Role of the solar main magnetic dipole field in the solar-tropospheric relations. Part I. Semiannual fluctuations in Europe

The influence of the solar corpuscular radiation on weather is demonstrated by characterizing the corpuscular impact by means of the geomagnetic aa-index and the terrestrial response by European temperature data. Considering different spatial and vectorial circumstances the following conclusions can be drawn: 1. the efficiency of the corpuscular impact depends on the Sun-Earth attitude (semiannual fluctuation); 2. this regularity depends on the polarity of the solar main magnetic dipole field; and 3. the whole complex of phenomena also depends on the geographic position - it exists at European middle latitudes but it does not exist in northern and southern Europe. We conclude that the periods of differently or oppositely working mechanisms should be separated in order to recognize the regularities.     

Dependence of geomagnetic activity during magnetic storms on the solar wind parameters for different types of streams

The dependence of the maximal values of the |Dst| and AE geomagnetic indices observed during magnetic storms on the value of the interplanetary electric field (E _y ) was studied based on the catalog of the large-scale solar wind types created using the OMNI database for 1976–2000 [Yermolaev et al., 2009]. An analysis was performed for eight categories of magnetic storms caused by different types of solar wind streams: corotating interaction regions (CIR, 86 storms); magnetic clouds (MC, 43); Sheath before MCs (Sh_MC, 8); Ejecta (95); Sheath (Sh_E, 56); all ICME events (MC + Ejecta, 138); all compression regions Sheaths before MCs and Ejecta (Sh_MC + Sh_E, 64); and an indeterminate type of storm (IND, 75). It was shown that the |Dst| index value increases with increasing electric field E _y for all eight types of streams. When electric fields are strong (E _y > 11 mV m⁻¹), the |Dst| index value becomes saturated within magnetic clouds MCs and possibly within all ICMEs (MC + Ejecta). The AE index value during magnetic storms is independent of the electric field value E _y for almost all streams except magnetic clouds MCs and possibly the compressed (Sheath) region before them (Sh_MC). The AE index linearly increases within MC at small values of the electric field (E _y < 11 mV m⁻¹) and decrease when these fields are strong (E _y > 11 mV m⁻¹). Since the dynamic pressure (Pd) and IMF fluctuations (σB) correlate with the E _y value in all solar wind types, both geomagnetic indices (|Dst| and AE) do not show an additional dependence on Pd and IMF δB. The nonlinear relationship between the intensities of the |Dst| and AE indices and the electric field E _y component, observed within MCs and possibly all ICMEs during strong electric fields E _y , agrees with modeling the magnetospheric-ionospheric current system of zone 1 under the conditions of the polar cap potential saturation.     

Superconcentration of photospheric sources of the large-scale open solar magnetic field in the main zone of active longitudes, differential rotation blocking, and origination of the four-sector structure. 1. The field and solar activity dynamics

The phenomena of superconcentration of the large-scale field photospheric sources in the main zone of active longitudes, blocking of regular differential rotation by these sources, and origination of the four-sector structure of the solar magnetic field during the decline phase of cycle 23 have been considered in more detail and taking into account the polar correction. It has been indicated that superconcentration was formed due to the penetration of photospheric sources into the zone from the western surroundings of this zone and owing to the generation of the large-scale field in the zone itself. The dynamics of a blocking-induced complex MHD disturbance with reflected from the zone and reconnecting photospheric sources of negative and positive polarity, respectively, and the transformation of the bisector structure into the four-sector one have been considered. It has been indicated that the dynamics of this MHD disturbance was responsible for that of associated solar activity: the generation of sunspot groups, appearance of flares, and, finally, origination of a powerful heliospheric storm and the solar-terrestrial extrastorm of July 22–27, 2004.     

强磁暴的时间分布特性

对比分析1957--2008年间Dst≤-100nT的强磁暴数与太阳黑子数的变化趋势,发现太阳黑子数和Dst≤-100nT的强磁暴数的变化趋势有很好的一致性。进一步统计强磁暴在太阳周不同阶段的分布后发现,同一太阳周内60％以上的强磁暴出现在下降年,但从太阳周各个阶段的平均磁暴年发生率来看,强磁暴平均年发生率最高的年份仍然是太阳活动极大年。     

Dependence of geomagnetic activity during magnetic storms on the solar wind parameters for different types of streams: 3. Development of storm

This paper is a continuation of (Nikolaeva et al., 2011, 2012) and it analyzes the development of the main phase of 190 magnetic storms with Dst ≤ −50 nT depending on the type of source in the solar wind (magnetic clouds, MC; corotating interaction regions, CIR; Ejecta; Sheath before them, Sh_E; Sheath before MC, Sh_MC; all Sheath regions before ICME, Sh_E + Sh_MC; all ICME, MC + Ejecta; and an indeterminate type of solar wind stream, IND).     

