Valentina V. Zharkova

Valentina V. Zharkova
Northumbria University · Department of Mathematics, Physics and Electrical Engineering

BSc, MSc , PhD, FRAS

About

271
Publications
53,826
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2,838
Citations
Additional affiliations
September 2013 - present
Northumbria University
Position
  • Professor (Full)
Description
  • Department of Mathematics and Information Sciences http://www.northumbria.ac.uk/sd/academic/ee/about/mis/ Pandon Building, Faculty of Engineering and Environment, University of Northumbria Newcastle upon Tyne NE2 1XE, UK
January 2013 - August 2016
Northumbria University
Position
  • Professor of Physics and Mathematics
July 2002 - August 2002
Stanford University
Position
  • Professor

Publications

Publications (271)
Article
Full-text available
Using full disk synoptic maps of solar background magnetic field (SBMF) captured from the Wilcox Solar Observatory for 30 latitudinal bands for cycles 21-24 principal components (PCs), or eigen vectors of magnetic oscillations are obtained. The PCs are shown to come in pairs assigned to magnetic waves produced by dipole, quadruple, sextuple and oct...
Preprint
Full-text available
Frequencies of volcanic eruptions in the past 270 years are compared with variations of solar activity and summary curve of principal components of the solar background magnetic field (SBMF).Frequency analysis with Morlet wavelet reveals the most pronounced period of volcanic eruptions of 22 years. There is a strong correlation (-0.84) between volc...
Article
Full-text available
In this article we aim to investigate the kinetic turbulence in a reconnecting current sheet (RCS) with X- and O-nullpoints and to explore its link to the features of accelerated particles. We carry out simulations of magnetic reconnection in a thin current sheet with 3D magnetic field topology affected by tearing instability until the formation of...
Chapter
Full-text available
Daily ephemeris of Sun-Earth distances in two millennia (600–2600) showed significant decreases in February–June by up to 0.005 au in millennium M1 (600–1600) and 0.011au in millennium M2 (1600–2600). The Earth’s aphelion in M2 is shorter because shifted towards mid-July and longer because shifted to mid January naturally explaining two-millennial...
Article
Aims. This research aims to explore variations of electron pitch-angle distributions (PADs) during spacecraft crossing of reconnecting current sheets (RCSs) with magnetic islands. Our results can benchmark the sampled characteristic features with realistic PADs derived from in situ observations. Methods. Particle motion is simulated in 2.5D Harris-...
Preprint
Full-text available
In this study we overview recent advances with prediction of solar activity using as a proxy solar background magnetic field and detection of grand solar cycles of about 400 years separated by grand solar minima (GSMs).The previous GSM known as the Maunder minimum was recorded from 1645 to 1715. The terrestrial temperature during Maunder Minimum wa...
Article
In this paper we present the interpretation of the observations of the flare from 6 September 2017 reported in Paper I. These include gamma-ray (GR), hard X-ray (HXR), soft X-rays, Lyα line, extreme ultraviolet (EUV), Hα, and white light (WL) emission, which were recorded during the two flaring events 1 (FE1) and 2 (FE2) that occurred at 11:55:37 U...
Article
Aims. The 6 September 2017 X9.3 solar flare produced very unique observations of magnetic field transients and a few seismic responses, or sunquakes, detected by the Helioseismic and Magnetic Imager (HMI) instrument aboard Solar Dynamic Observatory (SDO) spacecraft, including the strongest sunquake ever reported. This flare was one of a few flares...
Article
Full-text available
Suprathermal electrons with energies of ~70eV and above are observed at 1 AU as dispersionless halo electrons and magnetic field-aligned beams of strahls. For a long time, it has been thought that the both populations originate only from the solar corona, and the only active process impacting their properties in the solar wind is scattering. This v...
Preprint
Full-text available
Recently discovered long-term oscillations of the solar background magnetic field associated with double dynamo waves generated in inner and outer layers of the Sun indicate that the solar activity is heading in the next three decades (2019-2055) to a Modern grand minimum similar to Maunder one. On the other hand, a reconstruction of solar total ir...
Article
Full-text available
Aims. Particles are known to have efficient acceleration in reconnecting current sheets with multiple magnetic islands that are formed during a reconnection process. Using the test-particle approach, the recent investigation of particle dynamics in 3D magnetic islands, or current sheets with multiple X- and O-null points revealed that the particle...
