Modeling of Proton Acceleration in a Magnetic Island Inside the Ripple of the Heliospheric Current Sheet     

Mingalev  O. V.  Khabarova  O. V.  Malova  Kh. V.  Mingalev  I. V.  Kislov  R. A.  Mel’nik  M. N.  Setsko  P. V.  Zelenyi  L. M.  Zank  G. P. 《Solar System Research》2019,53(1):30-55

Crossings of the heliospheric current sheet (HCS) at the Earth’s orbit are often associated with observations of anisotropic beams of energetic protons accelerated to energies from hundreds of keV to several MeV and above. A connection between this phenomenon and the occurrence of small-scale magnetic islands (SMIs) near reconnecting current sheets has recently been found. This study shows how pre-accelerated protons can be energized additionally due to oscillations of multiple SMIs inside the ripple of the reconnecting HCS. A model of the electromagnetic field of an oscillating 3D SMI with a characteristic size of ~0.001 AU is developed. A SMI is supposed to be bombarded by protons accelerated by magnetic reconnection at the HCS to energies from ~1keV to tens of keV. Numerical simulations have demonstrated that the resulting longitudinal inductive electric fields can additionally reaccelerate protons injected into a SMI. It is shown that there is a local “acceleration” region within the island in which particles gain energy most effectively. As a result, their average escape energies range from hundreds of keV to 2 MeV and above. There is almost no particle acceleration outside the region. It is shown that energies gained by protons significantly depend on the initial phase and the place of their entry into a SMI but weakly depend on the initial energy. Therefore, low-energy particles can be accelerated more efficiently than high-energy particles, and all particles can reach the total energy limit upon their escape from a SMI. It is also found that the escape velocity possesses a strong directional anisotropy. The results are consistent with observations in the solar wind plasma.

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Sharp Changes of Solar Wind Ion Flux and Density Within and Outside Current Sheets     

Khabarova  O.  Zastenker  G. 《Solar physics》2011,270(1):311-329

Analysis of the Interball-1 spacecraft data (1995 – 2000) has shown that the solar wind ion flux sometimes increases or decreases abruptly by more than 20% over a time period of several seconds or minutes. Typically, the amplitude of such sharp changes in the solar wind ion flux (SCIFs) is larger than 0.5×10⁸ cm⁻² s⁻¹. These sudden changes of the ion flux were also observed by the Solar Wind Experiment (SWE), on board the Wind spacecraft, as the solar wind density increases and decreases with negligible changes in the solar wind velocity. SCIFs occur irregularly at 1 AU, when plasma flows with specific properties come to the Earth’s orbit. SCIFs are usually observed in slow, turbulent solar wind with increased density and interplanetary magnetic field strength. The number of times SCIFs occur during a day is simulated using the solar wind density, magnetic field, and their standard deviations as input parameters for a period of five years. A correlation coefficient of ∼0.7 is obtained between the modelled and the experimental data. It is found that SCIFs are not associated with coronal mass ejections (CMEs), corotating interaction regions (CIRs), or interplanetary shocks; however, 85% of the sector boundaries are surrounded by SCIFs. The properties of the solar wind plasma for days with five or more SCIF observations are the same as those of the solar wind plasma at the sector boundaries. One possible explanation for the occurrence of SCIFs (near sector boundaries) is magnetic reconnection at the heliospheric current sheet or local current sheets. Other probable causes of SCIFs (inside sectors) are turbulent processes in the slow solar wind and at the crossings of flux tubes.  相似文献   

The interplanetary magnetic field: Radial and latitudinal dependences     

O. V. Khabarova 《Astronomy Reports》2013,57(11):844-859

Results of the analysis of spacecraft measurements at 1–5.4 AU are presented within the scope of the large-scale interplanetary magnetic field (IMF) structure investigation. The work is focused on revealing of the radial IMF component (B _r ) variations with heliocentric distance and latitude as seen by Ulysses. It was found out that |B _r | decreases as ～r ^?5/3 in the ecliptic plane vicinity (±10° of latitude), which is consistent with the previous results obtained on the basis of the analysis of in-ecliptic measurements from five spacecraft. The difference between the experimentally found (r ^?5/3) and commonly used (r ^?2) radial dependence of B _r may lead to mistakes in the IMF recalculations from point to point in the heliosphere. This can be one of the main sources of the “magnetic flux excess” effect, which is exceeding of the distantly measured magnetic flux over the values obtained through the measurements at the Earth orbit. It is shown that the radial IMF component can be considered as independent of heliolatitude in a rough approximation only. More detailed analysis demonstrates an expressed |B _r | (as well as the IMF strength) increase in the latitudinal vicinity of ±30° relative to the ecliptic plane. Also, a slight increase of the both parameters is observed in the polar solar wind. The comparison of the B _r distributions confirms that, at the same radial distance, B _r values are higher at low than at high latitudes. The analysis of the latitudinal and radial dependences of the B _r distribution’s bimodality is performed. The B _r bimodality is more expressed at high than in the low-latitude solar wind, and it is observed at greater radial distances at high latitudes. The investigation has not revealed any dependence between B _r and the solar wind speed V. The two-peak distribution of the solar wind speed as measured by Ulysses is a consequence of a strong latitudinal and solar cycle dependence of V. It is shown that the solar wind speed in high latitudes (above ±40°) anti-correlates with a solar activity: V is maximum during solar-cycle minima and minimum at the maximum of solar activity.  相似文献   

Solar flux variations at 175 and 304 Å and their relation to solar wind parameters     

O. V. Khabarova  S. V. Kuzin  S. A. Bogachev  A. A. Pertsov 《Solar System Research》2006,40(4):341-347

Variations of solar emission in the spectral ranges corresponding to the transition region (304 Å) and corona (175 Å) and their relation to solar wind parameters are investigated for the maximum and declining phase of solar cycle 23 (2001–2004) based on the CORONAS-F/SPIRIT data. It is shown that the variations of solar flux in both ranges are similar and demonstrate a high correlation for long data series. Meanwhile, some time intervals were registered when the intensity variations at 304 Å are delayed with respect to those in 175 Å by, on average, two days. For long periods, the spectra of the full-disk flux at 175 Å and of the solar wind density are close to each other; the same is true for the solar flux spectrum in the 304-Å range and the spectrum of the solar wind velocity. The assumption is made that active processes in the lower corona mainly affect long-period density variations, while the velocity characterizes the kinetics of the total stream of the outflowing matter and its long-term variations are considerably related to the physics of processes occurring deeper in the Sun.  相似文献