arXiv subjects

B. Kirov

Publications and source records attributed to B. Kirov.

7 recordsLinked to original sources

arXiv2017

The ratio between the number of sunspot and the number of sunspot groups

Data from three solar observatories, Learmonth, Holloman, and San Vito, are used to study the variations in the average number of sunspots per sunspot group. It is found that the different types of sunspot groups and the number of sunspots in these groups have different solar cycle and cycle to cycle variations. The varying ratio between the average number of sunspots and the number of sunspot groups is shown to be a real feature and not a result of changing observational instruments, observers experience, calculation schemes, etc., and is a result of variations in the solar magnetic fields. Therefore, the attempts to minimize the discrepancies between the sunspot number and sunspot group series are not justified, and lead to the loss of important information about the variability of the solar dynamo.

astro-ph.SR↗

arXiv2016

Temporal Offsets between Maximum CME Speed Index and Solar, Geomagnetic, and Interplanetary Indicators during Solar Cycle 23 and the Ascending Phase of Cycle 24

On the basis of morphological analysis of yearly values of the maximum CME (coronal mass ejection) speed index, the sunspot number and total sunspot area, sunspot magnetic field, and solar flare index, the solar wind speed and interplanetary magnetic field strength, and the geomagnetic Ap and Dst indices, we point out the particularities of solar and geomagnetic activity during the last cycle 23, the long minimum which followed it and the ascending branch of cycle 24. We also analyze temporal offset between the maximum CME speed index and the above-mentioned solar, geomagnetic, and interplanetary indices. It is found that this solar activity index, analyzed jointly with other solar activity, interplanetary parameters, and geomagnetic activity indices, shows a hysteresis phenomenon. It is observed that these parameters follow different paths for the ascending and the descending phases of solar cycle 23. It is noticed that the hysteresis phenomenon represents a clue in the search for physical processes responsible for linking the solar activity to the near-Earth and geomagnetic responses.

astro-ph.SR↗

arXiv2013

Long-term variations of solar magnetic fields derived from geomagnetic data

Sunspots are dark spots on the solar surface associated with strong magnetic fields. The number, area, and brightness of sunspots are supposed to reflect the intensity of the solar magnetic fields and are often used as proxies for their long-term variations. However, the correlations between the sunspot parameters and solar magnetic fields are not constant, and the causes and the time profiles of the variations in these correlations are not quite clear. Therefore, the sunspot data alone cannot be used as proxy for deriving the variations of the sunspot magnetic fields for periods when no instrumental measurements are available. But the Earth is a sort of a probe reacting to interplanetary disturbances which are manifestation of the solar magnetic fields, so records of the geomagnetic activity can be used as diagnostic tools for reconstructing past solar magnetic fields evolution. In the present study we combine sunspot and geomagnetic data to estimate the long-term variations of sunspot magnetic fields.

astro-ph.SR↗

arXiv2013

Long-term variations of geomagnetic activity and their solar sources

Geomagnetic activity in each phase of the solar cycle consists of 3 parts: (1) a floor below which the geomagnetic activity cannot fall even in the absence of sunspots, related to moderate graduate commencement storms; (2) sunspot-related activity due to sudden commencement storms caused by coronal mass ejections; (3) graduate commencement storms due to high speed solar wind from solar coronal holes. We find that the changes in the floor depend on the global magnetic moment of the Sun, and on the other side, from the height of the floor we can judge about the amplitude of the sunspot cycle.

astro-ph.EP↗

arXiv2007

Long-term variations in solar meridional circulation from geomagnetic data: implications for solar dynamo theory

Geomagnetic activity has two main peaks in the 11-year sunspot cycle caused by two types of solar agents: coronal mass ejections and high speed solar wind streams, whose variations in number and intensity are related to the variations in solar toroidal and poloidal fields, respectively. From the long-term variations in the lag between the two aa-index peaks we derive the long-term variations in solar meridional circulation. We use these relations to test the flux-transport solar dynamo theory and to explain some well known characteristics of the solar cycle. Based on these relations, we give a prediction for the amplitude (125) and epoch of the maximum (April 2011) of sunspot cycle 24.

physics.space-ph↗

arXiv2005

Solar differential rotation and properties of magnetic clouds

The most geoeffective solar drivers are magnetic clouds - a subclass of coronal mass ejections (CME's) distinguished by the smooth rotation of the magnetic field inside the structure. The portion of CME's that are magnetic clouds is maximum at sunspot minimum and mimimum at sunspot maximum. This portion is determined by the amount of helicity carried away by CME's which in turn depends on the amount of helicity transferred from the solar interior to the surface, and on the surface differential rotation. The latter can increase or reduce, or even reverse the twist of emerging magnetic flux tubes, thus increasing or reducing the helicity in the corona, or leading to the violation of the hemispheric helicity rule, respectively. We investigate the CME's associated with the major geomagnetic storms in the last solar cycle whose solar sources have been identified, and find that in 10 out of 12 cases of violation of the hemispheric helicity rule or of highly geoeffective CME's with no magnetic field rotation, they originate from regions with "anti-solar" type of surface differential rotation.

astro-ph↗

arXiv2005

Secular cycle of the north-south solar asymmetry

The North-South asymmetry of solar activity has been recognized for different solar phenomena. Following Waldmeier, it is now assumed that solar activity dominates in the Northern solar hemisphere during the ascending part of the secular solar cycle, in the Southern one during the descending part, and in epochs of secular minima and maxima the asymmetry is small. The episodes when this rule does not hold (the Maunder minimum in the end of the 17th century, and 19th and 20th solar cycles in the 20th century secular maximum) are considered as "anomalies". Analyzing solar activity influence on climate, we come to the conclusion that the asymmetry differs not in the ascending and descending parts of the secular solar cycles, but in consecutive secular cycles. This hypothesis is in agreement with all available data and leaves no anomalies.

physics.space-ph↗