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1.
A ring current model has been obtained which permits calculations ofDst variations on the Earth's surface during magnetic storms. The changes in Dst are described by the equation
ddtDsto = F(EM)?Dstotau;
where Dsto = Dst-bp12+~tc; p = mnv2 is solar wind pressure; F(EM) is the function, controlled by the electromagnetic parameters of interplanetary medium, of injection into ring current ; τ is the constant of ring current decay. C = Cuτ?=18 nT, where C is the level of the Dst-variation field measurements; ? is the injection function characterizing the quasisteady-state injection of energy into the ring-current region. The constant Ç is determined from the condition that the change of the ring current energy from magnetic storm commencement to end should equal the difference between the injected and dissipated energy throughout the storm. The values of the factors b and τ were found by the method of minimizing the sum of the quadratic deviations of the calculated Dst from the values observed throughout the storm : b = 0.23 nT/(eV cm?3)12, τ = 8.2 h at Dst? ? 55 nT and τ = 5.8 h at -120 ? Dst ? — 55 nT. The injection function F(EM) is of the form F(EM) = d(Ey? A) at the values of the azimuthal component of the solar wind electric field Ey ? A, and F(EM) =0 at A?Ey.d = ? 1.2 × 10?3 Ts?1 (mV/m)?1 and A = ? 0.9 mV m?1 . Thus, the injection to ring current is possible at the northward Bz component of the IMF.  相似文献   

2.
A high time resolution study of the relationship between the solar wind-magnetosphere energy coupling function ? and the total energy dissipation rate UT of the magnetosphere is made using 5-min average values of solar wind data and of the geomagnetic indices AE and Dst. All the results are essentially the same as those obtained by the earlier studies which were based on the hourly average data set. Therefore, we confirm that the magnetosphere is primarily a driven system.  相似文献   

3.
The results of an experimental study of the variations in the intensity of the fluxes of the Earth radiation belt (ERB) particles in 0.3–6 and 1–50 MeV energy intervals for electrons and protons, respectively, are reported. ERBs were studied during strong magnetic storms from August 2001 through November 2003. The results of the CORONAS-F mission obtained during the magnetic storms of November 6 (D st = ?257 nT) and November 24, 2001 (D st = ?221 nT), October 29–30 (D st = ?400 nT) and November 20, 2003 (D st = ?465 nT) are analyzed. The electron flux is found to decrease abruptly in the outer radiation belt during the main phase of the magnetic storms under consideration. During the recovery phase, the outer radiation belt is found to recover much closer to Earth, near the boundary of the penetration of solar electrons during the main phase of the magnetic storm. We associate the decrease in the electron flux with the abrupt decrease of the size of the magnetosphere during the main phase of the storm. Note that, in all cases studied, the Earth radiation belts exhibited rather long (several days) variations. In those cases where solar cosmic-ray fluxes were observed during the storm, protons with energies 1–5 MeV could be trapped to form an additional maximum of protons with such energies at L >2.  相似文献   

4.
The diurnal variation of the high latitude outer zone boundary at 1400km has been determined for electrons ?140keV electrons, and for protons in two energy intervals: 0.56?E?1.1 MeV, 1.1?E?3.2 MeV, from detectors aboard the NOAA-2 satellite. The dependence of the 140 keV electron boundary on Dst has been examined as well?. A wel?l defined correlation of boundary position with Dst is found to exist during the main phase of disturbances, together with an evident local time dependence. All the boundaries are found to be consistent witn the supposition of adiabatic drift and demonstrate the stability of the boundary position over approximately ten years of comparable observation. No statistically significant hemispheric differences in boundary location were observed to occur.  相似文献   

5.
The geomagnetic activity is the result of the solar wind–magnetosphere interaction. It varies following the basic 11-year solar cycle; yet shorter time-scale variations appear intermittently. We study the quasi-periodic behavior of the characteristics of solar wind (speed, temperature, pressure, density) and the interplanetary magnetic field (B x , B y , B z , β, Alfvén Mach number) and the variations of the geomagnetic activity indices (D ST, AE, A p and K p). In the analysis of the corresponding 14 time series, which span four solar cycles (1966?–?2010), we use both a wavelet expansion and the Lomb/Scargle periodograms. Our results verify intermittent periodicities in our time-series data, which correspond to already known solar activity variations on timescales shorter than the sunspot cycle; some of these are shared between the solar wind parameters and geomagnetic indices.  相似文献   

