of a spiral magnetic field. The mean anisotropy amplitude based on the 32 samples is 0.55±0.21. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809512

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Two aspects of low‐energy (∼0.5–30 MeV/nucleon) anomalous cosmic ray (ACR) phenomena are unique. First, low‐rigidity (≲ 2 GV) ACRs are less affected by particle drifts than higher rigidity particles. Second, outer‐heliospheric ACRs having energies below the energy at the peak of the modulated spectrum, but above the adiabatic range, are governed by a different limit of the transport equation than higher‐energy ACRs, namely, the convection‐diffusion limit. It is therefore possible to uncover features of energetic particle transport in the heliosphere that are not readily apprehended using higher‐energy ACR measurements. We study the first property, in the context of outer‐heliospheric Voyager 1 (V1), Voyager 2 (V2), and Pioneer 10 (P10) particle intensity measurements made during the 1991–1999 cosmic ray recovery phase. In particular, we show that the effective “drift/convection pattern” of low‐rigidity particles during a period of positive heliomagnetic polarity (A> 0), such as this, is qualitatively different than the drift pattern usually discussed. The disagreement between radial and latitudinal intensity gradients determined using the new “quasi‐local” gradient (QLG) method and the standard non‐local gradient (NLG) method is discussed in light of models of the heliosphere showing longitudinal asymmetry. Earlier results regarding diminished high‐latitude transport suggest that the near‐equatorial region will have an enhanced role in the ACR transport. Absent this effect, the fact that the detected low energy particles are actually cooled products of higher energy populations would lead to the expectation that the cooled particles should show residual evidence of the drift undergone before the energy loss took place. The lack of such evidence suggests low latitudes are the more significant region. We will discuss these topics with the primary goal of highlighting the unique and necessary role low‐energy ACR measurements have in studying the heliosphere. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809513

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The Interstellar Boundary Explorer (IBEX) is one of five Small Explorer (SMEX) missions undergoing Phase A study for NASA’s Office of Space Science. Around November 2004, NASA expects to select at least one of missions for development and flight. If selected, IBEX will provide the first global views of the Sun’s interstellar boundaries by taking a set of global energetic neutral atom (ENA) images at a variety of energies. Recent advances in ENA imaging have made it possible to remotely image space plasmas and ENA imaging is now poised to image the interstellar interactions and interstellar boundaries at the edge of our heliosphere. IBEX makes these exploratory ENA observations using two ultra‐high sensitivity ENA cameras on a simple spinning spacecraft. IBEX’s highly elliptical Earth orbit allows viewing of the outer heliosphere from beyond the Earth’s relatively bright magnetospheric ENA emissions. IBEX’s sole, focused science objective is to discover the global interaction between the solar wind and the interstellar medium. IBEX achieves this objective by answering four fundamental science questions: (1) What is the global strength and structure of the termination shock? (2) How are energetic protons accelerated at the termination shock? (3) What are the global properties of the solar wind flow beyond the termination shock and in the heliotail? and (4) How does the interstellar flow interact with the heliosphere beyond the heliopause? The IBEX objective is central to the Sun‐Earth Connection (SEC) theme as demonstrated by both the 2003 SEC Roadmap and 2002 NRC’s Decadal Survey and is specifically identified in the 2003 NASA‐wide Strategic Plan. In short, the IBEX mission provides the first global views of the Sun’s interstellar boundaries, unveiling the physics of the heliosphere’s interstellar interaction, providing a deeper understanding of the heliosphere and thereby astrospheres throughout the galaxy, and creating the opportunity to make even greater unanticipated discoveries. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809514

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We review observations of plasma in the outer heliosphere The recent plasma data are dominated by merged interaction regions (MIRs). These MIRs differ from those observed last solar cycle in that the speed, density, magnetic field magnitude, and dynamic pressure all vary in phase. The most recent data show an increase in speed with a superposed sawtooth structure which is probably related to the equatorial extension of the solar polar coronal holes and their high‐speed solar wind. The solar wind dynamic pressure has started its solar‐cycle related increase, which should drive the termination shock outward. Comparison of the Voyager 2 plasma data with Voyager 1 energetic particle data shows a good correlation and may explain aspects of the timing of these events. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809515

