Rositza Koleva - Academia.edu (original) (raw)

Papers by Rositza Koleva

Annales Geophysicae, 2012

The problem of identification of the interface region between the lobe and the Plasma Sheet (PS) ... more The problem of identification of the interface region between the lobe and the Plasma Sheet (PS) -the Plasma Sheet Boundary Layer (PSBL) -using ion moments and magnetic field data often arises in works devoted to statistical studies of various PSBL phenomena. Our experience in the identification of this region based on the analysis of ion velocity distribution functions demonstrated that plasma parameters, such as the ion density and bulk velocity, the plasma beta or the dynamic pressure vary widely depending on the state of magnetotail activity. For example, while field-aligned beams of accelerated ions are often observed propagating along the lobeward edge of the PSBL there are times when no signatures of these beams could be observed. In the last case, a spacecraft moving from the lobe region to the PS registers almost isotropic PS-like ion velocity distribution. Such events may be classified as observations of the outer PS region. In this paper, we attempt to identify ion parameter ranges or their combinations that result in a clear distinction between the lobe, the PSBL and the adjacent PS or the outer PS regions. For this we used 100 crossings of the lobe-PSBL-PS regions by Cluster spacecraft (s/c) made in different periods of magnetotail activity. By eye inspection of the ion distribution functions we first identify and separate the lobe, the PSBL and the adjacent PS or outer PS regions and then perform a statistical study of plasma and magnetic field parameters in these regions. We found that the best results in the identification of the lobe-PSBL boundary are reached when one uses plasma moments, namely the ion bulk velocity and density calculated not for the entire energy range, but for the energies higher than 2 keV. In addition, we demonstrate that in many cases the plasma beta fails to cor-rectly identify and separate the PSBL and the adjacent PS or the outer PS regions.

Artificial Satellites

The model of Birn et al. (1977) is used to study the structure of the neutral sheet near the side... more The model of Birn et al. (1977) is used to study the structure of the neutral sheet near the side boundaries of the magnetosphere (a region in which the magnetospheric magnetic field is reconnected with the interplanetary magnetic field). Particular consideration is given to the behavior of the magnetic field, particle density, and the current distribution in this region.

1. SCIENTIFIC OBJECTIVES The AMEI-2 (Analyser by Mass and Energy of Ions) experiment is aimed to ... more 1. SCIENTIFIC OBJECTIVES The AMEI-2 (Analyser by Mass and Energy of Ions) experiment is aimed to study the 3-D distributions of the different ion species of low energy magnetotail plasma. To analyze the weak ion magnetotail fluxes by four parameters -mass m, energy E and two angles, and follow their quick, either dynamic or spatial variations, is not a routine problem. On the other hand quite a few instruments on board the Magnetotail probe study the 3-D or 2-D ion distributions. So the emphasis in AMEI-2 experiment is put on mass identification of the ions encountered in the magneto tail or involved in the various magnetosphere phenomena. The instrument is built to be able to find in the low energy range of the phase space (Ε ,θ, ϕ) and separate the fluxes of the major ion species in the magnetotail -H + , He ++ , He + and O + , and analyse their energy and angular distribution. It has to meet the following requirements: 1) energy range 0.3 -10 keV/q, respectively (m/q)x(E/q) = 0.3...

The Analyzer by Mass and Energy of the Ions (AMEI) designed to measure H(+), He(2+), He(+), and O... more The Analyzer by Mass and Energy of the Ions (AMEI) designed to measure H(+), He(2+), He(+), and O(+) ions in the energy range 0-10 keV in the magnetotail is examined. The spectrometer also performs angular scanning. The AMEI is composed of two identical sensors, and an electronics assembly; the design and operation of the sensors and the spectrometer's electronic components are described. The angular and energy characteristics of the system angular-scanner-cylindrical analyzer, and the patterns formed by the ion beam leaving the energy-mass analyzing system are examined.