6.
Numerical integration of particle trajectories is performed to evaluate the statistical acceleration coefficients D TT for 1 to 100 MeV protons in a solar wind corotating interaction region (CIR) seen at 2.5 and 5.0 AU. Acceleration is followed in the solar wind reference frame and is due to random wave-particle interactions and to random drift motion in moderate scale field gradients. D TT due to the first effect reaches a peak value of 4 × 10 –7 MeV2 s–1 post shock at 10 MeV at 2.5 AU consistent with estimates based both upon cyclotron resonance and transit time damping theory. D TT from the second effect is less well established but is of the order of 10–7 MeV2 s–1 at 10 MeV, 5 AU. A comparison is made between the time constant for statistical acceleration within this CIR and estimates for diffuse shock acceleration and adiabatic deceleration. All three time constants are of the same order, but deceleration is faster than shock acceleration which in turn is faster than statistical acceleration.  相似文献   

7.
B. R. Durney 《Solar physics》1973,30(1):223-234
The two-fluid equations for the solar wind are written down in a simplified form, similar to that suggested by Roberts (1971) for the one-fluid model. The equations are shown to depend only on one parameter, $$K = GM\kappa _e m_p (\varepsilon _\infty T_0 )^{{3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}} /4k^2 Fe,$$ , where G is the gravitational constant, M the mass of the star, κ e the thermal electron conductivity, m p the proton mass, k the Boltzman constant, k? ∞T0 the residual energy per particle at infinity and F e the electron-particle flux. For a variety of values of the density and temperature at the base of the corona we compute the solutions of the two-fluid solar wind model and compare the predicted and observed solar wind parameters at the Earth.  相似文献   

8.
Multilayer feed-forward neural network models are developed to make three-hour predictions of the planetary magnetospheric Kp index. The input parameters for the networks are the Bz-component of the interplanetary magnetic field, the solar wind density n, and the solar wind velocity V, given as three-hour averages. The networks are trained with the error back-propagation algorithm on data sequences extracted from the 21st solar cycle. The result is a hybrid model consisting of two expert networks providing Kp predictions with an RMS error of 0.96 and a correlation of 0.76 in reference to the measured Kp values. This result can be compared with the linear correlation between V(t) and Kp(t + 3 hours) which is 0.47. The hybrid model is tested on geomagnetic storm events extracted from the 22nd solar cycle. The hybrid model is implemented and real time predictions of the planetary magnetospheric Kp index are available at http://www.astro.lu. se/-fredrikb.  相似文献   

9.
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10.
Cargill  Peter J. 《Solar physics》2004,221(1):135-149
It is well known that the interaction of an interplanetary coronal mass ejection (ICME) with the solar wind leads to an equalisation of the ICME and solar wind velocities at 1 AU. This can be understood in terms of an aerodynamic drag force per unit mass of the form F D/M=−(ρe AC D/M)(V i−V e)∣V i−V e∣, where A and M are the ICME cross-section and sum of the mass and virtual mass, V i and V e the speed of the ICME and solar wind, ρe the solar wind density, C D a dimensionless drag coefficient, and the inverse deceleration length γ=ρe A/M. The optimal radial parameterisation of γ and C D beyond approximately 15 solar radii is calculated. Magnetohydrodynamic simulations show that for dense ICMEs, C D varies slowly between the Sun and 1 AU, and is of order unity. When the ICME and solar wind densities are similar, C D is larger (between 3 and 10), but remains approximately constant with radial distance. For tenuous ICMEs, the ICME and solar wind velocities equalise rapidly due to the very effective drag force. For ICMEs denser that the ambient solar wind, both approaches show that γ is approximately independent of radius, while for tenuous ICMEs, γ falls off linearly with distance. When the ICME density is similar to or less than that in the solar wind, inclusion of virtual mass effects is essential.  相似文献   

11.
Slitless spectra of the chromosphere, observed cinematographically at the total solar eclipse of 10 July 1972, were reduced. The surface brightness distribution of the helium D3 line in the undisturbed chromosphere was obtained in agreement with results by other observers. The available eclipse data on the D3 absolute brightness was analysed by means of theoretical curves of growth. Intensity data by some observers were found to be certainly too high. A trend was found that the D3 absolute brightness in the quiet chromosphere decreases with the increasing solar activity (sunspot number). This perhaps indicates a variation of the spicule number over the solar surface during a sunspot cycle.  相似文献   

12.
We have analyze the set of 70 intense geomagnetic storms associatedwith Dst decrease of more than 100 nT, observed duringthe period (1986–1991). We have compile these selected intensegeomagnetic storm events and find out their association with twotypes of solar wind streams and different interplanetary parameters.We concluded that the maximum numbers of intense geomagneticstorms are associated with transient disturbances in solar wind streams,which causes strong interplanetary shocks in interplanetary medium.The association of supersonic shocks and magnetic clouds with intensegeomagnetic storms have also been discussed.  相似文献   

