Marta Tyasto

A NEW PATTERN FOR THE NORTH-SOUTH ASYMMETRY OF SUNSPOTS

We study the solar cycle evolution during the last 8 solar cycles using a vectorial sunspot area called the LA (longitudinal asymmetry) parameter. This is a useful measure of solar activity in which the stochastic, longitudinally evenly distributed sunspot activity is reduced and which therefore emphasizes the more systematic, longitudinally asymmetric sunspot activity. Interesting differences are found between the LA parameter and the more conventional sunspot activity indices like the (scalar) sunspot area and the sunspot number. E.g., cycle 19 is not the highest cycle according to LA. We have calculated the separate LA parameters for the northern and southern hemisphere and found a systematic dipolar-type oscillation in the dominating hemisphere during high solar activity times which is reproduced from cycle to cycle. We have analyzed this oscillation during cycles 16–22 by a superposed epoch method using the date of magnetic reversal in the southern hemisphere as the zero epoch time. According to our analysis, the oscillation starts by an excess of the northern LA value in the ascending phase of the solar cycle which lasts for about 2.3 years. Soon after the maximum northern dominance, the southern hemisphere starts dominating, reaching its minimum some 1.2–1.7 years later. The period of southern dominance lasts for about 1.6 years and ends, on an average, slightly before the end of magnetic reversal.

Extremely strong geomagnetic storm of September 2-3, 1859, according to the archived data of observations at the Russian network

A retrospective analysis of the Russian magnetic observations of the Carrington event that occurred on September 2–3, 1859, has been performed. The conclusion has been made that this event was caused by the series of three recurrent eruptive solar flares during ∼40 h. The characteristics of the geomagnetic crochet, related to a considerable flux of the ionizing electromagnetic radiation during this flare, have been studied. The value and direction of a magnetic field disturbance, registered during the maximum of the geomagnetic storm of September 2, unambiguously indicate that all Russian stations were in the auroral oval zone, which was strongly expanded southward from its average position. The disturbance dependence on the station longitude—the absence of magnetometer pinning in Nerchinsk—is interpreted as the possible manifestation of a strong asymmetry in the effective contour of the current system, which was connected to the heliosphere and covered the disturbed magnetosphere and ionosphere during the short period that lasted only 1–3 h.

On the influence of solar activity and the solar magnetic field on the 27-day variation of galactic cosmic rays

The calculated amplitude of the 27-day variation using super neutron monitors data has been compared with changes of the distribution of solar activity on the Sun. Close correlation of the two-peaked pattern of the galactic cosmic rays 27-day variation with changes of the longitudinal asymmetry of the sunspot distribution at the maxima epochs of solar activity has been observed. It is reasonable to assume that drastic changes of the longitudinal asymmetry of solar activity near the solar maximum are reflected in the perturbation of the heliospheric structure, causing the depression of the 27-day modulation. Marked differences between the Suns magnetic polarity cycles, qA > 0 and qA 0 and qA 0 than in the qA < 0 solar magnetic cycles being in good agreement with the experimental data for the minima epochs of solar activity.

27-Day variations of galactic cosmic rays and changes of solar and geomagnetic activities

Abstract Neutron monitor, solar and geomagnetic activity data have been used to investigate variations of galactic cosmic ray intensity connected with the Suns rotation for different epochs of solar activity. Behaviors of longitudinal asymmetry of the sunspot distribution, coronal line emission and tilt angles of the heliospheric neutral sheet have been studied. A relationship of the temporal changes of the amplitudes of the 27-day variations of galactic cosmic rays and Kp index of geomagnetic activity with the tilt angles of the heliospheric neutral sheet have been investigated. It is shown that there are no any noticeable relationship between the amplitudes of the 27-day variations of galactic cosmic rays and the tilt angles of the heliospheric neutral sheet for both of the qA > 0 and the qA 0 cycle than for the qA

Photospheric Magnetic Field: Relationship Between North–South Asymmetry and Flux Imbalance

Photospheric magnetic fields were studied using the Kitt Peak synoptic maps for 1976 – 2003. Only strong magnetic fields (B>100 G) of the equatorial region were taken into account. The north–south asymmetry of the magnetic fluxes was considered as well as the imbalance between positive and negative fluxes. The north–south asymmetry displays a regular alternation of the dominant hemisphere during the solar cycle: the northern hemisphere dominated in the ascending phase, the southern one in the descending phase during Solar Cycles 21 – 23. The sign of the imbalance did not change during the 11 years from one polar-field reversal to the next and always coincided with the sign of the Sun’s polar magnetic field in the northern hemisphere. The dominant sign of leading sunspots in one of the hemispheres determines the sign of the magnetic-flux imbalance. The sign of the north–south asymmetry of the magnetic fluxes and the sign of the imbalance of the positive and the negative fluxes are related to the quarter of the 22-year magnetic cycle where the magnetic configuration of the Sun remains constant (from the minimum where the sunspot sign changes according to Hale’s law to the magnetic-field reversal and from the reversal to the minimum). The sign of the north–south asymmetry for the time interval considered was determined by the phase of the 11-year cycle (before or after the reversal); the sign of the imbalance of the positive and the negative fluxes depends on both the phase of the 11-year cycle and on the parity of the solar cycle. The results obtained demonstrate the connection of the magnetic fields in active regions with the Sun’s polar magnetic field in the northern hemisphere.

