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1.
We have studied the H+ velocity distribution function at Mars and Venus near the bow shock both in the solar wind and in the magnetosheath by a simple analytical one-dimensional model. We found that over half of the ions in the ring velocity distribution which moved towards the magnetosheath were scattered back into the bow shock. The original ring distribution is destroyed in less than an ion gyro period. Ions contained in the magnetosphere which hit the bow shock bounce back into the solar wind with a maximum energy exceeding twice the energy of solar wind protons. The ions finite gyroradius causes an asymmetric flow in the magnetosheath with respect to the direction of the convective electric field, which can be observed already a few ion gyroradius downstream of the bow shock. 相似文献
2.
《天文和天体物理学研究(英文版)》2016,(10)
The power-law frequency distributions of the peak flux of solar flare X-ray emission have been studied extensively and attributed to a system having self-organized criticality(SOC).In this paper,we first show that,so long as the shape of the normalized light curve is not correlated with the peak flux,the flux histogram of solar flares also follows a power-law distribution with the same spectral index as the powerlaw frequency distribution of the peak flux,which may partially explain why power-law distributions are ubiquitous in the Universe.We then show that the spectral indexes of the histograms of soft X-ray fluxes observed by GOES satellites in two different energy channels are different:the higher energy channel has a harder distribution than the lower energy channel,which challenges the universal power-law distribution predicted by SOC models and implies a very soft distribution of thermal energy content of plasmas probed by the GOES satellites.The temperature(T) distribution,on the other hand,approaches a power-law distribution with an index of 2 for high values of T.Hence the application of SOC models to the statistical properties of solar flares needs to be revisited. 相似文献
3.
We use the Vlasov equations for ions and electrons to develop a theory of a double layer in which there are both free and trapped electrons and ions. We find the equations which replace the Langmuir condition and the Bohm conditions and by numerically solving the resultant differential equation we find for particular choices of distribution functions the potential distribution in the layer. We discuss the applicability of this theory to solar flares, and show that conditions in solar flares may be such that double layers can exist for which the free particles have a power-law energy distribution. These particles will be accelerated in a double layer and may in this way account for the production of high-energy particles during the impulsive phase of solar flares. 相似文献
4.
Yūki Kubo 《Solar physics》2008,248(1):85-98
This article discusses statistical models for the solar flare interval distribution in individual active regions. We analyzed
solar flare data in 55 active regions that are listed in the Geosynchronous Operational Environmental Satellite (GOES) soft X-ray flare catalog for the years from 1981 to 2005. We discuss some problems with a conventional procedure to
derive probability density functions from any data set and propose a new procedure, which uses the maximum likelihood method
and Akaike Information Criterion (AIC) to objectively compare some competing probability density functions. Previous studies
of the solar flare interval distribution in individual active regions only dealt with constant or time-dependent Poisson process
models, and no other models were discussed. We examine three models – exponential, lognormal, and inverse Gaussian – as competing
models for probability density functions in this study. We found that lognormal and inverse Gaussian models are more likely
models than the exponential model for the solar flare interval distribution in individual active regions. The possible solar
flare mechanisms for the distribution models are briefly mentioned. We also briefly investigated the time dependence of probability
density functions of the solar flare interval distribution and found that some active regions show time dependence for lognormal
and inverse Gaussian distribution functions. The results suggest that solar flares do not occur randomly in time; rather,
solar flare intervals appear to be regulated by solar flare mechanisms. Determining a solar flare interval distribution is
an essential step in probabilistic solar flare forecasting methods in space weather research. We briefly mention a probabilistic
solar flare forecasting method as an application of a solar flare interval distribution analysis. The application of our distribution
analysis to a probabilistic solar flare forecasting method is one of the main objectives of this study. 相似文献
5.
