A search for north-south asymmetry of interplanetary magnetic field and solar plasma

An analysis of interplanetary magnetic field (IMF) and plasma data taken near 1 AU during solar activity cycle 21 reveals the following. 1. The yearly averaged spiral angle shows a solar cycle dependence. 2. The spiral angle north of the current sheet is 2.4○ higher than south of it during both epochs of positive and negative polarities. 3. The included angle is 4.8○ higher during the epoch of positive polarity than during the epoch of negative polarity. 4. The asymmetries in the number of away and toward IMF days are correlated with the asymmetries in solar activity. 5. The solar plasma north of the current sheet is hotter, faster and less dense than south of it during the epoch of negative polarity. 6. An asymmetry in the averaged filed magnitude is absent for solar cycle 21.     

Does the interplanetary magnetic field and the solar activity contribute to the tropospheric circulation?

A significant tendency is shown for both Etesians and (+, –) sector boundaries of the interplanetary magnetic field (IMF) to occur on the same solar rotation days, during the main period of the Etesians effect (July–August). In addition, the solar activity seems to control the Etesians distribution within the IMF sector structure. In the epoch of maximum there is a significant tendency of Etesians to occur during toward IMF days. In contrast, in the epoch of minimum Etesians occur mainly during away IMF days. Finally, in the epoch of intermediate the Etesians are uniformly distributed in away and toward IMF days. Since these conclusions are statistically significant at high confidence levels, it is fair to assume that IMF and solar activity seem to contribute, to some extent, to the Etesians occurrences, as well as to their distribution within the solar rotation and the IMF sector structure; that is, some solar contribution to the tropospheric circulation is implied.     

Geoeffectiveness of solar wind interplanetary magnetic structures

We address the geoeffectiveness of three interplanetary structures in the interplanetary space: magnetic clouds (MCs), interplanetary shocks (IPSs), and corotating interaction regions (CIRs). The geoeffectiveness is evaluated using the geomagnetic indices Kp, AE, and Dst. We find that MCs are more geoeffective than IPSs, or CIRs. The average values of magnetic indices are significantly enhanced during disturbed periods associated with MCs, IPSs and CIRs, compared to the whole interval. The highest effect is noted for MC disturbed periods.Results obtained for the three data sets are used to derive a theoretical (continuous) probability distribution function (PDF) by fitting the histograms representing the percentage of events against the intervals of magnetic index. PDFs allow estimation of the probability of a given level of geomagnetic activity to be reached after the detection, by in situ solar wind observations, of a given interplanetary structure approaching the Earth.     

日面方位磁场扰动和行星际磁场螺旋结构

文采用球坐标下2.5维理想MHD模型,对日球子午面内方位磁场扰动的传播进行数值模拟,重点分析它对行星际磁场螺旋角的影响. 本文认为,观测到的行星际磁场螺旋角大于Parker模型的预言值,是太阳表面不断向行星际发出同向方位磁场扰动的结果;太阳较差自转在太阳内部产生的方位磁场为这类扰动提供了源头. 模拟结果表明,采用持续时间等于周期的十分之一、扰动幅度为103nT量级的正向方位磁场扰动,就可使1 AU处行星际磁场的螺旋角增加2°左右,与有关观测结果相符. 模拟结果还表明,上述方位磁场扰动对日球子午面内的太阳风特性和磁场位形的影响基本上可以忽略.     

Tracing magnetic helicity from the solar corona to the interplanetary space

On October 14, 1995, a C1.6 long duration event (LDE) started in active region (AR) NOAA 7912 at approximately 5:00 UT and lasted for about 15 h. On October 18, 1995, the Solar Wind Experiment and the Magnetic Field Instrument (MFI) on board the Wind spacecraft registered a magnetic cloud (MC) at 1 AU, which was followed by a strong geomagnetic storm. We identify the solar source of this phenomenon as AR 7912. We use magnetograms obtained by the Imaging Vector Magnetograph at Mees Solar Observatory, as boundary conditions to the linear force-free model of the coronal field, and, we determine the model in which the field lines best fit the loops observed by the Soft X-ray Telescope on board Yohkoh. The computations are done before and after the ejection accompanying the LDE. We deduce the loss of magnetic helicity from AR 7912. We also estimate the magnetic helicity of the MC from in situ observations and force-free models. We find the same sign of magnetic helicity in the MC and in its solar source. Furthermore, the helicity values turn out to be quite similar considering the large errors that could be present. Our results are a first step towards a quantitative confirmation of the link between solar and interplanetary phenomena through the study of magnetic helicity.     

