Vertical Electric Currents Research Articles

Compact dual‐frequency patch antenna with large beamwidth diversity at flexible frequency ratio

AbstractA compact, single‐layer, dual‐frequency patch antenna with large beamwidth diversity, that is, broad beamwidth in the lower frequency and high‐gain radiation in the higher frequency is presented and analyzed in this paper. The antenna is in general composed of a square driven patch and two T‐shaped top‐loaded monopoles that are loaded beside the two radiating edges of the driven patch. Herein, the patch antenna to be operated in the fundamental TM01 mode intrinsically provides a pair of in‐phase magnetic currents and meanwhile, the top‐loaded monopoles produce a pair of out‐of‐phase vertical electric currents. In analysis, consistent broad beamwidth and high‐gain radiation pattern are, respectively, well maintained at the lower and higher frequencies, even with a frequency ratio as small as 1.02. Moreover, the antenna preserves simple geometry and high efficiency of a typical patch antenna. For verification, a prototype is in final fabricated and measured, which has experimentally confirmed its simulated radiation results.

The Precursor Phase of an X-class Flare: Magnetic Reconnection, Powering and Non-thermal Electrons

In this paper, we report three interesting phenomena that occurred during the precursor phase of the X1.6 class flare on 2014 September 10. (1) The magnetic reconnection initiating the flare occurs between one of the two J-shaped magnetic flux ropes that constitute a sigmoidal structure and the overlying sheared magnetic arcade that runs across the sigmoid over its middle part. The reconnection formed an erupting structure that ultimately leads to flare onset. Another J-shaped magnetic flux rope remains unaffected during the whole eruption. The phenomenon is revealed by the observation made by the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory (SDO) at 94 and 131 Å. (2) Being simultaneously with starting time of the precursor, photospheric vertical electric current (VEC) around the footpoint region of the overlying magnetic arcade underwent an obvious increase, as observed by the Helioseismic and Magnetic Imager (HMI) on board SDO. By only taking into account the VEC with current density over 3σ value (1σ: 10 mA m−2), we are able to pick out precursor-associated VEC increase starting from nearly the level of zero. We regard it as a kind of powering process for the magnetic reconnection between the two magnetic loops. (3) With high-resolution narrow-band Helium 10830 Å images taken by Goode Solar Telescope at Big Bear Solar Observatory (BBSO), we observe a narrow absorption (dark) front that runs along the erupting magnetic structure (or the erupting hot channel) and moves in the direction of the eruption during the precursor phase. Assuming the excitation mechanism of Helium atoms along the absorption front by non-thermal electrons, the phenomenon shows that the interaction between the erupted hot channel and the overlying (or surrounding) magnetic field has yielded electron acceleration.

Distributed electric current and its relation to ultraviolet radiation of the active region

We utilized full magnetic field vector magnetogramsacquired by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) to calculate vertical electric currents in the NOAA active region (AR) 12192. The AR was tracked between October 22, 2014 and October 25, 2014 with 720 s cadence. We revealed the presence of a large-scale electric current structure – distributed electric current – with the absolute magnitude varying in the range of (40–90)·1012 A. The distributed electric current is supposed to exist throughout the entire AR, and, extending to the upper layers of the solar atmosphere in one part of the AR, it closes through the chromosphere and corona in the remaining part of the AR. To test this assumption, we have compared the temporal variation of the distributed electric current value with the flare activity level (using GOES-15 data), as well as with intensity of ultraviolet radiation (UV) in the AR (using the Atmospheric Imaging Assembly (AIA/SDO) data in channels 94 Å, 193 Å, 304 Å, and 1600 Å). We found that: i) Time intervals of enhanced flare activity are co-temporal with intervals of increased values of the distributed electric current. The absence of rapid changes in the value of the distributed electric current during solar flares can be explained by high inductance of the current-carrying magnetic loops. ii) Rough estimates of the magnetic energy carried by the distributed electric current into the corona yield the values of about 1033–1034 erg for 12192. Onlya small amount of this energy is released during flare processes in the AR. Most of this energy seems to be consumed during other dissipative processes in the corona. iii) Comparison of the temporal variations of intensity in the 193 Å UV-radiation channel with dynamics of the distributed electric current in the AR reveals a good positive correlation between these values (Pearson’s R = 0.63). The absence of a correlation between the distributed electric current value and the intensity of UV radiation in channels 1600 Å, 304 Å and 94 Å might be explained by a low efficiency of the coronal loop heating by ohmic dissipation of electric currents in the corona due to the strong dependence of plasma conductivity on temperature. iv) Our results may support the concept of equivalent LRC circuit of a current-carrying coronal magnetic loop proposed by Alfven and Carlqvist in 1967 and developed by V.V. Zaitsev, A.V. Stepanov, and others. According to this model, the large-scale electric currents must exist in the upper layers of the solar atmosphere and take part in the coronal plasma heating.