Julius Feit 《Solar physics》1973,28(1):211-231
It has been recently suggested by several investigators that the accelerated charged particles provide the energy of the optical flare by the ionization loss process. We have examined this mechanism assuming different forms of the spectrum of the accelerated protons at lower chromosphere. The flux and the energy spectrum of protons of energy 0.1–100 MeV have been calculated at successive heights, from 103 to 40 × 103 km from the solar surface taking into account the ionization loss, pitch angle distribution and density distribution of the neutral and ionized hydrogen in the chromosphere and lower corona. Hence the energy spectrum of the protons escaping from the Sun and the amount of energy dissipated in the solar chromosphere are computed. Comparing the calculated results with the observational data on the solar event of September 28, 1961 it is found that the ionization loss of the accelerated protons and heavier nuclei in the solar atmosphere may supply a significant part of the energy of the optical flare assuming that the fraction, f, of magnetic tubes of force extending out of the solar atmosphere is about 1 %. The accelerated proton spectrum in the form of power law in kinetic energy seems to be the most appropriate form. In the event of September 28, 1961 best estimates are made on this basis of the total number and the energy spectrum of protons at injection, the flux and energy spectrum of escaping protons and the energy dissipated in the solar atmosphere by the accelerated ions. It is found that the possible range of variation of the height of injection level hardly affects the total energy dissipated. The high variability of the intensity of protons released by the Sun is interpreted in terms of the variations of the parameter, f, determined by the configurations of the magnetic field lines.Preliminary results were presented at the International Symposium on Solar-Terrestrial Physics, Leningrad, May, 1970.Presently at NASA/Goddard Space Flight Center, Greenbelt, Maryland, U.S.A., on leave from T.I.F.R., Bombay. 相似文献
6.
It has been suggested that the distribution functions characterizing the constituents of the solar coronal plasma are non-Maxwellian. If so, an accurate treatment of the collisional momentum and energy exchange between the plasma constituents within the framework of hydrodynamic models requires a re-evaluation of the general transfer integrals in multi-component plasmas. We have evaluated these integrals numerically for both Maxwellian and non-Maxwellian distribution functions of the plasma species avoiding the standard approximation for the collision cross sections frequently employed in the literature. Significant differences are shown to exist in the energy exchange rates for different distributions. We also demonstrate the inadequacy of the assumption of thermodynamic equilibrium in the innermost solar wind and reveal the importance of an accurate evaluation of the transfer integrals for the solar coronal plasma based on more realistic velocity distributions.Presented at the CESRA-Workshop on Coronal Magnetic Energy Release at Caputh near Potsdam in May 1994. 相似文献
7.
A certain class of non-thermal electron distributions can exhibit more mono-energetic shape and a higher peak than the Maxwellian
distribution. This type of electron distribution can be observed mainly in flaring plasmas. We have studied the influence
of this kind of electron energy distribution on the excitation equilibrium of Fe VIII – Fe XVI in the solar corona. The changes
in synthetic spectra of the emission lines belonging to these ions due to this non-thermal distribution are shown. The possibilities
of finding the shape of the energy distribution function of electrons from the Fe line ratios are also discussed. The results
can be used for diagnostics of coronal plasmas where the deviations of particle energy distributions from the Maxwellian one
can be significant. 相似文献
8.
In a weakly ionized plasma, the evolution of the magnetic field is described by a 'generalized Ohm's law' that includes the Hall effect and the ambipolar diffusion terms. These terms introduce additional spatial and time-scales which play a decisive role in the cascading and the dissipation mechanisms in magnetohydrodynamic turbulence. We determine the Kolmogorov dissipation scales for the viscous, the resistive and the ambipolar dissipation mechanisms. The plasma, depending on its properties and the energy injection rate, may preferentially select one of these dissipation scales, thus determining the shortest spatial scale of the supposedly self-similar spectral distribution of the magnetic field. The results are illustrated taking the partially ionized part of the solar atmosphere as an example. Thus, the shortest spatial scale of the supposedly self-similar spectral distribution of the solar magnetic field is determined by any of the four dissipation scales given by the viscosity, the Spitzer resistivity (electron–ion collisions), the resistivity due to electron–neutral collisions and the ambipolar diffusivity. It is found that the ambipolar diffusion dominates for reasonably large energy injection rate. The robustness of the magnetic helicity in the partially ionized solar atmosphere would facilitate the formation of self-organized vortical structures. 相似文献
9.
