I. V. Chashei

On the thermodynamics of MHD wave-heated solar wind protons

It has been clearly observed by the NASA deep-space probes that the solar wind protons do not adiabatically cool as expected towards larger solar distances, but appear to be heated by non-collisional energy sources. In some papers these heating sources were directly or indirectly ascribed to pick-up ions incorporated as suprathermal ions into the background solar wind. Neutral interstellar H-atoms penetrate into the inner heliosphere and at ionization they are converted into pick-up ions. Here we do not consider how the magnetized solar wind flow incorporates these ions into the plasma bulk when enforcing their co-motion. We simply take the first step of their incorporation for guaranteed, namely the fast redistribution of pick- ups from an initially unstable toroidal to a quasistable bi-spherical distribution. The free energy lost by pick-ups during this redistribution goes into the turbulent MHD waves, and as such cascades down to the proton dissipation scale and finally is absorbed by solar wind protons. Here we investigate the thermodynamics of solar wind protons being heated by absorption of this free energy of pick-ups. In addition we also consider as a relevant and competing proton heat source the heating due to absorption of wave energy of convected MHD turbulences, showing that the latter source always dominates inside some critical solar distance, whereas the first one dominates in the outer heliospheric regions. We then solve the resulting dierential equation for the solar wind proton temperature and show in the solutions obtained that a quasipolytropic behaviour of the solar wind protons with a distance-dependent polytropic index is found. The expression for the pressure clearly shows the change from an adiabatic to a quasipolytropic behaviour with a decreasing polytropic index at increasing distances as observed by the VOYAGERs. The quantitative run of the temperature and the polytropic index with solar distance thereby is strongly influenced by the interstellar H-atom density. The (pick-up ion)-induced heating also evidently leads to a wind-asymmetric solar wind temperature distribution with higher temperatures occuring in upwind direction compared to downwind direction.

Injection to the pick-up ion regime from high energies and induced ion power-laws

Though pick-up ions (PUIs) are a well-known phenomenon in the inner heliosphere, their phase-space distribution nevertheless is a theoretically unsettled problem. Especially the question of how PUIs form their suprathermal tails, extending to far above their injection energies, still now is unsatisfactorily answered. Though Fermi-2 velocity diffusion theories have revealed that such tails are populated, they nevertheless show that resulting population densities are much less than seen in observations showing power-laws with a velocity index of “−5”. We first investigate here, whether or not observationally suggested power-laws can be the result of a quasi-equilibrium state between suprathermal ions and magnetohydrodynamic turbulences in energy exchange with each other. We demonstrate that such an equilibrium cannot be established, since it would require too high PUI pressures enforcing a shock-free deceleration of the solar wind. We furthermore show that Fermi-2 type energy diffusion in the outer heliosphere is too inefficient to determine the shape of the distribution function there. As we can show, however, power-laws beyond the injection threshold can be established, if the injection takes place at higher energies of the order of 100 keV. As we demonstrate here, such an injection is connected with modulated anomalous cosmic ray (ACR) particles at the lower end of their spectrum when they again start being convected outwards with the solar wind. Therefore, we refer to these particles as ACR-PUIs. In our quantitative calculation of the PUI spectrum resulting under such conditions we in fact find again power-laws, however with a velocity-power index of “−4” and fairly distance-independent spectral intensities. As it seems these facts are observationally well supported by VOYAGER measurements in the lowest energy channels.

Solar wind bulk velocity fluctuations acting as velocity space diffusion on comoving ions

From most in-situ plasma observations made in the outer heliosphere it became evident that above the injection border of pick-up ions (� 1 keV), an extended suprathermal ion tail is found which in most cases can be fitted by a power law with velocity power indices of (−6) ≤ γv ≤ (−4). As has been shown by theory such energetic ion tails cannot be explained by Fermi-2 type velocity diffusion, since in the outer heliosphere both Alfvenic and magnetoacoustic turbulences become too weak. Here we come to a new solution of this unsolved problem by studying the action of solar wind bulk velocity fluctuations on ions co-moving with the wind. As we show the passage of such fluctuations results in energization of each individual ion and systematic evolution of the ion distribution function towards suprathermal tails. From the basic knowledge that we can obtain on this process we can calculate the velocity divergence of the ion phasespace flow and thus can derive a velocity diffusion operator. As we can show here this operator leads to a velocity diffusion coefficient proportional to the square of the ion velocity and, when employed in the phasespace transport equation, together with terms for convective changes, cooling processes and pick-up ion injection, interestingly enough, permits to find solutions for suprathermal power law tails with power indices of γv �− 5 as very often observed.