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Lomb‐Scargle periodograms clearly show the presence of periodicities withT≈ 150 days in the Voyager 2 plasma bulk‐speed and density data. In this paper wavelet analysis is employed to investigate the time‐variation of these periodicities. It is shown that the 142 day signal is a low‐power but persistent signal requiring unusually (temporally) large wavelets to detect significant power. An episode of significant 142 day periodicity is found in the speed data around 1982 and two significant episodes are found in the density data around 1983 and 1990. There may also be a significant episode developing in the density data in recent (2003) data along with a possible relation to solar activity. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809516

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The existence of a secondary stream of neutral atoms inside the heliosphere arriving from about 285° ecliptic longitude, which is about 30° higher than the nominal upstream direction of the inflowing interstellar gas, has been proposed recently based on a wide variety of observations from many different missions. We will discuss the LENA/IMAGE measurements in detail and conclude that the secondary stream is composed mainly of hydrogen atoms at an energy of about 1 keV. We will discuss some possible explanations for the origin of the secondary stream, with the most likely source being the region upstream of the termination shock. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809517

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Interstellar pickup ions are dynamically important in the outer heliosphere where they mass‐load and heat the solar wind. Some of these pickup ions are transformed into energetic neutral atoms (ENAs) by charge exchange with the residual cold interstellar gas that is the primary constituent of the outer heliosphere. The most detailed measurements of interstellar pickup ions in the heliosphere are currently available only between ∼1 and ∼5 AU. Among the most interesting and least expected observations are those of ubiquitous suprathermal tails on the distribution of pickup and solar wind protons and all heavier ions that can be measured. Here we report new measurements of solar wind proton and alpha particle distributions and of pickup He+spectra upstream and downstream of Jupiter’s bow shock. We find that in the magnetosheath, 27&percent; of the total pickup H+density is in the tail portion of the distribution, compared to only 0.4&percent; in the upstream spectrum. For He+the entire core distribution is apparently heated in crossing the shock. These results have important implications for particle acceleration at the heliospheric termination shock, and for predicting the fluxes of energetic neutral atoms in the inner heliosphere produced from solar wind and pickup ions heated and accelerated at the termination shock. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809518

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Pickup ion distributions vary substantially on a variety of time scales, although their sources may be relatively steady. This complicates their use as probes of the heliospheric and local interstellar particle populations. Interstellar He+ pickup ion observations from SOHO/CTOF and measurements of interplanetary conditions from SOHO and WIND enable a quantitative statistical analysis of these variations. Pickup ion distributions have been shown to correlate with IMF orientation, solar wind density, and IMF strength. Correlations of the pickup ions with IMF fluctuations are demonstrated, and it is shown that these are consistent with pitch angle scattering by waves. Further questions in pickup ion flux variations are discussed. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809519

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Observed properties of the magnetic field in the outer heliosphere are generally well described by the Parker model but evidence has accumulated of significant departures in the components and field magnitude. The radial component is independent of solar latitude at both solar minimum and maximum implying non‐radial solar wind flow near the Sun driven by differential magnetic pressure. The azimuthal component deviates from the Parker values at high latitudes as a result of the non‐radial flow near the Sun that causes fields to originate at higher latitudes than those at which they are observed far from the Sun. A turning of the spiral angle toward the radial direction by tens of degrees is often observed inside co‐rotating rarefaction regions (dwells). A recent model attributes this effect to a motion of the field across polar coronal hole boundaries that results in different solar wind speeds along parts of the field line. The north‐south component can depart from zero for many days as a result of the tilting of the interface between fast and slow streams. Recent Voyager observations show that, during solar minimum, the field magnitude is smaller than extrapolations outward from 1 AU. This “flux deficit,” seen earlier in Pioneer data, may be explained by any of several physical models. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809520

出版商:AIP    

年代:1904

数据来源: AIP