Naked emergence of an anti-Hale active region

Aims. In order to understand the emergence of the active region, we investigate the emerging process and magnetic properties of a naked anti-Hale active region during the period between August 24 to 25, 2018. Methods. Using the data from Helioseismic and Magnetic Imager on board the Soar Dynamic Observatory and the New Vacuum Solar Telescope, we calculated different evolving parameters (such as pole separation, tilt angle) and magnetic parameters (such as vertical electric current, force-free parameter, relative magnetic helicity) during the emergence of the active region. With these calculated parameters and some reasonable assumptions, we use two different methods to estimate the twist of the active region. Results. The magnetic flux and pole separation continue increasing while the tilt angle exhibits a decreasing pattern during the emergence of the active region. The increase of the pole separation is mainly contributed as a result of the enhancement in the longitude direction. A power-law relationship between pole separation and total flux is found during the emergence of the active region. On the other hand, it is found that both the positive and negative electric currents increased equivalently and the average flux-weighted force-free parameter α̃ remains almost consistently positive, on the order of ∼10−8 m−1. The relative magnetic helicity is mainly contributed by the shear term, while the relative magnetic helicity injection flux of the shear term changes its sign at the latter stage of the emergence. The twist number of the whole active region remains on the order of 10−1 turns during the emergence of the active region. Conclusions. We find that the magnetic flux tube with low twist also could emerge into the solar atmosphere.

Density Distribution of Photospheric Vertical Electric Currents in Flare-Active Regions of the Sun

Electric currents flow in active regions of the sun. Information on the distribution of the currents is important for understanding energy release processes on the sun’s surface and in overlying layers. This is an analysis of the probability density function (PDF) of the absolute value of the density of photospheric vertical electric currents | jz | in 48 active regions from 2010 through 2015 at times before and after flares. | jz | is calculated by applying a differential form of the magnetic field circulation theorem (Ampere’s law) to photospheric vector magnetograms from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). It is shown that for the active regions studied here PDF (| jz |) can be calculated in a first approximation by a model consisting of a folded normal distribution at low values (| jz |≲ 9·103 statampere/cm2) and a falling power law function at higher values. A least squares method yields the model parameters for all regions, histograms of their distributions are plotted, and the mathematical expectations and mean square deviations are calculated. No systematic changes in the model parameters over the time of a flare were observed. Neither an explicit relation of the parameters to the class of a flare, nor to the Hale magnetic class was found in terms of the approach used for the limited sample of flares and active regions examined here. Arguments are presented in favor of the proposition that a folded normal distribution at low values represents noise in the data, while a power-law “tail” may reflect the nature of the processes that generate the currents in active regions of the sun.