Article
Full-text available
Recently discovered long-term oscillations of the solar background magnetic field associated with double dynamo waves generated in inner and outer layers of the Sun indicate that the solar activity is heading in the next three decades (2019–2055) to a Modern grand minimum similar to Maunder one. On the other hand, a reconstruction of solar total ir...
Article
Aims. Hydrogen Lyman continuum emission is greatly enhanced in the impulsive kernels of solar flares, with observations of Lyman lines showing impulsive brightening and both red and blue wing asymmetries, based on the images with low spatial resolution. A spate of proposed instruments will study Lyman emission in more detail from bright, impulsive...
Article
Aims. Magnetic reconnection in large Harris-type reconnecting current sheets (RCSs) with a single X-nullpoint often leads to the occurrence of magnetic islands with multiple O- and X-nullpoints. Over time these magnetic islands become squashed, or coalescent with two islands merging, as has been observed indirectly during coronal mass ejection and...
Article
Active region NOAA 11283 produced two X-class flares on 6 and 7 September 2011 that have been well studied by many authors. The X2.1 class flare occurred on September 6, 2011 and was associated with the first of two homologous white light flares produced by this region, but no sunquake was found with it despite the one being detected in the second...
Article
Full-text available
Aim. Sharp rises of hard X-ray (HXR) emission accompanied by H α line profiles with strong red-shifts up to 4 Å from the central wavelength, often observed at the onset of flares with the Specola Solare Ticinese Telescope (STT) and the Swedish Solar Telescope (SST), are not fully explained by existing radiative models. Moreover, observations of whi...
Article
Full-text available
In this communication we provide our answers to the comments by Usoskin (2017) on our recent paper (Popova et al, 2017a). We show that Principal Component Analysis (PCA) allows us to derive eigen vectors with eigen values assigned to variance of solar magnetic field waves from full disk solar magnetograms obtained in cycles 21-23 which came in pair...
Article
Full-text available
Additional acceleration of protons and electrons passing through a 3D reconnecting current sheet (RCS) of the solar corona and heliosphere is investigated with PIC approach. The simulation confirms spatial separation of electrons and protons and generation of a polarisation electric field induced by separated particles. In the heliospheric current...
Article
Full-text available
The observations of solar flare onsets show rapid increase of hard and soft X-rays, ultra-violet emission with large Doppler blue shifts associated with plasma upflows, and Hα hydrogen emission with red shifts up to 1–4 Å. Modern radiative hydrodynamic models account well for blue-shifted emission, but struggle to reproduce closely the red-shifted...
Article
Full-text available
Using a summary curve of two eigen vectors of solar magnetic field oscillations derived with Principal Components Analysis (PCA) from synoptic maps for solar cycles 21-24 as a proxy of solar activity, we extrapolate this curve backwards three millennia revealing 9 grand cycles lasting 350-400 years each. The summary curve shows a remarkable resembl...
Article
Full-text available
In this paper we revise our prediction of solar activity using a solar background magnetic field as a proxy by the inclusion of eigen vectors of solar magnetic waves produced by quadruple magnetic sources, in addition to the principal eigen modes generated by two-layer dipole sources (Zharkova et al., 2015). By considering the interference of two d...
Article
In this paper we consider simultaneous analytical solutions of continuity equations for electron beam precipitation a) in collisional losses and b) in Ohmic losses, or mixed energy losses (MEL), by applying the iterative method to calculate the resulting differential densities at given precipitation deph. The differential densities of precipitating...
Article
Full-text available
Observations of solar flares with sunquakes by space- and ground-based instruments reveal essentially different dynamics of seismic events in different flares. Some sunquakes are found to be closely associated with the locations of hard X-ray (HXR) and white-light (WL) emission, while others are located outside either of them. In this article we in...
Article
Full-text available
We derive two principal components (PCs) of temporal magnetic field variations over the solar cycles 21-24 from full disk magnetograms covering about 39% of data variance, with λ=-0.67. These PCs are attributed to two main magnetic waves travelling from the opposite hemispheres with close frequencies and increasing phase shift. Using symbolic reger...
Article
We present updated analytical solutions of continuity equations for power-law beam electrons precipitating in (a) purely collisional losses and (b) purely ohmic losses. The solutions of continuity equation (CE) normalized on electron density presented in Dobranskis & Zharkova are found by method of characteristics eliminating a mistake in the densi...
Article
Full-text available
Acceleration of protons and electrons in a reconnecting current sheet (RCS) is investigated with the test particle and particle-in-cell (PIC) approaches in a 3D magnetic topology. PIC simulations confirm a spatial separation of electrons and protons with respect to the midplane depending on the guiding field. Simulation reveals that the separation...
