Weak solar events

Soft X-ray solar bursts were investigated in the framework of the Interball—Tail Probe project by using an RF-15I-2 X-ray photometer. When studying microflares over the period from September to December 1995, weak bursts with intensities of less than 10^?8 W/m² were detected. All these data are confirmed by observations performed in the framework of the GOES project. The characteristics of solar microflares were determined, and the physical mechanism of weak solar events was considered. The distribution of microflares over their intensities was obtained. It is found that the distribution of solar flares over released energies do not obey a power law, and a lower limit is revealed in this distribution. This result is confirmed by the data obtained in the framework of the RHESSI project. Correlation between the daily average values of the maximum intensities of X-ray bursts of different classes of microflares and the daily average values of the thermal background of the solar corona is revealed.     

Small-Scale Structure of Thermal X-Ray Background of the Solar Corona and Microflares in the Photon Energy Range of 3-16 keV

The small-scale structure of the thermal X-ray background of the solar corona and microflares in the photon energy range from 3 to 16 keV according to the RHESSI data obtained on March–April 2003 is analyzed. The study of the reduction in the X-ray intensity in this spectral range is continued. A reduction and, in some cases, an increase in the X-ray intensity of the thermal background of the solar corona and microflares in narrow subranges of the X-ray spectrum of the quiet Sun are revealed in the photon energy range of 3–11 keV.     

Spectroscopic diagnostics of the solar coronal plasma

The review is addressed to problems of spectroscopic diagnostics of the solar coronal plasma by its radiation in the X-ray and extreme ultraviolet (EUV) bands. Physical conditions in the corona, elementary processes and mechanisms of radiation formation, and methods and results of the temperature and density diagnostics of diverse coronal structures (such as active and quiet solar regions, coronal holes, and the extended corona) are considered. The types and main parameters of instruments for investigation of the corona by its X-ray and EUV emission in space experiments are given.     

Variations in the X-ray Intensity of the Solar Corona and Heating of the Coronal Plasma in the Context of the Quantum Theory of Photon Pairs

Data obtained in the framework of the INTERBALL–Tail Probe (1995–2000) and RHESSI (from 2002 to the present) projects have revealed variations in the X-ray intensity of the solar corona in the photon energy range of 2?15 keV during the period of the quiet Sun. Previously, a hypothesis was proposed that this phenomenon could be associated with the effect of coronal heating. In the present study, a new mechanism of coronal plasma heating is proposed on the basis of the experimental data and the quantum theory of photon pairs that are produced from vacuum in the course of the Universe’s expansion. A similar mechanism based on the splitting of photon pairs in the interplanetary and intergalactic space is also proposed to explain the observed microwave background radiation.     

Dynamics of accelerated ions in coronal loops and model of a gamma-ray source

The dynamics of ions accelerated to energies of 10–100 MeV/nucleon in an electric field of ～0.01–0.1 V/cm, which has a component directed along the magnetic field of solar coronal loops with a characteristic size of ～100000 km, is considered. The motion of fast ions trapped in a current-carrying magnetic loop that has a magnetic mirror at its base (the mirror trap model) is analyzed. The applicability of the obtained theoretical results to interpret gamma-ray bursts that, according to the data of the RHESSI space observatory, occurred on July 23, 2002 and October 28, 2003, is discussed. In those two bursts, a single and a pair gamma source displaced relative to the hard X-ray sources were localized in the 2.223-MeV neutron-capture line. On the basis of complex analysis of multi-wavelength (X-ray, gamma-ray, and optical) observations and the data on fast solar protons, a new topological model of the source of accelerated particles (of the mirror trap type) and a new scenario of the event that occurred on July 23, 2002 are proposed. Evidence of the possibility of particle acceleration by the electric field in coronal mass-ejection loops during large solar flares is obtained. The simulation results indicate that the gamma-ray source in the excitation lines (4.1–6.7 MeV) should coincide with the region where the accelerated ions interact with the background plasma of the solar atmosphere above the spot of the flare active region.     

