Boris Yu. Yushkov

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.

Acceleration of Relativistic Protons During the 20 January 2005 Flare and CME

The origin of relativistic solar protons during large flare/CME events has not been uniquely identified so far. We perform a detailed comparative analysis of the time profiles of relativistic protons detected by the worldwide network of neutron monitors at Earth with electromagnetic signatures of particle acceleration in the solar corona during the large particle event of 20 January 2005. The intensity – time profile of the relativistic protons derived from the neutron monitor data indicates two successive peaks. We show that microwave, hard X-ray, and γ-ray emissions display several episodes of particle acceleration within the impulsive flare phase. The first relativistic protons detected at Earth are accelerated together with relativistic electrons and with protons that produce pion-decay γ rays during the second episode. The second peak in the relativistic proton profile at Earth is accompanied by new signatures of particle acceleration in the corona within ≈1R⊙ above the photosphere, revealed by hard X-ray and microwave emissions of low intensity and by the renewed radio emission of electron beams and of a coronal shock wave. We discuss the observations in terms of different scenarios of particle acceleration in the corona.

On the Onset Time of Several SPE/GLE Events: Indications from High-Energy Gamma-Ray and Neutron Measurements by CORONAS-F

We analyzed the high-energy gamma and neutron emissions observed by the SONG instrument onboard the CORONAS-F satellite during August 25, 2001, October 28, 2003, November 4, 2003, and January 20, 2005 solar flares. These flares produced neutrons and/or protons recorded near Earth. The SONG response was consistent with detection of the pion-decay gamma emission and neutrons in these events. We supposed that a time profile of the soft X-ray derivative was a good proxy of time behavior of the flare energy release. Then we showed that time intervals of the maximum both of energy release and pion-decay-emission coincided well. We determined the onset time of GLEs 65, 69 on the basis of neutron monitor data using the superposed epoch method. The time of high-energy proton onset on November 4, 2003 was found from the GOES data. The time delay between the high-energy gamma ray observation and the high-energy protons onset time was <5 minutes. This time lag corresponds to the least possible proton propagation time. So, we conclude that in these events both protons interacted in the solar atmosphere and the first protons which arrived to Earth, belonged to one and the same population of the accelerated particles.

Determination of Acceleration Time of Protons Responsible for the GLE Onset

Appearance in the solar atmosphere of high-energy protons during major solar flares can be identified from the observation of a broad gamma-ray line in the 70-100 MeV range of the flare emission spectrum. This emission line results from the decay of neutral pions, which, in turn, are produced in interactions of high-energy (> 300 MeV) protons with dense layers of the solar atmosphere. We considered 12 events with clear observations of the pion-decay gamma emission and compared the light curves of this emission with time profiles of different emissions. In 9 events out of 12 we found the onset and peak times of high-energy gamma-rays to be close to the peak times of other electromagnetic emissions and the derivative of the soft X-ray emission. This closeness indicates that efficient acceleration of protons up to sub-relativistic energies starts typically close to the time of the main flare energy release. The further study dealt with the data recorded since 1972 by the world neutron monitor network related to 44 Ground level enhancements (GLEs) and light curves of neutral emissions of the associated flares. The study revealed that a delay of the earliest arrival time of high-energy protons at 1 AU with respect to the observed peak time of the solar bursts did not exceed 10 min in 30 events. This result indicates that in the majority of events, efficient acceleration of protons responsible for the GLE onset should be close to the time of the main energy release in flares.

Near-Earth Radiation Environment for Extreme Solar and Geomagnetic Conditions

Abstract The near-Earth environment can be considered a unique place where different space radiation fields exist and can play a significant role in the estimation of radiation risks both for robotic and manned space missions. One cannot exclude the cumulative effect for particular spacecraft orbits the result of simultaneous impact of the different radiation fields. Among the types of space radiation, we consider: trapped radiation at low Earth orbits (LEO): solar energetic particles (SEP) penetration in the magnetosphere, including ground level enhancement events (GLE); and variations of galactic cosmic rays (GCR) during the different extreme levels of geomagnetic and solar activity. Results of empirical modeling of these different radiation fields and some results of measurements of their physical parameters (energy spectra, space and time variations) for different solar (extreme solar maxima and solar minima) and geomagnetic (the major magnetic storms) conditions are analyzed. The models are based on quantitative relationships between the particle fluxes, taking into account the solar activity (sunspot numbers). Examples of using these models to estimate changes of radiation hazards in interplanetary space for the possible case of solar activity reduction during the nearest solar cycles 25 and 26 are analyzed.

Dynamics of the Earth's Radiation Belts During the Time Period April 14‐24, 2002 – Experimental Data

We analysed the variations of radiation belt electrons observed during 14-24 April 2002 obtained on board CORONAS-F satellite (polar orbit at altitude of ∼500 km). Measurements of April 14 and 16 correspond to the quiet state of the radiation belts before a magnetic storm. The first storm connected with the M1/CME which occurred April 15 was observed near noon of the following day, next magnetic storm, connected with M2/CME which took place April 17, occurred April 19. As consequence the short time interval between both events strong changes have been observed in the Earths radiation belt. Significant decrease of electron fluxes in wide energy range was observed in the outer radiation belt April 17 and early morning April 18. During April 18 and 19 the electron flux intensity increased in the outer radiation belt and the location of the peak flux shifted from 4.5 to 3.2 in the nightside and from 5 to 3.5 in the dayside. The next increase of electron flux was observed after the next magnetic storm during April 19-20 both in the inner and outer radiation belts.