Unipolar Regions Research Articles

Estimation of the Lifetime of Slow-Decaying Unipolar Active Regions in the Framework of the Turbulent Erosion Model

Estimation of the Lifetime of Slow-Decaying Unipolar Active Regions in the Framework of the Turbulent Erosion Model

Toward a Live Homogeneous Database of Solar Active Regions Based on SOHO/MDI and SDO/HMI Synoptic Magnetograms. I. Automatic Detection and Calibration

Recent studies indicate that a small number of rogue solar active regions (ARs) may have a significant impact on the end-of-cycle polar field and the long-term behavior of solar activity. The impact of individual ARs can be qualified based on their magnetic field distribution. This motivates us to build a live homogeneous AR database in a series of papers. As the first of the series, we develop a method to automatically detect ARs from 1996 onward based on SOHO/MDI and SDO/HMI synoptic magnetograms. The method shows its advantages in excluding decayed ARs and unipolar regions and being compatible with any available synoptic magnetograms. The identified AR flux and area are calibrated based on the cotemporal SDO/HMI and SOHO/MDI data. The homogeneity and reliability of the database are further verified by comparing it with other relevant databases. We find that ARs with weaker flux have a weaker cycle dependence. Stronger ARs show a weaker cycle 24 compared with cycle 23. Several basic parameters, namely, the location, area, and flux of negative and positive polarities of the identified ARs, are provided in the paper. This paves the way for ARs’ new parameters quantifying the impact on the long-term behavior of solar activity to be presented in the subsequent paper of the series. The constantly updated database covering more than two full solar cycles will be beneficial for the understanding and prediction of the solar cycle. The database and the detection codes are accessible online.

Appearance of active regions at the end of solar cycle 24 and at the beginning of cycle 25

The spatial-temporal picture of appearance of active regions and the relationship of their appearance with the structure and development of a large-scale magnetic field were studied during the transition from solar cycle 24 to 25. During this period, solar activity is low, and therefore the dynamics of a large-scale magnetic field in the appearance of new active regions is most noticeable. We have used SDO/HMI data on the longitudinal magnetic field to determine the time and heliographic coordinates of the origin of an active region, as well as daily WSO maps (Wilcox Solar Observatory) to compare with the structure of the large-scale magnetic field. We have obtained the following results. During the transition from one cycle to another, new active regions appeared in half of the cases in the polarity inversion line of the large-scale magnetic field, and almost exclusively at the Hale boundaries in the corresponding hemispheres and solar cycles. In other cases, the places of appearance were unipolar regions of the large-scale magnetic field without a clear advantage in the location of the field regions according to the Hale law. The formation of active regions is preceded or accompanied by changes in the structure of the large-scale magnetic field. At the same time, in the fine structure of the magnetic field in the photosphere we can observe an increase in the magnetic field network on a spatial scale of the size of supergranules and larger, as well as the appearance of small regions of a new magnetic field of both polarities. The appearing active regions were concentrated in two narrow longitudinal zones that covered both hemispheres of the Sun. The new cycle began in the same longitudinal zones, where the activity of the old cycle decayed.

Появление активных областей в период завершения 24-го и начала 25-го циклов активности

The spatial-temporal picture of appearance of active regions and the relationship of their appearance with the structure and development of a large-scale magnetic field were studied during the transition from solar cycle 24 to 25. During this period, solar activity is low, and therefore the dynamics of a large-scale magnetic field in the appearance of new active regions is most noticeable. We have used SDO/HMI data on the longitudinal magnetic field to determine the time and heliographic coordinates of the origin of an active region, as well as daily WSO maps (Wilcox Solar Observatory) to compare with the structure of the large-scale magnetic field. We have obtained the following results. During the transition from one cycle to another, new active regions appeared in half of the cases in the polarity inversion line of the large-scale magnetic field, and almost exclusively at the Hale boundaries in the corresponding hemispheres and solar cycles. In other cases, the places of appearance were unipolar regions of the large-scale magnetic field without a clear advantage in the location of the field regions according to the Hale law. The formation of active regions is preceded or accompanied by changes in the structure of the large-scale magnetic field. At the same time, in the fine structure of the magnetic field in the photosphere we can observe an increase in the magnetic field network on a spatial scale of the size of supergranules and larger, as well as the appearance of small regions of a new magnetic field of both polarities. The appearing active regions were concentrated in two narrow longitudinal zones that covered both hemispheres of the Sun. The new cycle began in the same longitudinal zones, where the activity of the old cycle decayed.