Psychophysiological and cardiohemodynamic effects of solar,geomagnetic, and meteorological factors in humans under the conditions of the arctic region

The influence of variations in solar, geophysical, and meteorological factors, as well as of the lunar cycle phases, on cardiohemodynamic, emotional and CNS parameters has been studied in 12 men (19–38 years old) permanently residing in the Arctic region (the town of Apatity, 67°57′ N, 33°39′ E). The period of observation was characterized by M1 and M2 class solar flares and G1-G3 class geomagnetic storms. The study has demonstrated the adaptive modulation effects of environmental factors on autonomic regulation systems and the perturbing influences of geomagnetic storm and solar chromospheric flares on human functional state. Multiple regression analysis was used to identify the dominant environment factors by the degree of their influence on functional parameters and to assess their combined effect. The coefficient of determination was no more than 0.5 on average; however, in some subjects, it reached 0.7–0.8 for certain parameters. All subjects were shown to respond to the permanent fluctuations of climatic-geographical and cosmophysical factors under the extreme conditions of high latitudes; however, response pattern and intensity depended on individual sensitivity to their isolated and combined effects.     

Nonlinear periodic space-charge waves in plasma

A solution is obtained in the form of coupled nonlinear periodic space-charge waves propagating in a magnetoactive plasma. The wave spectrum in the vicinity of the critical point, where the number of harmonics increases substantially, is found to fall with harmonic number as ∝ s ^?1/3. Periodic space-charge waves are invoked to explain the zebra pattern in the radio emission from solar flares.     

Radiation exposure in supersonic transport by solar flares

Summary The following discourse presents the result of a theoretical analysis of the radiation exposure for solar proton beams and their secondaries in the altitude region of SST (supersonic transport) and pole regions. A statistical analysis of forms and intensities of measured solar flares has been made. The radiation dosage is calculated as a function of atmospheric depth for several characteristic flares. The dosage in rems from secondary neutrons exceeds the dosage in rems from protons in the altitude region of SST for flare events with low characteristic slopeparameterG, In general the radiation is — without some rare extreme events — beyond of dangerous limits and the rare extreme exposure values will be of some hundred mrem/h.     

The dynamics of and radiation from a copper-wire corona in a megaampere Z-pinch

Evolution of the extreme ultraviolet (XUV) and soft X-ray (SXR) emission in the 50-to 2000-eV photon energy range from a plasma corona formed by loading a relatively thick Cu wire (with an initial diameter of 120 µm) was observed in a Z-pinch discharge with a maximum current of 2 MA and current rise time of 100 ns. A diagnostic complex consisting of a five-channel SXR polychromator, a four-frame X-ray pinhole camera, and a mica crystal spectrograph shows that double-humped emission pulses in the XUV and SXR spectral ranges are generated 70–130 ns after the onset of the discharge current. The total energy of the pulses is 5 kJ, and the maximum power is 60 GW. A part of the observed kiloelectronvolt X-ray emission from three to five spots with diameters of 1–2 mm consists of the Cu K-and L-shell lines.     

Concerning mechanisms for the zebra pattern formation in the solar radio emission

The nature of the zebra patterns in continuous type-IV solar radio bursts is discussed. The most comprehensively developed models of such patterns involve mechanisms based on the double plasma resonance and plasma wave-whistler interaction. Over the last five years, there have appeared a dozen papers concerning the refinement of the mechanism based on the double plasma resonance, because, in its initial formulation, this mechanism failed to describe many features of the zebra pattern. It is shown that the improved model of this mechanism with a power-law distribution function of hot electrons within the loss cone is inapplicable to the coronal plasma. In recent papers, the formation of the zebra pattern in the course of electromagnetic wave propagation through the solar corona was considered. In the present paper, all these models are estimated comparatively. An analysis of recent theories shows that any types of zebra patterns can form in the course of radio wave propagation in the corona, provided that there are plasma inhomogeneities of different scales on the wave path. The superfine structure of zebra stripes in the form of millisecond spikes with a strict period of ～30 ms can be attributed to the generation of continuous radio emission in the radio source itself, assuming that plasma inhomogeneities are formed by a finite-amplitude wave with the same period.     

Current scaling for the radiative characteristics of a micropinch discharge

The absolute VUV and soft X-ray (hν > 100 eV) yield from a micropinch discharge is measured for a fixed current of 150 kA. The current scaling in the range of 30–250 kA is found for a number of the discharge parameters: the VUV and soft X-ray yield, the electron temperature, the effective temperature of suprathermal electrons, and the energy of bremsstrahlung emission from thermal electrons. The experimental data are in good agreement with the simulations performed by using the model of radiative collapse in fast Z-pinches in plasmas of high-Zelements.     

