共查询到20条相似文献,搜索用时 31 毫秒
1.
John H. Cushman Moongyu Park Monica Moroni Natalie Kleinfelter-Domelle Daniel O��Malley 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(1):1-10
When formulated properly, most geophysical transport-type process involving passive scalars or motile particles may be described
by the same space–time nonlocal field equation which consists of a classical mass balance coupled with a space–time nonlocal
convective/dispersive flux. Specific examples employed here include stretched and compressed Brownian motion, diffusion in
slit-nanopores, subdiffusive continuous-time random walks (CTRW), super diffusion in the turbulent atmosphere and dispersion
of motile and passive particles in fractal porous media. Stretched and compressed Brownian motion, which may be thought of
as Brownian motions run with nonlinear clocks, are defined as the limit processes of a special class of random walks possessing
nonstationary increments. The limit process has a mean square displacement that increases as tα+1 where α > −1 is a constant. If α = 0 the process is classical Brownian, if α < 0 we say the process is compressed Brownian while
if α > 0 it is stretched. The Fokker–Planck equations for these processes are classical ade’s with dispersion coefficient
proportional to tα. The Brownian-type walks have fixed time step, but nonstationary spatial increments that are Gaussian with power law variance.
With the CTRW, both the time increment and the spatial increment are random. The subdiffusive Fokker–Planck equation is fractional
in time for the CTRW’s considered in this article. The second moments for a Levy spatial trajectory are infinite while the
Fokker–Planck equation is an advective–dispersive equation, ade, with constant diffusion coefficient and fractional spatial
derivatives. If the Lagrangian velocity is assumed Levy rather than the position, then a similar Fokker–Planck equation is
obtained, but the diffusion coefficient is a power law in time. All these Fokker–Planck equations are special cases of the
general non-local balance law. 相似文献
2.
V. V. Zharkova N. S. Meshalkina L. K. Kashapova A. T. Altyntsev A. A. Kuznetsov 《Geomagnetism and Aeronomy》2011,51(8):1029-1040
The kinetics of beam electron precipitation from the top of a loop into the solar atmosphere with density gradients and an
increasing magnetic field have been generally described. The Fokker-Planck equations are solved with regard to Coulomb collisions
and the effect of the electric field induced by this beam. The photon spectra and polarization degree in hard X-ray (10–300
keV) and microwave (1–80 GHz) emissions are simulated under different assumptions regarding the beam electron distribution
function. The simulation results are compared with the flare observations on March 10, 2001, and July 23, 2002, visible at
different position angles. It has been indicated that the coincidence of the theoretical photon spectra with simultaneous
observations of the hard X-ray and microwave emissions of these flares is the best for models that not only take into account
collisions, but also the electric field induced by electron fluxes propagating in flare loops with very weakly or moderately
converging magnetic fields. 相似文献
3.
4.
I. S. Veselovsky 《Geomagnetism and Aeronomy》2009,49(8):1148-1153
At what evolutionary stage of the Sun as a star the accumulation of its matter from the interstellar medium ended and the
dominant outflow of solar wind (SW) streams started is one of the main outstanding questions in the astrophysical aspect of
the problem of SW origin. It is unknown when and how this happened in detail, although the onset of thermonuclear reactions
in the solar interior undoubtedly played a crucial role in the energetics and dynamics of the star, which could lead to such
a change of the regimes. Therefore, it is hypothesized that the accretion or plasma outflow from the star was determined by
the preceding evolution, i.e., by the “memory“ and not just by the distribution of instantaneous density, temperature, magnetic
field, and other macroscopic parameters of the system that consists of this star, its nearest stellar environment, and interstellar
gas. Depending on this, neighboring stars can serve as donors or acceptors of interstellar gas. Some of them can simultaneously
or alternately play both roles. The polytropic solution for centrally symmetric flows obtained by Bondi is degenerate in the
sign of the radial velocity. It is suitable for describing the quasi-stationary regimes of both types. However, the theory
of transient processes has not been developed. Hence, the question of whether there exist stars similar in their internal
structure and parameters to the present-day Sun but without stellar wind emission or even with interstellar gas accretion
can be answered only observationally. The possibility that such stars exist is not ruled out; it does not contradict any laws
of nature. The plasma-physical aspect of the problem of SW origin concerns much shorter time intervals than the main evolutionary
time scale measured in billions of years. Hence, this aspect of the problem has been studied much better, although it is also
fairly complex and has not yet been solved in much detail due to the multi-scale character of the flow formation processes.
The SW as a permanent supermagnetosonic plasma outflow in the radial direction appears against the background of much more
powerful nonequilibrium and unsteady motions, which are ordered only partially in the upper solar atmosphere and corona (turbosphere).
The instantaneous SW state is controlled by the fluxes of free energy, matter, and momentum that enter the corona from the
convection zone and underlying solar atmospheric layers. Although the main physical mechanisms of the transport of free energy
of the electromagnetic field and plasma are generally well known, they need a quantitative analysis as applied to specific
realizations in frequent and rare particle collisions in the solar corona to ascertain the nonlocal processes of the formation
of fields and plasma flows, including the SW. 相似文献
5.
