共查询到20条相似文献，搜索用时 31 毫秒
1.
A. V. Mordvinov 《Solar physics》2007,246(2):445-456
A comparative analysis of solar and heliospheric magnetic fields in terms of their cumulative sums reveals cyclic and long-term
changes that appear as a magnetic flux imbalance and alternations of dominant magnetic polarities. The global magnetic flux
imbalance of the Sun manifests itself in the solar mean magnetic field (SMMF) signal. The north – south asymmetry of solar
activity and the quadrupole mode of the solar magnetic field contribute the most to the observed magnetic flux imbalance.
The polarity asymmetry exhibits the Hale magnetic cycle in both the radial and azimuthal components of the interplanetary
magnetic field (IMF). Analysis of the cumulative sums of the IMF components clearly reveals cyclic changes in the IMF geometry.
The accumulated deviations in the IMF spiral angle from its nominal value also demonstrate long-term changes resulting from
a slow increase of the solar wind speed over 1965 – 2006. A predominance of the positive IMF B
z
with a significant linear trend in its cumulative signal is interpreted as a manifestation of the relic magnetic field of
the Sun. Long-term changes in the IMF B
z
are revealed. They demonstrate decadal changes owing to the 11/22-year solar cycle. Long-duration time intervals with a dominant
negative B
z
component were found in temporal patterns of the cumulative sum of the IMF B
z
. 相似文献
2.
The monthly probability of occurrence of southward (B
z
–
) component of IMF estimated independent of the sector polarity observed near earth is found to change with the magnitude of solar wind velocity. The above analysis is done for each month during two years around sunspot minima and maxima in cycle 21. The results will be interpreted in terms of association of southwardB
z
events with solar wind flows of distinct solar origin such as low and high speed solar wind. 相似文献
3.
Measurements of the north-south (B
z
component of the interplanetary field as compiled by King (1975) when organized into yearly histograms of the values of ¦B
z
¦ reveal the following. (1) The histograms decrease exponentially from a maximum occurrence frequency at the value ¦B
z
¦ = 0. (2) The slope of the exponential on a semi-log plot varies systematically roughly in phase with the sunspot number in such a way that the probability of large values of ¦B
z
¦ is much greater in the years near sunspot maximum than in the years near sunspot minimum. (3) There is a sparsely populated high-value tail, for which the data are too meager to discern any solar cycle variation. The high-value tail is perhaps associated with travelling interplanetary disturbances. (4) The solar cycle variations of B
z
and the ordinary indicators of solar activity are roughly correlated. (5) The solar cycle variation of B
z
is distinctly different than that of the solar wind speed and that of the geomagnetic Ap disturbance index.Now at the Aerospace Corporation, El Segundo, Calif. 90245, U.S.A. 相似文献
4.
The geometry of the open flux area in the polar region is computed by superposing a uniform interplanetary magnetic field (IMF) with various orientation angles to a model of the magnetosphere. It is confirmed that the IMF By component is as important as the Bz component in “opening” the magnetosphere. It is also shown that the computed area of open field lines is remarkably similar to the observed ones which were determined by using the entry of solar electrons. In particular, when the IMF vector is confined in the X-Z-plane and the Bz component has a large positive value, the open area becomes crescent-shaped, coinciding approximately with the cusp region. 相似文献
5.
The characteristics of latitudinal angles of solar wind flow (θv) observed near earth have been studied during the period 1973-2003. The average magnitude of θv shows distinct enhancements during the declining and maximum phases of the sunspot cycles. A close association of Bz component of IMF in the GSE system and the orientation of meridional flows in the solar wind is found which depends on the IMF sector polarity. This effect has been studied in typical geomagnetic storm periods. The occurrence of non-radial flows is also found to exhibit heliolatitudinal dependence during the years 1975 and 1985 as a characteristic feature of non-radial solar wind expansion from polar coronal holes. 相似文献
6.
Global images of the Earth's inner magnetosphere and its response to the coronal mass ejection (CME) on the 15 July 2000 were
obtained by the IMAGE spacecraft. The images were taken in energetic neutral atoms (ENA) by the High-Energy Neutral Atom (HENA)
imager. ENAs are produced by charge exchange between the hot ion population of the magnetosphere and the cold neutral hydrogen
geocorona. The ENA images show how plasma is injected into the nightside magnetosphere as the interplanetary magnetic field
(IMF) turns strongly southward. As the IMF B
z increases and the storm intensity decreases, the ENA images show that the ring current becomes closed and symmetric as IMF
B
z reaches positive values. 相似文献
7.