The relation between the basic physical dimensions of a cylindrical electrostatic spectrometers a... more The relation between the basic physical dimensions of a cylindrical electrostatic spectrometers and its focusing and resolution properties is discussed. The model of the cylindrical electrostatic analyzer consists of two infinitely-long cylindrical surfaces enclosed in a sector angle Theta. An expression is derived for the dependence of the energy-angle transfer function of the sector angle theta over a range of instrument geometries and operating energies. The expression can be used to derive an optimum instrument geometry for measuring particles which pass near the entrance and exit of the measuring slit.

Geomagnetism and Aeronomy, 2010

ABSTRACT We present an analysis of two crossings of the plasma sheet boundary layer (PSBL) in Ear... more ABSTRACT We present an analysis of two crossings of the plasma sheet boundary layer (PSBL) in Earth’s magnetotail by a quartet of Cluster satellites, accomplished both in the absolutely quiet geomagnetic interval and in the restoration period between two substorms. It is found that in the quiet period, field-aligned electric currents were not observed in the PSBL, in spite of presence in this region of high-velocity ions moving toward Earth along the magnetic field lines at velocities of ∼1400 km/s. This means that in the given event, ions and electrons moved together; i.e., high-velocity ions were a part of the accelerated plasma flow. In the disturbed period, the Cluster satellites detected a system of two oppositely directed field-aligned currents, which can be associated with the presence of the X line rather close to the Earth. Owing to multipoint Cluster observations, we managed to estimate the spatial size of a current structure (along the normal to the PSBL surface), which was equal, for a current flowing toward Earth along the high-latitude PSBL boundary, to about 1600 km, which is comparable with the value of the inertial radius of ions. This agrees with the scenario of spatial separation of charges and formation of the Hall system of currents in the magnetic reconnection region. The duration of observation of the given current structure was ∼12 min., which points to the quasi-steady-state character of reconnection.

We investigate the characteristics of the ion population in the near-Earth (distances from 5 Re t... more We investigate the characteristics of the ion population in the near-Earth (distances from 5 Re to 10 Re) magnetotail region poleward of the exterior cusp and the auroral field lines. The study presented is based on data from the Low Energy Plasma Composition Experiment (AMEI-2) aboard the high-apogee INTERBALL-1 satellite. Characteristic features of the region are the low plasma density and the low electron energy. We discuss several cases of ion spectral and composition measurements, using He++ as a tracer of SW plasma and O+ as a tracer of ionospheric plasma. Ion fluxes exhibit complex structure bearing the history of ions origin and consecutive acceleration. Both Solar wind and ionospheric ions are present in this region. O+ beams are regularly observed, as expected, going away or towards the Earth, with energies up to about 2 keV/q. A small amount of isotropic, high-temperature plasma sheet ions is always present. But dominating is a He++ population with energies in the interva...

The magnetospheric tail lobes are vast regions between the plasma sheet and the mantle filled wit... more The magnetospheric tail lobes are vast regions between the plasma sheet and the mantle filled with very rarefied and low temperature plasma Apart from this tenuous plasma distinct plasma structures are often observed We use data from the ion and electron spectrometers aboard the INTERBALL Tail Probe satellite IB-1 to study the characteristics of the enhanced plasma fluxes in the midtail lobes -27Re X -10Re As the magnetotail lobes are magnetically connected with the polar cap we separated the observations according the substorm activity and analysed representative cases for the following four groups i high substorm activity during the whole lobe observation and preceding sequence of substorms ii moderate substorm activity and similar preceding conditions iii quiet conditions before and during the first part of the observations and then intensive substorms iv quiet conditions after prolonged quiet period In the lobe regions with enhanced electron populations several different morphol...

Both Solar wind and the Earth ionosphere serve as sources of magnetospheric plasma. Having entere... more Both Solar wind and the Earth ionosphere serve as sources of magnetospheric plasma. Having entered (SW ions) or being ejected (ionospheric ions) into the magnetosphere, ions are involved in the magnetospheric circulation. The common idea is that ions, convected to the lobe region, due to the ExB drift, enter the region of the plasma sheet and get energized by different processes. Magnetospheric plasma flows have been widely investigated, using mainly energy-per-charge measurements. While this method successfully differentiates ion species, which have near - equal flow speed and low thermal velocities [e.g. Seki et al., J. Geophys. Res., 1998], the ionic composition of hot magnetospheric flows could only be revealed in mass or mass-per-charge measurements. Recent plasma flows studies based on ion composition measurements [Lennartson, J. Geophys. Res., 2001] showed a great deal of similarity between the tailward drifts of the different ions, especially in the transition region between...

