Intensity and polarization of the hard X-ray radiation of solar flares at the top and footpoints of a magnetic loop

The spatial distributions of the intensity and polarization of hard X-rays (HXR) were modeled based on a numerical solution of the nonstationary kinetic Fokker-Plank equation. Two cases of nonstationary long injections (??10 s) of nonthermal electrons at the top of a flaring loop are considered. In the first case, the injection occurs anisotropically in a cone directed along the field to one of the loop??s footpoints. In the second case, electrons are injected isotropically. In the case of the anisotropic injection, the degree of HXR polarization in the footpoints is low and does not exceed 8%. At the same time, the polarization of the radiation from the top in a range of photon energies from 30 to 60 keV reaches 43% at the beginning of injection. Significantly different spatial distributions of HXR characteristics are obtained for the isotropic injection of electrons. In this case, the calculated degree of HXR polarization from the top exhibits a strong variability: it reaches 15?C18% at the beginning of injection at photon energies of 30?C90 keV, decreases to zero after 5 s, and then, changing its sign, increases to 8%. In the footpoint of the loop, HXR is in fact nonpolarized. The features of the spatial distributions obtained in the simulation process can be measured with X-ray telescopes-polarimeters in future experiments and used for diagnosing the pitch angle distribution of accelerated electrons.     

Superfine time structure and polarization of hard X-ray emission during solar flares: Simulation of isolated pulses

A superfine time structure has been detected recently via hard X-ray satellite observations during solar flares. Some pulses are hundreds of milliseconds in length. Time series are sharply nonstationary sequences of overlapping pulses. We interpreted a similar time structure in a model of the nonstationary kinetics of accelerated electron beams. In this work, we present calculation results of the degree of polarization of the hard X rays of solar flares with millisecond pulses. The dependence of the polarization degree on the plasma concentration, radiation energy, and the observation angle has been derived from calculations with the thick-target nonstationary kinetics model for rectangular and triangular individual pulses of accelerated electrons in the region of injection with the angular dependence cos²ⁿ θ. It is shown that the degree of polarization does not exceed 78% and decreases down to 50–65% 20 s after the beginning of the injection.     

Hard X-ray generation in the turbulent plasma of solar flares

The influence of scattering of accelerated electrons in the turbulent plasma on the transformation of their distribution function is studied. The turbulence is connected with the emergence of magnetic inhomogeneities and ion-sound mode. The level of ion-sound turbulence is specified by the ratio W ^s/nk _B T _e = 10^?3, while the value of magnetic fluctuations is δB/B = 10^–3. Different initial angular distributions of the function of accelerated-electron source are regarded: from isotropic to narrow directional distributions. For the chosen energy-density values of the ion-sound turbulence and the level of magnetic fluctuations, it is shown that both types of turbulence lead to a qualitative change in the hard X-ray brightness along the loop, moreover their influence was found to be different. Models with magnetic fluctuations and the ion sound can be distinguished not only by the difference in the hard X-ray distribution along the loop but also by the photon spectrum.     

On the relation between high frequency acoustic emissions in near-surface rocks and the electric field in the near-ground atmosphere

A field instrument package was installed for synchronous measurements of acoustic emission in rocks at frequencies of 0.1–10000 Hz and the vertical gradient of electric potential in near-ground atmosphere. These investigations for the first time revealed a relationship between emission disturbances in the kilohertz frequency range due to deformation of near-surface rocks and the electric field. The relationship may be observed both during seismically quiet periods and at the final phase of earthquake precursory periods.     

Flare coronal loop heating and hard X-ray emission from solar flares of August 23, 2005, and November 9, 2013

The thermal balance and hard X-ray emission of coronal loops for two solar events have been considered in the scope of a “standard” flare model. An important role of the thermal energy release is justified by the event of August 23, 2005, as an example. For the flare of November 9, 2013, it has been established that electrons accelerated at a flare loop top cannot maintain the observed hard X-ray fluxes from the flare footpoints, which indicates that charged particles are additionally accelerated in the chromosphere.

     

Some studies on low-frequency signal in relation to X-ray flares and climatic conditions

The statistical behaviour of the sudden enhancement in signal strength (SES) in relation to solar X-ray flares has been studied for the near east-west propagation of 40 kHz radio waves from Sanwa (36°11’N; 139°51’E) in Japan to Calcutta (22°34’N; 88°24’E) over a long distance path of 5100 km for a period of two years. The period has been divided into four phases - P1, P2, P3 and P4, according to the position of the overhead sun. The change in signal strength during X-ray flares is dependent on the solar zenith angle and climatic conditions. The statistical modal values of the time lag of the SES peak with respect to that solar X-ray flare is found to increase as solar zenith angle increases. The relative rates of increase and decrease of the signal strength (RRISS and RRDSS respectively) have been evaluated for a number of SES which are related to large X-ray flares. Their characteristics have also been investigated. The modal values of the relaxation time have been found to be highly correlated with climatic conditions like temperature and humidity of the propagation path.     