Article
Full-text available
We present observations of energetic particle flux increases up to 1 MeV at 1 AU, which cannot be associated with ordinary mechanisms of particle acceleration, such as acceleration at shocks or at the Sun. Such unusual energetic particle events very likely have a local origin. Multi-spacecraft observations show that numerous cases of energetic part...
Article
Full-text available
Particles of fast solar wind in the vicinity of the heliospheric current sheet (HCS) or in a front of interplan-etary coronal mass ejections (ICMEs) often reveal very peculiar energy or velocity profiles, density distributions with double or triple peaks, and well-defined streams of electrons occurring around or far away from these events. In order...
Article
Full-text available
A comprehensive spectral analysis of both the solar background magnetic field (SBMF) in cycles 21-23 and the sunspot magnetic field in cycle 23 reported in our recent paper showed the presence of two principal components (PCs) of SBMF having opposite polarity, e.g., originating in the northern and southern hemispheres, respectively. Over a duration...
Article
Full-text available
The original continuity equation (CE) used for the interpretation of the power law energy spectra of beam electrons in flares was written and solved for an electron beam flux while ignoring an additional free term with an electron density. In order to remedy this omission, the original CE for electron flux, considering beam's energy losses in Coulo...
Article
Full-text available
Principle component analysis (PCA) of the solar background magnetic field (SBMF) measured from Wilcox Solar Observatory (WSO) magnetograms revealed the following principal components (PCs) in latitudes: two main symmetric components, which are the same for all cycles 21-23, and three pairs of asymmetric components, which are unique for each cycle....
Article
Full-text available
In the present paper we derive some subordination and superordination results for p-valent functions in the open unit disk by using certain fractional derivative operator. Relevant connections of the results presented in the paper with various known results are also considered.
Poster
Full-text available
The solar wind plasma dynamics in the vicinity of the heliospheric current sheet are considered as observed at different heliocentric distances
Article
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We present results of our preliminary analysis of acoustically active X-class flare of September 7, 2011. We report two acoustic sources detected via acoustic holography and verified by finding a ridge in time-distance diagrams. We compare the directional information extracted from time-distance and acoustic holography, showing a good agreement in...
Article
Full-text available
This paper studies the sufficient conditions for the starlikeness and convexity of a class of fractional integral operators of certain analytic and p-valent functions in the open unit disk. Further characterization theorems associated with the Hadamard product (or convolution) are also considered.
Article
In the present paper, we derive some results for the first order linear strong differential subordination of p-valent functions in the open unit disk involving certain fractional derivative operator.
Article
Full-text available
The first near-side X-class flare of Solar Cycle 24 occurred in February 2011 (SOL2011-02-05T01:55) and produced a very strong seismic response in the photosphere. One sunquake was reported by Kosovichev (Astrophys. J. Lett. 734, L15, 2011), followed by the discovery of a second sunquake by Zharkov, Green, Matthews et al. (Astrophys. J. Lett. 741,...
Article
This timely book presents new research results on high-energy particle physics related to solar flares, covering the theory and applications of the reconnection process in a clear and comprehensible way. It investigates particle kinetics and dynamics in flaring atmospheres and their diagnostics from spectral observations, while providing an analysi...
Article
Full-text available
Observations of the lower atmosphere and below the surface of flares, including changes in the photospheric magnetic field and appearance of strong optical and seismic emission, are challenging tasks to explain in the context of existing flare models. Such observations indicate the poorly understood connections between the primary energy release oc...
Article
Full-text available
The aim of this paper is to derive the principal components (PCs) in variations of (i) the solar background magnetic field (SBMF), measured by the Wilcox Solar Observatory with low spatial resolution for solar cycles 21-23, and (ii) the sunspot magnetic field (SMF) in cycle 23, obtained by SOHO/MDI. For reduction of the component dimensions, princi...
Article
In this paper we investigate stability of an electron beam with power law energy distributions to generation of Langmuir waves during its precipitation into the solar atmosphere in a presence of collisional and Ohmic losses. We explore analytically and numerically electron beam instabilities and derive the conditions of the beam pinching with forma...
Article
Full-text available
In this paper, we apply an assumption of the reconnecting heliospheric current sheet (HCS) for explanation of some contradictory results in the experimental detection of the sector boundaries (SBs) from the interplanetary magnetic field and electron pitch-angle measurements. Trajectories, densities, velocity, and pitch-angle distributions of partic...