Field-aligned beams of accelerated ions and plasma structures of various durations with quasi-iso... more Field-aligned beams of accelerated ions and plasma structures of various durations with quasi-isotropic velocity distribution functions are often observed in the interface region between the magnetotail lobe and the plasma sheet. We present and discuss one case of multipoint Cluster observations which demon-strates that during a long interval of northward IMF and low geomagnetic ac-tivity this interface region represents a mixture of discrete magnetic tubes filled with plasma with different characteristics. The magnetic tubes connected with the current sheet (CS) localized acceleration sources are filled with ions with field-aligned velocity distribution function streaming earthward with velocity ∼ 700 km/s. Magnetic tubes which are not connected with the acceleration sources are filled with "old" already isotropic plasma. Multipoint observations revealed that both types of structures have spatial origin and co-exist. These findings conform to previous studies demonstratin...

Cluster and DSP fortunate locations in the Central Plasma Sheet (CPS) of magnetotail allowed stud... more Cluster and DSP fortunate locations in the Central Plasma Sheet (CPS) of magnetotail allowed studies of accelerated plasma flows and currents observed in the tail and Earth side of near-Earth magnetic X-line located between the spacecrafts. The observed delays in registration of magnetic dipolarization fronts by DSP spacecraft and negative Bz enhancements by Cluster s/c provide an estimation of X-line location at ~-14 Re. Current Sheet (CS) thinning (<0.17 Re)and bifurcation were clearly observed by Cluster s/c. An analysis of ion velocity distribution functions measured by both spacecrafts revealed that magnetic reconnection occurred at Plasma Sheet (PS) field lines and had a duration ~7 min. After cessation of acceleration process both spacecraft stay in the PS and do not observe any X-line manifestations. But after ~ 8 min Cluster and DSP again start to observe accelerated plasma flows moving earthward at both locations. This indicates on restart of acceleration process in the...

The plasma sheet boundary layer (PSBL) is characterised by field-aligned high-velocity ion beams ... more The plasma sheet boundary layer (PSBL) is characterised by field-aligned high-velocity ion beams and it is naturally to expect associated field-aligned currents (FAC) streaming in the lobe-plasma sheet interface. Recent statistical analysis revealed two different types of ion beams. Ion beams typical for quiet and slightly disturbed geomagnetic periods (Type I) are collimated in energy and are accompanied by isotropic electrons. Under these conditions no FACs or FACs of very small current density are registered. In active periods, powerful field-aligned ion beams with large parallel temperatures are observed, along with anisotropic electron fluxes, with distributions bearing the signature of a separatrix. Electrons produce a pair of FACs: at the lobeward edge directed earthward, and inside PSBL - tailward. We studied statistically a database of 364 CLUSTER observations of PSBL ion beams. Their auroral and ground manifestation was investigated using POLAR and IMAGE UV images and magn...

Journal of Geophysical Research-Space Physics, 2013

1] Fortunate positioning of Cluster and TC-1 in the plasma sheet (PS) of the Earth's magnetotail ... more 1] Fortunate positioning of Cluster and TC-1 in the plasma sheet (PS) of the Earth's magnetotail has allowed studies of the current sheet (CS) structure and particle dynamics in mesoscale and microscale in both sides of the near-Earth reconnection, which took place between 03:42 and 03:55 UT on 22 September 2004. The distinctive feature of this event was the presence of a strong negative B Y field forming a "bell-like" spatial profile with the maximum absolute value near the neutral plane. The magnitude of this B Y field was almost two times larger than the interplanetary magnetic field (IMF) and therefore could not be explained solely by the IMF penetration into the magnetotail. We propose a possible intrinsic mechanism of the B Y field enhancement near the neutral plane based on peculiarities of the nonadiabatic ion interaction with the thin CS. An analysis of test particle trajectories shows that in the presence of a guide field with the "bell-like" spatial profile, a pronounced north-south asymmetry appears in the refraction/reflection properties of nonadiabatic ions from the CS. In a region tailward of the reconnection (B Z < 0), this asymmetry results in an increase of the density of the keV ions ejected into the northern PS and moving tailward. These ions can carry the tailward current which may be responsible for the strong negative B Y near the neutral plane, i.e., self-consistent enhancement of a B Y field could occur near the neutral plane. Citation: Grigorenko, E. E., et al. (2013), Current sheet structure and kinetic properties of plasma flows during a near-Earth magnetic reconnection under the presence of a guide field,