Распределенный электрический ток и его связь с ультрафиолетовым излучением активной области

Используя магнитограммы компонент вектора магнитного поля на уровне фотосферы, получаемые инструментом Helioseismic and Magnetic Imager (HMI), установленным на борту космического аппарата Solar Dynamics Observatory (SDO), вычислены вертикальные электрические токи для активной области NOAA 12192 за период с 22 по 25 октября 2014 года с временным разрешением 12 минут. Выявлено наличие в исследуемой активной области (АО) крупномасштабной токовой структуры – распределенного электрического тока, имеющего абсолютные значения в диапазоне (40–90)·1012 А. Предполагается, что распределенный ток охватывает всю АО, и, выходя в верхние слои солнечной атмосферы в одной части области, замыкается через хромосферу и корону на оставшейся ее части. Для проверки этого предположения проанализирована связь временных изменений величины распределенного тока с уровнем корональной активности, а также с интенсивностью ультрафиолетового излучения (УФ) АО в диапазонах длин волн 1600 Å, 304 Å, 193 Å и 94 Å. Показано, что: 1) Временные интервалы максимумов величины распределенного тока совпадают по времени с повышенной вспышечной активностью АО. Отсутствие резких изменений величины распределенного тока во время вспышек может быть объяснено высокой индуктивностью токонесущих петель. 2) Грубая оценка магнитной энергии, выносимой распределенным током в корону, дает для АО NOAA 12192 значения 1033–1034 эрг. Только небольшой объем этой энергии реализуется во время вспышечных процессов в АО, большая ее часть тратится на иные диссипативные процессы в короне. 3) Сравнение временных вариаций интенсивности излучения в канале 193 Å с динамикой распределенного тока в АО показывает хорошую взаимосвязь этих величин (коэффициент корреляции k = 0.63). В то же время отсутствует корреляции между величиной распределенного тока и интенсивностью УФ-излучения в диапазонах 1600 Å, 304 Å и 94 Å. 4) Полученные нами результаты, возможно, могут объясняться концепцией LRC-контура токонесущей корональной петли, предложенной в 1967 году Альфвеном и Карлквистом и развитой в работах В.В. Зайцева, А.В. Степанова и др. Согласно данной модели, крупномасштабные электрические токи должны существовать в верхних слоях солнечной атмосферы и принимать участие в нагреве коронального вещества.

Relationships between Photospheric Vertical Electric Currents and Hard X-Ray Sources in Solar Flares: Statistical Study

Abstract There are still debates over whether particle acceleration in solar flares may occur due to interruption of electric currents flowing along magnetic loops. To contribute to this debate, we performed the first statistical study of relationships between flare hard X-ray (HXR; 50–100 keV) sources observed by the Ramaty High-Energy Solar Spectroscopic Imager and photospheric vertical electric currents (PVECs, j r ) calculated using vector magnetograms obtained with the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. We analyzed a sample of 48 flares from the C3.0 to X3.1 class and were observed in the central part of the solar disk by both instruments in 2010–2015. We found that ≈70% of all HXR sources overlapped with islands or ribbons of enhanced ( statampere cm−2) PVECs. However, less than ≈40% of the HXR sources overlapped with PVEC maxima, with an accuracy of ±3″. In more than half of the flares, there were HXR sources outside of regions of enhanced PVECs. We found no correlation between the intensity of the HXR sources and PVEC density or total PVEC under them. No systematic dissipation of PVECs under the HXR sources was found during the flares. Collectively, the results do not support the current-interruption flare models. However, the results indicate the importance of the presence of longitudinal currents in flare regions. To understand their specific role in the processes of energy release, plasma heating, and acceleration of particles requires further investigation.

Distributed Electric Currents in Solar Active Regions

Using magnetographic data provided by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, we analyzed the structure of magnetic fields and vertical electric currents in six active regions (ARs) with different level of flare activity. We found that electric currents are well balanced over the entire AR: for all of them the current imbalance is below 0.1%, which means that any current system is closed within an AR. Decomposition of the transverse magnetic field vector into two components allowed us to reveal the existence of large-scale vortex structures of the azimuthal magnetic field component around main sunspots of ARs. In each AR, we found a large-scale electric current system occupying a vast area of an AR, which we call distributed electric current. For ARs obeying the Hale polarity law and the hemispheric helicity sign rule, the distributed current is directed upward in the leading part of an AR and it appears to be closing back to the photosphere in the following part of an AR through the corona and chromosphere. Our analysis of the time variations of the magnitude of the distributed electric currents showed that low-flaring ARs exhibit small variations of the distributed currents in the range of $\pm 20 \times 10^{12}$ A, whereas the highly flaring ARs exhibited significant slow variations of the distributed currents in the range of $30-95 \times 10^{12}$ A. Intervals of the enhanced flaring appear to be co-temporal with smooth enhancements of the distributed electric current.

