Yu. I. Logachev

Coronal and interplanetary transport of solar energetic protons and electrons

We present a new method to separate interplanetary and coronal propagation, starting from intensity variations observed by spaceprobes at different heliolongitudes. In general, a decrease in absolute intensities is observed simultaneously with an increase in temporal delays. The coupling of these two effects can be described by Reids model of coronal diffusion and can in principle be used to determine the two coronal time constants, diffusion time tc and escape time A. In addition, a least-squares fit method is used to determine the parameters of interplanetary transport, assuming a radial dependence as λ(r) = λ0(r/1 AU)b. The method is applied to the two solar events of 27 December, 1977 and 1 January, 1978 which were observed by the spaceprobes Helios 1, Helios 2, and Prognoz 6. Energetic particle data are analysed for 13–27 MeV protons and ∼-0.5 MeV electrons. For the regions in space encountered during these events the mean free path of electrons is smaller than that of protons. Straight interpolation between the two rigidities leads to a rather flat rigidity dependence λ(P) ∼ Pn with n = 0.17–0.25. This contradicts the prediction of a constant mean free path or of the transition to scatter-free propagation below about 100 MV rigidity. In three of the four cases the mean free path of 13–27 MeV protons is of the order 0.17 AU, the mean free path of electrons of the order 0.06 AU. For protons we find b ∼- 0.7 for the exponent of the radial variation.The concept of two different coronal propagation regimes is confirmed. It is remarkable that in both regimes electrons are transported more efficiently than protons. This holds for the temporal delay as well as for the amplitude decrease. This is in contrast with the long existing concept of ‘rigidity independent transport’ and puts severe limits to any model of coronal transport. For the December event all three spaceprobes are in the fast propagation regime up to an angular distance of 62°. For protons we find a finite delay even in the fast propagation region, corresponding to a coronal delay rate of about 0.8 hr rad-1 up to 60° angular distance. In contrast, relativistic electrons may reach this distance within a few minutes.The fast transport of electrons and the different behaviour of electrons and protons is in contradiction to the expanding bottle concept. An explanation of coronal transport by shock acceleration directly on open field lines could in principle work in case of protons in the fast propagation region, but would fail in case of the electrons. The fast and efficient transport of electrons is most likely due to a region of field lines extending over a wide range of longitudes directly from the active region into interplanetary space. The much slower transport of both particle types at large azimuthal distances can neither be explained by direct access to open field lines not by the direct shock acceleration concept. A possible explanation is the loop reconnection model in a modified version, allowing for a faster lateral transport of electrons.

Polarization, Temporal, and Spectral Parameters of Solar Flare Hard X-rays as Measured by the SPR-N Instrument Onboard the CORONAS-F Satellite

The SPR-N polarimeter onboard the CORONAS-F satellite allows the X-ray polarization degree to be measured in energy ranges of 20–40, 40–60, and 60–100 keV. To measure the polarization, the method based on the Thompson scattering of solar X-ray photons in beryllium plates was used; the scattered photons were detected with a system of six CsI(Na) scintillation sensors. During the observation period from August 2001 to January 2005, the SPR-N instrument detected the hard X-rays of more than 90 solar flares. The October 29, 2003, event showed a significant polarization degree exceeding 70% in channels of E = 40–60 and 60–100 keV and about 50% in the 20-to 40-keV channel. The time profile of the polarization degree and the projection of the polarization plane onto the solar disk were determined. For 25 events, the upper limits of the part of polarized X-rays were estimated at 8 to 40%. For all the flares detected, time profiles (with a resolution of up to 4 s), hard X-ray radiation fluxes, and spectral index estimates were obtained.

Propagation of Solar and Galactic Cosmic Rays of Low Energies in Interplanetary Medium

The report summarizes the results of measurements of low-energy cosmic rays from Zond-3, Venus-2, Venus-3, and Venus-4 space probes for the period from 1965 to 1967 as well as preliminary results from Venus-5 and Venus-6 space probes. It has been shown on the basis of solar cosmic ray bursts and Forbush-decreases of galactic cosmic rays that the solar cosmic rays propagate rapidly from the ejection region near the sun along the beam of magnetic lines of force emerging from the active region on the sun and slowly when they are retarded in the region of the field knee created by the shock wave from the burst and move together with the knee at the velocity of the wave. It has been shown that the observed retardation of shock waves from the bursts results in disappearance of Forbush-decreases and accumulation of solar cosmic rays at distances of ~ 2 AU from the sun. It has been shown on the basis of the observations of variations in galactic cosmic rays that the variation parameters (amplitude, steepness of the fall) are determined by the dynamics, latitude, and development phase of active regions.

Statistical properties of SEP event flux declines

Abstract The interplanetary space is not a passive medium, which merely constitutes a scene for the propagation of previously accelerated energetic particles, but influences the distribution of particles by changing their energies as well due to interactions with magnetic field inhomogeneities. Such processes manifest themselves in the energy spectra of solar energetic particle (SEP) events. In this paper the fluxes of protons with energies of 4–60 MeV are investigated on the basis of two data sets. Both sets are homogeneous, obtained by the CPME instrument aboard the IMP 8 satellite between 1974 and 2001. The first includes all SEP events where the integral fluxes of >4 MeV protons exceeded 2 particle/cm 2 s sr. The other set consists of fluxes recorded in differential energy windows between 0.5 and 48 MeV. Important characteristics of SEP events include the rates of decrease of particle flux, which, as well as peak flux time, is an integral feature of the interplanetary medium within a considerable region, surrounding the observation point. The time intervals selected cover the decay phases of SEP events following flares, CMEs and interplanetary shocks of different origin. Only those parts of declines were selected, that could reasonably be described by exponential dependence, irrespective of the gradual/impulsive character of the events. It is shown that the average values of characteristic decay time, τ , and energy spectral index, γ , are all changing with the solar activity phase. Distributions of τ and γ values are obtained in SEPs with and without shocks and during different phases of events: just after peak flux and late after maximum.

