L. K. Kashapova

Forecasting the Velocity of Quasi-Stationary Solar Wind and the Intensity of Geomagnetic Disturbances Produced by It

A brief review is given of contemporary approaches to solving the problem of medium-term forecast of the velocity of quasi-stationary solar wind (SW) and of the intensity of geomagnetic disturbances caused by it. At the present time, two promising models of calculating the velocity of quasi-stationary SW at the Earth’s orbit are realized. One model is the semi-empirical model of Wang-Sheeley-Arge (WSA) which allows one to calculate the dependence V(t) of SW velocity at the Earth’s orbit using measured values of the photospheric magnetic field. This model is based on calculation of the local divergence fS of magnetic field lines. The second model is semi-empirical model by Eselevich-Fainshtein-Rudenko (EFR). It is based on calculation in a potential approximation of the area of foot points on the solar surface of open magnetic tubes (sources of fast quasistationary SW). The new Bd-technology is used in these calculations, allowing one to calculate instantaneous distributions of the magnetic field above the entire visible surface of the Sun. Using predicted V(t) profiles, one can in EFR model calculate also the intensity of geomagnetic disturbances caused by quasi-stationary SW. This intensity is expressed through the Kp index. In this paper the EFR model is discussed in detail. Some examples of epignosis and real forecast of V(t) and Kp(t) are discussed. A comparison of the results of applying these two models for the SW velocity forecasting is presented.

Culmination of the flare activity of Group 10786 in July 2005: X-Ray observations from near-mars and near-earth orbits

A detailed study of two major solar flares that occurred in Group 10786 at the time of its disappearance behind the western limb is presented. The flares of July 14, 2005 were previously studied fairly poorly, as no RHESSI hard X-ray observations were available for themaxima of the twomost powerful of these flares. Observations carried out using the HEND equipment (on the Mars Odyssey spacecraft) developed at the Institute for Space Research in Moscow are used here to fill this gap. In the first flare, an intense, impulsive burst occurred at 07:23 UT, about 1.5 h after the onset of a weak, prolonged event. While processes in the neighborhood of the northern spot dominated in the flares of July 5–9, a powerful impulsive energy release on July 14 emerged when the flare process that originated in the North reached the southern spot. Our analysis of the flare activity of this medium-sized group reveals a gradual enhancement of the flare activity and a strong interaction between the acceleration above the magnetic-field neutral line and in the immediate vicinity of the spots. At the time of the culmination of the flare activity in the group on July 13 and 14, the pattern of nonstationary processes changes: fast coronal mass ejections form after a series of impulsive energy-release events. Spacecraft observations of the burst of July 14 after 11 UT at points separated in longitude (on RHESSI and Mars Odyssey) revealed clear anisotropy of the flare emission at energies exceeding 80 keV.

Eruptive processes at the beginning of development of powerful flare-active regions on the sun

The evolution of large solar activity centers is studied, and the conditions resulting in powerful nonstationary processes are clarified. In addition to the factors that are usually considered (changes in sunspot area, the structure of magnetic fields, the character of motions), we examine to what extent observations of nonstationary processes (flares and associated coronal mass ejections) can be used to predict the development of such processes in the subsequent evolution of the activity center. We considered the example of a powerful group in October 2003, which could be observed before its appearance at the eastern limb using a spacecraft in near-Mars orbit. We plotted for events occurring in 2003 images of flares in various spectral ranges and analyzed high-energy processes in group 486, which was isolated at the beginning of its development, and then in the interrelated groups 486 and 484. The analysis of the peculiar early development of group 486 suggested that an intensification of the activity could be expected due to the emergence of new magnetic flux (and satellite groups), as well as the interaction and synchronization of two and then three large groups of the end of October 2003. In other words, in this case, extremely powerful nonstationary processes are associated with a relatively higher contribution of large-scale magnetic fields. We compare our results to analyses of motions and magnetic fields in this activity center throughout its transit across the disk from October 23 to November 5, 2003.

Properties of the magnetic fields of coronal holes with active regions

AbstractWe determine the structure of the magnetic fields of coronal holes (CHs) and investigate its change in connection with the emergence of active regions (ARs) in CHs. Based on our observations in the HeI 1083 nm line performed with the CrAO TST-2 telescope, we have selected CHs of two types: without (15 CHs) and with (28 CHs) ARs. Magnetograms obtained at the Kitt Peak National Solar Observatory have been used to calculate the magnetic fields of the same objects.We have calculated magnetic field characteristics by Rudenko’s method in the potential approximation at several heights in the corona, namely, the average (over the CH area) radial field component 〈Br〉 and its magnitude 〈|Br|/B〉 and the maximum and minimum (over the CH area) values of Br. The distributions of the isolines of these parameters superimposed on the CH images and the field lines of the calculated magnetic field have been constructed with resolutions of 33.4″ and 100.2″ on the solar surface. Analysis of these data has yielded the following results: The field lines originating in CHs without ARs are open or very high loops that are closed outside CHs. The latter occurs in completely or partially closed CHs.The system of open loops is stable, changes little with the birth of ARs, and is completely restored after the disappearance of ARs.ARs emerging inside CHs are bipolar or multipolar magnetic structures. They are formed by closed field lines.The field lines originating in ARs are closed either inside ARs or in the immediate neighborhood of ARs in CHs.There is virtually no connection of ARs inside CHs with external ARs or other places outside CHs.