Granular-scale Magnetic Flux Emergence and its Associated Features in an Emerging Active Region

Abstract Using the high-resolution photosphere and chromosphere observations made by the 1 m New Vacuum Solar Telescope, we studied the granular-scale magnetic flux emergence occurring in emerging active region NOAA 12579. Supplementary observations are also provided by the spacecraft Solar Dynamics Observatory. The studied granular-scale flux emergence took place at two different locations. One is completely embedded in the unipolar region of the following sunspots (Case 1), while another is located at the central part in the active region (Case 2). We find that both cases initially emerge from a dark patch like a wide intergranular lane, but showing the different subsequent features. In Case 1, the emerging granule grows in an elongated feature and reaches its maximum size of almost of 5″ × 3″, with an elongated speed of about 2–3 km s−1. An eruption (i.e., surge) with bright footpoints is observed after the emerging granule reaches its maximum scale. There is a time delay of more than 10 minutes between the appearance of the abnormal granule and the Hα surge. Furthermore, its footpoints are clearly rooted at the intergranular lane. We propose that the eruptive surge could be triggered by the reconnection between the emerging magnetic flux and the preexisting ambient field, leading to the localized heating and bidirectional flows. In Case 2, the granular cell emerging is simultaneously associated with bright points with opposite magnetic polarity, showing the separating motion between them and a bunch of newly formed arch filament systems. We infer that the bright points are due to the strong-field magnetic concentration in the dark intergranular lanes rather than the instantaneous Ellerman bombs.

Sunspot tilt angles revisited: Dependence on the solar cycle strength

Context. The tilt angle of sunspot groups is crucial in the Babcock-Leighton (BL) type dynamo for the generation of the poloidal magnetic field. Some studies have shown that the tilt coefficient, which excludes the latitudinal dependence of the tilt angles, is anti-correlated with the cycle strength. If the anti-correlation exists, it will be shown to act as an effective nonlinearity of the BL-type dynamo to modulate the solar cycle. However, some studies have shown that the anti-correlation has no statistical significance. Aims. We aim to investigate the causes behind the controversial results of tilt angle studies and to establish whether the tilt coefficient is indeed anti-correlated with the cycle strength. Methods. We first analyzed the tilt angles from Debrecen Photoheliographic Database (DPD). Based on the methods applied in previous studies, we took two criteria (with or without angular separation constraint Δs > 2.​​°5) to select the data, along with the linear and square-root functions to describe Joy’s law, and three methods (normalization, binned fitting, and unbinned fitting) to derive the tilt coefficients for cycles 21–24. This allowed us to evaluate different methods based on comparisons of the differences among the tilt coefficients and the tilt coefficient uncertainties. Then we utilized Monte Carlo experiments to verify the results. Finally, we extended these methods to analyze the separate hemispheric DPD data and the tilt angle data from Kodaikanal and Mount Wilson. Results. The tilt angles exhibit an extremely wide scatter due to both the intrinsic mechanism for its generation and measurement errors, for instance, the unipolar regions included in data sets. Different methods to deal with the uncertainties are mainly responsible for the controversial character of the previous results. The linear fit to the tilt-latitude relation of sunspot groups with Δs > 2.​​°5 of a cycle carried out without binning the data can minimize the effect of the tilt scatter on the uncertainty of the tilt coefficient. Based on this method the tilt angle coefficient is anti-correlated with the cycle strength with strong statistical significance (r = −0.85 at 99% confidence level). Furthermore, we find that tilts tend to be more saturated at high latitudes for stronger cycles. The tilts tend to show a linear dependence on the latitudes for weak cycles and a square-root dependence for strong cycles. Conclusions. This study disentangles the cycle dependence of sunspot group tilt angles from the previous results that were shown to be controversial, spurring confusion in the field.

