V. A. Slemzin

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.

Long-lived hot coronal structures observed with CORONAS-F/SPIRIT in the Mg XII line

Large-scale hot features were detected and observed several times high in the solar corona in the high-temperature Mg XII line (T = 5–20 MK, Tmax = 10 MK) with the soft X-ray telescope of the SPIRIT instrumentation complex onboard the CORONAS-F spacecraft. These features look like a spider up to 300000 km in size and live up to a few days. Their bright cores observed at heights were from 0.1 to 0.3 solar radii are connected with active regions by darker legs, giant loops. These features are disposed above arcades, which are simultaneously observed in cooler emission lines sensitive to temperatures of 1 to 2 MK. For the core of such a feature observed December 28–29, 2001, Zhitnik et al. (2003a) estimated an electron temperature of 10 MK and a number density of ne ≈ 1010 cm−3. A high activity and an association with eruptive phenomena were found for such features in continuous (up to 20-day) observations with a cadence of 0.6–1.7 min. In the present paper, we discuss the relation of such features to coronal structures, which are known from previous studies. We identify such off-limb features observed with SPIRIT on October 22, November 12, and December 28–29, 2001, with hot upper parts of post-eruptive arcades. The results of multifrequency analysis of these features based on the data obtained in various spectral ranges by different instruments (Yohkoh/SXT, SOHO/EIT, SOHO/LASCO, Nobeyama and SSRT radioheliographs) are briefly discussed. We address the physical conditions of the long-term existence of giant hot coronal structures. It is demonstrated that the post-eruptive energy release must be prolonged and the condition β ≪ 1 is not satisfied in these structures. It is argued that the so-called “standard flare model” should be better considered as a “standard post-eruptive energy release model.”

Effects of the Absorption of Solar XUV Radiation by the Earth's Upper Atmosphere at Altitudes of 100–500 km in the X-ray Solar Images Obtained Onboard the Coronas-I (TEREK Telescope) and Coronas-F (SPIRIT X-ray Complex) Satellites

We consider the effects of the absorption of solar XUV radiation by the Earths atmosphere that were observed in the solar images obtained with the TEREK-K telescope onboard the Coronas-I satellite in May–June 1994 at low solar activity and with the SPIRIT instrumentation onboard the Coronas-F satellite in October–November 2001 at maximum solar activity. The solar images were recorded during the satellite occultation: in the 175- and 304-A spectral ranges onboard Coronas-I with the TEREK-K telescope and in the 175-, 304-, and 8.42-A ranges onboard Coronas-F with the SPIRIT instrumentation. Based on the XUV solar images obtained during atmospheric sounding, apart from the total absorption, we can determine the direction of the atmospheric density gradient and study the local absorption variations with altitude on spatial scales of less than 1 km. The described method can significantly supplement the data obtained in studies of the upper atmosphere by the methods of mass spectrometry, incoherent radar scattering, and the drag of orbital spacecraft.

Possible causes of the discrepancy between the predicted and observed parameters of high-speed solar wind streams

We have considered the possible causes of discrepancies between the predicted and observed at 1 AU parameters of the recurrent solar wind (SW) streams in the maximum of the 24th solar cycle. These discrepancies have been observed in both the SW velocity profile and the SW stream arrival time, as well as in the absence of the expected high-speed SW stream. The degree of discrepancy depends on the model used for the SW prediction; however, in some cases, different prediction methods provide a similar discrepancy with the observed SW parameters at 1 AU. For several cases, we show that the probable cause of the discrepancies can be a deflection of the high-speed SW stream from the radial direction due to the interaction with the transient SW streams at certain configuration of the magnetic fields of high-speed and transient SW sources in the solar corona.

The effect of solar activity on the evolution of solar wind parameters during the rise of the 24th cycle

The dynamics of parameters of the near-Earth solar wind (SW) and the effect of solar activity on the parameters of three SW components (fast SW from large-scale coronal holes (CHs); slow SW from active regions, streamers, and other sources; and transient flows related to sporadic solar activity) at the beginning of the 24th solar cycle (2009–2011) are analyzed. It is demonstrated that temperaturedependent parameters of ionic composition (C+6/C+5 and O+7/O+6) of the transient SW component in the profound minimum of solar activity in 2009 were correlated with the variation of the rate of weak (type C and weaker) flares. This verifies the presence of a hot component associated with these flares in the SW. The variations in the velocity and the kinetic temperature of fast SW from CHs with an increase in activity are more pronounced in the bulk of the high-speed stream, and the variations of O+7/O+6 and Fe/O ratios and the magnitude of the interplanetary magnetic field are the most prominent in the region of interaction between fast and slow SW streams. The analysis reveals that a value of O+7/O+6 = 0.1 serves as the criterion to distinguish between fast SW streams and interplanetary coronal mass ejections in the 2009 activity minimum. This value is lower than the one (0.145) determined earlier based on the data on the 23rd cycle (Zhao et al., 2009). Therefore, the distinguishing criterion is not an absolute one and depends on the solar activity level.