O. A. Pokhotelov M. Parrot E. N. Fedorov V. A. Pilipenko V. V. Surkov V. A. Gladychev 《Annales Geophysicae》1995,13(11):1197-1210
A review is presented of the effects influencing the ionosphere which are caused by acoustic emission from different sources (chemical and nuclear explosions, bolides, meteorites, earthquakes, volcanic eruptions, hurricanes, launches of spacecrafts and flights of supersonic jets). A terse statement is given of the basic theoretical principles and simplified theoretical models underlying the physics of propagation of infrasonic pulses and gravity waves in the upper atmosphere. The observations of “quick” response by the ionosphere are pointed out. The problem of magnetic disturbances and magnetohydrodynamic (MHD) wave generation in the ionosphere is investigated. In particular, the supersonic propagation of ionospheric disturbances, and the conversion of the acoustic energy into the so-called gyrotropic waves in the ionospheric E-layer are considered. 相似文献
6.
7.
五矩二流太阳风等离子体特性的数值研究 总被引:4,自引:0,他引:4
本文数值求解了各向同性二流太阳风的五矩方程组,得出了1 Rs-2AU区域内太阳风密度、速度、电子和质子温度、它们的热流通量密度q以及非麦克斯韦分布尾部粒子过剩量ξ随日心距离的变化关系.文中比较了二流太阳风五矩模型、四矩模型(ξ=0)和低阶矩模型(不包括q和ξ二个矩方程)的等离子体特性,着重讨论了量ξ对质子温度及其热流通量的影响.结果表明,包括言的五矩方程可改善Te/Tp和qe/qp的计算值与观测值的符合程度. 相似文献
8.
This paper addresses observed variations in cosmic ray (CR) intensity, the interplanetary magnetic field (IMF), the solar
wind (SW) turbulence energy spectrum, and the energy spectrum index of Forbush decreases in the 20th–23rd solar cycles. Unlike
the previous three cycles, there are some distinctive features in the 23rd solar cycle. The entire cycle shows a considerable
increase in the index of the SW turbulence energy spectrum inclination and an substantially harder energy spectrum of Forbush
decreases. The anomalously high flux of high-energy CRs and the anomalously low level of the IMF strength were recorded at
the end of this cycle. The conclusion has been made that such unusual CR behavior is associated with a decrease in the degree
of scattering in the resonance interaction between CR fluxes and SW inhomogeneities with spatial scales of ∼1012 cm. 相似文献
9.
The influence of whistlers on the distribution and gyrosynchrotron radiation of fast electrons injected into a coronal magnetic trap is considered. The kinetic equation in the Fokker–Planck approximation with consideration of fast electron scattering, both on background plasma particles and on whistlers, is solved for an inhomogeneous trap. It is supposed that the source of whistlers is a nonstationary process of flare energy release. Having found the fast electron distribution, we can calculate their gyrosynchrotron microwave emission. The influence of nonthermal electron scattering on whistlers are compared with the effects of scattering on Coulomb collisions. It is shown that whistlers considerably modify the emission characteristics of a loop at a certain energy density; in particular, they steepen the frequency spectrum. This is useful for microwave diagnostics of plasma turbulence in the flare loop. 相似文献
10.
The excitation of long-period irregular pulsations in the 2.0–6.0 mHz range (ipcl pulsation series) in the Earth’s magnetosphere, depending on the set of solar wind plasma and IMF parameters, has been studied experimentally. It has been found that burst regimes are observed when the solar wind dynamic pressure and velocity are higher than V ∼ 320 km/s and P ∼ 1 nPa, respectively. It has been indicated that the dynamics of the ipcl pulsation intensity and fractal structure largely depend on the solar wind plasma velocity and magnetic pressure, respectively. An analysis of the relationship between the appearance of ipcl pulsation burst series and large-scale solar wind streams and polar coronal holes made it possible to identify solar geoeffective regions, which can cause solar wind streams and Alfvén waves that promote the generation of burst regimes. On the basis of the studied conditions of the interplanetary medium, favourable for the excitation of ipcl pulsation burst series, and generalization of morphological patterns, the possible mechanisms of their generation have been considerded. It has been demonstrated that ipcl burst regimes are most probably generated as wind instability in hydrodynamics (the Miles-Phillips mechanism). The Miles-Phillips instability is related to different factors in the solar wind stream, among which turbulence, the threshold velocity value, and pressure fluctuations play a defining role. Precisely these regularities are typical of the ipcl burst regime generation conditions. 相似文献
11.