The pitfalls of unipolar voltage mapping of the right ventricle

Abstract Funding Acknowledgements Type of funding sources: Other. Main funding source(s): The department of cardiology from Leiden University Medical Center receives unrestricted grants from Edwards Lifesciences, Biotronik, Medtronik, Boston Scientific and BioSense Webster. MS was supported by the Research Fellowship of the European Society of Cardiology 2017/2018. Background The current golden standard to accurately delineate scar potentially related to ventricular tachycardia relies on electroanatomical voltage mapping. Endocardial unipolar voltage (UV) mapping is increasingly used to detect intramural or subepicardial non-ischemic scars. 3D mapping systems determine and display the largest peak-to-peak amplitude of the electrogram within the window-of interest usually set from the QRS onset, but cannot not identify far-field electrograms or artifacts. Purpose To evaluate the influence of manual adjustment of the window-of-interest on the amplitude of endocardial and epicardial right ventricular (RV) unipolar electrograms. Methods Patients who underwent ablation of a RV scar-related VT with combined endo- and epicardial RV mapping were included. Endo- and epicardial points were reviewed with special interest towards the unipolar signal. In case a far-field, ST-segment elevation/depression or artifact was present, the window-of-interest was adjusted and the corresponding unipolar amplitude was collected. Results Thirty-three patients were included (age 50 ± 14years and 79% male). The underlying aetiology was definite arrhythmogenic right ventricular cardiomyopathy (ARVC; n = 17), athlete’s right ventricular outflow tract scar in (n = 9), cardiac sarcoidosis in (n = 3), scar of unknown origin (n = 2), borderline ARVC (n = 1) or myocarditis (n = 1). In total, 4225 endocardial points and 1960 epicardial points were re-analyzed. In 2987 (71%) endocardial points and 689 (65%) epicardial points the window-of-interest needed to be adjusted. Reason for this adjustment was ‘inclusion of far-field’ in 1380 (33%) endocardial- and 700 (36%) epicardial points; ‘inclusion of ST-segment elevation/depression’ in 1246 (29%) endocardial- and 316 (16%) epicardial points; RV-pacing artefact in 266 (6%) endocardial- and 116 (6%) epicardial points; and miscellaneous (e.g. unstable baseline or ablation point with artifact) in 95 (2%) endocardial- and 139 (7%) epicardial points (Figure). The median difference between the ‘automatically generated’ UV and the ‘adjusted’ UV was 0.81mV (IQR: 0.40-1.39) for the endocardial points and 0.54mV (IQR: 0.27-0.98) for the epicardial points. In 320 (8%) endocardial points the UV was changed from >5.5mV to <5.5mV, in 412 (10%) points from >4.4 to <4.4mV and in 396 (9%) points from >3.8mV to <3.8mV. Conclusion In the majority of endocardial and epicardial points the window-of-interest for unipolar voltage mapping needs to be adjusted to exclude far-field signal or ST-segment elevation/depression contributing to the automatically determined amplitude. Unadjusted unipolar voltage mapping underestimates low UV regions. RV-pacing generates a large unipolar far-field signal, which can obscure the local unipolar near-field signal. Accordingly, RV UV mapping during RV pacing should be used with caution. Abstract Figure. The pitfalls of UV mapping of the RV

A morphological study of unipolar magnetic fields and the relationship with sunspots

A morphological examination of the Kitt Peak photospheric magnetic maps has been made over three sunspot cycles in order to study the morphology of unipolar magnetic regions and sunspots. Unipolar magnetic regions (positive and negative) are a series of weak, large-scale longitudinal bands, extending from 0° to 60° in latitude and alternatively aligned in longitude. The first finding is that unipolar regions grow and decay with the sunspot cycle and thus are likely to be a part of the basic solar (dipolar) magnetism, not old active regions located below 30° in latitude (as have long been considered). The second finding is that positive pores and single spots (coalesced pores, often called ‘isolated’ spots or ‘independent’ spots) occur in a positive unipolar region (vice vera). Thus, the unipolar regions could be the source of single spots. The third finding is that a pair (positive and negative) of dense clusters of pores, single spots and large spots (a coalesced single spots) occur at each side of the boundary of neighboring (positive and negative) unipolar regions, forming pairs of spots across the boundary; in fact, pairs of spots do not occur in the middle of a unipolar region. The boundaries of unipolar regions are tentatively identified as the Hale boundary, where solar activities (including solar flares) occur). Thus, it is suggested that the presently accepted magnetic tube theory may need a new consideration.

Spatial–temporal evolution of photospheric weak-field shifts in solar cycles 21–24