Effect of Oxygen Content on Current Stress-Induced Instability in Bottom-Gate Amorphous InGaZnO Thin-Film Transistors.

The effect of oxygen content on current-stress-induced instability was investigated in bottom-gate amorphous InGaZnO (a-IGZO) thin-film transistors. The observed positive threshold voltage shift (ΔVT) was dominated by electron trapping in the gate insulator (GI), whereas it was compensated by donor creation in a-IGZO active regions when both current flows and a high lateral electric field were present. Stress-induced ΔVT increased with increasing oxygen content irrespective of the type of stress because oxygen content influenced GI quality, i.e., higher density of GI electron traps, as well as typical direct current (DC) performance like threshold voltage, mobility, and subthreshold swing. It was also found that self-heating became another important mechanism, especially when the vertical electric field and channel current were the same, independent of the oxygen content. The increased ΔVT with oxygen content under positive gate bias stress, positive gate and drain bias stress, and target current stress was consistently explained by considering a combination of the density of GI electron traps, electric field relaxation, and self-heating-assisted electron trapping.

Seismogenic Disturbances of the Ionosphere During High Geomagnetic Activity

Herein, we analyze the variations in the ionosphere for the period of two weeks before the M6.7 earthquake in India on 3 January 2016. The earthquake occurred after a series of magnetic substorms on 31 December 2015 and 1 January 2016. The relative total electron content (TEC) disturbances have been estimated using global TEC maps and calculated numerically using the 3D global first-principle Upper Atmosphere Model (UAM) for the whole period including the days before, during, and after the substorms. Numerical simulations were repeated with the seismogenic vertical electric currents switched on at the earthquake epicenter. The UAM calculations have reproduced the general behavior of the ionosphere after the main phase of the geomagnetic storm on 1 January 2016 in the form of negative TEC disturbances propagating from high latitudes, being especially strong in the Southern (summer condition) Hemisphere. It was shown that the local ionospheric effects of seismic origin can be identified in the background of the global geomagnetic disturbances. The seismo-ionospheric effects are visible in the nighttime regions with the additional negative TEC disturbances extending from the eastern side of the epicenter meridian to the western side, both in the observations and in the UAM simulations. It was found that the vertical electric field and corresponding westward component of the electromagnetic [E × B] drift played a decisive role in the formation of the ionospheric precursors of this earthquake.

СОВРЕМЕННОЕ СОСТОЯНИЕ ЭЛЕКТРОРАЗВЕДКИ ТМ-ПОЛЯРИЗАЦИИ

A brief analysis of the main achievements and directions of development of the method of vertical electrical currents sounding is given.

Vertical Electric Currents in Active Regions: Calculation Methods and Relation to the Flare Index

In the scope of the performed work, two problems are solved. The first is the analysis of two existing methods for calculating vertical electric currents, differential and integral. The integral method has some advantages compared to the differential method. Among them, one can mention there is no need to differentiate the magnetic field and a good smoothing of noises without losing significant information about the current structures. The integral method of calculating vertical currents has been tested for the NOAA AR 11158 using the data of two instruments, the Helioseismic and Magnetic Imager of the Solar Dynamics Observatory (HMI/SDO) spacecraft and the Solar Optical Telescope of the Hinode satellite (SOT/Hinode). There was a good correlation between the calculated data (the coefficient of correlation k = 0.77). This result indicates a sufficient reliability of data on currents calculated by the integral method, regardless of the observation instrument. In the second part of the work, we analyze the data on the relation between the flare activity of groups of spots and the magnitude of the vertical current in them. A direct dependence between these quantities has been established: the greater the mean squared vertical current density, the higher the flare activity of the region (the coefficient of correlation k1 = 0.91).