Coronal mass ejections in July 2005 and an unusual heliospheric event

Using the events in July 2005 as an example, the causes and peculiarities of Forbush effects produced by solar sources remote from the central zone are discussed. The event in question differs from other effects observed at the periphery of interplanetary disturbances by strong variations in cosmic rays on the background of weak disturbances in the solar wind and magnetic field of the Earth. The cloud of magnetized plasma ejected from the Sun was large and fast, but it passed to the west from the Sun-Earth line. According to performed estimates, the mass of the ejected substance was close to the upper boundary of mass for coronal mass ejections (CMEs). Anomalous parameters and high modulation capability of the formed solar wind disturbance are explained, in particular, by the fact that it combined several CMEs and that the last fast disturbance was prepared by a series of impulsive events in the active region of the Sun. Usually, such a great mass is ejected directly after the main energy release in strong solar flares. In the given case, a powerful MHD disturbance occurred approximately half an hour after a maximum of hard X-ray burst under the conditions when gas pressure in the flare loops became close to magnetic pressure, which was just a premise of the largescale ejection.

Observation of the powerful solar flare of October 27, 2002 on the far side of the sun

Observations of the hard X-ray and radio event of October 27, 2002 are analyzed. This flare was observed from near-Martian orbit by the HEND instrument developed at the Space Research Institute of the Russian Academy of Sciences and installed on the Mars Odyssey satellite. Although this powerful flare was observed far over the eastern solar limb, the extended source associated with the flare was detected by RHESSI at energies up to about 60 keV. The eruptive event was observed in the radio at the Nobeyama Radio Observatory. The properties of the X-ray radiation are used to calculate the spectrum of the accelerated electrons responsible for the observed radiation, assuming that the target is thick for a Martian observer and thin for a terrestrial observer. The results are compared with the results of radio observations. The conditions for electron propagation in the corona are discussed.

Physics of post-eruptive solar arcades: Interpretation of RATAN-600 and STEREO spacecraft observations

Results of simultaneous measurements of radiation fluxes from post-eruption arcades on the Sun at 171, 195, 284, and 304 Å (from STEREO spacecraft data) and at radio wavelengths (from the RATAN-600 radio telescope) are presented. An original probabilistic approach developed earlier by Urnov was used to determine the differential emission measure. This method requires no regularization, and the obtained results do not depend on the choice of the temperature grid. This approach has yielded the differential measure of emission at temperatures approximately from 0.3 to 15 MK. The subsequent calculation of thermal magnetobremsstrahlung in a multi-temperature model with the magnetic field decreasing with height produces a spectrum similar to that observed on RATAN-600. Thus, in many non-stationary events with modest powers, a thermal multi-temperature model is quite able to explain the emission of post-eruption arcade systems, and it is not necessary to invoke the emission of accelerated particles. The proposed model enables direct estimation of the ratio of the magnetic and gas pressures at the tops of post-eruption arcades, and determination of the conditions required for the origin of secondary nonstationary processes in the decay stage of the main flare.

Time delays in the nonthermal radiation of solar flares according to observations of the CORONAS-F satellite

In 2001–2003, the X-ray and microwave observations of ten solar flares of M- and X-classes were carried out by the CORONAS-F orbital station, the RSTN Sun service, and Nobeyama radio polarimeters. Based on these observations, a correlation analysis of time profiles of nonthermal radiation was performed. On average, hard X-ray radiation outstrips the microwave radiation in 9 events, i.e., time delays are positive. The appearance of negative delays is associated with effective scattering of accelerated electrons in pitch angles, where the length of the free path of a particle is less than the half-length of a flare loop. The additional indications are obtained in favor of the need to account for the effect of magnetic mirrors on the dynamics of energetic particles in the coronal arches.

Dynamics of the Hard X-ray, Gamma-ray, and Microwave Emission of Solar Flares Produced by the Active Region NOAA 0069 in August 2002

Regularities have been searched for in the dynamics of characteristics of flare solar radiation during the development of the active region NOAA 0069 in the interval of August 14–24, 2002. The SONG (Solar Neutrons and Gamma rays) instrument onboard the Russian CORONAS-F Solar Observatory recorded hard X-ray and gamma-ray radiation in nine of the 30 flares of class above C5 in this active region within the indicated time interval. It was obtained that, in accordance with the development of the active region, the X- and gamma-ray flux tended to increase at the flare maxima while the hard X-ray spectral index tended to decrease; flares with a harder radiation spectrum occurred in the sunspot umbra, i.e., in the region with the strongest magnetic fields.

First results of radio observations of the sun and powerful discrete radio sources using the Irkutsk Radar

Using the Irkutsk Incoherent Scattering Radar, it is demonstrated that the high sensitivity of such radars, which are usually used for studies of the Earth’s ionosphere, also enables their use in a passive mode for observations of astronomical radio sources. Observations of solar flares accompanied by coronal mass ejections and of quasi-stationary radio sources on the Sun have been carried out. In addition, scintillations of several of the brightest discrete radio sources (Cygnus A, Cassiopeia A, and the Crab Nebula) have been studied over several months. These data can also be useful for studies of the ionosphere and interplanetary space.