Volume scattering model for interpretation of solar radar experiments

It is shown that solar radar experiments carried out at λ = 8 m can be explained on the assumption that the reflected signal is formed as a result of multiple volume scattering on large-scale (about 1 km) irregularities of the outer corona. The region of effective scattering is located at the heliocentric distancer ≃ 2R⊙, i.e., considerably higher than the region of surface mirror reflection. Measured characteristics of reflected signals are in good agreement with the theoretical model.

Traveling solar-wind bulk-velocity fluctuations and their effects on electron heating in the heliosphere

Ambient plasma electrons undergo strong heating in regions associated with compressive bulk-velocity jumps ΔU that travel through the interplanetary solar wind. The heating is generated by their specific interactions with the jump-inherent electric fields. After this energy gain is thermalized by the shock passage through the operation of the Buneman instability, strong electron heating occurs that substantially influences the radial electron temperature profile. We previously studied the resulting electron temperature assuming that the amplitude of the traveling velocity jump remains constant with increasing solar distance. Now we aim at a more consistent view, describing the change in jump amplitude with distance that is caused by the heated electrons. We describe the reduction of the jump amplitude as a result of the energy expended by the traveling jump structure. We consider three effects: energy loss due to heating of electrons, energy loss due to work done against the pressure gradient of the pick-up ions, and an energy gain due to nonlinear jump steepening. Taking these effects into account, we show that the decrease in jump amplitude with solar distance is more pronounced when the initial jump amplitude is higher in the inner solar system. Independent of the initial jump amplitude, it eventually decreases with increasing distance to a value of about ΔU/U � 0.1 at the position of the heliospheric termination shock, where ΔU is the jump amplitude, and U is the average solar-wind bulk velocity.The electron temperature, on the other hand, is strongly correlated with the initial jump amplitude and leads to electron temperatures between 6000 K and 20 000 K at distances beyond 50 AU. We compare our results with in situ measurements of the electron-core temperature from the Ulysses spacecraft in the plane of the ecliptic for 1. 5A U≤ r ≤ 5 AU, where r is the distance from the Sun. Our results agree very well with these observations, which corroborates our extrapolated predictions beyond r = 5A U.

Heating of distant solar wind ion species by wave energy dissipation

Abstract Primary solar wind protons do not cool off adiabatically with distance, but appear to be heated. Also secondary protons, comoving with the solar wind as pick-up ions, appear to behave quasi-isothermal at their motion outwards to the outer heliosphere. In a synoptic view presented here we see these two phenomena as closely related. This is proven by solving a coupled set of enthalpy flow conservation equations for the two-fluid solar wind system consisting of primary and secondary protons. The coupling of these equations comes by the relevant heat sources, namely by dissipation of MHD turbulence power to both ion species. We take into, account the dissipation of both convected turbulences and turbulences locally driven by newly injected pick-up ions. Initial conversion of free kinetic energy of freshly injected secondary ions into turbulence power is followed by partial reabsorption of this energy both by primary and secondary ions. We integrate the coupled set of differential two-fluid equations, study the primary proton temperature within this two-fluid context and find a non-adiabatic behaviour with radially and latitudinally variable polytropic indices. Inspecting latitudinally variable solar wind conditions as found from observations by McComas et al. (2000) we predict latitudinal variations of primary proton temperatures and show that the secondary proton temperature with increasing radial distance asymptotically attains a constant value with a magnitude essentially determined by the actual solar wind velocity. From that we also conclude higher pick-up ion temperatures and pressures at higher latitudes.

Search for and detection of pulsars inmonitoring observations at 111 MHz

In the course of monitoring interplanetary scintillations of a large number of sources using the Big Scanning Antenna of the Lebedev Physical Institute, a search for pulsars with periods ≥0.4 s at declinations −9◦ < δ < 42◦ and right ascensions 0h < α < 24h was simultaneously carried out. The search was conducted using four years of observations carried out at 110.25MHz in six frequency channels making up a 2.5 MHz band and having a time resolution of 100 ms. The initial identification of pulsar candidates was done using Fourier power spectra averaged over the entire observational period; the pulsar candidates were then verified using observations with higher frequency and time resolution: 32 frequency channels and a time resolution of 12.5 ms. Eighteen new pulsars were discovered in the studied area, whose main characteristics are presented.

Detection of Five New RRATs at 111 MHz

Results of 111-MHz monitoring observations carried out on the Big Scanning Antenna of the Pushchino Radio Astronomy Observatory during September 1–28, 2015 are presented. Fifty-four pulsating sources were detected at declinations −9° < δ < 42°. Forty-seven of these are known pulsars, five are new sources, and two are previously discovered transients. Estimates of the peak flux densities and dispersion measures are presented for all these sources.