Energy spectra of high energy electrons and hard X-rays as observed onboard the space probe Venera 11 during the solar flare event of April 13 1979

The event was observed onboard the space probe Venera 11 at a heliolongitude close to 57°. Electron spectra in the energy range from 60 to 2100 keV are determined and compared with X ray spectra. As a result it was found that conditions of the “thin target” model were realized in the April 13, 1979 flare. Estimates of the total number of accelerated electrons and the energy of the flare are presented.     

Time Variations of Low-Energy Protons and Helium Nuclei (0.3–10 MeV/nucleon) during the Quiescent Time of Solar Activity in the Inner Heliosphere

Time variations with a duration of 0.6–1.5 years are studied in the interplanetary space for protons and helium nuclei with energies of 0.3–10 MeV per nucleon at a quiescent time of solar activity. It is shown that at 1 AU in the periods 1978–1981 and 1988–1990, at the phases of growth of the 21st and 22nd solar cycles, the background fluxes of these particles determined as minimum intensity levels in every month increased demonstrating steplike variations. At the same time, the intensity of galactic cosmic rays (GCRs) decreased also with the formation of modulation steps. Each step of low-energy particles was finished by a deep minimum of intensity (gap) in both protons and helium nuclei and with a simultaneous short-term increase of the GCR intensity. We present the results of studying five such steps in the intensity of low-energy particles that were observed simultaneously and were opposite in phase with modulation steps of galactic particles. The lowest values of the H/He ratio were recorded at the end of every step, at the lowest intensities of these particles, i.e., in the gap. The true background population at 1 AU was detected precisely at these time intervals, when the contributions of flare particles and those accelerated in the international space were minimum. Various possibilities of the origination of the steplike variations of the background fluxes of protons and helium nuclei with energies of 0.3–10 MeV per nucleon, correlated with similar GCR variations, are discussed.     

Dynamics of the 0.3–100 MeV Proton Energy Spectra in the Inner Heliosphere in Quiet Periods of 1974–1991

Variations of the proton spectra in the 0.3–100 MeV energy range based on the data of various instruments installed onboard the IMP-8 satellite are studied for very quiet, quiet, and quasi-stable solar activity periods during the years 1974–1991. As many as 118 spectra were approximated by two power laws: the left-hand and galactic branches of the spectrum were fitted by the AE ^– function and a dependence of the CE type, respectively, the sum J(E) = AE ^– + CE providing the total spectrum. It is shown that the spectra vary within a solar cycle with a shift of the minimum energy (E _min) to higher energies with increasing solar activity. It follows from the relations between the spectrum parameters thus obtained that, in particular periods of time, an increase (decrease) of the particle flux in the low-energy branch of the spectrum and an intensification (depression) of the GCR particle flux modulation take place simultaneously. This is manifested in a shift of the spectrum parallel to the energy axis. The study of the spectra in the most quiet time during three successive solar minima have shown that low-energy (0.3–10 MeV) protons, as well as GCR, are subject to the 22-year variation in the solar magnetic cycle.     

Energetic electrons in the tail and transition region of the magnetosphere

A comparative analysis has been carried out of the parameters of energetic electrons in the tail of the Earth’s magnetosphere that belong to three sources, i.e., electrons of solar origin, electrons generated in the magnetosphere of Jupiter, and electrons in the Earth’s magnetosphere. The differences in the time profiles of fluxes and energy spectra of the three electron sources, their relation to fluxes outside the magnetosphere, and periods of the occurrence of electron fluxes of each type are considered.     

Statistical properties of SEP event flux declines

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/cm² 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.     

Characteristics of the decay phase of proton fluxes in solar events as a function of observer’s heliolongitude

Events in energetic solar protons with the energy > 4 MeV at the stage of their decay are considered for the period from 1974 to 2001. It is shown that in the events with the exponential shape of decay for west flares (relative to the observation point), the characteristic decay time τ and the power index γ of the energy spectrum decrease with an increase in the angular distance between the observer and the source of the particles on the Sun, while this effect is absent for east flares.     

Relative ion Fe,C and O abundances in quiet time particle fluxes in the 23 SC

Using ACE and SOHO data the origin of quiet-time low-energy particle fluxes at 1 AU is studied in the 23rd solar cycle. One of the selection criteria of quiet-time periods is to demand that H/He < 10 provided that periods with noticeable contribution of remnants of gradual events have been excluded from consideration. Our results suggest different origin of 0.03–3 MeV/nucleon particles – different seed populations accelerated and different acceleration processes. During the ascending, maximum and descending phases of solar activity quiet-time ions consist of coronal particles accelerated to suprathermal energies in about a half of the quiet periods, the rest of quiet-time fluxes originates from particle acceleration in processes similar to those in small impulsive solar flares rich in Fe. At solar minimum the bulk solar wind particles serve as seed population.     

On the belt of energetic electrons at <Emphasis Type="Italic">L</Emphasis> = 2.75 in the Earth’s magnetosphere

In 1964, during flights of the ELECTRON satellites the narrow belts of energetic electrons (E _e ≈ 6MeV) have been discovered in the Earth’s magnetosphere at L ≈ 2.75. The same structures approximately at the same magnetic shells were found in 2004 by the CORONAS-F and SERVIS-1 satellites. A comparison of the results of these experiments is presented. It is shown that the additional narrow belts of energetic electrons occur after intense magnetic storms (D _st > 100 nT), in our cases, having a double-triple structure. The lifetime of these belts is a few months and their disappearance had a gradual character. The obtained results separated in time by 40 years suggest the constancy of the sources of particles of the Earth’s radiation belts and processes occurring in the magnetosphere, which ensures not only existence of the radiation belts, but also the recurrence of various exotic phenomena in the belts similar to the belt of energetic electrons at the inner magnetic shells.     

The rigidity dependence of characteristic decay time and mean free path in SCR events

Combination of data on declined intensities of particles of different nature (e, p, and α) into a single dependence of characteristic decline time τ on particle rigidity in a wide range of R reveals the diversity of forms of τ(R) in different events: regular increase, decrease, and independence of R, as well as the presence in some events of maxima and minima. The problem of studying τ(R) has something in common with long standing problem of the rigidity dependence of mean free path λ(R). The considered set of forms of τ(R) allows one to conclude that at present there is no uniform dependence τ(R), as well as λ(R), and, therefore, no their common model interpretation in a wide range of rigidities exists.     

Contribution of solar cosmic rays to the formation of the Earth’s proton radiation belt

The significance of the contribution of solar protons to fluxes of trapped radiation in the Earth’s outer radiation belt (L > 2) is estimated for various phases of solar activity. In periods of high solar activity, proton fluxes with the energy 1–5 MeV at L = 2–3 for the bulk of time have SCR as a source, during a minimum of solar activity, trapped proton fluxes are determined by the conventional diffusive mechanism under the action of sudden IMF impulses.