A.V. Dmitriev

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.

Magnetic storms in October 2003

Preliminary results of an analysis of satellite and ground-based measurements during extremely strong magnetic storms at the end of October 2003 are presented, including some numerical modeling. The geosynchronous satellites Ekspress-A2and Ekspress-A3, and the low-altitude polar satellites Coronas-F and Meteor-3M carried out measurements of charged particles (electrons, protons, and ions) of solar and magnetospheric origin in a wide energy range. Disturbances of the geomagnetic field caused by extremely high activity on the Sun were studied at more than twenty magnetic stations from Lovozero (Murmansk region) to Tixie (Sakha-Yakutia). Unique data on the dynamics of the ionosphere, riometric absorption, geomagnetic pulsations, and aurora observations at mid-latitudes are obtained.

Dayside magnetopause models

Abstract A review of empirical data-based models of the magnetopause and a comparative analysis are given with special attention to the dynamics of the dayside boundary. Recently different research groups have presented new magnetopause models as an alternative to the model of Roelof and Sibeck (1993, J. Geophys. Res. 94, 15, 125). All models have a greater parametric extent than the model of Roelof and Sibeck and allow prediction of the magnetopause location during extreme solar wind and IMF conditions. The models of Shue et al. (1997, J. Geophys. Res. 102, 9497–9511) and Kuznetsov et al. (1998) , developed using classic multi-factor regression analysis are two-dimensional and bivariate. The model of Dmitriev et al. (1999) created using artificial neural networks (ANNs) is three-dimensional and contains multiple parameters. A statistical study of Kuznetsov et al. confirmed by the ANN modeling of Dmitriev et al. has shown that the shape of dayside magnetopause has dawn–dusk asymmetry. The uncertainty in the determination of the dayside magnetopause position is practically the same for these models in spite of some discrepancies of the model results caused by different data sets, different assumptions and functional forms, different treatment methods of the models.

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.

UV Radiation from the Night-Time Atmosphere seen from the “Universitetsky-Tatiana” Satellite

Detectors on the “Universitetsky‐Tatiana” satellite measured a smoothly varying intensity of UV radiation from the night‐time atmosphere in the nadir direction and the intensity of the energetic electron flux at the orbit. At high latitudes the UV intensity in the auroral oval is interpreted as being due to electrons penetrating into the atmosphere. At middle latitudes the UV intensity is an order of magnitude less and more data are needed to reveal the origin of this radiation. Millisecond flashes of UV radiation were observed. The flashes’ energy, temporal profile and global distribution are similar to these parameters for Transient Luminous Events (TLEs). These studies will be continued aboard the next satellite “Tatiana‐2”.

Solar Wind Disturbances and Their Sources in the EUV Solar Corona

We investigate possible links between the activity manifestations in the solar corona and conditions in the solar wind. For the reduction of this immense task we have selected 206 events in the solar wind in 1997 – 2000 corresponding to geomagnetic events with Ap > 20 (compiled into a database at http://alpha.sinp.msu.ru/apev). Up to now, 24 events during the epoch of low solar activity (January 1997 – January 1998) are investigated. The solar wind conditions monitored by ACE and WIND spacecraft were traced back to the solar corona observed by SOHO/EIT. The search for coronal signatures which are probably associated with the disturbed solar wind conditions was performed. The coronal sources of these 24 events are identified, namely: eruptions in active regions, filament eruptions and coronal holes. It is shown that halo and partial halo CMEs observed within the SOHO/LASCO sensitivity limits are not necessary indicators of Earth‐directed eruptions, and coronal EUV dimmings can be used as a complementary in...

Solar and Heliospheric Causes of Geomagnetic Perturbations during the Growth Phase of Solar Cycle 23

A database is compiled for the study of solar and heliospheric causes of geomagnetic perturbations with the daily average index Aр > 20 that were observed in the period 1997–2000. The number of such events (more than 200) progressively increased and fluctuated as the current solar cycle developed. It is established that geomagnetic storms are generated by dynamical processes and structures near the center of the solar disk in a zone of several tens of degrees, and these processes are responsible for the appearance in the Earths region, within several tens of hours, of quasistationary and transient solar wind streams with a sufficiently strong southward component of the heliospheric magnetic field. These streams lasted more than a few hours. The following structures can serve as morphological indicators for the prediction of the appearance of such streams: (1) active and disappearing filaments derived from synoptic Нα-maps of the Sun, (2) solar flares, (3) coronal holes and evolving active regions, and (4) the heliospheric current sheet. The geometry of coronal mass ejections needs further observational study.

The role of solar wind pressure jumps in the initiation and control processes of magnetospheric substorms

By the example of commencement and development of two successive substorms on August 1, 1998, the mechanism resulting in the initiation of auroral processes (substorms) is discussed. These events were chosen due to the favorable position of satellites in the solar wind, magnetosphere, and plasma sheet, as well as due to the availability of satellite and ground-based observation data.The isolated spontaneous substorm was caused by the accumulation of excess energy in the magnetic tail and by energetic electron injection from the plasma sheet. Thirty minutes after the end of the spontaneous substorm, solar wind pressure jumps against the background of the strong induced dawn-dusk electric field resulted in significant variations with a high degree of correlation between the magnetic field and energetic particle fluxes at geosynchronous orbit and ground-based stations, and caused new auroral activations. The second substorm occurred as an abrupt intensification of auroral electrojets in the premidnight sector and four successive activations of auroras observed by the Polar satellite. As assumed from analysis of the development of geophysical phenomena caused by variations in the solar wind pressure, this event was characterized by the mechanism of direct energy transmission from the solar wind into the auroral zone through two channels simultaneously: the induced electric field and compressive intensification of magnetospheric currents.From analysis of the development of two substorms caused by different mechanisms, such as reconnection in the first case and direct energy transmission in the second, it can be assumed that both mechanisms can result in the same substorm phenomena.The statistical analysis with the use of the method of superimposed epochs includes additional arguments in favour of formulated suggestions.