Aerosols and seismo-ionosphere coupling: A review

The role of atmosphere aerosols in the global electric circuit, particularly during earthquakes preparation periods, is discussed in this review paper. Aerosols participate in production and transport of electric charges as well as in clouds formation. Satellite imagery shows increased aerosol optical depth over the tectonic faults and formation of the anomalous clouds aligned with the faults shortly before the earthquake shocks. At the same time variations of the ionospheric electric field and total electron content (TEC) are observed. We assume that the vertical electric current is generated over the fault due to the separation and vertical transport of charges with different masses and polarities. This charges the ionosphere positively relative to the Earth in the same way as the thunderstorm currents do. The resulting electric field in the ionosphere drives F2-layer plasma via the electromagnetic [E→×B→] drift and decreases or increases electron density depending on the configuration of the electric field, thus, creating observed negative or positive TEC disturbances. The important role of the electric dynamo effect in these processes is underlined.

Formation and Eruption Process of a Filament in Active Region NOAA 12241

Abstract In order to better understand active-region filaments, we present an intensive study on the formation and eruption of a filament in active region NOAA 12241 during the period from 2014 December 18 to 19. Using observations from the Helioseismic and Magnetic Imager (HMI) vector magnetograms, we investigate the helicity injection rate, Lorentz force, and vertical electric current in the entire region associated with the filament. The helicity injection rate before eruption is found to be larger than that after eruption, while the vertical electric current undergoes an increase at first and then a gradual decrease, similar to what the magnetic flux undergoes. Meanwhile, we find that the right part of the filament is formed by magnetic reconnection between two bundles of magnetic field lines while the left part originated from shearing motion. The interaction of the two parts causes the eruption of this filament. The mean horizontal magnetic fields in the vicinity of the magnetic polarity inversion line (PIL) enhance rapidly during the eruption. Another striking phenomenon, where the vertical electric currents close to the magnetic PIL suddenly expand toward two sides during the eruption, is found. We propose that this fascinating feature is associated with the release of energy during the eruption.

Effects of space weather on GOCE electrostatic gravity gradiometer measurements

We examine the presence of residual nongravitational signatures in gravitational gradients measured by GOCE electrostatic gravity gradiometer. These signatures are observed over the magnetic poles during geomagnetically active days and can contaminate the trace of the gravitational gradient tensor by up to three to five times the expected noise level of the instrument (\(\sim \)11 mE). We investigate these anomalies in the gradiometer measurements along many satellite tracks and examine possible causes using external datasets, such as interplanetary electric field measurements from the ACE (advanced composition explorer) and WIND spacecraft, and Poynting vector (flux) estimated from equivalent ionospheric currents derived from spherical elementary current systems over North America and Greenland. We show that the variations in the east-west and vertical electrical currents and Poynting vector components at the satellite position are highly correlated with the disturbances observed in the gradiometer measurements. The results presented in this paper reveal that the disturbances are due to intense ionospheric current variations that are enhanced by increased solar activity that causes a very dynamic drag environment. Moreover, successful modelling and removal of a high percentage of these disturbances are possible using external geomagnetic field observations.

MAGNETIC ENERGY DISSIPATION DURING THE 2014 MARCH 29 SOLAR FLARE

We calculated the time evolution of the free magnetic energy during the 2014-Mar-29 flare (SOL2014-03-29T17:48), the first X-class flare detected by IRIS. The free energy was calculated from the difference between the nonpotential field, constrained by the geometry of observed loop structures, and the potential field. We use AIA/SDO and IRIS images to delineate the geometry of coronal loops in EUV wavelengths, as well as to trace magnetic field directions in UV wavelengths in the chromosphere and transition region. We find an identical evolution of the free energy for both the coronal and chromospheric tracers, as well as agreement between AIA and IRIS results, with a peak free energy of $E_{free}(t_{peak}) \approx (45 \pm 2) \times 10^{30}$ erg, which decreases by an amount of $\Delta E_{free} \approx (29 \pm 3) \times 10^{30}$ erg during the flare decay phase. The consistency of free energies measured from different EUV and UV wavelengths for the first time here, demonstrates that vertical electric currents (manifested in form of helically twisted loops) can be detected and measured from both chromospheric and coronal tracers.