Local maximum in the microwave spectrum of solar active regions as a factor in predicting powerful flares

We discuss the results of a study of microwave radiation from three flare-active regions??NOAA 10300, 10930, and 11158??with powerful eruptive events (X-class flares and coronal mass ejections) recorded on July 15, 2002; December 13, 2006; and February 15, 2011, when the regions were in the central part of the disk. There exists evidence of a ??-configuration in the structure of the photospheric magnetic field formed one or two days prior to the eruptive process as a result of the emergence of a new magnetic flux and shifting movements of the sunspots and accompanied by changes in the spectral characteristics of the microwave radiation of the active regions (ARs), which suggests the development of a peculiar radio source. The analysis of these regions continues a series of studies of eruptive events carried out at RATAN-600 in the 1980s?C1990s and gives a reason to conclude that early detections of peculiar sources in the microwave radiation of ARs, which are essentially areas of high energy release in the solar atmosphere, can be used as a factor in predicting powerful eruptive (geoeffective) processes on the Sun.     

Determining wind field and electric field by a barium release experiment in the ionosphere

Barium release experiment is an effective way to study the near-earth environment, in which artificial plasma cloud is created via ionization of neutral gases released from a rocket or a satellite. The first barium release experiment in China was successfully carried out by a sounding rocket at a height of about 190 km on April 5, 2013. The observed barium cloud images show that the neutral cloud follows a damping motion, whose velocity decreases exponentially and finally tends towards the wind velocity of the background. But for the ion cloud, the motion is controlled mainly by the Lorentz force and a E×B drift happens. This work is devoted to calculating the wind and electric field of the background by analyzing the observed images from different stations. It turns out that the wind has a magnitude of 51.28 m/s, which is mainly in the northeast direction but also has an appreciable vertical component; the ion cloud has a drift velocity of 71.38 m/s, with a large vertical velocity component besides the horizontal components, then the electric field is obtained from the drift velocity as 2.49 m V/m. It is interesting that the wind field shows a better agreement with GITM model than the other empirical or theoretical models, and the GITM model can also give a good prediction for the ion velocity observed by us, which is consistent with the ISR observation at Jicamarca as well.     

Effect of magnetic storms in variations in the atmospheric electric field at midlatitudes

The observations of the variations in the vertical component of the atmospheric electric field (E _z ) at Swider midlatitude Poland observatory (geomagnetic latitude 47.8°) under the conditions of fair weather during 14 magnetic storms have been analyzed. The effect of the magnetic storm main phase in the daytime midlatitude variations in E _z in the absence of local geomagnetic disturbances has been detected for the first time. Considerable (～100–300 V m^?1) decreases in the electric field strength (E _z ) at Swider observatory were observed in daytime simultaneously with the substorm onset in the nighttime sector of auroral latitudes (College observatory). The detected effects indicate that an intensification of the interplanetary electric field during the magnetic storm main phase, the development of magnetospheric substorms, and precipitation of energetic electrons into the nighttime auroral ionosphere can result in considerable disturbances in the midlatitude atmospheric electric field.     

On the random motion of a uniform beam in a magnetic field

Summary The present note is concerned with the investigation of responses under random processes of a beam-plate placed in a magnetic field which is transverse in nature. The distinctive features of the motion have been pointed out.     

直流电场对沉水植物苦草(Vallisneria natans)生长的影响

沉水植物对维持湖泊生态系统平衡有重要作用,广泛应用在水体和沉积物污染修复领域.利用电场强化沉水植物修复过程是一种新的植物修复强化方法.本文研究了不同电压强度作用下沉水植物苦草的生长和生理响应,以期为应用电场强化沉水植物修复过程提供依据.结果表明:0.2~1.0 V电压可以促进苦草生长,而1.5~3.0 V电压则会抑制其生长.其中,0.5 V电压对苦草生长的促进效果最明显,生物量、平均株高、平均叶长、根尖数、新芽数和总叶绿素含量都比对照组显著增加;而3.0 V电压处理组的苦草在实验结束时出现萎蔫和凋亡,与对照组相比,叶绿素含量显著降低,丙二醛含量则极显著增加,表明苦草生长受到严重胁迫.系统上覆水的温度在不同处理组之间没有显著变化,上覆水的p H值在电压为1.0、1.5和3.0 V时显著下降,最终接近中性,上覆水的溶解氧浓度只在3.0 V电压处理组时表现显著下降;沉积物表层5 cm处的氧化还原电位随着电压增大显著下降,最终对苦草的生长形成胁迫.因此,本实验的结论是:0.2~1.0 V电压有助于沉水植物苦草的生长和强化植物修复过程,而1.5~3.0 V电压会破坏苦草组织,同时导致苦草生境变差,不利于沉水植物苦草的生长.     

