V. G. Yanke

Solar and Heliospheric Phenomena in October-November 2003: Causes and Effects

We present new observational data on the phenomena of extremely high activity on the Sun and in the heliosphere that took place in October–November 2003. A large variety of solar and heliospheric parameters give evidence that the interval under consideration is unique over the entire observation time. Based on these data, comparing them with similar situations in the past and using available theoretical concepts, we discuss possible cause-and-effect connections between the processes observed. The paper includes the first results and conclusions derived by the collaboration “Solar Extreme Events-2003” organized in Russia for detailed investigations of these events. As a result of our consideration, it is beyond question that the physical causes of solar and heliospheric phenomena in October–November 2003 are not exclusively local and do not belong only to the active regions and solar atmosphere above them. The energy reservoirs and driving forces of these processes have a more global nature. In general, they are hidden from an observer, since ultimately their sources lie in the subphotospheric layers of the Sun, where changes that are fast and difficult to predict can sometimes take place (and indeed they do). Solar flares can serve as sufficiently good tracers of these sudden changes and reconstructions on the Sun, although one can still find other diagnostic indicators among the parameters of magnetic fields, motions of matter, and emission characteristics.

What determines the magnitude of forbush decreases

Abstract Cosmic ray Forbush effects (FEs) have been studied for more than 60 years, but even today this phenomenon has no universally accepted definition, which leads to misunderstanding among researchers. There are no complete and convincing answers to the following questions: What are the distinctive features of FEs? What determines the magnitude of FEs and their variety? How are FEs associated with disturbances of the interplanetary medium, coronal mass ejections and high speed flows of the solar wind? What relation exists between FEs and geomagnetic storms? In order to answer these and other questions a data base of transient effects in cosmic rays and in the interplanetary medium is constructed and is being upgraded continuously. It combines variations in cosmic ray densities and anisotropies obtained from data of the world-wide neutron monitor (NM) network, characteristics of solar wind disturbances, solar and geomagnetic data. This data base presently contains more than 1400 events, observed during 1978–1996. The preliminary analysis allowed us to get the main characteristics of FEs, to determine what distinguishes this phenomenon among other cosmic ray variations, and propose a definition of the Forbush effect. In addition, an interplanetary disturbance parameter was derived, which is most closely associated with the magnitude of a FE. Using this large observational database, a relation between FEs and geomagnetic activity was analyzed statistically as a dependence of the FE magnitude on the maximum Kp-index measured during the associated magnetic storm.

Monitoring and forecasting of great solar proton events using the neutron monitor network in real time

Obtaining online information on the onset of great solar energetic particle (SEP) events from real-time data of the neutron monitor network (NMN) is considered and the corresponding algorithm and program are proposed. Determination of the particle energy spectrum outside the atmosphere at different moments of the flare is considered on the basis of coupling functions method. The spectra defined in diffusion and kinetic approaches are compared. Using this information, the time of the SEP ejection into solar wind, the energy spectrum of a SEP event in the source inside the solar corona, and the SEP diffusion coefficient in the interplanetary space during the flare can be estimated. In this work, the significant possibility of the expected SEP fluxes and the energy spectrum forecasting on the early part of the increasing SEP intensity (about 20-30 min after the onset) is considered. Available satellite data in real-time scale combined with real time-data from neutron monitors (NM) are used for extrapolation of this forecast to the region of very small energy particles. The method is checked on the SEP event of September 1989. It is important to note that the accuracy of the developed method sufficiently increases with the increasing dangerous level of the SEP event. The method is not CPU damaging and can run in real time, providing inexpensive means of SEP prediction.

Ground level enhancements of solar cosmic rays during the last three solar cycles

The catalog of ground level enhancements of solar cosmic rays during cycles 21—23 of solar activity has been presented. The main properties, time distribution, and relation of these events to solar sources and proton enhancements observed on satellites have been studied.

Neutron Monitor Network in Real Time and Space Weather

Relativistic cosmic rays (galactic and solar) registered by neutron monitors at the Earth, bring valuable information on their interaction with interplanetary disturbances. Therefore, they can play a useful role in forecasting space weather storms and in specifying magnetic properties of CME shocks and may be derived from ground level cosmic ray (CR) observations well in advance of the onset of geomagnetic storm. This can be used for forecasting. High energy solar particle events during powerful solar flares are registered at the Earth well before the main development of particle profiles recorded onboard GOES. This provides a good chance of a preventive prognosis of dangerous particle flux by ground level observations. To produce real-time prediction of the phenomena, only real time data from Neutron Monitor Network (NMN) should be employed. The increased number of NM stations operating in real-time gives a good basis for using NMN as a single multidirectional tool and for improving the definition of the onset of GLEs in powerful SPEs and to give an immediate forecast of the arrival of the interplanetary disturbance at the Earth. The properties of the Neutron Monitor Network and its possibilities for Space Weather tasks are discussed in this paper. Different real time Neutron Monitor Network topologies, different synchronization methods and the ways of collecting data in a central data server accessible to the users, are also discussed.

Temperature effect of the muon component and practical questions for considering it in real time

A method for real-time practical consideration of the temperature effect on the cosmic ray muon component using muon telescopes of different geometries is developed. The method is applied to the real-time data of muon detectors. It is shown that the accuracy attainable in such an approach is sufficient for studying all classes of variations.

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.

Efficiency of detection for neutron detectors with different geometries

The response of neutron detectors to the flux of secondary cosmic radiation particles incident on the detectors is simulated mathematically and detection efficiencies are found for neutron detectors of various designs.

Estimation of long-term stability of detectors within the global network of neutron monitors

Results of the continuous ground-based monitoring of the cosmic ray flux by neutron monitors are used as an experimental material for many works devoted to studying cosmic ray variations. Long-term stability of detectors is the problem of an extreme importance. Two independent methods for estimating long-term stability of neutron monitor operation have been proposed. The quantitative estimates have been obtained for 90 detectors that operated and have been operating during more than one solar cycle. The conditions responsible for long-term stability of a detector and the causes of instability have been considered.

Isotropic and anisotropic cosmic ray variations in March–June 1991

Abstract Through March–June 1991 the rigidity spectrum of isotropic variation and three-dimensional anisotropy of cosmic rays (CR) were obtained for each hour by the data of 38 neutron monitors. The maximum variation of 10 GV CR density is >36% with very hard spectrum (index ≈ 0.4). The average vector of CR anisotropy for these four months has a magnitude (≈0.6%) and direction (94°) as typical for cycle 22. Forbush decreases (FDs) in this period are characterised by complicated structure caused by the simultaneous action of numerous transients. Estimations of anisotropy and spatial CR gradients on the recovery phase of Forbush decreases indicate the existance of closed and open structures in the heliomagnetosphere.