Context. Weak magnetic field elements make a dominant contribution to the total magnetic field on the solar surface. Even so, little is known of their long-term occurrence. Aims. We study the long-term spatial–temporal evolution of the weak-field shift and skewness of the distribution of photospheric magnetic field values during solar cycles 21−24 in order to clarify the role and relation of the weak field values to the overall magnetic field evolution. Methods. We used Wilcox Solar Observatory (WSO) and the Synoptic Optical Long-term Investigations of the Sun Vector SpectroMagnetograph synoptic maps to calculate weak-field shifts for each latitude bin of each synoptic map, and thereby constructed a time–latitude butterfly diagram for shifts. We also calculated butterfly diagrams for skewness for all field values and for weak field values only. Results. The weak-field shifts and (full-field) skewness depict a similar spatial–temporal solar cycle evolution to that of the large-scale surface magnetic field. The field distribution has a systematic non-zero weak-field shift and a large skewness already at (and after) the emergence of the active region, even at the highest resolution. We find evidence for coalescence of opposite-polarity fields during the surge evolution. This is clearly more effective at the supergranulation scale. However, a similar dependence of magnetic field coalescence on spatial resolution was not found in the unipolar regions around the poles. Conclusions. Our results give evidence for the preference of even the weakest field elements toward the prevailing magnetic polarity since the emergence of an active region, and for a systematic coalescence of stronger magnetic fields of opposite polarities to produce weak fields during surge evolution and at the poles. We also find that the supergranulation process is reduced or turned off in the unipolar regions around the poles. These observations improve the understanding not only of the development of the weakest magnetic field elements, but also of the dynamics of magnetic fields at large, and even of processes below the solar surface.

Vortex flow properties in simulations of solar plage region: Evidence for their role in chromospheric heating

Context. Vortex flows exist across a broad range of spatial and temporal scales in the solar atmosphere. Small-scale vortices are thought to play an important role in energy transport in the solar atmosphere. However, their physical properties remain poorly understood due to the limited spatial resolution of the observations. Aims. We explore and analyze the physical properties of small-scale vortices inside magnetic flux tubes using numerical simulations, and investigate whether they contribute to heating the chromosphere in a plage region. Methods. Using the three-dimensional radiative magnetohydrodynamic simulation code MURaM, we perform numerical simulations of a unipolar solar plage region. To detect and isolate vortices we use the swirling strength criterion and select the locations where the fluid is rotating with an angular velocity greater than a certain threshold. We concentrate on small-scale vortices as they are the strongest and carry most of the energy. We explore the spatial profiles of physical quantities such as density and horizontal velocity inside these vortices. Moreover, to learn their general characteristics, a statistical investigation is performed. Results. Magnetic flux tubes have a complex filamentary substructure harboring an abundance of small-scale vortices. At the interfaces between vortices strong current sheets are formed that may dissipate and heat the solar chromosphere. Statistically, vortices have higher densities and higher temperatures than the average values at the same geometrical height in the chromosphere. Conclusions. We conclude that small-scale vortices are ubiquitous in solar plage regions; they are denser and hotter structures that contribute to chromospheric heating, possibly by dissipation of the current sheets formed at their interfaces.

The rotation rate of solar active and ephemeral regions – I. Dependence on morphology and peak magnetic flux

ABSTRACT Using magnetic field maps acquired by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, we measured rotation rates of 864 active and 322 ephemeral regions observed between 2010 and 2016. We found smaller magnetic tracers to show a tendency to rotate faster as compared to larger ones. Thus, ephemeral regions exhibit on average the fastest rotation rate. We further divided active regions into three classes. Class A comprised magnetic bipoles obeying Hale’s polarity law, Joy’s law, and exhibiting more coherent leading polarity in comparison with the following one. The second class B included active regions violating at least one of the aforementioned empirical laws. The third class U comprised unipolar active regions. We found no significant difference between the rotation rates of active regions of classes A and B. In contrast, unipolar active regions exhibited on average lower rotation rate and narrower distribution of the rotation rate differences. Assuming the rotation rate to indicate the anchoring depth of the magnetic structure within the convection zone, we supposed that active regions of classes A and B might be anchored throughout the entire convective envelope while unipolar active regions a rooted within a thin layer located either near the base of the convection zone or at a shallow near-surface depth.

Activity Complexes and a Prominent Poleward Surge during Solar Cycle 24

Abstract Long-lasting activity complexes (ACs), characterized as a series of closely located, continuously emerging solar active regions (ARs), are considered generating prominent poleward surges from observations. The surges lead to significant variations of the polar field, which are important for the modulation of solar cycles. We aim to study a prominent poleward surge during solar cycle 24 on the southern hemisphere, and analyze its originating ACs and the effect on the polar field evolution. We automatically identify and characterize ARs based on synoptic magnetograms from the Solar Dynamics Observatory. We assimilate these ARs with realistic magnetic configuration into a surface flux transport model, and simulate the creation and migration of the surge. Our simulations well reproduce the characteristics of the surge and show that the prominent surge is mainly caused by the ARs belonging to two ACs during Carrington rotations 2145–2159 (2013 December–2015 January). The surge has a strong influence on the polar field evolution of the southern hemisphere during the latter half of cycle 24. Without the about one-year-long flux emergence in the form of ACs, the polar field around the cycle minimum would have remained at a low level and even reversed to the polarity at cycle 23 minimum. Our study also shows that the long-lived unipolar regions due to the decay of the earlier emerging ARs cause an intrinsic difficulty of automatically identifying and precisely quantifying later emerging ARs in ACs.

