Jana Šafránková

Jana Šafránková
Charles University in Prague | CUNI · Department of Surface and Plasma Science

About

477
Publications
13,193
Reads
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4,470
Citations
Citations since 2016
70 Research Items
2083 Citations
20162017201820192020202120220100200300400
20162017201820192020202120220100200300400
20162017201820192020202120220100200300400
20162017201820192020202120220100200300400
Additional affiliations
January 1972 - present
Charles University in Prague
Position
  • Professor (Full)

Publications

Publications (477)
Article
Full-text available
The magnetopause is treated as a boundary where the pressure of the incoming solar wind is balanced by the pressure of the geomagnetic field and the plasma pressure inside the magnetopause is often neglected. However, published studies of pressure balance at the magnetopause reveal an excess of the magnetosheath pressure. Moreover, our survey of ab...
Article
Full-text available
The Martian ionosphere, modulated by the solar wind from the topside and remnant crustal magnetic fields close to the surface, possesses unique structures different from Earth and Venus. Integrated observations by the plasma and magnetic field instruments onboard the Mars Atmosphere and Volatile Evolution spacecraft show evidence of ionospheric pla...
Article
Full-text available
Long-lasting radial interplanetary magnetic field (IMF) intervals in which IMF points along the solar wind velocity for several hours have many interesting properties. We investigate the average parameters and the behavior of magnetic field fluctuations within 419 such radial intervals. The power spectral density (PSD) calculated over 1-h intervals...
Article
Less abundant but still dynamically important solar wind components are the proton beam and alpha particles, which usually contribute similarly to the total ion momentum. The main characteristics of alpha particles are determined by the solar wind source region, but the origin of the proton beam and its properties are still not fully explained. We...
Article
Full-text available
Understanding plasma turbulence below the ion characteristic scales is one of the key open problems of solar wind physics. The bulk of our knowledge about the nature of the kinetic-scale fluctuations comes from the high-cadence measurements of the magnetic field. The spacecraft frame frequencies of the sub-ion scale fluctuations are frequently arou...
Article
Full-text available
Magnetic pressure inside the magnetopause is usually balanced with a sum of thermal plasma and magnetic pressures on the magnetosheath side. However, observations reveal that the magnetosheath magnetic field can be frequently larger than that in the magnetosphere (inverse magnetic field gradient across the magnetopause), and thus, the enhanced pres...
Article
Full-text available
Turbulent cascade transferring the free energy contained within the large scale fluctuations of the magnetic field, velocity and density into the smaller ones is probably one of the most important mechanisms responsible for heating of the solar corona and solar wind, thus the turbulent behavior of these quantities is intensively studied. The temper...
Article
Full-text available
Observations of proton density fluctuations of the solar wind at 1 au have shown the presence of a decade-long transition region of the density spectrum above sub-ion scales, characterized by a flattening of the spectral slope. We use the proton density fluctuations data collected by the BMSW instrument on-board the Spektr-R satellite in order to d...
Article
Full-text available
We present a large statistical study of the fluctuation anisotropy in minimum variance (MV) frames of the magnetic field and solar wind velocity. We use 2, 10, 20, and 40 minute intervals of simultaneous magnetic field (the Wind spacecraft) and velocity (the Spektr-R spacecraft) observations. Our study confirms that magnetic turbulence is a composi...
Article
Full-text available
The paper reviews the interaction of collisionless interplanetary (IP) shocks with the turbulent solar wind. The coexistence of shocks and turbulence plays an important role in understanding the acceleration of particles via Fermi acceleration mechanisms, the geoeffectiveness of highly disturbed sheaths following IP shocks and, among others, the na...
Article
Faraday cups can measure velocity distribution functions of space plasmas and are frequent instruments on heliophysics missions. A new version of a Faraday cup instrument is in development for the Luna 26 mission and will be used for fast monitoring of the solar wind plasma parameters. The prototype of this instrument is exposed to dust impacts in...
Article
Full-text available
Empirical models of bow shock and magnetic pileup boundary locations are typically based on the identification of individual boundary crossings and their subsequent fitting by properly chosen dependences. Such an approach, however, requires a large set of identified crossings, whose compilation can be easily a source of a significant bias. Moreover...
Article
Full-text available
High-speed streams (HSSs) are believed to be only slightly affected by different interactions on their path from the Sun to Earth and thus the analysis of their observations can provide information on the structure and temporal variations of the magnetic field and plasma parameters at the source region. We have chosen three coronal holes supplying...