Article
In this paper trajectories, densities, velocity and pitch angle distributions of particles accelerated by a super-Dreicer electric field are investigated with 2.5D full kinetic particle-in-cell (PIC) approach in the heliospheric current sheet (HCS) assumed to undergo a slow magnetic reconnection process with magnetic field configurations deduced fr...
Article
In this study we carry out Principle Component Analysis (PCA) (a) the solar background magnetic field (SBMF) measured by the Wilcox Solar Observatory with low spatial resolution for solar cycles 21-23, and, (b) the sunspot excess magnetic field (SEMF) in cycle 23 obtained by SOHO/MDI. PCA analysis reveals two independent temporal SBMF components of...
Article
Full-text available
Energetic particles are critical components of plasma populations found throughout the universe. In many cases particles are accelerated to relativistic energies and represent a substantial fraction of the total energy of the system, thus requiring extremely efficient acceleration processes. The production of accelerated particles also appears coup...
Article
We obtain sharp bounds for some subclasses of p-valent functions in the open unit disk involving certain fractional derivative operator.
Article
Full-text available
In the present paper we derive some results for strong differential subordination of p-valent functions involving certain fractional deriva-tive operator.
Article
In the present paper, we derive some results for strong differential superordination of p-valennt functions involving certain fractional derivative operator.
Article
Full-text available
The object of the present paper is to give an application of the fractional derivative operator for p-valent functions in the open unit disk to the differential inequalities.
Article
In the present paper we obtain sharp bounds for some subclasses of p-valent functions in the open unit disk involving certain fractional derivative operator.
Article
The kinetics of beam electron precipitation from the top of a loop into the solar atmosphere with density gradients and an increasing magnetic field have been generally described. The Fokker-Planck equations are solved with regard to Coulomb collisions and the effect of the electric field induced by this beam. The photon spectra and polarization de...
Article
Analysis of seismic emission (sun-quakes) induced in the solar interior in the vicinity of flares offers us an opportunity to explore the physical processes of energy transport in flaring atmospheres. Only about 17 M and X-class flares have been reported to show seismic signatures in the form or ripples or egression sources, revealing that some of...
Article
In this paper we discuss the effects of different energy loss mechanisms on resulting hard X-ray and MW emission of beam electrons injected in the loop top in the corona and precipitating into loop footpoints. For this purpose we use numeric solutions of Fokker-Planck equation considering collisional and Ohmic energy losses and anisotropic scatteri...
Article
Magnetic reconnection at the heliospheric current sheets (CS) is likely to be one of the important sources of high energy electrons and protons/ions in the interplanetary space. There are several unexplained features in-situ observations, such as the accelerated particles asymmetry, velocity profile asymmetry and high energy electron densities abou...
Article
Full-text available
We present an analysis of the 2011 February 15 X-class solar flare, previously reported to produce the first sunquake in solar cycle 24. Using acoustic holography, we confirm the first, and report a second, weaker, seismic source associated with this flare. We find that the two sources are located at either end of a sigmoid, which indicates the pre...
Article
Full-text available
High-energy X-rays and gamma-rays from solar flares were discovered just over fifty years ago. Since that time, the standard for the interpretation of spatially integrated flare X-ray spectra at energies above several tens of keV has been the collisional thick-target model. After the launch of the Reuven Ramaty High Energy Solar Spectroscopic Image...
Article
Full-text available
Some of the most challenging observations to explain in the context of existing flare models are those related to the lower atmosphere and below the solar surface. Such observations, including changes in the photospheric magnetic field and seismic emission, indicate the poorly understood connections between energy release in the corona and its impa...
Article
Full-text available
The first observations of seismic responses to solar flares were carried out using time-distance (TD) and holography techniques applied to SOHO/Michelson Doppler Imager (MDI) Dopplergrams obtained from space and unaffected by terrestrial atmospheric disturbances. However, the ground-based network GONG is potentially a very valuable source of sunqua...
Article
Full-text available
We review basic theoretical concepts in particle acceleration, with particular emphasis on processes likely to occur in regions of magnetic reconnection. Several new developments are discussed, including detailed studies of reconnection in three-dimensional magnetic field configurations (e.g., current sheets, collapsing traps, separatrix regions) a...
Article
Full-text available
Acceleration of protons and electrons in a reconnecting current sheet (RCS) is investigated with the test particle and particle-in-cell (PIC) approaches in the 3D magnetic configuration including the guiding field. PIC simulations confirm a spatial separation of electrons and protons towards the midplane and reveal that this separation occur as lon...