Wave effects in the field of a high-frequency horizontal electric dipole

A normal electromagnetic field of the high-frequency horizontal electric dipole is analyzed with allowance for the displacement currents in the earth and air. The components of the field are calculated by the method of partial integration for nonsmooth behavior of the integrand. The boundary between the quasistationary and wave zone of the source is established according to the results of calculations. The effects arising in the wave zone due to the displacement currents in the air are considered. The results of the calculations are confirmed by field experiments.     

地球电场与地球磁场的形成机理

为探讨地球磁场的形成机理,应用经典电磁理论以微分的思维方式建立起三种自激发电机模型,用球形自激发电机模型简明地描述地球磁场的形成和分布;从分析地轴参考系中相对于自转地球静止的电荷间洛仑兹力的特点以及地球上的电荷在地球电场和地球磁场作用下的漂移规律,阐述中心磁场的形成及反转机理;分析电荷相对于地球的漂移以阐述偏磁场的形成.理论分析表明:地球上每一点的磁场都可以看成是由该点的几个分磁场叠加而成;地球具有自身的电场;地球电场与地球磁场同时产生、同时变化,且都源自于地球的自转和地球上正负电荷的非对等分布.     

Dynamics of accelerated electron beams and X rays in solar flares with sub-THz radiation

Unique measurements by a solar submillimeter radio telescope (SST) have been carried out in the sub-THz radiation at 212 and 405 THz over the past decade. The spectrum of RF radiation in this region increased with frequency for the three flares of November 2 and 4, 2003, and December 6, 2006, and the flux value reached 5 × 10³?2 × 10⁴ sfu at 405 GHz (Kaufman et al., 2009). In this work, we consider a set of nonlinear equations for an accelerated electrons beam and the Langmuir wave energy density. The distribution functions of the accelerated electron beam and wave energy density are calculated taking into account Coulomb collisions, electron scattering by waves, and wave scattering by plasma ions. In addition, the source of accelerated particles and the heat level of the Langmuir turbulence are specified. The beam and plasma parameters are chosen based on the aims of a problem. The plasma concentration varies from n = 10¹³ to 10¹⁵ cm^?3, the electron plasma frequency f _p = (3 × 10¹⁰?3 × 10¹¹) Hz in this case. The ratio of plasma and beam concentrations, sufficient to explain the value of the radio flux at a frequency of 300 GHz, is n _b/n = 10^?3. The Langmuir turbulence is excited due to the instability of the accelerated electron beam with an initial distribution function of the ??bump-in-tail?? type. Then, the parameters of radiowaves are calculated in the sub-THz range under the assumption of coalescence of two plasma waves. The calculation results show that a sub-THz radio flux can be obtained under the condition of injection of accelerated electrons. The fine time structure of radio flux observed is easily simulated based on this statement by the pulsed time structure of electron beams and their dynamics in overdense plasma. X-ray and gamma radiation was recorded during the events under study. Hard X-ray radiation is bremsstrahlung radiation from accelerated electron beams.     

On the connection between the atmospheric electric field measured at the surface and the ionospheric electric field in the Central Antarctica

Regular measurements of the atmospheric electric field made at Vostok Station (φ=78.45°S; λ=106.87°E, elevation 3500 m) in Antarctica demonstrate that extremely intense electric fields (1000–5000 V/m) can be observed during snow storms. Usually the measured value of the atmospheric electric field at Vostok is about 100–250 V/m during periods with “fair weather” conditions. Actual relation between near-surface electric fields and ionospheric electric fields remain to be a controversial problem. Some people claimed that these intense electric fields produced by snowstorms or appearing before strong earthquakes can re-distribute electric potential in the ionosphere at the heights up to 300 km. We investigated interrelation between the atmospheric and ionospheric electric fields by both experimental and theoretical methods. Our conclusion is that increased near-surface atmospheric electric fields do not contribute notably to distribution of ionospheric electric potential.     

Refined representations of the horizontal electric components of the normal field of a high-frequency horizontal electric dipole

Among the components of normal dipole fields useful in high-frequency electric prospecting, the electric components E and E _y of the normal field of the horizontal electric dipole are considerably complicated in structure. By checking these values by means of computer mathematics in combination with the development of the classical (dynamical) theory of interference soundings, the above expressions alluded to in geophysical literature were shown to contain considerable errors. The present paper is devoted to this question.     

Anomalies of the natural electric field on Lake Baikal

The paper presents results of observations of the electromagnetic field conducted on the ice and coast of Lake Baikal. The horizontal and vertical components of the electric field contain anomalous disturbances coinciding in time with earthquakes and with the origination of a crevice in the ice cover of the lake. A possible origin of the anomalous disturbances is considered.