The TESIS Solar imaging spectroscopy experiment on board the CORONAS-Photon satellite

The CORONAS-Photon spacecraft was successfully launched in January 2009. Its scientific payload included the TESIS complex of telescopes and spectrometers, designed to obtain high spectral, temporal and spatial resolution solar corona images in soft X-ray to far UV spectral range.

Identification of coronal sources of the solar wind from solar images in the EUV spectral range

Methods of localizing coronal sources of the solar wind (SW), such as coronal holes, quasi-stationary fluxes from active regions, and transient sources associated with small-scale active phenomena are considered based on vacuum-ultraviolet (EUV) images of the corona at low solar activity during the initial period of the 24th solar cycle (2010). It is shown that a SW velocity profile can be calculated from the relative areas of coronal holes (CH) at the central part of the disk based on the images in the ranges of 193 and 171 Å. The images in the 193 Å describe the geometry of large HCs that represent sources of fast SW well. The images in 171 Å are a better visualization of small CHs, based on which the profile of a slow SW component was calculated to a high accuracy (up to 65 km/s). According to Hinode/EIS data of October 15, 2010, using the Doppler spectroscopy method at the streamer base over the active region 11112, the source of the outgoing plasma flux with the mean velocity of 17 km/s was localized in the magnetic field region with an intensity of less than 200 Gauss. According to the estimate, the density of the plasma flux from this source is an order of magnitude greater than the value required for explaining the distinction between the calculated and measured profiles of a slow SW velocity. For finding the transient SW component based on small-scale flare activity, SW parameters were analyzed for the periods of flares accompanied by coronal mass ejections (CMEs), and for the periods without flares, according to the data obtained in 2010 from the ACE and GOES satellites and by coronagraphs on the STEREO-A and -B spacecraft. The ion ratios C+6/C+5 and O+7/O+6 and the mean charge of Fe ions for periods with flares were shown to be shifted toward large values, suggesting the presence of a hot SW component associated with flare activity. A noticeable correlation between the maximum charge of Fe ions and the peak power of a flare, previously observed for flares of a higher class, was confirmed. The mean value of the SW flux density during the periods of flares was 30% higher than that in the periods without flares, which is possibly associated also with the growth of fluxes from other sources with an increasing solar activity level. Based on the example of a series of flares of October 13–14, 2010, it was supposed that transient SW fluxes from the weak flares at low solar activity can manifest themselves in the form of interplanetary ICME-transients.

On the processing and analysis of the data of the CORONAS-F/SPIRIT and other solar experiments

More than 300000 solar images in the extreme ultraviolet and soft X-ray regions were obtained using two telescopes and four spectroheliometers of the CORONAS-F/SPIRIT device from August 2001 to December 2005. Methods for the processing of such data and extracting physical information are presented, taking into account the experience of processing and analysis of other space experiments on solar research. Some results on applications of the considered methods are presented.

Interaction of high-speed and transient fluxes of solar wind at the maximum of solar cycle 24

The interaction of the interplanetary coronal mass ejection (ICME) and the high-speed solar wind flux (HSSWF) associated with the coronal hole (CH) is considered. By the examples of two events at the maximum of solar cycle 24 from June 4 to June 16 and from June 30 to July 10, 2012 it is shown that the temperature-dependent parameters of the SW ionic composition appear closer to the values in the HSSWF than in the ICME due to mixing of fluxes in the corona when the ICME source is near the CH boundary.

Processing of data from the instrumentation system of the SPIRIT telescope-spectroheliograph

The scientific purpose of the SPIRIT experiment is to study the space-time structures of phenomena of the solar activity using a set of X-ray instruments aboard the Koronas-F satellite. The system consists of the SRT-C six-channel telescope and the RES-C four-channel spectroheliometer for 8.4- to 335-Å wavelengths and the SPR-N five-range polarimeter for 20- to 100-keV energies. For a 3.5-yr flight (since July, 2001 to January, 2005), over 40000 observation sessions were conducted and over 1 million spectral pictures were obtained during the SPIRIT experiment. The volume of electronic archive of the experiment reached 220 Gbyte. The software package was developed for prompt control of the scientific system and used in the semiautomatic mode to form the sequence diagrams of energizing, create control files (CFs) via the dialog line, and schedule CF delivery. The software package is based both on the electronic table in the Excel-2000 format, which displays the basic procedures and control events, and on the database in the Access-2000 format, which is automatically filled with the information on all created CFs. For archiving, viewing, and selecting scientific data of the experiment, a graphic database in the Access-2000 format was created. The software for automatic filling of the database and a graphic interface for prompt viewing of the database and retrieval of pictures based on some parameters were designed. An automatic augmentable ballistic database containing basic parameters of the satellite orbit over the full flight period was created.