Forecast of the solar wind velocity and the interplanetary magnetic field radial component polarity at the phase of decay of solar cycle 23

The solar wind velocity and polarity of the B _x-component of the interplanetary magnetic field have been analyzed for the first eight months of 2005. The interplanetary magnetic field had a four-sector structure, which persisted during nine Carrington rotations. Three stable clusters of a high-speed solar wind stream and one cluster of a low-speed stream were observed during one solar rotation. These clusters were associated with the interplanetary magnetic field sectors. The predicted solar wind velocity was calculated since July 2005 one month ahead as an average over several preceding Carrington rotations. The polarity of the B _x-component of the interplanetary magnetic field was predicted in a similar way based on the concept of the sector structure of the magnetic field and its relation to maxima of the solar wind velocity. The results indicate a satisfactory agreement of the forecast for two rotations ahead in July–August 2005 and pronounced violation of agreement for the next rotation due to a sudden reconfiguration of the solar corona and strong sporadic processes in September 2005.     

Trends and the sector structure of the interplanetary magnetic field

Large-scale variations in the interplanetary magnetic field (IMF) are studied using its measurements by the Advanced Composition Explorer (ACE) spacecraft. To reveal the sector structure, an algorithm for estimating trends of long time series is proposed. The algorithm makes it possible to determine the sectors as well as to trace the tendencies in changes in the “long-lived” IMF structures for various degrees of initial data smoothing.     

Effects of the interplanetary magnetic field sector structure in the winter ionosphere

Summary The ionospheric effects of the interplanetary magnetic field (IMF) sector boundary crossings are studied for the winters of 1963–69. They are considerably stronger for proton than for non-proton sector boundaries. There are two different types of effects. The geomagnetic type is a disturbance, observed in geomagnetic activity, the night-time ionosphere and the day-time F2 region near the geomagnetic equator. The effect in the ionosphere is interpreted in terms of the IMF sector boundary crossing related changes in geomagnetic activity. The tropospheric type is aquietening, observed in tropospheric vorticity and in the day-time mid-and low-latitude ionosphere (except the geomagnetic equator region). The mechanism of this effect remains unexplained.

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¶rt;m u m nu mau nam aum n () ¶rt; u 1963–69. u m u ¶rt; nm ¶rt; a mau. mm ¶rt;a m¶rt; muna m. aum m u, a¶rt;a aum amumu, u u ¶rt; F2 amu uuaum ama. mu u m ¶rt;mu uu aum amumu, m a nu mau . n mun m nu, a¶rt; aumu mn u ¶rt; ¶rt;- u uum u (a uu amuaum ama). au m ma um.

     

Effect of the ns component of the interplanetary magnetic field on geomagnetic storms

Summary The individual storm-time variations of the geomagnetic field were compared with the variations of the B_z-component of the interplanetary magnetic field over 24 and 48-hour intervals of storm time. Good correlation between B_z and Dst was observed in about one half of the 166 cases analysed (1965–72), the time lag of the manifestations of the interplanetary field at the Earth's surface having been taken into account. The effect of the B_z-field is reflected to a considerably larger extent in intense storms (Dst –80 nT). Good correlation was observed in 80% of the total number of 35 intense storms. Preliminary investigations have shown that Dst-variations, constructed from B_z-data using the relations derived herein, are quite close to the observed, particularly as regards the main phase (3 examples are given).     

