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We report here observations of magnetic waves recorded by the Voyager spacecraft in the solar wind near Jupiter that are possibly the result of excitation by newborn pickup H+. Consideration of growth rates due to the known interstellar ion sources strongly disfavor an interstellar source. To determine the likely source of the waves, we compute the minimum ion production rate by equating wave growth to turbulent cascade rates and derive a lower limit for the production of H+ at the times of observations. The only available source of neutral H at these times and at the levels required is the Jovian system, most notably charge exchange between energetic protons and the neutral clouds around Io and Europa's orbits. Further refinement of the source identity is not possible at this time. We provide an estimate for the neutral H source subject to assumptions of the latitudinal extent of the population which is not constrained by observation. Plain Language Summary: The Voyager spacecraft instruments include a fluxgate magnetometer called MAG that measures the changing ambient magnetic field. We report observations by MAG of low‐frequency waves in the solar wind outside the Jovian magnetosphere that are seen at frequencies and with characteristics that suggest the waves are excited by protons that originate as neutral hydrogen. Collision with solar wind protons ionize the neutral hydrogen to produce an energetic ion population called pickup ions. We use known characteristics of wave excitation by pickup ions to estimate the rate of pickup ion production. The only source that is strong enough to produce the pickup ions with the number density required is the Jovian system. Key Points: Magnetic waves were measured by Voyagers 1 and 2 in the solar wind near the magnetosphere of JupiterThese waves have signatures of excitation by local pickup H+ ionsA neutral H loss rate of ∼5 × 1028 s−1 from the Jovian system is estimated [ABSTRACT FROM AUTHOR]

We have examined Ulysses magnetic field measurements for the years 1993 through 1996 as the spacecraft moved sunward from 5 au at high southern latitudes, passing through perihelion during the first fast-latitude scan to achieve high northern latitudes, and finally returning to 5 au. These years represent near-solar-minimum activity, providing a clear measure of high-latitude solar-wind turbulence. We apply a series of tests to the data, examining both the magnetic variance anisotropy and the underlying wavevector anisotropy, finding them to be consistent with past 1 au observations. The variance anisotropy depends upon both the thermal proton temperature parameter and the amplitude of the magnetic power spectrum, while the underlying wavevector anisotropy is dominated by the component perpendicular to the mean magnetic field. We also examine the amplitude of the magnetic power spectrum as well as the associated turbulent transport of energy to small scales that results in the heating of the thermal plasma. The measured turbulence is found to be stronger than that seen at low latitudes by the Voyager spacecraft as it traverses the distance from 1 to 5 au during the years approaching solar maximum. If the high- and low-latitude sources are comparable, this would indicate that while the heating processes are active in both regions, the turbulence has had less decay time in the transport of energy to small scales. Alternatively, it may also be that the high-latitude source is stronger. [ABSTRACT FROM AUTHOR]

We adopt the theory for turbulent transport of energy by solar wind fluctuations and apply that theory to observations by the Voyager 1 and 2 spacecraft to obtain rates of thermal proton heating that are controlled by two sources: the large-scale fluctuations in the solar wind that arise from solar sources and the excitation of waves by newborn interstellar ions. In the process, we compute magnetic spectra for 839 data intervals spanning the range from 1 to 35 au when thermal ion data is available and use those spectra to obtain independent estimates for the energy cascade rates at intermediate scales that we assume equals the rate of thermal proton heating by the turbulence. We compare three analyses that describe different aspects of the solar wind heating problem: the rate of energy cascade through the intermediate scales of the magnetic spectrum, the rate at which energy is supplied to that cascade from the large-scale fluctuations as described by magnetohydrodynamic transport theory, and the rate at which energy is injected into the spectrum via wave excitation by newborn interstellar ions. The first two expressions are found to be in good agreement while the latter source dynamics become important beyond 10 au. [ABSTRACT FROM AUTHOR]