Coherent propagation of non-relativistic solar electrons

An experimental study of the propagation of solar electrons with energyEe > 30 keV was carried out. Measurements were made during the period 1972-1974 using the ‘Prognoz’ satellite-borne instruments.A two-component structure of electron fluxes was found. The fast component, rather well-observed after solar flares of minor importance, consists of a compact beam of electrons propagating without scattering inside a narrow cone with an opening ⩽10° along interplanetary magnetic field lines. Characteristics of this component are given.Peculiarities of the slow or diffusive component of electron fluxes are compared with the diffusive component of solar protons. It is shown that the diffusion coefficient for non-relativistic electrons is the function of the number of particles injected in the event. A model of ‘coherent’ propagation of non-relativistic electrons is offered, which takes into account the presence of the fast and slow components and their interaction with solar wind plasma oscillations.

Relaxation of electron and proton radiation belts of the earth after strong magnetic storms

During strong magnetic storms in July and November of 2004 the fluxes of trapped particles (protons and electrons of MeV energies) in the Earth’s radiation belts have increased by orders of magnitude and then decreased remaining on an enhanced level for several months. These enhancements allowed us to study the processes of relaxation of the radiation belts. Measurements of energetic particles by low-altitude satellites Coronas-F and Servis-1 have shown that predictions of the theory about the rate of pitch-angle diffusion are not always correct, giving both overestimated and underestimated values for the lifetime of energetic particles.

Dynamics and Energetics of the Thermal and Nonthermal Components in the Solar Flare of January 20, 2005, Based on Data from Hard Electromagnetic Radiation Detectors Onboard the CORONAS-F Satellite

Based on data from the SONG and SPR-N multichannel hard electromagnetic radiation detectors onboard the CORONAS-F space observatory and the X-ray monitors onboard GOES satellites, we have distinguished the thermal and nonthermal components in the X-ray spectrum of an extreme solar flare on January 20, 2005. In the impulsive flare phase determined from the time of the most efficient electron and proton acceleration, we have obtained parameters of the spectra for both components and their variations in the time interval 06:43–06:54 UT. The spectral index in the energy range 0.2–2 MeV for a single-power-law spectrum of accelerated electrons is shown to have been close to 3.4 for most of the time interval under consideration. We have determined the time dependence of the lower energy cutoff in the energy spectrum of nonthermal photons Eγ0(t) at which the spectral flux densities of the thermal and nonthermal components become equal. The power deposited by accelerated electrons into the flare volume has been estimated using the thick-target model under two assumptions about the boundary energy E0 of the electron spectrum: (i) E0 is determined by Eγ0(t) and (ii) E0 is determined by the characteristic heated plasma energy (≈5kT (t)). The reality of the first assumption is proven by the fact that plasma cooling sets in at a time when the radiative losses begin to prevail over the power deposited by electrons only in this case. Comparison of the total energy deposited by electrons with a boundary energy Eγ0(t) with the thermal energy of the emitting plasma in the time interval under consideration has shown that the total energy deposited by accelerated electrons at the beginning of the impulsive flare phase before 06:47 UT exceeds the thermal plasma energy by a factor of 1.5–2; subsequently, these energies become approximately equal and are ∼(4–5) × 1030 erg under the assumption that the filling factor is 0.5–0.6.

Hard X-ray Radiation from Solar Flares in the Second Half of 2001: Preliminary Results of the SPR-N Experiment Onboard the Coronas-F Satellite

The first results of the experiment with the SPR-N hard X-ray (20–100 keV) polarimeter onboard the Coronas-F observatory (the experiment started on August 15, 2001) are presented. Hard X-ray radiation was detected from several solar flares. The spectral and temporal parameters were determined and the polarization was estimated. Comparison with the GOES observations of thermal X-ray radiation shows that hard X-ray bursts occur at the growth phase of the thermal radiation and that they are associated with the bremsstrahlung of energetic electrons precipitating into the solar atmosphere.

Jovian electrons and the solar wind during the minimum of the 23rd–24th solar activity cycle

Jovian electrons in Earth orbit can be regarded as probes of the inner heliosphere’s structure. They readily penetrate into the inner heliosphere in periods of the optimum magnetic connection between Earth and Jupiter. Such a penetration is also occasionally observed at arbitrary Earth-Jupiter dispositions. This phenomenon can be explained by the occurrence of long-lived magnetic traps extending from the Sun to Jupiter and rotating along with the Sun.

Ion abundances of low-energy quiet period particle fluxes at 1 AU

The ion abundances of charged particle fluxes with energies of 0.032–1.28 MeV/nucleon during the quiet period of solar activity are investigated using spacecraft data. The values of Fe/O ratios obtained in 35 such periods in the 23rd solar cycle are compared with the mean ion abundances in the solar corona, in the gradual and impulsive solar energetic particle events, and in the solar wind. It is believed that coronal holes near the equator could be one of possible source of background low energy particle fluxes.