The recent measurements of the vertical distribution and optical properties of haze aerosols as well as of the absorption coefficients for methane at long paths and cold temperatures by the Huygens entry probe of Titan permit the computation of the solar heating rate on Titan with greater certainty than heretofore. We use the haze model derived from the Descent Imager/Spectral Radiometer (DISR) instrument on the Huygens probe [Tomasko, M.G., Doose, L., Engel, S., Dafoe, L.E., West, R., Lemmon, M., Karkoschka, E., See, C., 2008a. A model of Titan's aerosols based on measurements made inside the atmosphere. Planet. Space Sci., this issue, doi:10.1016/j.pss.2007.11.019] to evaluate the variation in solar heating rate with altitude and solar zenith angle in Titan's atmosphere. We find the disk-averaged solar energy deposition profile to be in remarkably good agreement with earlier estimates using very different aerosol distributions and optical properties. We also evaluated the radiative cooling rate using measurements of the thermal emission spectrum by the Cassini Composite Infrared Spectrometer (CIRS) around the latitude of the Huygens site. The thermal flux was calculated as a function of altitude using temperature, gas, and haze profiles derived from Huygens and Cassini/CIRS data. We find that the cooling rate profile is in good agreement with the solar heating profile averaged over the planet if the haze structure is assumed the same at all latitudes. We also computed the solar energy deposition profile at the 10°S latitude of the probe-landing site averaged over one Titan day. We find that some 80% of the sunlight that strikes the top of the atmosphere at this latitude is absorbed in all, with 60% of the incident solar energy absorbed below 150 km, 40% below 80 km, and 11% at the surface at the time of the Huygens landing near the beginning of summer in the southern hemisphere. We compare the radiative cooling rate with the solar heating rate near the Huygens landing site averaging over all longitudes. At this location, we find that the solar heating rate exceeds the radiative cooling rate by a maximum of 0.5 K/Titan day near 120 km altitude and decreases strongly above and below this altitude. Since there is no evidence that the temperature structure at this latitude is changing, the general circulation must redistribute this heat to higher latitudes. 相似文献
10.
CELIAS - Charge, Element and Isotope Analysis System for SOHO 总被引：1，自引：0，他引：1
D. Hovestadt M. Hilchenbach A. Bürgi B. Klecker P. Laeverenz M. Scholer H. Grünwaldt W. I. Axford S. Livi E. Marsch B. Wilken H. P. Winterhoff F. M. Ipavich P. Bedini M. A. Coplan A. B. Galvin G. Gloeckler P. Bochsler H. Balsiger J. Fischer J. Geiss R. Kallenbach P. Wurz K. -U. Reiche F. Gliem D. L. Judge H. S. Ogawa K. C. Hsieh E. Möbius M. A. Lee G. G. Managadze M. I. Verigin M. Neugebauer 《Solar physics》1995,162(1-2):441-481
The CELIAS experiment on SOHO is designed to measure the mass, ionic charge and energy of the low and high speed solar wind, of suprathermal ions, and of low energy flare particles. Through analysis of the elemental and isotopic abundances, the ionic charge state, and the velocity distributions of ions originating in the solar atmosphere, the investigation focuses on the plasma processes on various temporal and spatial scales in the solar chromosphere, transition zone, and corona. CELIAS includes 3 mass- and charge-discriminating sensors based on the time-of-flight technique: CTOF for the elemental, charge and velocity distribution of the solar wind, MTOF for the elemental and isotopic composition of the solar wind, and STOF for the mass, charge and energy distribution of suprathermal ions. The instrument will provide detailed in situ diagnostics of the solar wind and of accelerated particles, which will complement the optical and spectroscopic investigations of the solar atmosphere on SOHO. CELIAS also contains a Solar Extreme Ultraviolet Monitor, SEM, which continously measures the EUV flux in a wide band of 17 – 70 nm, and a narrow band around the 30.4 nm He II line.Principal-InvestigatorPrincipal-Investigator for data phase 相似文献
11.
It has been known for years now that pick-up ions (PUIs) are produced by ionization of interstellar neutral atoms in the heliosphere and are then convected outwards with the solar wind flow as a separate suprathermal ion fluid. Only poorly known is the thermal behaviour of these pick-ups while being convected outwards. On the one hand they drive waves since their distribution function is unstable with respect to wave growth, on the other hand they also experience Fermi-2 energizations by nonlinear wave-particle interactions with convected wave turbulences. Here we will show that this complicated network of interwoven processes can quantitatively be balanced when adequate use is made of transport-kinetic results according to which pick-up ions essentially behave isothermally at their convection to large solar distances. We derive the adequate heat source necessary to maintain this pick-up ion isothermy and use the negative of that source to formulate the enthalpy flow conservation for solar wind protons (SWPs). This takes care of a consistent PUI-induced heat source guaranteeing that the net energy balance in the SWP–PUI two-fluid plasma is satisfied. With this PUI-induced heat input to SWPs we not only obtain the well-observed SWP polytropy, but we can also derive an expression for the percentage of intitial pick-up energy fed into the thermal proton energy. By a first-order evaluation of this expression we then can estimate that, dependent on the actual PUI temperature, about 40 to 50% of the initial pick-up energy is globally passed to solar protons within the inner heliosphere. 相似文献
12.
Thomas Pettauer 《Solar physics》1994,151(1):195-198
The reconnecting current sheet model for energy accumulation and release during solar flares results in the flare frequency
distribution that is a power-law function of total flare energy, with the index 7/4 for sufficiently large energies. The distribution
is predicted to be much steeper in the low-energy region, implying the significance of microand nanoflares for coronal heating. 相似文献
13.