Ten years data set is used to separate the influence of IMF Bz-component and solar wind speed on the dawn-dusk component of magnetic variations in the summer polar cap. The reference level was chosen from most quiet periods of winter solstices (small polar cap and auroral zone conductivity) to exclude the inner source component. The linear regression analysis was then used to calculate the PC variation response to Bz under different ranges of solar wind speed. As a result, taking into account the value of polar cap conductivity and effects of induced currents, the response of dawn-dusk electric field component to Bz and V was obtained and the potential difference across the polar cap was estimated to be for Bz ? + 1γ. The results give a proof for simultaneous operation in the magnetosphere of two electric field generation mechanisms, related to the boundary layer processes and magnetic field reconnection. The above-mentioned functional form was shown to correlate effectively with AE index (R = 0.73). 相似文献
8.
One year of magnetic field data from the geostationary spacecraft ATS 6 have been analysed for effects associated with the equatorial plane components of the interplanetary magnetic field (IMF). It is shown that perturbation fields in the Y (dawn to dusk) direction appear in association with the Y component of the IMF, in agreement with previous theoretical suggestions. On average a fraction 0.28 ± 0.02 of the IMF Y field appears at geostationary orbit, such that the average ATS 6 By field is 1.9 ± 0.4 nT larger when IMF By is positive than when it is negative. The perturbation field magnitudes are also found to depend strongly on local time, however, with largest effects appearing in the midnight and dawn quadrants, where the average perturbation fields are nearly half the simultaneous IMF Bv. field. At noon this fraction drops to one fifth, and no average effect occurs in the dusk quadrant. Both the daily mean perturbation fields and the diurnal modulation are also found to depend upon the level of magnetic disturbance as measured by KP, or equivalently upon IMF Bz, and upon season of the year. Overall stronger daily mean perturbation fields occur when KP is low or when IMF Bz is positive, than when KP is high or when IMF Bz is negative. This effect is not linear, however, and there is also a trend in the data towards increasing perturbation fields with IMF Bz negative and decreasing. On dividing the data according to season, increasingly strong daily mean effects are found in the order winter, summer and equinox for both quiet and disturbed magnetospheres. Diurnal modulations of the perturbation field magnitudes for low KP (IMF Bz > 0) take the form of large amplitude quasi-sinusoidal variations about mean values which are very marked in the equinox data, are present to a lesser degree during summer and are absent during winter conditions. When Kp is high (IMF Bz < 0) significant deviations from mean perturbation field values occur generally only during nightside hours and little seasonal dependence is evident. Finally, it is shown that the highest correlation between the IMF data and the ATS 6 perturbation fields occurs with zero time delay between the two data sets, showing that a prompt response to IMF conditions occurs at geostationary orbit within the 1 h time resolution available in this study. Although many details of the above ATS 6 response remain to be understood, these results overall demonstrate in a very direct manner the magnetically “open” nature of the Earth's magnetosphere. 相似文献
9.
Coronal mass ejections (CMEs) carry magnetic structure from the low corona into the heliosphere. The interplanetary CMEs (ICMEs)
that exhibit the topology of helical magnetic fluxropes are traditionally called magnetic clouds (MCs). MC fluxropes with
axis of low (high) inclination with respect to the ecliptic plane have been referred to as bipolar (unipolar) MCs. The poloidal
field of bipolar MCs has a solar cycle dependence. We report a cyclic reversal of the poloidal field of low inclination MC
fluxropes during 1976 to 2009. The MC poloidal field cyclic reversal on the same time scale of the solar magnetic cycle is
evident over three sunspot cycles. Approximately 48% of ICMEs are MCs, and 40% of IMCs are bipolar MCs during solar cycle 23.
The speed of the bipolar MCs has essentially the same distribution as all ICMEs, which implies that they are not from any
special type of CMEs in terms of the solar origin. Although CME fluxropes may undergo a number of complications during the
eruption and propagation, a significant group of MCs retains sufficient similarity to the source region magnetic field to
posses the same cyclic periodicity in polarity reversal. The poloidal field of bipolar MCs gives the out-of-ecliptic-plane
field or B
z
component in the IMF time series. MCs with southward B
z
field are particularly effective in causing geomagnetic disturbances. During the solar minima, the B
z
field IMF sequence within MCs at the leading portion of a bipolar MC is the same with the solar global dipole field. Our
finding shows that MCs preferentially remove the like polarity of the solar dipole field, and it supports the participation
of CMEs in the solar magnetic cycle. 相似文献
10.
This paper reports the study concerning the latitudinal dispalacement of the auroral oval as a function of the northward orientation of the Bz-component IMF and the relation between southward Bz and the auroral dynamics in the night sector. 相似文献
11.
