A. Czechowski

Acceleration of the High Speed Solar Wind in Coronal Holes

We outline a theory for the origin and acceleration of the fast solar wind as a consequence of network microflares releasing a spectrum of high frequency Alfvén waves which heat (by cyclotron absorption) the corona close to the Sun. The significant features of our model of the fast wind are that the acceleration is rapid with the sonic point at around two solar radii, the proton temperatures are high (~ 5 million degrees) and the minor ions are correspondingly hotter, roughly in proportion to their mass. Moreover we argue that since the energy flux needed to power the quiet corona in closed field regions is about the same as that needed to drive the fast solar wind, and also because at deeper levels (< 2 × 105 K) there is no great difference in the properties of supergranules and network in closed and open field regions, the heating process (i.e., dissipation of high frequency waves) must be the same in both cases.

Anomalous cosmic rays and the generation of energetic neutrals in the region beyond the termination shock

Some characteristics of the neutral hydrogen flux of 55-80 keV detected by CELIAS/HSTOF on board SOHO (in particular, the intensity peaks during the periods when the instrument was directed towards the anti-apex of the local interstellar medium) suggest that the observed atoms may be created in the distant heliosphere, beyond the termination shock, from the anomalous cosmic ray protons which become neutralized by charge-exchange with the background gas. The theoretical models on which this conclusion was first based were very simple and missed some important features. Here we report about the first study of transport of low energy anomalous cosmic rays beyond the solar-wind termination shock employing a model of the heliosphere treating self-consistently the flows of plasma and neutral atoms and including the pressure of cosmic rays. The energetic neutral-atom (ENA) flux created by charge-exchange is calculated and compared with the observations of CELIAS/HSTOF. The viability of using ENAs as a means of imaging the structure of the termination shock, the distant heliosphere and the very local interstellar medium is discussed. We also include some results which may be interesting in connection to possible observations by INCA/Cassini and HENA/IMAGE.

Pick-up ions upstream and downstream of the termination shock

Hydrogen pick-up ions produced in the inner heliosphere are convected outwards with the solar wind and suffer energy-diffusion by quasilinear wave-particle interactions. When arriving at the solar wind termination shock, the big majority of these pick-ups passes directly from the preshock to the postshock plasma regime. While crossing the shock these ions suffer a characteristic change in their density and velocity distribution which sensitively reflects the local shock properties. We extend the earlier model calculations to derive the pre-shock and postshock pick-up proton spectrum in the ecliptic plane, taking into account the global structure of the heliosphere and the termination shock. The proton distribution is used to calculate the energetic neutral hydrogen flux and the results are compared with the CELIAS/HSTOF data. There is a satisfactory agreement as regards the flux intensity scale and the directional dependence of the flux. The calculated energy spectrum is steeper than the data.

Generalized sonic points and acceleration of multi-ion solar wind

Abstract The acceleration of the solar wind plasma near the Sun is governed by the critical (sonic point) structure of the appropriate fluid equations. For a multi-ion solar wind plasma with the components coupled by electric field and other interactions the generalized sonic points cannot be associated with any of the components alone. In this contribution the critical solution describing the passage of two-ion plasma from subsonic to supersonic region is obtained assuming sharply peaked ion temperature profiles, of interest in view of recent SOHO data. The topology of the generalized critical points follows as a by-product of the method.

Heliospheric energetic Hydrogen Atoms as a Source of Interplanetary Energetic Protons

Heliospheric energetic hydrogen atoms below 100 keV have been detected at 1 AU with a strong anisotropy toward the heliotail by the instrument CELIAS on SOHO (1). These energetic neutrals are seen as results of anomalous cosmic-ray (ACR) protons transcharging with the local interstellar medium (LISM) in the outer heliosphere. The resulting neutrals then travel on ballistic trajectories, unaffected by the interplanetary magnetic field (IMF), to the inner heliosphere. In the vicinity of the sun, a fraction of these energetic neutrals are ionized again by photoionisation or collision with the solar wind protons and electrons. These energetic protons will then travel along the IMF and contribute to the quiet-time interplanetary energetic proton flux in the energy range below about 100 keV. This contribution should be proportional to the integrated energetic hydrogen atom flux in the heliosphere and therefore the production of energetic neutral hydrogen at the edge of the heliosphere. We estimate the flux uppe...

Studying the Heliosphere in Energetic Neutral H and He Atoms above 30 keV/amu

Energetic neutral atoms (ENA) are energetic ions neutralized by charge exchange with atoms in an ambient gas. The dynamics of charge exchange and the neutrality of ENA allow their sue to sample the mass and energy distributions of the ion population in regions of ENA production far away across magnetic fields. For ENA of energies > 30 keV/amu in the heliosphere, the energetic ions include anomalous cosmic rays in the heliosheath and pickup ions accelerated in interplanetary shocks; and the ambient gas is the neutral component of the local interstellar medium that permeates the heliosphere. ENA provide unique access to all regions of the heliosphere. We review some aspects of using ENA of energies > 30 keV/amu to study the heliosphere and suggest what can be done to fully utilize ENA in gaining a global view of the different particle populations linked by the acceleration and transport processes in the heliosphere.

Imaging the global distribution of anomalous cosmic rays

Since the discovery of the anomalous component of cosmic rays (ACR), more detailed information on the composition and intensity variations over solar cycles have been accumulated and studied. As the two Voyagers approach the solar-wind termination shock, anticipation of a decisive test on the theory of transport and acceleration of ACR heightens. The fact that all existing ACR measurements have been in situ, i.e. by directly detecting the modulated particles along specific trajectories of ACR-measuring spacecraft; that ACR is an important link in our understanding of our plasma environment; and that the opportunity to explore the outer edges of the heliosphere will not be readily available; all suggest that the means to survey the global distribution of ACR should be examined and implemented. Since the use of detecting energetic neutral atoms (ENA) as a means to study ACR at and beyond the termination shock was first proposed, the idea has gained acceptance and the techniques for detecting ENA have mature...

Minor ions and acceleration of the fast solar wind

The critical solution describing the acceleration of the solar wind minor ion component is obtained taking the temperature profiles (based on the one-ion model of McKenzie et al. 1997) as input. The model includes preferential heating of the heavy ion species and the temperature anisotropy expected if the heating is caused by ion-cyclotron damping of Alfven waves.