Utility-scale solar impacts to volant wildlife

To reduce carbon emissions from fossil fuel combustion, United States government agencies, including those in California, initiated aggressive programs to hasten development of utility-scale solar energy. Much of California's early development of solar energy occurred in deserts and annual grasslands, much of it on public land. Measurement of solar energy's impacts to wildlife has been limited to mortality caused by features of solar facilities, and has yet to include impacts from habitat loss and energy transmission. To estimate species-specific bird and bat fatality rates and statewide mortality, I reviewed reports of fatality monitoring from 1982 to 2018 at 14 projects, which varied in duration, level of sampling, search interval, search method, and carcass detection trials. Because most monitors performed carcass detection trials using species of birds whose members were larger than birds and bats found as fatalities, I bridged the monitors' onsite trial results to offsite trial results based on the same methods but which also measured detection probabilities across the full range of body sizes of species represented by fatalities. This bridge preserved the project site's effects on detection probabilities while more fully adjusting for the effects of body size. My fatality estimates consistently exceeded those reported. Projected to California's installed capacity of 1,948.8 MW of solar thermal and 12,220 MW of photovoltaic (PV) panels in 2020 (14,168.8 MW total), reported estimates would support an annual statewide fatality estimate of 37,546 birds and 207 bats, whereas I estimated fatalities of 267,732 birds and 11,418 bats. Fatalities/MW/year averaged 11.61 birds and 0.06 bats at PV projects and 64.61 birds and 5.49 bats at solar thermal projects. Fatalities/km/year averaged 113.16 birds and zero bats at generation tie-ins, and 14.44 birds and 2.56 bats along perimeter fences. Bird fatality rates averaged 3 times higher at PV projects searched by foot rather than car. They were usually biased low by insufficient monitoring duration and by the 22% of fatalities that monitors could not identify to species. I estimated that construction grading for solar projects removed habitat that otherwise would have supported nearly 300,000 birds/year. I recommend that utility-scale solar energy development be slowed to improve project decision-making, impacts assessment, fatality monitoring, mitigation efficacy, and oversight.     

Dynamics of the implosion of a tungsten wire array onto the central aluminum wire

Results are presented from the studies of the magnetic implosion of a tungsten wire liner onto an aluminum wire at currents of 2.0–2.6 MA. The experiments were carried out in the S-300 high-power pulsed facility at the Russian Research Centre Kurchatov Institute. The liner is composed of 50 wires 6 μm in diameter and 1 cm in length, which are equally spaced on a circle 1 cm in diameter. An aluminum wire 120 μm in diameter is positioned at the array axis. The liner implosion was accompanied by the generation of VUV and soft X-ray emission. The parameters of the pinch plasma produced during the liner implosion onto the aluminum wire were determined from the time-resolved spectral measurements by a five-channel polychromator. The ion and electron densities turned out to be equal to n _i≈4×10¹⁹ cm⁻³ and n _e≈4×10²⁰ cm⁻³, respectively, and the electron temperature was T _e≈40 eV. The radiation energy measured in the range 50–600 eV was 2–10 kJ. The sources of soft X-ray emission in hydrogen-and helium-like aluminum lines were the bright spots and local objects (clouds) formed in the plasma corona at an electron temperature of 200–500 eV and electron density of 10²¹–10²² cm⁻³. The possibility of both the generation of an axial magnetic field during the liner implosion and the conversion of the energy of this field into soft X-ray emission is discussed. __________ Translated from Fizika Plazmy, Vol. 28, No. 6, 2002, pp. 514–521. Original Russian Text Copyright ? 2002 by Bakshaev, Blinov, Dan'ko, Ivanov, Klír, Korolev, Kravárik, Krása, Kubeš, Tumanov, Chernenko, Chesnokov, Shashkov, Juha.     

Manifestation of quasilinear diffusion on whistlers in the fine-structure radio sources of solar radio bursts

The zebra structure and fiber bursts in the dynamic spectra of the solar type IV radio burst recorded on October 25, 1994, are analyzed using observational data from ground-based stations and Earth-orbiting satellites. The fine structure is observed when new hot magnetic loops, in which high-and low-frequency plasma instabilities develop, ascend to the solar corona. The frequency range of the fine structure is determined by the dimensions of these loops. The main features of the zebra structure are analyzed in terms of the interaction of plasma waves with whistlers. The results obtained are compared to the predictions from the double plasma resonance model.     