Dependence of geomagnetic activity during magnetic storms on the solar wind parameters for different types of streams: 2. Main phase of storm

The paper analyses the development of the main phase of magnetic storms with Dst ≤ −50 nT, the interplanetary source of which consists of eight types of solar wind streams: magnetic clouds (MC, 17 storms); corotating interaction regions (CIR, 49 storms); Ejecta (50 storms); compressed region (Sheath) before Ejecta Sh_E (34 storms); the Sheath before a magnetic cloud Sh_MC (6 storms); all Sheath before all ICME, Sh_E + Sh_MC (40 storms); all ICME, MC + Ejecta (67 storms); and an indeterminate type of stream IND (34 storms).     

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.     

Motion of the north magnetic pole within the scope of the dynamic model of the main geomagnetic field sources

The dipole model of the main geomagnetic field sources has been developed by the authors for several years. At present, the model includes 13 sources that existed and continuously developed during the 20th century. It has been assumed that the main dipole motion can be related to the motion of the Earth’s axis of inertia. At the same time, the known sharp changes in the direction of this motion, the so-called “wanderings” of the axis of inertia coincide in time with a change in the coordinates of the exit point of the main dipole magnetic moment vector on the Earth’s surface, dependent mostly on changes in the vector inclination. The motion of the north magnetic pole has been studied based on the model. It has been obtained that the dynamics of the main dipole parameters and, mainly, a stable variation in the inclination of the magnetic moment vector are responsible for the westward pole motion. At the same time, the observed rapid northward motion of the pole is related to the time variations in the parameters of 12 sources approximating the so-called nondipole part of the main field.     

Large-scale structure of the solar corona magnetic field

The configuration of the solar corona magnetic field has been studied. Data on the position of the K-corona emission polarization plane during the solar eclipses of September 21, 1941; February 25, 1952; and August 1, 2008, were used as an indicator of the magnetic field line orientation. Based on an analysis of these data, a conclusion has been made that the studied configuration has a large-scale organization in the form of a cellular structure with an alternating field reversal. The estimated cell size was 61° ± 6° (or 36° ± 2°) in longitude with a latitudinal extension of 40°?C50° in the range of visible distances 1.3?C2.0 R _Sun . A comparison of the detected cellular structure of the coronal magnetic field with synoptic {ie908-1} maps indicated that the structure latitudinal boundaries vary insignificantly within 1.1?C2.0 R _Sun . The possible causes of the formation of the magnetic field large-scale cellular configuration in the corona and the conditions for the transformation of this configuration into a two-sector structure are discussed.     

Superconcentration of photospheric sources of the large-scale open solar magnetic field in the main zone of active longitudes,blocking of differential rotation,and origination of the four-sector structure: 2. Geoeffectiveness

The effectiveness of the series of powerful heliospheric storms, originated during the decline phase of cycle 23 owing to the superconcentration of the open field photospheric sources in the main zone of active longitudes, has been studied. The geoeffectiveness of the storm of July 16—27, 2004, was closely related to the origination of the four-sector structure and depended on the destabilization of two activity centers weakly and strongly geoeffective with ARs 10649 and 10652. The first center was localized in one of the new sectors; the second center, in the western surroundings of the zone of active longitudes. The departure of coronal mass ejections from AR 10649 was substantially hindered: they were completely absent after the series of powerful X-ray flares, and a rare phenomenon of “sunquake” was observed: shock waves did not reach the Earth in spite of its favorable position. The Earth was strongly shielded by new sector boundaries from coronal ejections from AR 10652 with a gradual weakening and disappearance of this region, as a result of which the cascade of three near-Earth storms with an increasing power and Ap, indices of 52, 154, and 186 originated. Rare phenomena in AR 10649 and the cascade of solar—terrestrial heliospheric storms made the storm of July 16— 27 a unique phenomenon in cycle 23, and a short-term prediction of its geoeffectiveness was impossible.     

Long-period variations in the magnetic field of small-scale solar structures

Thirty small-scale structures in the solar atmosphere, i.e., facula nodes at ±(20°–46°) latitudes, have been studied in order to analyze quasi-periodic variations in the magnetic field. SDO/HMI magnetograms have been used for this purpose. Long-period variations in the magnetic field strength of the considered objects in the 60–280 min range have been revealed as a result of data processing. It has been shown that there are no dependences between the magnetic field and period, nor between the magnetic field and object area. It has been assumed that the discovered variations are not natural oscillations of the magnetic field strength.     