13.
We present the results of magnetic field measurements in three active prominences, July 24, 1981, July 24, 1999, and July 12, 2004, obtained from observations with the echelle spectrograph of the horizontal solar telescope at the Astronomical Observatory of the Taras Shevchenko Kiev National University. The magnetic fields were measured from the Zeeman splitting of the I ± V profiles in the He I D3 and H?? lines in the atmosphere at heights from 3 to 14 Mm. Our measurements of the effective magnetic fields B eff from the shift of the profile centroids have shown that the magnetic fields averaged over the entrance slit area were within the range from ?600 to +1500 G. The amplitude values of the local fields have been estimated from the splitting of the bisectors of the central parts of the line profiles at 0.9 of the peak intensity. The corresponding fields B 0.9 have turned out to be approximately twice B eff and reached 4000 G in absolute value. Narrow (1?C2 Mm) height peaks at heights of 6?C11 Mm have been found in the height distributions of the magnetic field. We have found an interesting effect in two prominences-an anticorrelation between the magnetic field strengths measured from the D3 and H?? lines.  相似文献   

14.
We investigated the NLTE formation of the solar spectrum of neutral silicon using 3D hydrodynamic model of the solar atmosphere and realistic atomic model. We show that, within the intergranular region, combined action of the deficit in the source function and excess in opacity due to the overpopulation of the lower Si I levels leads to a considerably higher increase in the central depth D and equivalent width W of these lines as compared to the granules. We have fitted silicon abundances A W and A D from the equivalent widths W and central depths D for 65 Si I lines using a 3D model. We show that a total error in the calculated silicon abundance due to neglecting NLTE and 3D effects, as well as the uncertainty in the van der Waals broadening constant γ6, turns out to be ?0.1 dex. Using a semiclassical theory by Anstee, Barklem, and O’Mara in calculating γ6 yields a fair coincidence between the values of A W and A D , because the average difference A W — A D does not exceed 0.01 dex for both NLTE and LTE. When applying the Unsold’s approximation in calculating γ6 with an enhancement factor E = 1.5, the abundances A W and A D proved to be in disagreement with one another. We analyzed the “solar” oscillator strength scale by Gurtovenko and Kostik, as well as the experimental one by Garz and Becker et al. We show that using “solar” oscillator strengths log gfw leads to a minimum trend with the equivalent widths for NLTE abundances A W , A D , their difference A W — A D , and standard deviations. The NLTE abundance of silicon obtained using solar oscillator strength scale by Gurtovenko and Kostik is A W NTLE = 7.549 ± 0.016. This value is in good agreement with the value of silicon abundance recommended by Grevesse and Sauval for the CI chondrite meteorites.  相似文献   

15.
Takakura  T.  Degaonkar  S. S.  Ohki  K.  Kosugi  T.  Enome  S. 《Solar physics》1983,83(2):379-384
New solar wind data from Helios-2 are used to study, in a statistical fashion, the relation between proton number density n, flow speed u and heliocentric distance r. It is shown that the average of nu 2 r 2 does not depend on flow speed nor on distance, verifying the previously established invariance of momentum flux density (mnu2) carried by the solar wind. Averages of mnu2 from different spacecraft do not show correlation with the solar cycle. Rather, the close agreement (to within 1.8%) of values from Helios-1 and Helios-2 suggests that the momentum flux density carried by the solar wind may be also constant during the solar cycle.  相似文献   

16.
The distance to the dayside magnetopause is statistically analyzed in order to detect the possible dependence of the dayside magnetic flux on the polarity of the interplanetary magnetic field. The effect of changing solar wind pressure is eliminated by normalizing the observed magnetopause distances by the simultaneous solar wind pressure data. It is confirmed that the normalized size of the dayside magnetosphere at the time of southward interplanetary magnetic field is smaller than that at the time of northward interplanetary magnetic field. The difference in the magnetopause position between the two interplanetary field polarity conditions ranges from 0 to 2RE. Statistics of the relation between the magnetopause distance and the magnetic field intensity just inside the magnetopause testifies that the difference in the magnetopause position is not due to a difference in the magnetosheath plasma pressure. The effect of the southward interplanetary magnetic field is seen for all longitudes and latitudes investigated (|λGM|? 45°, |φSM|? 90°). These results strongly suggest that a part of the dayside magnetic flux is removed from the dayside at the time of southward interplanetary magnetic field.  相似文献   