Cosmic-ray forecasting features for big forbush decreases

It is well known that big geomagnetic storms have an adverse influence on technological devices and radio wave propagation. Major geomagnetic storms, associated with Forbush decreases (FDs) in cosmic ray (CR) intensity, have also been found to increase the incidence of some diseases (in particular, the frequency of myocardial infarction increases by 13 ± 1.4%). We discuss here three phenomena that can be used for forecasting FDs: 1) CR intensity increase, of non solar-flare origin, occurring before sudden commencement of a major geomagnetic storm connected with FD (preincrease effect), 2) CR intensity decrease before FD (predecrease effect), 3) change in CR fluctuations before FD. First we investigate several such events by the global survey method for the years 1989–1991. We analyse the behaviour of the isotropic CR intensity and of the 3-dimensional vector of CR anisotropy before FDs, as well as results on CR scintillation of 1-hour and 5-minute data. We discuss a possible procedure of data treatment for future FD-forecasting analyses.

Effect of Geomagnetic Disturbances on the Operation of Railroad Automated Mechanisms and Telemechanics

Geomagnetic variations generate electric currents in long conductors such as high-voltage lines, pipelines, and telecoms cables. The aim of our work is to study the possible effect of geomagnetic disturbances on the operation of automated systems and telemechanics of a midlatitude railroad based on the data on the malfunctions and breakdowns registered in 2004 on the East Siberian railroad (VSZhD). It has been obtained that the total daily duration of malfunctions and breakdowns (T) during disturbed periods is controlled by geomagnetic activity. When a peak of geomagnetic activity is reached during a storm, T increases about three times. Moreover, a correlation between T and the local index of geomagnetic activity (A), measured at Podkamennaya Tunguska Siberian observatory, is high during disturbed periods. Specifically, the correlation coefficient (K) is equal to 0.83 and 0.71 for the strongest two storms of 2004 that occurred in July 17–August 2 and November 4–18, respectively.

Long-term longitudinal asymmetries in sunspot activity: Difference between the ascending and descending phase of the solar cycle

We study the longitudinal distribution of sunspot activity in 1917–1995 using vector sums of sunspot areas. The vector sum of sunspots of one solar rotation gives a total vector whose amplitude characterizes the size of longitudinal asymmetry and whose phase describes the location of the momentarily dominating longitude. We find that when the phase distributions are calculated separately for the ascending phase and maximum (AM) on the one hand and for the declining phase and minimum (DM) on the other hand, they behave differently and depict broad maxima around roughly opposite longitudes. While the maximum of the phase distribution for the AM period is found around the Carrington longitude of 180°, the maximum for the DM period is at the longitude of about 0°. This difference can be seen in both solar hemispheres, but it is more pronounced in the southern hemisphere where the phase distribution has a particularly clear pattern. No other division of data into two intervals leads to similar systematic differences.

Sporadic and recurrent geomagnetic disturbances in 1859–1860 according to the archived data from the Russian network of stations

Based on an analysis of the available archived data from the Russian network of geomagnetic stations, it has been indicated that the known event of August–September 1859 was the first and the greatest event in the series of the recurrent geomagnetic storms. Similar series were repeatedly observed in the next years. These series are caused by the processes on the Sun and in the heliosphere related to the superposition of the solar wind flows. The sporadic and regular components in joint activity of the complex, including active regions and coronal holes on the rotating Sun, play the role of the Bartels M regions responsible for initiation and development of geomagnetic storms. Neither coronal holes nor active regions can separately explain observations. During interpretation, active regions and coronal holes should be considered as a unified complex.

Reflection of the solar wind parameters in the CR geomagnetic cutoff rigidity before a strong magnetic storm in November 2003

The time variations in the CR geomagnetic cutoff rigidity and their relation to the interplanetary parameters and the Dst index during a strong magnetic storm of November 18–24, 2003, have been analyzed. The Tsyganenko (Ts03) model of a strongly disturbed magnetosphere [Tsyganenko, 2002a, 2002b; Tsyganenko et al., 2003] have been used to calculate effective geomagnetic thresholds with the help of the method for tracing CR particle trajectories in the magnetospheric magnetic field. The geomagnetic thresholds have been calculated using the method of global spectrographic survey (GSS), based on the data from the global network of CR stations, and the results have been compared with the effective geomagnetic cutoff rigidities. The daily anisotropy of effective geomagnetic thresholds during the Dst variation minimum have been estimated. The relation of the theoretical and experimental geomagnetic thresholds, obtained using the GSS method, to the interplanetary parameters and Dst variation is analyzed. The Dst variations, IMF Bz, and solar wind density are most clearly defined in the geomagnetic thresholds during this storm. The correlation between By and experimental geomagnetic thresholds is higher than such a correlation between this parameter and theoretical thresholds by a factor 2–3, which suggests that a real dawn-dusk asymmetry during this storm was stronger than such an asymmetry represented by the Ts03 model.