Four Subjects in Solar Physics from the Point of View of the Electric Current Approach

Four major subjects in solar physics, the heating of the corona, the cause of the solar wind, the formation of sunspots and the cause of solar flares, are discussed on the basis of the electric current approach, a sequence of processes consisting of power supply(dynamo), transmission (currents/circuits) and dissipation(high coronal temperature, solar wind, sunspots and solar flares).This is because the four subjects have hardly been considered in terms of the electric current approach in the past, in spite of the fact that these subjects are various manifestations of electromagnetic processes. It is shown that this approach provides a new systematic way of considering each subject; (1) the long-standing issue of the coronal temperature, (2)the long-standing problem on the cause of the solar wind, (3)the presence of single spots(forgotten or dismissed in the past) and its relation to unipolar magnetic regions and (4) the crucial power/energy source and subsequent explosive processes of solar flares. The four subjects are obviously extremely complicated and difficult subjects, but it is hoped that the electric current approach might provide a new insight in considering the four subjects.

Long-term Evolution of the Sun’s Magnetic Field during Cycles 15–19 Based on Their Proxies from Kodaikanal Solar Observatory

Abstract The regular observation of the solar magnetic field is available only for about the last five cycles. Thus, to understand the origin of the variation of the solar magnetic field, it is essential to reconstruct the magnetic field for the past cycles, utilizing other data sets. Long-term uniform observations for the past 100 yr as recorded at the Kodaikanal Solar Observatory (KoSO) provide such an opportunity. We develop a method for the reconstruction of the solar magnetic field using the synoptic observations of the Sun’s emission in the Ca II K and Hα lines from KoSO for the first time. The reconstruction method is based on the fact that the Ca II K intensity correlates well with the unsigned magnetic flux, while the sign of the flux is derived from the corresponding Hα map that provides the information of the dominant polarities. Based on this reconstructed magnetic map, we study the evolution of the magnetic field in Cycles 15–19. We also study bipolar magnetic regions (BMRs) and their remnant flux surges in their causal relation. Time–latitude analysis of the reconstructed magnetic flux provides an overall view of magnetic field evolution: emergent magnetic flux, its further transformations with the formation of unipolar magnetic regions (UMRs), and remnant flux surges. We identify the reversals of the polar field and critical surges of following and leading polarities. We found that the poleward transport of opposite polarities led to multiple changes of the dominant magnetic polarities in poles. Furthermore, the remnant flux surges that occur between adjacent 11 yr cycles reveal physical connections between them.

Multioperation-Mode Light-Emitting Field-Effect Transistors Based on van der Waals Heterostructure.

2D semiconductors have shown great potential for application to electrically tunable optoelectronics. Despite the strong excitonic photoluminescence (PL) of monolayer transition metal dichalcogenides (TMDs), their efficient electroluminescence (EL) has not been achieved due to the low efficiency of charge injection and electron-hole recombination. Here, multioperation-mode light-emitting field-effect transistors (LEFETs) consisting of a monolayer WSe2 channel and graphene contacts coupled with two top gates for selective and balanced injection of charge carriers are demonstrated. Visibly observable EL is achieved with the high external quantum efficiency of ≈6% at room temperature due to efficient recombination of injected electrons and holes in a confined 2D channel. Further, electrical tunability of both the channel and contacts enables multioperation modes, such as antiambipolar, depletion,and unipolar regions, which can be utilized for polarity-tunable field-effect transistors and photodetectors. The work exhibits great potential for use in 2D semiconductor LEFETs for novel optoelectronics capable of high efficiency, multifunctions, and heterointegration.

Restructuring of the Solar Magnetic Fields and Flare Activity Centers in Cycle 24

The development of the solar magnetic activity in cycle 24 has been analyzed. It has been shown that the significant north–south asymmetry of magnetic activity was accompanied by the asynchronous reorganization of solar magnetic fields in the northern and southern hemispheres. The formation of unipolar magnetic regions after the decay of activity centers has been studied. The meridional transport of unipolar magnetic regions leading to changes in the zonal structure of the solar magnetic field has been shown. Long-lived centers of flare activity have been found to exist during the periods of magnetic field restructuring. The spatiotemporal analysis of the flare ensemble making it possible to diagnose non-stationary processes in the solar atmosphere has been shown.