Response of ionospheric electric fields to variations in the interplanetary magnetic field

The STARE system (Scandinavian Twin Auroral Radar Experiment) provides estimates of electron drift velocities, and hence also of the electric field in the high-latitude E-region ionosphere between 65 and 70 degrees latitude. The occurrence of drift velocities larger than about 400 m/s (equivalent to an electric field of 20 mV/m) have been correlated with the magnitude of the Interplanetary Magnetic Field (IMF) components B_z and B_y at all local times. Observation days have been considered during which both southward (B_z<0) and northward (B_z>0) IMF occurred. The occurrence of electric fields larger than 20 mV/m increases with increases in B_z magnitudes when B_z<0. It is found that the effects of southward IMF continue for some time following the northward turnings of the IMF. In order to eliminate such residual effects for B_z<0, we have, in the second part of the study, considered those days which were characterized by a pure northward IMF. The occurrence is considerably lower during times when B_z>0, than during those when B_z is negative. These results are related to the expansion and contraction of the auroral oval. The different percentage occurrences of large electric field for B_y>0 and B_y<0 components of the IMF during times when B_z>0, clearly display a dawn-dusk asymmetry of plasma flow in the ionosphere. The effects of the time-varying solar-wind speed, density, IMF fluctuations, and magnetospheric substorms on the occurrence of auroral-backscatter observations are also discussed.     

The interplanetary magnetic field sector structure and meteorological microseisms

Summary Meteorological microseisms, recorded at the Prague seismic station and, similarly, at other Central Europe stations, reflect certain meteorological situations in the North Atlantic frontal zone. Meteorological elements in this zone are affected by some factors of extra-terrestrial origin, among others by the interplanetary magnetic field (IMF) sector structure. The analysis of the 68 IMF sector boundary passage effects in microseismic activity, expressed in microseismic amplitudes, showed a well-developed minimum of microseismic activity on the day of the boundary passage in winter, but no such effect in spring and autumn. In spring and autumn, however, a tendency was observed to slightly higher microseismic activity in the away (+) sector, whereas no such tendency was observed in winter. These results agree with the IMF effect found in the troposphere. Generally, the IMF sector structure is only a modulating rather than a major factor controlling the microseismic activity.     

Effects of the interplanetary magnetic field clock angle on the shape of bow shock

Using the global magnetohydrodynamics(MHD) simulation model, we investigated the effects of the interplanetary magnetic field(IMF) clock angle on the shape of bow shock, including its rotational asymmetry and subsolar point. For general northward IMF( z component Bz 0), the rotational symmetry of the bow shock is broken by the effects of fast magnetosonic Mach number(Mms), and the cross-sectional line of the bow shock is an ellipse with the semi-major axis along the direction perpendicular to the IMF. The ratio or D-value between semi-major and semi-minor axis can be used to illustrate the extent of asymmetry of the bow shock. On the basis of the multiple parameters fitting, we obtain the changing relationship of both semi-axes with the clock angle and the distance away from the Earth. For general southward IMF(Bz 0), the cross sectional line of the bow shock is highly asymmetrical under the multiple effects of magnetopause and Mms. The effects of IMF clock angle on subsolar point depend mainly on the changing subsolar point of magnetopause as an obstacle. The distance of subsolar point of bow shock from the Earth increases with the increasing IMF clock angle for Bz 0, and decreases with the increasing IMF clock angle for Bz 0.     

Three-dimensional MHD simulation of interplanetary magnetic field changes at 1 AU as a consequence of simulated solar flares

A fully three-dimensional (3D), time-dependent, MHD interplanetary global model (3D IGM) has been used, for the first time, to study the relationship between different forms of solar activity and transient variations of the north-south component, B_z, of the interplanetary magnetic field (IMF) at 1 AU. One form of solar activity, the flare, is simulated by using a pressure pulse at different locations near the solar surface and observing the simulated IMF evolution of B (=-B_z) at 1 AU. Results show that, for a given pressure pulse, the orientation of the corresponding transient variation of B_z has a strong relationship to the location of the pressure pulse and the initial conditions of the IMF. Two initial IMF conditions are considered: a unipolar Archimedean spiral with outward polarity and a flat heliospheric current sheet (HCS) with outward polarity in the northern hemisphere and which gradually reverses polarity in the solar equatorial plane to inward polarity in the southern heliospheric hemisphere. The wave guide effect of the HCS is also demonstrated.     