Continuous wavelet transform and cross‐wavelet transform have been used to investigate the phase periodicity and synchrony of the monthly mean Wolf (Rz) and group (Rg) sunspot numbers during the period of June 1795 to December 1995. The Schwabe cycle is the only one common period in Rg and Rz, but it is not well‐defined in case of cycles 5–7 of Rg and in case of cycles 5 and 6 of Rz. In fact, the Schwabe period is slightly different in Rg and Rz before cycle 12, but from cycle 12 onwards it is almost the same for the two time series. Asynchrony of the two time series is more obviously seen in cycles 5 and 6 than in the following cycles, and usually more obviously seen around the maximum time of a cycle than during the rest of the cycle. Rg is found to fit Rz better in both amplitudes and peak epoch during the minimum time time of a solar cycle than during the maximum time of the cycle, which should be caused by their different definition, and around the maximum time of a cycle, Rg is usually less than Rz. Asynchrony of Rg and Rz should somewhat agree with different sunspot cycle characteristics exhibited by themselves (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
12.
The geometry of the open field line region in the polar region is computed for a variety of the interplanetary magnetic field (IMF) orientation. The open field line region can be identified as the area bounded by the auroral oval, namely the polar cap. The polar cap geometry varies considerably with the orientation of the IMF and magnitude, particularly when the IMF Bz component is positive and large. The corresponding exit points of the open field lines on the magnetopause are also examined. The results will be a useful guide in interpreting various upper atmospheric phenomena in the highest latitude region of the Earth and also in observing chemical releases outside the magnetopause. 相似文献
13.
U. Anzer 《Solar physics》1969,8(1):37-52
In this paper the stability of the Kippenhahn-Schlüter model of solar filaments against arbitrary perturbations is investigated. The problem is treated in the MHD approximation and a modification of the energy principle of Bernstein et al. is used. Two necessary and sufficient stability conditions are found: (a) [B
z] dB
x/dz 0 and (b) B
x d[B
z]/dz 0. Condition (a), in the limit of small currents, leads to the condition already discussed by Kippenhahn and Schlüter; condition (b) requires that the current density in the stable filament decreases with height.On leave from the Max-Planck-Institut für Physik und Astrophysik, München, Germany. 相似文献
14.
Wavelet Analysis of solar,solar wind and geomagnetic parameters 总被引：3，自引：0，他引：3
The sunspot number, solar wind plasma, interplanetary magnetic field, and geomagnetic activity index A
p have been analyzed using a wavelet technique to look for the presence of periods and the temporal evolution of these periods. The global wavelet spectra of these parameters, which provide information about the temporal average strength of quasi periods, exhibit the presence of a variety of prominent quasi periods around 16 years, 10.6 years, 9.6 years, 5.5 years, 1.3 years, 180 days, 154 days, 27 days, and 14 days. The wavelet spectra of sunspot number during 1873–2000, geomagnetic activity index A
p during 1932–2000, and solar wind velocity and interplanetary magnetic field during 1964–2000 indicate that their spectral power evolves with time. In general, the power of the oscillations with a period of less than one year evolves rapidly with the phase of the solar cycle with their peak values changing from one cycle to the next. The temporal evolution of wavelet power in R
z, v
sw, n, B
y, B
z, |B|, and A
p for each of the prominent quasi periods is studied in detail. 相似文献
15.
After reviewing the basic characteristics of the polar cap arcs, it is suggested that their appearance can be explained if the open region splits into two, one located in the dawn sector and the other in the dusk sector. It is suggested that a distinct splitting occurs temporarily when an IMF tangential discontinuity passes by the magnetosphere and the sign of the IMF By component changes at the discontinuity, provided that the IMF Bz component is positive on both sides. As a result, the dawn or the dusk side of the polar region will be connected to either the front side or the hind side of the discontinuity, depending on the sign of the By component across the discontinuity. As the dynamo process is expected to operate in each of the two open regions (as is the case in the single open region), it is reasonable to infer that a sheet of plasma and of field-aligned currents forms in the region between the two open regions, resulting in the polar cap arcs across the polar region. The four-cell convection pattern may also appear. A model of the magnetosphere is constructed to demonstrate such a possibility. 相似文献
16.
Powerful flares are closely related to the evolution of the complex magnetic field configuration at the solar surface. The
strength of the magnetic field and speed of its evolution are two vital parameters in the study of the change of magnetic
field in the solar atmosphere. We propose a dynamic and quantitative depiction of the changes in complexity of the active
region: E=u×B, where u is the velocity of the footpoint motion of the magnetic field lines and B is the magnetic field. E represents the dynamic evolution of the velocity field and the magnetic field, shows the sweeping motions of magnetic footpoints,
exhibits the buildup process of current, and relates to the changes in nonpotentiality of the active region in the photosphere.