The impact of coronal hole characteristics and solar cycle activity in reconstructing coronal holes with EUHFORIA

Modelling with high accuracy the open magnetic field and the fast solar wind in the heliosphere is essential for space weather forecasting purposes. Primary sources of open magnetic field flux are Coronal Holes (CH), uni-polar regions that appear as dark patches in the solar corona when observed in X-ray and extreme-ultraviolet (EUV) images due to having significantly lower density and temperature to their surroundings. Therefore, when assessing how well the open magnetic field and the fast solar wind are modelled one can look at how well the model performs on one of its fundamental functions, that of reconstructing coronal hole areas. In this study we investigate how the CH morphology (i.e. latitudinal position of the centre of mass, area, intensity, elongation) and the solar variability, from high to low activity periods, can affect the results. We also investigated the possibility that the model is reconstructing CHs that are systematically shifted with respect to their observed position. The study is applied on 15 CHs exhibiting different latitudinal position and geometry. We compare the modelled CH areas with boundaries obtained by remote sensing EUV observations using the CATCH tool (Collection of Analysis Tools for Coronal Holes). We found no apparent effect of the CH characteristics on the modelling capabilities. In addition, solar cycle activity seems not to have any effect either. However, we emphasize that our sample is small and this outcome highlights the need for an extended research.

Simulations Show that Vortex Flows Could Heat the Chromosphere in Solar Plage

Abstract The relationship between vortex flows at different spatial scales and their contribution to the energy balance in the chromosphere is not yet fully understood. We perform three-dimensional (3D) radiation-magnetohydrodynamic simulations of a unipolar solar plage region at a spatial resolution of 10 km using the MURaM code. We use the swirling-strength criterion that mainly detects the smallest vortices present in the simulation data. We additionally degrade our simulation data to smooth out the smaller vortices, so that also the vortices at larger spatial scales can be detected. Vortex flows at various spatial scales are found in our simulation data for different effective spatial resolutions. We conclude that the observed large vortices are likely clusters of much smaller ones that are not yet resolved by observations. We show that the vertical Poynting flux decreases rapidly with reduced effective spatial resolutions and is predominantly carried by the horizontal plasma motions rather than vertical flows. Since the small-scale horizontal motions or the smaller vortices carry most of the energy, the energy transported by vortices deduced from low-resolution data is grossly underestimated. In full-resolution simulation data, the Poynting flux contribution due to vortices is more than adequate to compensate for the radiative losses in plage, indicating their importance for chromospheric heating.

Performance Limits of Vertical Unipolar Power Devices in GaN and 4H-SiC

GaN and 4H-SiC are emerging wide-bandgap semiconductors that have unipolar power-device figures-of-merit 350– $400\times $ higher than silicon, but precise design and performance information on GaN has been unavailable due to lack of ionization rate data in that material. In this paper we calculate performance limits of unipolar vertical drift regions in GaN using recently published impact ionization data, and compare these limits to those of silicon and 4H-SiC. To assist in the design of power devices, we include equations for the doping and thickness of optimum unipolar drift regions in both materials.

The propagation of the Ion-Flow Near the AC Transmission Lines

The series of physical processes contained in the corona layer is the source of space ions formed by the corona discharge of the high-voltage AC line. However, since these physical processes are difficult to calculate accurately and the corona layer thickness is usually small, the corona layer is ignored in the published literature on the corona discharge of the AC line, and the ions are considered to be emitted directly from the conductor surface. In this paper, the distribution area of the charged particles is divided into the corona plasma region and the unipolar drift region. A mathematical physical model of the photoionization and photoemission, which sustain self-sustaining discharge in the positive and negative half-cycle of corona plasma region of the AC conductor in dry air, are established. The influence of the ions generated in the previous cycle is also considered in the numerical simulation process. Finally, a complete microscopic physical model describing the corona discharge of the AC conductor under dry air is established. The validity of the physical model proposed in this paper is demonstrated by comparison with experimental results reported in the literature. Through the numerical simulation of the ion flow field of positive and negative half-cycle and the corona current, the physical process of the corona discharge around the AC line is better understood and analysed. Further positive and negative half-cycle charged particle motion and corona plasma regions were compared and analyzed. This work provides a brand new mathematical physics method for understanding and applying AC corona discharge.