Rotation of sunspots in active region NOAA 10930

The rotation of sunspots of the active region NOAA 10930 has been investigated using a time series of vector magnetic field maps from the Solar Optical Telescope aboard Hinode. The vertical, radial and azimuthal axisymmetrical components of the magnetic field vector have been reconstructed from the magnetic field line-of-sight component for both sunspots of this active region. The existence of an azimuthal field component means that the magnetic field lines are twisted. The azimuthal components of both sunspots are of same sign. The magnetic flux tubes which form the sunspots of the active region on the solar surface are twisted clockwise. The vertical electric currents generated as a result of rotation and twisting of the magnetic flux tubes have the same direction.

FINE STRUCTURE OF FLARE RIBBONS AND EVOLUTION OF ELECTRIC CURRENTS

Emission of solar flares across the electromagnetic spectrum is often observed in the form of two expanding ribbons. The standard flare model explains the flare ribbons as footpoints of magnetic arcades, emitting due to interaction of energetic particles with the chromospheric plasma. However, the physics of this interaction and properties of the accelerated particles are still unknown. We present results of multiwavelength observations of C2.1 flare of August 15, 2013, observed with New Solar Telescope (NST) of Big Bear Solar Observatory, Solar Dynamics Observatory (SDO), GOES and FERMI spacecraft. The observations reveal previously unresolved sub-arcsecond structure of the flare ribbons in regions of strong magnetic field consisting from numerous small-scale bright knots. We observe red-blue asymmetry of H alpha flare ribbons with a width as small as 100 km. We discuss the relationship between the ribbons and vertical electric currents estimated from vector magnetograms, and show that Joule heating can be responsible for energization of H alpha knots in the ribbons.

Modeling of total electron content disturbances caused by electric currents between the Earth and the ionosphere

The results of simulation of ionospheric total electron content (TEC) caused by the electric field induced by an electric current between the Earth and the ionosphere are reported. The calculations are performed using a model of the upper atmosphere of the Earth (UAM). The equation for the electric potential in the UAM is solved by specifying vertical electric currents in a limited area of the lower boundary of the ionosphere, presumably over the epicenter of a forthcoming earthquake. The dependence of the intensity of TEC disturbances on the electric current direction, latitudinal location of the sources, and their configurations is examined. The most intense TEC disturbance are predicted when the sources are located within 30°–45° geomagnetic latitude. Simulating the concurrent action of vertical currents and compensating “return” currents uniformly distributed around the globe outside the region of “direct” currents showed no significant changes in the TEC disturbances compared with the situation where merely “direct” currents are considered. The role of the vertical and horizontal components of the electromagnetic drift of ionospheric plasma in the variations of the electron density in different areas relative to the electric current source is discussed.

Natural convection in square enclosures filled with fluid-saturated porous media under the influence of the magnetic field induced by two parallel vertical electric currents

The paper investigates numerically the effects of a magnetic field upon natural convection of electrically conducting fluids contained in differentially heated square enclosures filled with fluid-saturated porous media. The magnetic field is induced by two electric currents flowing parallel to the vertical walls of the enclosures. The Darcy flow model is used to describe the fluid flow inside the fluid-saturated porous media. It is shown that the magnetic field depends only on the distance to the vertical electric currents and, based on the physical model, is demonstrated that the overall effect of the induced magnetic field is to decrease the intensity of natural convection inside the enclosure; therefore, the overall heat transfer crossing the enclosure also decreases. Results are obtained for some particular combinations of the dimensionless governing parameters, and especially for some particular values of the Hartmann number, showing that a reduction in natural convection occurs, when the intensity of the magnetic field increases. Fluid flow structure and thermal field are analyzed through the streamlines and the isotherms. For the physical configuration under analysis, it is shown the effect of the induced magnetic field is always a reduction of the natural convection taking place inside the enclosure, and the consequent reduction of the overall heat transfer crossing it.