C. Gontikakis A. Anastasiadis C. Efthymiopoulos 《Monthly notices of the Royal Astronomical Society》2007,378(3):1019-1030
The acceleration of charged particles in a site of magnetic reconnection is analysed by detailed numerical simulations. Single or multiple encounters of the particles with Harris-type reconnecting current sheets (RCSs) are modelled as an overall stochastic process taking place within an active region. RCS physical parameters are selected in a parameter space relevant to solar flares. Initially, the charged particles form a thermal (Maxwellian) distribution corresponding to coronal temperature ≃2 × 106 K . Our main goal is to investigate how the acceleration process changes the shape of the particles' kinetic energy distribution. The evolution of the kinetic energy distribution, calculated numerically after one encounter of the particles with a single RCS, is found to be in good agreement with our previously published analytical formulae. In the case of consecutive encounters, we find that the kinetic distribution tends to converge to a practically invariant form after a relatively small number of encounters. We construct a discrete stochastic process that reproduces the numerical distributions and we provide a theoretical interpretation of the asymptotic convergence of the energy distribution. We finally compute the theoretical X-ray spectra that would be emitted by the simulated particles in a thick target model of radiation. 相似文献
14.
《天文和天体物理学研究(英文版)》2015,(7)
We present a study of seven large solar proton events in the current solar cycle 24(from 2009 January up to the current date). They were recorded by the GOES spacecraft with the highest proton fluxes being over 200 pfu for energies 10 Me V. In situ particle measurements show that:(1) The profiles of the proton fluxes are highly dependent on the locations of their solar sources, namely flares or coronal mass ejections(CMEs), which confirms the "heliolongitude rules" associated with solar energetic particle fluxes;(2) The solar particle release(SPR) times fall in the decay phase of the flare emission, and are in accordance with the times when the CMEs travel to an average height of 7.9 solar radii; and(3) The time differences between the SPR and the flare peak are also dependent on the locations of the solar active regions. The results tend to support the scenario of proton acceleration by the CME-driven shock,even though there exists a possibility of particle acceleration at the flare site, with subsequent perpendicular diffusion of accelerated particles in the interplanetary magnetic field. We derive the integral time-of-maximum spectra of solar protons in two forms: a single power-law distribution and a power law roll-over with an exponential tail. It is found that the unique ground level enhancement that occurred in the event on 2012 May 17 displays the hardest spectrum and the largest roll-over energy which may explain why this event could extend to relativistic energies. 相似文献
15.
Power-law distribution for solar energetic proton events 总被引：1，自引：0，他引：1
Analyses of the time-integrated fluxes of solar energetic particle events during the period 1965–1990 show that the differential distribution of events with flux F is given by a power law, with indices between 1.2 and 1.4 depending on energy. The power law represents a good fit over three to four orders of magnitude in fluence. Similar power-law distributions have been found for peak proton and electron fluxes, X-ray flares and radio and type III bursts. At fluences greater than 109 cm–2, the slope of the distribution steepens and beyond 1010 cm–2 the power-law index is estimated to be 3.5. At energies greater than 10 MeV, the slope of the distribution was found to be essentially independent of solar cycle, when the active years of solar cycles 20, 21, and 22 were analysed. The results presented are the first for a complete period of 27 years, covering nearly 3 complete solar cycles. Other new aspects of the results include the invariance of the exponent with solar cycle and also with integral energy. 相似文献
16.
We derive a perturbation inside a rotating star that occurs when the star is accelerated by orbiting bodies. If a fluid element
has rotational and orbital components of angular momentum with respect to the inertially fixed point of a planetary system
that are of opposite sign, then the element may have potential energy that could be released by a suitable flow. We demonstrate
the energy with a very simple model in which two fluid elements of equal mass exchange positions, calling to mind a turbulent
field or natural convection. The exchange releases potential energy that, with a minor exception, is available only in the
hemisphere facing the barycenter of the planetary system. We calculate its strength and spatial distribution for the strongest
case (“vertical”) and for weaker horizontal cases whose motions are all perpendicular to gravity. The vertical cases can raise
the kinetic energy of a few well positioned convecting elements in the Sun’s envelope by a factor ≤7. This is the first physical
mechanism by which planets can have a nontrivial effect on internal solar motions. Occasional small mass exchanges near the
solar center and in a recently proposed mixed shell centered at 0.16R
s would carry fresh fuel to deeper levels. This would cause stars like the Sun with appropriate planetary systems to burn somewhat
more brightly and have shorter lifetimes than identical stars without planets. The helioseismic sound speed and the long record
of sunspot activity offer several bits of evidence that the effect may have been active in the Sun’s core, its envelope, and
in some vertically stable layers. Additional proof will require direct evidence from helioseismology or from transient waves
on the solar surface. 相似文献
17.