17.
Nearly 1000 magnetopause crossings from HEOS-2, HEOS-1, OGO-5 and 5 IMP space-craft covering most of the northern and part of the southern dayside and near-Earth tail magnetopause (X >?15 RE) have been used to perform a detailed study of the three-dimensional shape and location of the magnetopause. The long-term influence of the solar wind conditions on the average magnetopause geometry has been reduced by normalising the radial distances of the observed magnetopause crossings to an average dynamical solar wind pressure. Best-fit ellipsoids have been obtained to represent the average magnetopause surface in geocentric solar ecliptic (GSE) and (as a function of tilt angle) in solar magnetic (SM) coordinates. Average geocentric distances to the magnetopause for the 1972–1973 solar wind conditions (density 9.4 cm?3, velocity 450 km s?1) are 8.8 RE in the sunward direction, 14.7 RE in the dusk direction, 13.4 RE in the dawn direction and 13.7 RE in the direction normal to the ecliptic plane. The magnetopause surface is tilted by 6.6° ± 2° in a direction consistent with that expected from the aberration effect of the radial solar wind. Our data suggest that the solar wind plasma density and the interplanetary magnetic field (IMF) orientation affect the distance to the polar magnetopause, larger distances corresponding to higher plasma density and southward fields. Our best-fit magnetopause surface shows larger geocentric distances than predicted by the model of Choe et al. [Planet Space Sci. 21, 485 (1973).] normalised to the same solar wind pressure.  相似文献   

18.
Solar wind interaction with neutral interstellar helium focused by the Sun's gravity in the downwind solar cavity is discussed in a hydrodynamical approach. Upon ionization the helium atoms “picked up” by the (single fluid) solar wind plasma cause a slight decrease in the wind speed and a corresponding marked temperature increase. For neutral helium density outside the cavity nHe∞ = 0.01 atoms cm?3 and for interstellar kinetic temperature THe= 10,000 K, the reduction is speed of the solar wind on the downwind axis at 10 AU from the Sun amounts to about 2kms?1; the solar wind temperature excess attains 7000 K. The resulting pressure excess leads to a non-radial flow of the order of 0.25 km s?1. The possibility of experimental confirmation is discussed.  相似文献   

19.
Hidalgo  M.A. 《Solar physics》2003,216(1-2):311-324
Using an elliptical cross-section model for the study of the magnetic topology of magnetic clouds (MCs) in the interplanetary medium, we develop an analytical approach to their relationship with geomagnetic storms. Assuming an axially symmetric ring current and once we have obtained the disturbances produced in its current density due to the passage of a MC through it (whose axis has a latitude θ, a longitude φ, and its cross-section has an orientation ζ), then we determine the decrease in the value of the geomagnetic field at the Earth's equator, i.e., the D st index. The D st model presented allows us to estimate the physical parameters which characterize the symmetric ring current during the recovery phase of the storm time. The theoretical and experimental D st indexes are compared for four intense geomagnetic storms (D st<−100 nT), all of them associated with MCs. As seen in the figures presented, the fits are good for every storm. In view of these results we conclude that the effects of a MC over the symmetric ring current can explain the main profile of the recovery phase of a geomagnetic storm.  相似文献   

20.
Crank-Nicholson solutions are obtained to the time-dependent Fokker-Planck equation for propagation in the interplanetary medium following a point in time injection of energetic solar particles and including the acceleration terms $$\frac{\partial }{{\partial T}}\left( {D_{TT} \frac{{\partial U}}{{\partial T}}} \right) - \frac{\partial }{{\partial T}}\left( {\frac{{D_{TT} U}}{{2T}}} \right)$$ . The diffusion coefficient in kinetic energyD TT is allowed to be either independent of radial distance,R(AU), or follow the lawD TT=D0T2R 0 2 /(A2+R2) in either case with the 1 AU value ofD TT at 10 MeV ranging between 10?4 (MeV)2 s?1 and zero. The spatial diffusion mean free path at the Earth's orbit is fixed at λ‖ AU at 10 MeV according to numerical estimates made by Moussas and Quenby. However, a variety ofR dependences are allowed. Reasonable agreement with experimental data out to 4 AU is obtained with the above values ofD TT and the spatial diffusion coefficientK r=K0R?2 forR«1 andK r=K0R0.4 forR»1 AU. It is only in the decay phases of prompt events as seen at 2–4 AU that significant differences in the temporal behaviour of the events can be distinguished, depending on the value ofD TT chosen within the above range. Experimental determination of the decay constant is difficult.  相似文献   

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