On the structure of the interplanetary magnetic field under non-stationary boundary conditions

Summary The structure of the interplanetary magnetic field (IMF) is investigated theoretically in a kinematic approximation under frozen-in conditions in the solar wind and non-stationary boundary conditions. As an example, a time-dependent model of the IMF, created in the case of a change of the general magnetic field of the Sun represented by the dipole term, is analyzed. Very simple assumptions as to the field of velocities in the solar wind are made. The results show the formation of zero IMF points of two types(O, X). Points of theO-type are formed and move radially in the equatorial plane. They are surrounded by magnetic clouds with loops of lines of force. Points of theX-type are formed and move radially above the poles.

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muu u¶rt;aa mma nam aum n() uamu nuuuu nu uu mu m u mauaau uu. am nua ama ¶rt; , ua nu uuu aum n a, n¶rt;ma ¶rt;un , auu m u. mum n m m ¶rt;a nmu n¶rt;nu. mam naam aau m ¶rt; mun(O, X). uO-muna uam u ¶rt;um a¶rt;ua amua nmu. u aumu aau nmu u uu. uX-muna uam u ¶rt;um a¶rt;ua a¶rt; nau.

     

Observation of a double-onset substorm during northward interplanetary magnetic field

For the first time, a substorm event with double onsets is shown observationally under northward IMF condition in this study. Magnetic field data from ground stations and from geosynchronous satellite, and aurora data from IMAGE satellite are examined to study the substorm activity. The results show that the intensity and the spatial extent of the event are as large as those of typical substorms. Another interesting finding is that two expansion onsets seem to occur during the event. A possible mechanism for the two onsets was proposed. The energy source for the event was also discussed.     

Chaotic behaviour of interplanetary magnetic field under various geomagnetic conditions

In the present study, the deterministic chaotic behaviour of interplanetary magnetic field (IMF) under various geomagnetic conditions of low and high solar active periods was analyzed, using the time series of IMF |B| and B_z, by employing chaotic quantifiers like, Lyapunov exponent, Tsallis entropy, correlation dimension, and non-linear prediction error. We have investigated whether the chaotic behaviour of interplanetary magnetic field would modify, when it produces major geomagnetic storms, and how it depends on the phase of solar activity. The yearly average values of Lyapunov exponent for the time series of IMF |B| and B_z, show solar flux dependence, whereas those values of entropy, correlation dimension and non-linear prediction error had no significant solar flux dependence. The yearly average values of entropy for quiet periods are higher compared to those values for major storm periods belonging to low/high solar active conditions, for both the time series |B| and B_z.     

Verification of magnetic field models based on measurements of solar cosmic ray protons in the magnetosphere

Measurements of solar cosmic ray (SCR) protons in the magnetosphere can be used to verify models of the Earth’s magnetic field. The latitudinal profiles of precipitating SCRs with energies of 1–90 MeV were measured on the CORONAS-F low-orbiting satellite during a strong magnetic storm on October 29–30, 2003. A flux of precipitating protons can remain equal to the interplanetary flux only due to a strong pitch angle diffusion that originates when the radius of the field line curvature is close to that of the particle rotation Larmor radius. The observed boundaries of the strong diffusion region can be compared with the boundaries anticipated according to the models of the magnetic field of the Earth’s magnetosphere. The adiabaticity parameter values, calculated for several instants of the CORONAS-F satellite pass based on the TS05 and parabolic models, do not always correspond to measurements. How possible changes in the model configurations of the magnetic field can allow us to eliminate discrepancies with the experiment and to explain why solar protons with energies of several megaelectronvolts penetrate deep in the Earth’s inner magnetosphere is considered here.     

Magnetopause magnetic barrier parameters in dependence on the solar wind magnetic field orientation

Some theories predict the magnetosheath magnetic field strength will decrease and the density increase just outside the dayside magnetopause as the interplanetary magnetic field turns southward. Two studies have recently reported results which confirm these expectations. In contrast, we briefly review our own theoretical predictions which indicate that precisely the opposite effect is expected. We survey new and previously reported magnetosheath observations and demonstrate that they are consistent with the predictions of our model. The conflicting results indicate a need for further theoretical and observational work.