Secular variations in the main geomagnetic field within the scope of the dynamic model of field sources

The effect of different-level sources on the spatial structure of the secular variations has been considered based on the dynamic model of sources of the main geomagnetic field developed by us. It has been obtained that the development of 13 most powerful dipoles only roughly characterizes global anomalies of the secular variations, and each anomaly results from the superposition of the dynamics of several sources. The model secular variations have been compared with the data from the observatories. It has been obtained that it is impossible to describe local anomalies of the observed secular variations ignoring sources of the third order of smallness as compared to the main dipole. It has been assumed that topographic vortices, originating around inhomogeneities of the core-mantle boundary, can be physical sources responsible for dipoles of the third order.     

Sector spherical harmonic analysis of the solar magnetic field

The theory of sector harmonic analysis has been developed as applied to the specific conditions of the solar magnetic field. A computer program has been developed. The possibilities of the program are illustrated in an analysis of a large-scale open solar field “singularity” observed on August 11, 2004, using MDI magnetometer data.     

Anomalies in the secular variations in the main geomagnetic field in the context of the hierarchic dipole model

The developed dynamic model of the main geomagnetic field (MGF) includes the sources of three levels, which have existed and continuously changed during the 100-year period. The spatial-temporal dynamics of the secular variations in MGF has been considered based on this model. It has been indicated that, at different times, the formation of anomalies (located in similar regions) depended on the total dynamics of different combinations of sources, including a change in the parameters of the dipoles of the secondorder smallness. Anomalies generated by the dynamics of the dipoles of the third-order smallness do not evidently manifest themselves in the total secular variations but are responsible for the specific shapes of isodynamic lines. Based on the stability and continuity of the constructed model, the conclusion is made that long-living turbulent flows of different scales can exist in the liquid core.     

Calculation of the interplanetary magnetic field based on its value in the solar photosphere

The difficulties associated with calculating the parameters of the interplanetary magnetic field (IMF) from solar magnetic data have been considered. All conventional calculation patterns and available input databases have been analyzed from a unified standpoint. It has been shown that these assumptions and limitations cannot affect the general structure and dependence on cycle of solar and interplanetary data. At the same time, the measured solar field values are underestimated as a result of the magnetograph signal saturation effect. It has been shown that the correction should depend on the heliocentric observation latitude and cycle phase. The correction method responsible for good agreement between the calculated and measured values has been proposed. The created database makes it possible to quantitatively calculate the magnetic fields in the solar wind near the Earth.     

NOC model of the earth's main magnetic field

The international geomagnetic reference field (IGRF) is a standard model for describing the spatial structure and temporal variation of the earth抯 main magnetic field[1—3]. The first IGRF model, designated IGRF 1965, was adopted by IAGA in 1968[4]. In l…     

Fractal dimension of changes in the solar magnetic field energy and quasi-biennial solar activity variations

Using the data of 1960–1999 on solar magnetic fields on the source surface and the Higuchi method, the fractal dimension of changes in the solar magnetic field energy at various heliolatitudes and in different time intervals is analyzed. The fractal dimension obtained on a moving 1-year interval displays substantial time variations. The 11-year cycle, which dominates at high latitudes, and quasi-biennial variations (QBVs), which dominate at low latitudes and are similar to QBVs of solar activity indices, are traced in these variations. Thus, solar QBVs that appear in all heliomagnetic activity indices are also present in the fractal structure of the solar magnetic field variations.     

Induced currents in a conducting sphere placed in the field of an oscillating magnetic dipole

Summary Expressions are obtained for the currents induced inside a conducting sphere placed in the field of an oscillating magnetic dipole. Interesting conclusions can be drawn from an analysis of the formulas for the current induced due to different orientations of the dipole.     

Dependence of volumes of magnetic flux tubes on plasma pressure and disturbance in the magnetic field in the axially symmetric case

We have analyzed the applicability of the approximation of the axially symmetric magnetic field created by the dipole field and the currents flowing in the plasma for describing the Dst variation value during magnetic storms and the dependence of the position of the pressure maximum on the volumes of magnetic flux tubes on the plasma pressure. We have determined the dependence of the disturbance in the field on the geocentric distance. We have shown that the experimentally obtained dependence on the position of the pressure maximum on Dst is described in the assumption on the correctness of the adiabatic law on changes in pressure with a change in geocentric distance. We have calculated the values of the magnetic field distortion and the value of the Dst variation for the experimentally determined radial pressure profile for three magnetic storms with Dst ∼ 100 nT. We have shown that, with allowance for nonlinear magnetic field distortions, the axially symmetric part of the ring current makes the main contribution to the value of the Dst variation.