On the Formation of Filamentary Structures in the Early Phase of Solar Flares

Plasma Physics Reports - A model describing the initial phase of the heating of a flare in the solar corona is proposed. The energy equation for a flare plasma in a magnetic tube is reduced to the...     

Thermal self-focusing during solar flares

By solving a nonlinear equation for a heat source with a power proportional to Т ^β (β > 1), it is shown that heat localization in the transverse cross section of a magnetic tube with a classical thermal conductivity occurs in the blowup regime in the form of microstructures—temperature background cells bounded by hot walls with a spatial scale of <100 m. The reduction in the integral X-ray emissivity observed on board of spacecrafts in the early stage of the flare is attributed to thermal self-focusing, i.e., a decrease in the factor of filling of the flare volume with hot plasma due to the narrowing of the hot walls of the microstructure.     

New mechanism for the formation of discrete stripes in the solar radio spectrum

Dispersion relations are derived for the eigenfrequency spectrum of a spatially periodic nonlinear plasma resonators created in the solar atmosphere due to the development of thermal instability. The eigenfrequency spectra of such resonators are calculated, and it is shown that they are capable of generating tens of discrete stripes (a so-called zebra structure) the number of which is independent of the ratio of the plasma frequency to the gyrofrequency in the source. This may help to overcome all difficulties in explaining the large number of stripes in the zebra structure, as well as the small magnitude of the magnetic field. The spatially periodic plasma resonators under consideration act as a filter with numerous transparency windows separated from one another by opaque regions. The number of stripes and their frequencies in the zebra structure depend on the spatial period of plasma nonuniformity, which is equal to meters or decameters for conditions typical of the solar atmosphere. The high brightness temperature of radio emission in the zebra structure is attributed to coherent emission from a large number of identical small-scale plasma sources. Some regular properties of the observed zebra structure are explained.     

A possible biophysical mechanism of the solar activity effect on the central nervous system in man

A biophysical mechanism of interaction between the man and environment is proposed, which treats these components as two correlated oscillation contours with discrete resonance frequencies. The coincidence of biocurrent frequencies of the human brain with the resonance frequencies of the cavity formed by the Earth surface and the lower ionosphere boundary allows one to consider the influence of solar flares on the human organism in terms of variations of the cavity frequencies due to changes in the parameters of its upper wall.     

Influence of the solar wind on the distribution of the electric potential near the Moon’s surface

The Moon’s surface illuminated by the Sun acquires an electric charge due to photoelectron emission and interaction with the solar wind plasma. The influence of the solar wind on the nonmonotonic distribution of the electric potential near the Moon’s surface is studied in a wide range of the densities of emitted photoelectrons. It is found that, for any photoelectron density, the surface potential reaches its minimum value for a slow solar wind. Although the electron thermal velocity can exceed the solar wind velocity by several times, taking into account the directed flow velocity in the electron velocity distribution function substantially affects the value of the potential in the lunar regolith regions not enriched with hydrogen, for which the photoelectric work function under solar irradiation is significantly higher than for regions enriched with hydrogen.     

Study of X-ray and neutron emission in experiments with Al wires in an MA plasma focus

Results are presented from experimental studies of the correlation between X-ray and neutron emissions generated in the implosion of a deuteron plasma shell onto an Al wire. The experiments were carried out on the PF-1000 facility at currents of 1.5–1.8 MA. An Al wire 80 μm in diameter and 7–9 cm in length was placed at the end of the inner electrode. During the implosion of the plasma shell, Al K-shell X-rays were first emitted at the dip of the current derivative. After the X-ray pulse, a relatively stable corona with a diameter of 2–3 mm and lifetime of a few hundred nanoseconds formed around the wire. The presence of the wire did not considerably reduce the total neutron yield (at most 10¹¹ neutrons per shot) in comparison to discharges without a wire. As a rule, the intensity of neutron emission was maximal a few tens of nanoseconds after the peak of X-ray emission. A detailed comparison of two shots with low and high neutron yields have shown that the neutron yield depends on the configuration and dynamics of the discharge. The possible influence of the self-generated axial component of the magnetic field on the development of the plasma focus and the acceleration of fast deuterons is discussed.