Article
Full-text available
Observations of the magnetic field for two passages through the Earth's magnetosheath are used for comparison with two simple models of the magnetosheath field that describe it as a potential field. We apply the Kobel and Flückiger (1994, https://doi.org/10.1029/94JA01778) model and the Romashets and Vandas (2019, https://doi.org/10.1029/2006JA0120...
Chapter
The magnetopause is the principal boundary dividing the magnetic field of the solar origin from the region of space that is occupied by the Earth's magnetic field. The shape and location of this boundary varies in response to upstream driving as well as to the internal state of the magnetosphere. Since solar wind mass and momentum entering the magn...
Presentation
Full-text available
Турбулентность в солнечном ветре, как правило, описывается в рамках подходов развитой турбулентности. Однако наблюдения показывают, что развитие турбулентности может сдерживаться границами между различными крупномасштабными структурами в межпланетном околоземном пространстве, что приводит к отличиям спектров флуктуаций от вида, предсказанного общеп...
Article
Various solar wind ion species move with different speeds and theoretical considerations as well as limited observations in a region close to the Sun show that heavy solar wind ions tend to flow faster than protons, at least in less-aged fast solar wind streams. The solar wind flow carries the frozen-in interplanetary magnetic field (IMF) and this...
Article
Full-text available
We present the results of a 2.5‐D (2‐D in space and 3‐D in currents and electromagnetic fields) electromagnetic hybrid simulation run for foreshock wave activity during an interval of a radial interplanetary magnetic field (IMF). The simulation predicts nonlinear waves and foreshock expansion in connection with the development of cavitons and the f...
Article
Full-text available
We present an analysis of 1‐year data of dust impacts observed on two of the Earth‐orbiting Magnetospheric Multiscale mission (MMS) spacecraft. The dust impact signals were identified in observations of the electric field probes and were registered simultaneously by monopole and dipole configurations of the instrument. This unique setup allows us t...
Article
Full-text available
The structure of subcritical interplanetary shocks was studied using high time resolution from the BMSW plasma instrument onboard the Spektr-R satellite and MFI magnetometer measurements from WIND. Ion scales of the ramp and wavelength of precursor waves were obtained and compared with results of the bow shock structure study. The comparison of pre...
Article
Full-text available
This Letter presents an analysis of the sunward Poynting flux throughout magnetosheath and foreshock (directly measured by INTERBALL-1, CLUSTER-4 and DOUBLE STAR TC1) and its correlation and bicorrelation with the dynamic pressure of the solar plasma flow. It demonstrates, for the first time, that perturbations, caused by the resonances in the magn...
Presentation
Full-text available
The speed value is traditionally considered as one of the most important parameters in the formation of turbulent fluctuation cascade in the solar wind. The fast streams are characterized by higher level of turbulent fluctuations, with steeper frequency spectra at proton scales (Bruno et al., APJL 2009). However the division into fast and slow stre...
Article
Full-text available
The terrestrial foreshock as a region permeated by different types of plasma waves, various particle populations, and strong wave activity is a subject of intensive investigations. Our statistical study of the solar wind proton velocity deceleration in the foreshock uses multipoint observations of the THEMIS mission and compare them with the Wind s...
Article
Full-text available
Ion velocity distribution functions (VDFs) measured in-situ in the solar wind show often large deviations from a simple Maxwellian distribution. Even a main part of the proton VDF (proton core) situated around the global maximum maintains a bi-Maxwellian character. Moreover, skewness, related to a non-thermal tail or proton beam, is often observed....
Article
Abstract Kinetic-scale fluctuations in magnetized collisionless plasmas, such as a solar wind, attract attention owing to their vital role in the dynamics of the dissipation of free energy to random particle motion. As the free energy cascades in the inertial range of turbulence, fluctuations at ion characteristic scales become more compressible. M...
Presentation
Full-text available
The theoretical models are worked out as a rule for the developed turbulence. In classical approach the turbulent cascade is described by two power laws respectively for magnetohydrodynamic and kinetic scales with break between them. Actually this situation is observed for plasma and magnetic field fluctuations basically in the slow steady solar wi...
Article
Full-text available
We use both solar wind observations and empirical magnetopause models to reconstruct time series of the magnetopause standoff distance for nearly five solar cycles. Since the average annual interplanetary magnetic field (IMF) Bz is about zero, and the annual IMF cone angle varies between 54.0° and 61.2°, the magnetopause standoff distance on this t...