It is actually the induced electric field in the photosphere. It can be deduced observationally from velocities computed by
the local correlation tracking (LCT) technique and vector magnetic fields derived from vector magnetograms. The relationship
between E and ten X-class flares of four active regions (NOAA 10720, 10486, 9077, and 8100) has been studied. It is found that (1)
the initial brightenings of flare kernels are roughly located near the inversion lines where the intensities of E are very high, (2) the daily averages of the mean densities of E and its normal component (E
n) decrease after flares for most cases we studied, whereas those of the tangential component of E (E
t) show no obvious regularities before and after flares, and (3) the daily averages of the mean densities of E
t are always higher than those of E
n, which cannot be naturally deduced by the daily averages of the mean densities of B
n and B
t. 相似文献
17.
《Planetary and Space Science》1987,35(10):1301-1316
The magnetic field vector residuals observed from the Magsat satellite have been used to obtain the dependence of the polar cap boundary and the current system on IMF for quiet and mildly disturbed conditions (Kp ⩽ 3 +). The study has been carried out for the summer months in the Southern Hemisphere. “Shear reversals” (SRs) in vector residuals indicative of the infinite current sheet approximation of the field-aligned currents (FACs) indicate roughly the polar cap boundary or the poleward boundary of the plasma sheet. This is also the poleward edge of the region 1 FACs. The SR is defined to occur at the latitude where the vector goes to minimum and changes direction by approximately 180°.It is found that SRs mainly occur when the interplanetary magnetic field (IMF) has a southward-directed Bz- component and in the latitude range of about 70°–80°. SRs in the dusk sector occur predominantly when the azimuthal component By is positive and in the dawn sector when By is negative, irrespective of the sign of Bz These results agree with the known merging process of IMF with magnetopause field lines. When SRs occur on both dawn and dusk sectors, the residuals over the entire polar cap are nearly uniform in direction and magnitude, indicating negligible polar currents. Similar behaviour is observed during highly disturbed conditions usually associated with large negative values of Bz.Forty-one Magsat orbits with such SRs are quantitatively modelled for preliminary case studies of the resulting current distribution. It is found that SRs, in the plane perpendicular to the geomagnetic field, for the current vectors and the magnetic vector residuals (perturbations relative to the unperturbed field) occur at almost the same latitudes. The electrojet intensities range from 1.2 × 104 to 6.5 × 105 A (amperes). A preliminary classification of polar cap boundary crossings characterized by vector rotations rather than SRs also shows that they tend to occur mainly for negative Bz. 相似文献
18.
The variation of the geomagnetic activity index Ap at the IMF sector boundaries (+ to ? and ? to +) has been studied for three solar cycles, separating data into vernal and autumnal equinoxes. It was found that a reported increase in Ap as an effect of a Hale boundary can be better attributed to the occurrence of a negative IMF Bz component in the geocentric solar magnetospheric coordinate system and to the occurrence of high speed solar wind streams. 相似文献
19.
We experiment with a method of measuring the frequency of solar p modes, intended to extend the passband for the variations of the frequency spectrum as high as possible. So far this passband is limited to a fraction of μ Hz for the classical analysis based on numerical fits of a theoretical line profile to a power spectrum averaged over periods lasting at least several weeks. This limit for the present analysis can be shifted to the mHz range, corresponding to some of the “5 min” oscillations, but in this range we use a lower resolution which allows us to separate odd and even p modes. We show an example of the results for long term variations and apply this analysis to search for a modulation of the p‐mode frequency spectrum by asymptotic series of solar g modes. A faint signal is found in the analysis of 10 years of GOLF data. This very preliminary result possibly indicates the detection of a small number of g modes of degree l = 1. A tentative determination of an observational value of the parameter P0 follows. P0 is the scaling factor of the asymptotic series of g modes and is a key data for solar core physics. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
20.
Two quiescent solar prominences were observed in July 2000 from SUMER aboard SOHO and from the two German solar telescopes at Tenerife. Two‐dimensional images taken at the VTT simultaneously in the spectral lines Hβ at 4862 Å and Ca II at 8542 Å show no significant spatial variation of their pressure‐sensitive emission ratio. Slit spectra of the Ca II 8542 Å and He I 10830 Å lines obtained at the Gregory‐Coudé telescope yield 8000 K < Tkin < 9000 K and 3 km/s < Vn–th < 8 km/s. Among the various spectral ranges observed with SUMER, we first investigate the Lyman emission lines, which were fitted by Gaussians yielding reliable spectral radiances and line widths for the series members 5 < k < 18. A determination of the level population gives for the lower series members a Boltzmann temperature of 60 000 K, the higher members being over‐populated. This temperature indicates an origin of the Lyman lines from hot surroundings of the cool prominence body seen in the ground‐based data; this also holds for the ‘hotter’ SUMER lines. 相似文献