Solar proton events have been studied for over thirty years and a great deal of lore has grown around them. It is the purpose of this paper to test some of this lore against the actual data. Data on solar proton events now exist for the period from 1956 to 1985 during which time 140 events took place in which the event integrated fluxes for protons of energy > 30 MeV was larger than 105 particles cm-2. We have studied statistical properties of event integrated fluxes for particles with energy > 10 MeV and for particles with energy > 30 MeV. Earlier studies based on a single solar cycle had resulted in a sharp division of events into ordinary and anomalously large events.Two such entirely separate distributions imply two entirely separate acceleration mechanisms, one common and the other very rare. We find that the sharp division is neither required nor justified by this larger sample. Instead the event intensity forms a smooth distribution for intensities up to the largest observed implying that any second acceleration mechanism cannot be rare. We have also studied the relation of event sizes to the sunspot number and the solar cycle phase. We find a clear bimodal variation of annual integrated flux with solar cycle phase but no statistically significant tendency for the large events to avoid sunspot maximum. We show there is almost no relation between the maximum sunspot number in a solar cycle and the solar cycle integrated flux. We also find that for annual sunspot numbers greater than 35 (i.e., non-minimum solar cycle conditions) there is no relation whatsoever between the annual sunspot numbers and annual integrated flux. 相似文献
18.
The distribution of axial rotation velocities of near-Earth asteroids (NEAs) substantially differs from that of the Main-Belt asteroids by an excess of both quickly and slowly rotating objects. Among the possible causes of this difference is the influence of the solar radiation—the so-called YORP effect—that arises from the absorption of solar energy and its reemission in the thermal range by a rotating body of irregular shape. It is known that the magnitude of this effect depends on the asteroid size and the quantity of received solar energy (the insolation). Analysis of the observational data showed that the mean diameter of NEAs decreases from the middle of the distribution to the edges, i.e., the excess of both slowly (ω ≤ 2 rev/day) and quickly (ω = 8–11 rev/day) rotating objects is formed due to the asteroids with sizes smaller than those in the middle of the distribution, which agrees well with the influence of the YORP effect. Moreover, the dependence of the axial rotation velocity of NEAs on the relative insolation shows that, for the NEAs referred to, both excesses are found in orbits where, on average, they receive 8–10% more solar energy than the NEAs in the middle of the distribution. This result also agrees with the character of the influence of the YORP effect and can be considered as an additional argument in its support. Thus, the study showed that one can infer that the currently available observational data suggest the possible influence of the YORP effect on the axial rotation of the near-Earth asteroids having sizes of D ～ 2 km and less. This is the first attempt to find the influence of the YORP effect on the axial rotation of the NEA family as a whole. 相似文献
19.
Results of measurements of the energy distribution of thermal electrons below 1 eV in a midlatitude upper atmosphere are presented and compared with some recent measurements at other places. Measurements are based on the Druyvesteyn method using Langmuir probes.In the periods without solar light, distribution does not depart much from Maxwellian above 0.3 eV. Below 0.2 eV, depletion and sometimes double humps are seen. In the periods with solar light, bumps are sometimes observed on the high energy tail at altitudes between 100 and 160 km. Energy distribution in the F layer above 180 km fits the Maxwellian distribution rather well. The reason for the appearance of such non-thermal electrons at lower altitudes may be due to super-elastic collisions with vibrationally excited nitrogens. 相似文献
20.
The behaviour of the thermal electrons escaping from a hot plasma to a cold one during a solar flare is investigated. We suppose that the direct current of fast electrons is compensated by the reverse current of the thermal electrons in ambient plasma. It is shown that the direct current strength is determined only by the regular energy losses due to Coulomb collisions. The reverse-current electric field and the distribution function of fast electrons are found in the form of an approximate analytical solution to the self-consistent kinetic problem of the dynamics of a beam of escaping thermal electrons and its associated reverse current.The reverse-current electric field in solar flares leads to a significant reduction of the convective heat flux carried by fast electrons escaping from the high-temperature plasma to the cold one. The spectrum and polarization of hard X-ray bremsstrahlung, and its spatial distribution along flare loops are calculated and can be used for diagnostics of flare plasmas and escaping electrons.Send offprint requests to B. V. Somov. 相似文献