Ground-based geomagnetic Pc5 (2–7 mHz) pulsations, caused by the passage of dense transients (density disturbances) in the solar wind, were analyzed. It was shown that intensive bursts can appear in the density of the solar wind and its fluctuations, up to Np ~ 30–50 cm3, even during the most magnetically calm year in the past decades (2009). The analysis, performed using one of the latest methods of discrete mathematical analysis (DMA), is presented. The energy functional of a time-series fragment (called “anomaly rectification” in DMA terms) of two such events was calculated. It was established that fluctuations in the dynamic pressure (density) of the solar wind (SW) cause the global excitation of Pc5 geomagnetic pulsations in the daytime sector of the Earth’s magnetosphere, i.e., from polar to equatorial latitudes. Such pulsations started and ended suddenly and simultaneously at all latitudes. Fluctuations in the interplanetary magnetic field (IMF) have turned up to be less geoeffective in exciting geomagnetic pulsations than fluctuations in the SW density. The pulsation generation mechanisms in various structural regions of the magnetosphere were probably different. It was therefore concluded that the most probable source of ground-based pulsations are fluctuations of the corresponding periods in the SW density. 相似文献
12.
13.
D. V. Erofeev 《Geomagnetism and Aeronomy》2013,53(7):822-826
Compressible fluctuations in solar wind plasma are analyzed on the basis of the 1995–2010 WIND and Advanced Composition Explorer (ACE) spacecraft data. In the low-speed solar wind (V 0 < 430 km/s), correlations between fluctuations in the magnetic field direction and plasma density, as well as between velocity fluctuations and plasma density, are found. The covariance functions of these parameters calculated as functions of the local magnetic field direction are axially symmetric relative to the axis, which is oriented nearly along the regular magnetic field of the heliosphere (the Parker spiral). Fluctuations in the magnetic field and velocity are polarized in the plane that is orthogonal to the axis of symmetry. Plasma oscillations of these properties can be caused by fast magnetosonic waves propagating from the Sun along the Parker spiral. 相似文献
14.
15.
Cesar Bertucci Christian Mazelle Mario H. Acua 《Journal of Atmospheric and Solar》2005,67(17-18):1797
The observations of the magnetometer/electron reflectometer (MAG/ER) investigation onboard the Mars Global Surveyor (MGS) have greatly contributed to improve our understanding of the interaction of the solar wind with Mars. These observations established conclusively that a global dynamo-generated magnetic field does not exist at Mars, and that the interaction with solar wind is of the atmospheric type. This article reviews the most important results obtained from MGS MAG/ER on the study of two major features in the Mars solar wind interaction. The first feature is the occurrence of large-amplitude, highly coherent waves at the proton cyclotron frequency in the region upstream from the Martian bow shock. The second feature is the magnetic pileup boundary (MPB), a well-defined plasma boundary inside of which the planetary exospheric ions outnumber the solar wind ions. The study of these two elements is crucial to characterize the properties of the Martian exosphere. In addition, the occurrence of an MPB at comets and Venus reveals common processes to all these unmagnetized atmospheric bodies in spite of their different physical nature and characteristic scales. 相似文献
16.
Simple dynamic models of long-term variations in river runoff are suggested. The models are based on a small number of parameters. Stochastic differential equations associated with these models are investigated. The theoretical density of probability distribution of river runoff values--stationary solutions of the Fokker–Planck–Kolmogorov equation--coincide with the distribution densities widely used in stochastic hydrology. 相似文献
17.
《Journal of Atmospheric and Solar》2008,70(5):774-793
A new empirical atmospheric density model is developed using the CIRA72 (Jacchia 71) model as the basis for the diffusion equations. New solar indices based on orbit-based sensor data are used for the solar irradiances in the extreme and far ultraviolet wavelengths. New exospheric temperature and semiannual density equations are employed to represent the major thermospheric density variations. Temperature correction equations are also developed for diurnal and latitudinal effects, and finally density correction factors are used for model corrections required at high altitude (1500–4000 km). The new model, Jacchia–Bowman 2006, is validated through comparisons of accurate daily density drag data previously computed for numerous satellites. For 400 km altitude the standard deviation of 16% for the standard Jacchia model is reduced to 10% for the new JB2006 model for periods of low geomagnetic storm activity. 相似文献
18.
19.
Using a simple time-lagged correlation technique, present study aims to identify the solar wind (SW) parameter, which is better associated with the ground magnetic field variations of shorter time duration near equator, during intense geomagnetic storms. It is found that out of all SW parameters, successively occurring enhancements in the SW dynamic pressure have substantial influence on the horizontal component of magnetic field at ground. Present analysis reveals a time lag of ~30–45 min between the SW pressure changes seen at L1 location and ground magnetic field variations, and hence providing a good approximation of an averaged propagation time during entire storm interval; the time lag varies with solar wind velocity. Separate study during day and nighttime suggests that the SW dynamic pressure enhancements recorded by the dayside outer magnetospheric satellite have impact on the ground horizontal magnetic field measurements near equator, irrespective of day or nighttime. 相似文献
20.
Riazantseva M. O. Rakhmanova L. S. Zastenker G. N. Yermolaev Yu. I. Lodkina I. G. 《Geomagnetism and Aeronomy》2019,59(2):127-135
Geomagnetism and Aeronomy - The turbulent characteristics of plasma fluctuations in the solar wind (SW) may substantially change depending on the SW conditions. Large-scale streams of different... 相似文献