Poster
Full-text available
The turbulent cascade in the solar wind is not stable and strongly affected by surrounding plasma conditions. In particular the large scale solar wind structures play a critical role in its formation. Classical turbulent spectra are observed as a rule in the steady solar wind whereas solar wind disturbed by some transient events can spawn spectra s...
Article
Full-text available
Plain Language Summary The Sun is continuously emitting a stream of charged particles—called the solar wind—from its upper atmosphere. The terrestrial magnetosphere forms the obstacle to its flow. Due to supersonic speed of the solar wind, the bow shock is created ahead of the magnetosphere. This abrupt transition region between supersonic and subs...
Article
A corotating interaction region (CIR) develops between the solar wind streams with different bulk speeds emanating from distinct coronal sources. The arising pressure perturbations redistribute momentum between adjacent streams forming the regions of the compressed solar wind around the stream interface. We focus on properties of α-particles with r...
Article
Full-text available
We investigate the influence of two typically unconsidered parameters—Earth's magnetic dipole eccentricity and ring current—on the location of the magnetopause. Although empirical magnetopause models generally assume the Earth's magnetic field to be axially symmetric, the terrestrial magnetic dipole is shifted by as much as 500 km out of the Earth'...
Article
We study the polarization properties of the velocity fluctuations in solar wind turbulence using high-resolution data from the Spektr-R spacecraft. The ratio of perpendicular to parallel velocity fluctuations in the inertial range is smaller than the equivalent ratio for magnetic fluctuations, but gradually increases throughout this range. In the k...
Article
Full-text available
The APEX mother-daughter project (Active Plasma EXperiments) was launched into an elliptical polar orbit (440–3,080 km) in December 1991. It consisted of the main Russian Interkosmos–25 (IK–25) satellite and the Czech MAGION–3 subsatellite, both with international scientific payloads. The mission used intensive modulated electron beam emissions and...
Article
The solar wind is not stationary and variations of the magnetic field magnitude and/or direction and plasma parameters are frequent. Interactions of fast forward shocks and interplanetary magnetic field discontinuities with the bow shock were analyzed in details theoretically as well as experimentally. However, an oblique interaction between a fast...
Article
Observed delays in the ground response to solar wind directional discontinuities have been explained as the result of larger than expected magnetosheath propagation times. Recently, Samsonov et al. (2017, https://doi.org/10.1002/2017GL075020) showed that the typical time for a southward interplanetary magnetic field (IMF) turning to propagate acros...
Article
The global structure of magnetopause boundary layers under the radial interplanetary magnetic field (IMF) conditions is studied by a comparison of experimental and simulation results. In magnetohydrodynamic simulations, the hemispherical asymmetry of the reconnection locations was found. The draped field adjacent to the magnetopause points northwar...
Article
The properties of inertial and kinetic range solar wind turbulence have been investigated with the arbitrary-order Hilbert spectral analysis method, applied to high-resolution density measurements. Due to the small sample size, and to the presence of strong non-stationary behavior and large-scale structures, the classical structure function analysi...
Conference Paper
The role of dust in the space environment is of increasing interest in recent years and also the fast development of fusion devices with a magnetic confinement brought new issues in the plasma–surface interaction. Among other processes, secondary electron emission plays an important role for dust charging in interplanetary space and its importance...
Conference Paper
Full-text available
Low-affinity materials (as MgO, CaO, LiF) are known to vary their Mie scattering profile with a changing charge. These materials are also predisposed to autoionize themselves. Although the oxides, opposite to lithium fluoride, are expected within the space environment, the presented investigations were carried out on LiF, since the aforementioned p...
Article
The paper presents for the first time observations of unusual reconnection events in the solar wind. In all solar wind types, we identify magnetic reconnection exhausts accompanied by one or two side jets. This complex structure is created around a single current sheet and the jet(s) oriented in the same direction as the main exhaust is (are) spati...
Article
Relative properties of solar wind protons and α particles are often used as indicators of a source region on the solar surface, and analysis of their evolution along the solar wind path tests our understanding of physics of multicomponent magnetized plasma. The paper deals with the comprehensive analysis of the difference between proton and α parti...
Article
Melamine formaldehyde microspheres are widely used in dusty plasma experiments for their monodispersity, sphericity, low mass density, and well defined sizes. This paper summarizes problems that were encountered in numerous applications of these grains in different laboratory simulations. and the already published results are discussed in view of n...