We examine both Voyager and Advanced Composition Explorer magnetic field measurements at frequencies that characterize the inertial range and evaluate the anisotropy of the fluctuations as they relate to both the compressive component and underlying wavevector anisotropy of the turbulence. The magnetic fluctuation anisotropy as it relates to the compressive component is directly dependent upon both the plasma beta of the thermal proton component and the ratio of magnetic fluctuation magnitude to the strength of the mean magnetic field. This has been seen before at 1 au. The magnetic fluctuation anisotropy in the plane perpendicular to the mean magnetic field, which is a measure of the anisotropy of the underlying wavevector distribution, should depend on the angle between the mean magnetic field and the radial direction and should be confined to values between one and the index of the power spectrum, which is typically 5/3. Our results show that the average of this anisotropy exceeds the value of the spectral index and is out of bounds with the theory. Although the results are suggestive of past analyses, we find that spherical expansion of the turbulence may offer at least a partial explanation of the apparent amplification of this measured anisotropy. [ABSTRACT FROM AUTHOR]

We examine both Voyager and Advanced Composition Explorer magnetic field measurements at frequencies that characterize the inertial range using traditional polarization techniques that are designed to characterize plasma waves. Although we find good agreement with both the anticipated spectral index of the power spectrum and the scaling of magnetic power with heliocentric distance, we do not find that the polarization analyses yield results that can be readily described by plasma wave theory. The fluctuations are not circularly polarized and there is a markedly reduced coherence between the components of the fluctuation. The degree of polarization is also generally low, although not as low as the coherence, and the minimum variance direction is essentially random. We conclude that traditional plasma wave theory may not offer a good description for inertial-range fluctuations. [ABSTRACT FROM AUTHOR]

As part of a published effort to study low-frequency magnetic waves excited by newborn interstellar pickup ions seen by the Voyager spacecraft, we developed a set of control intervals that represent the background turbulence when the observations are not dominated by wave excitation. This paper begins an effort to better understand solar wind turbulence from 1 to 45 au while spanning greater than one solar cycle. We first focus on the diagnostics marking the onset of dissipation. This includes an expected break in the power spectrum at frequencies greater than the proton cyclotron frequency and a resultant steepening of the spectrum at higher frequencies. Contrary to what is established at 1 au, we only see the spectral break in rare instances. The expected scaling of the spectral index with the turbulence rate is seen, but it is not as clearly established as it was at 1 au. We also find that both Voyager data from 1 to 45 au and Advanced Composition Explorer data from 1 au show significant bias of the magnetic helicity at dissipation scales when the dissipation-range power-law spectral index steepens. We conclude that dissipation dynamics are similar throughout the heliosphere in so far as we have examined to date. [ABSTRACT FROM AUTHOR]

A recent examination of 1.9 s magnetic field data recorded by the Voyager 2 spacecraft in transit to Jupiter revealed several instances of strongly aliased spectra suggestive of unresolved high-frequency magnetic fluctuations at 4.4 AU. A closer examination of these intervals using the highest resolution data available revealed one clear instance of wave activity at spacecraft frame frequencies from 0.2 to 1 Hz. Using various analysis techniques, we have characterized these fluctuations as Bernstein mode waves excited by newborn interstellar pickup ions. We can find no other interpretation or source consistent with the observations, but this interpretation is not without questions. In this paper, we report a detailed analysis of the waves, including their frequency and polarization, that supports our interpretation. [ABSTRACT FROM AUTHOR]

The low-frequency magnetic waves that arise from the isotropization of newborn interstellar pickup ions (PUIs) are reasonably well described by linear and quasi-linear kinetic theory in so far as those theories predict the wave frequency and polarization in the spacecraft frame. Those theories fail to describe the scarce observability of the waves. Quasilinear theory predicts that the wave power should accumulate over long periods of time as the relatively weak kinetic instability slowly adds power to the observed spectrum. At the same time it has been argued that the same wave energy must serve as a secondary source of thermal ion heating in the outer heliosphere once the initial turbulence is depleted. To the extent that turbulent transport of the wave energy acts against the spectrally confined accumulation of wave energy, turbulence should be a limiting factor in observability. We argue that turbulence does limit the observability of the waves and we use turbulence theory to predict the observed wave energy. We compare this prediction against a database of 502 wave observations attributed to newborn interstellar PUIs observed by the Ulysses spacecraft. [ABSTRACT FROM AUTHOR]