A.V. Suvorova

Algebra and statistics of the solar wind

Statistical studies of properties of the solar wind and interplanetary magnetic field, based on an extended database for the period 1963–2007 including four solar cycles, show that the Gaussian approximation well suites for some parameters as the probability distribution of their numerical values, while for others the lognormal law is preferred. This paper gives an interpretation of these results as associated with predominance of linear or nonlinear processes in composition and interaction of various disturbances and irregularities propagating and originating in the interior of the Sun and its atmosphere, including the solar corona and the solar wind running away from it. Summation of independent random components of disturbances leads, according to the central limit theorem of the probability theory, to the normal (Gaussian) distributions of quantities proper, while their multiplication leads to the normal distributions of logarithms. Thus, one can discuss the algebra of events and associate observed statistical distinctions with one or another process of formation of irregularities in the solar wind. Among them there are impossible events (having null probability) and reliable events (occurring with 100% probability). For better understanding of the relationship between algebra and statistics of events in the solar wind further investigations are necessary.

Expected hysteresis of the 23-rd solar cycle in the heliosphere

Abstract Solar wind and interplanetary magnetic field parameters are investigated using the data obtained at the Earths orbit for the 20–23 solar cycles. The time-epoch analysis and hysteresis curves of the heliospheric parameters show some general and specific properties of the cycles. We have found specific hysteresis behaviour when the solar wind energy flow and the induced electric field are plotted against the sunspot number during 20–22 solar cycles. Based on these finding and using measured heliospheric parameters during the rising phase of the current 23-rd solar cycle we are able to present some semi-quantitative estimations of the expected solar wind energy flux and the induced electric field for the time period after the solar maximum. The similarity between the rising phases of the 23-rd and 20-th solar cycles presents additional grounds for expectations of the lower maximum of the current solar cycle and the geomagnetic activity in the present solar cycle as compared with the 21-st and 22-nd solar cycles.

Solar Wind Variation with the Cycle

The cyclic evolution of the heliospheric plasma parameters is related to the time-dependent boundary conditions in the solar corona. “Minimal” coronal configurations correspond to the regular appearance of the tenuous, but hot and fast plasma streams from the large polar coronal holes. The denser, but cooler and slower solar wind is adjacent to coronal streamers. Irregular dynamic manifestations are present in the corona and the solar wind everywhere and always. They follow the solar activity cycle rather well. Because of this, the direct and indirect solar wind measurements demonstrate clear variations in space and time according to the minimal, intermediate and maximal conditions of the cycles. The average solar wind density, velocity and temperature measured at the Earth’s orbit show specific decadal variations and trends, which are of the order of the first tens per cent during the last three solar cycles. Statistical, spectral and correlation characteristics of the solar wind are reviewed with the emphasis on the cycles.

Artificial neural network model of the dayside magnetopause: Physical consequences

Abstract Empirical model of the dayside magnetopause developed by means of Artificial Neural Network (ANN) package ‘NeuroShell 2` is discussed. ANN model describes 3D shape of the magnetopause as a function of four external parameters: solar wind velocity, density, By and B z components of interplanetary magnetic field. The model shows that the magnetopause shape has the dawn-dusk asymmetry under any solar wind conditions independently on the By direction. The cusp region is modeled. Using ANN model an expression for sebsolar point distance is obtained in terms of modified logistic functions. The magnetopause dynamics is interpreted as a transition between two regimes of the magnetopause formation that is controlled by B z component of interplanetary magnetic field.

Global impulse burst of geomagnetic pulsations in the frequency range of 0.2-5 Hz as a precursor of the sudden commencement of St. Patrick's Day 2015 geomagnetic storm

We have analyzed a short-term (3–4 s) burst of geomagnetic pulsations in the frequency range of 0.2–5 Hz observed during the commencement of a magnetic storm on March 17, 2015. The burst was observed by a network of observatories in different sectors of local time and at different latitudes. The spectra of pulsations involves a resonant structure with a global maximum at a frequency of 2.78 ± 0.38 Hz, despite some differences at different observatories. There is a delay by almost 4 s in the maximum of the train amplitude at nightside observatories with respect to a dayside observatory. The burst of pulsations has been shown to be on the front of the magnetic disturbance associated with sudden storm commencement (SSC) and, therefore, can be considered as a precursor. The observations of particle fluxes by low-orbit satellites have shown that the SSC is accompanied by a dramatic increase in the fluxes of precipitating protons and electrons. We have suggested that the mechanism of oscillation generation may be the ion–cyclotron instability of ring current protons and the resonant structure of pulsations may be associated with the ionospheric Alfvén resonator.

Solar Wind Data Analysis Using Self-Organizing Hierarchical Neural Network Classifiers

Recently, we have proposed an algorithm for construction of a hierarchy of neural network classifiers based on a modification of error backpropagation. It combines supervised learning with self-organization. Recursive use of the algorithm results in creation of compact and computationally effective self-organized structures of neural classifiers. The algorithm is applicable for unsupervised analysis of both static objects and dynamic objects, described by time series. In the latter case, the algorithm performs segmentation of the analyzed time-series into parts characterized by different types of dynamics. The algorithm has been successfully tested on pseudo-chaotic maps. In this paper the above algorithm is applied to Solar wind data analysis. Preliminary results indicate that new structural classes in the Solar wind could be distinguished aside from the traditional two- and three-state concepts.

Solar wind and interplanetary magnetic field parameters at the Earth's orbit during three solar cycles

Abstract Time series of the solar wind and interplanetary magnetic field parameters, as well as solar and geomagnetic indexes were compared during different phases of the 20, 21 and 22-d solar cycles. General trends and solar cycle variations are evaluated and compared with published results. Points of correspondence and differences are noticed. New features in the density and the temperature are found. Possible interpretations are suggested using the concepts of the magnetically open, closed and intermittent types of the solar wind sources. We conclude that the observed variations at the Earths orbit are related to the space-time evolution of the mentioned sources on the Sun and their different proportions during different solar cycle phases. Magnetic fields of the Sun and the heliospheric current sheet play the mediating role.

Coronal imprints in the heliospheric plasma and magnetic fields at the Earth’s orbit during the last three solar minima

Abstract The periods 1975–1977, 1985–1987 and 1995–1997 were selected between pivot points of the solar cycles to analyze available spacecraft data for three successive solar minima. The mean values of the solar wind velocity, dynamic pressure, and temperature are decreasing during each indicated time interval. All variations are of several 0.1. The interplanetary magnetic field is minimal at solar minima. There is no strong difference between solar wind and interplanetary magnetic field parameters as well as solar activity indices for these solar cycles. Nevertheless, the proton cosmic ray intensities and spectra during these especially quiet periods possibly show the remarkable 22-year variation with the minimal proton fluxes in 1985–1987.