Article
Transient clouds of a plasma generated by hypervelocity dust particles impacting onto the spacecraft were observed in-situ by many experiments over the last 20 years. The reported observations analyze sensitive measurements of plasma waves that are transmitted to the Earth with a sufficient time resolution. The detection is based on a fact that hyp...
Article
The paper presents laboratory investigations of the response of a scaled down model of the Cassini spacecraft to impacts of submicron iron grains accelerated to velocities 5-25 km/s. The aim of the study is to help in a detailed analysis and interpretation of signals provided by the RPWS (Radio Wave Plasma Science) instrument that were attributed t...
Article
The properties of turbulent fluctuations of the solar wind plasma near the interplanetary shock observed at September 12, 2014 by the BMSW instrument are considered. The spectra of the density fluctuations in the solar wind and their statistical characteristics up-and downstream of the shock front are analyzed. They are compared with each other and...
Article
The ability of a prediction of the magnetopause location under various upstream conditions can be considered as a test of our understanding of the solar wind-magnetosphere interaction. The present magnetopause models are parametrized with the solar wind dynamic pressure and usually with the north-south interplanetary magnetic field (IMF) component....
Conference Paper
The interplanetary shocks (IS) arise due to the movement of stream of one large scale phenomena in interplanetary medium relative to stream of another with supersonic/ super-Alfvenic local velocity (interactions of coronal mass ejections, magnetic clouds etc.). They separate the large scale flows of the solar wind with significantly different plasm...
Article
The paper is devoted to the shapes of the solar wind ion flux fluctuation spectrum at the transition between the inertial and the kinetic range using in situ high-resolution measurements of the Russian mission Spektr-R. We analyse the variability of the transition region and select five typical types of spectral shapes: (i) spectra with two slopes...
Article
Full-text available
We investigate the decay of magnetic and kinetic energies behind IP shocks with motivation to find a relaxation time when downstream turbulence reaches a usual solar wind value. We start with a case study that introduces computation techniques and quantifies a contribution of kinetic fluctuations to the general energy balance. This part of the stud...
Article
We use the Time History Events and Macroscale Interactions During Substorms (THEMIS) data to investigate the magnetic field structure just outside the magnetopause and its time evolution for radial IMF events. When the magnetic field drapes around the magnetopause in the magnetosheath region, an asymmetric magnetic field orientation in different he...
Article
Full-text available
This paper presents a method for taking into account changes of solar wind parameters in the foreshock using global MHD simulations. We simulate four events with very distant subsolar magnetopause crossings that occurred during quasi-radial interplanetary magnetic field (IMF) intervals lasting from one to several hours. Using previous statistical r...
Article
Voyager 1 (V1) crossed the heliopause into the local interstellar medium (LISM) in 2012. The LISM is a dynamic region periodically disturbed by solar transients with outward-propagating shocks, cosmic-ray intensity changes and anisotropies, and plasma wave oscillations. Voyager 2 (V2) trails V1 and thus may observe the solar transients that are lat...
Poster
Full-text available
The statistical properties of density fluctuations in a turbulent solar wind flow in the vicinity of interplanetary (IP) shocks are observed. We analyze probability distribution functions (PDFs) of density fluctuations in the frequency range of 0.01-10 Hz according to measurements of the BMSW instrument on board of Spektr-R. We determine high order...
Article
The solar wind is a highly turbulent medium, with a high level of field fluctuations throughout a broad range of scales. These include an inertial range where a turbulent cascade is assumed to be active. The solar wind cascade shows intermittency, which however may depend on the wind conditions. Recent observations have shown that ion-scale magneti...
Article
Voyager 1 (V1) crossed the heliopause into the local interstellar medium (LISM) in 2012. The LISM is a dynamic region periodically disturbed by solar transients with outward-propagating shocks, cosmic-ray intensity changes and anisotropies, and plasma wave oscillations. Voyager 2 (V2) trails V1 and thus may observe the solar transients that are lat...
Article
We present the first observation of the Kelvin-Helmholtz (KH) rolled-up vortex at the dayside magnetopause layers under a radial interplanetary magnetic field (IMF). The study uses measurements of four THEMIS probes aligned along the YGSE axis about 10 RE upstream of the Earth and located in different regions of the near-Earth environment. THEMIS C...