The INTERBALL-1 (IB-1) orbit gave the rare opportunity to study the near (up to -27 RE ) magnetot... more The INTERBALL-1 (IB-1) orbit gave the rare opportunity to study the near (up to -27 RE ) magnetotail lobes. The analysis of magnetic field, electron and ion measurements during 576 hours of lobe observations shows that several types of plasma regimes are encountered, but they can be organized in two main classes reflecting their origin: plasmas in which both electrons

Using ULF electromagnetic measurements carried aboard the Magion-4 subsatellite of the Interball-... more Using ULF electromagnetic measurements carried aboard the Magion-4 subsatellite of the Interball-1 spacecraft, we study the wave activity in the high-latitude magnetopause and magnetosheath. The observed ULF wave activity is characterized by two types of spectra: a) monochromatic waves of frequency ~0.33 Hz observed near the magnetopause and b) turbulent events of broadband spectrum having discrete bursts of ~ minute duration. We focus on the case a) in this article. These monochromatic waves occur rarely, mostly under northward IMF conditions. Their frequency seems stable while their intensity is modulated. The characteristics of the monochromatic ULF events are reminiscent of 3 seconds period ULF events observed by ISEE spacecraft at foreshock environment, except for that they are observed near the magnetopause. A possible generation mechanism for the observed ULF waves is briefly proposed. We suggest that the emergence of monochromatic ULF events at magnetopause region at frequen...

Planetary and Space Science, 2005

Using ULF electromagnetic measurements obtained by the Magion-4 subsatellite of the Interball-1 s... more Using ULF electromagnetic measurements obtained by the Magion-4 subsatellite of the Interball-1 spacecraft, we study the wave activity in the high-latitude magnetopause and magnetosheath. The observed ULF wave activity is characterized by two types of spectra: (a) narrow-band waves of frequency ∼0.33Hz observed near the magnetopause and (b) broadband spectrum of turbulent nature having discrete bursts of ∼ minute duration. We focus on the case (a) in this article. These narrow-band waves occur rarely, mostly under northward IMF conditions. Their frequency seems stable while their intensity is modulated. The characteristics of the narrow-band ULF events are reminiscent of 3s—period ULF waves observed by ISEE spacecraft in the foreshock environment, except that the waves discussed in this paper are observed near the magnetopause, inside the magnetosphere. A possible generation mechanism for the observed ULF waves is briefly proposed. We suggest that the emergence of narrow-band ULF events in the magnetopause region at a frequency below the ion cyclotron frequency may be associated with anisotropic ion fluxes flowing just inside the magnetopause.

Journal of Atmospheric and Solar-Terrestrial Physics, 2008

The magnetotail lobes are two vast regions between the plasma sheet (PS) and the magnetotail boun... more The magnetotail lobes are two vast regions between the plasma sheet (PS) and the magnetotail boundary layers at the magnetopause, where the plasma has very low temperature and densities. The open magnetic field lines of the lobes directly couple the ionospheric polar caps with the solar wind (SW) through the magnetosheath. The survey of 576 h INTERBALL-1 measurements in the near (X GSM 4À27R E ) lobes in October-November 1997 shows that they are populated with plasmas of various origin and properties. Presented and discussed in details are four cases of lobe measurements under different geomagnetic conditions. Discrete plasma structures encountered in the lobes could originate from the PS, from the magnetosheath or the mantle. A ubiquitous picture in the lobes is the registration of 'clouds' of anisotropic electrons with energies up to 300-500 eV, with no accompanying ions. The electron distributions are highly variable and complex, with different degree of anisotropy. The earthward flowing electrons originate in the SW, the anisotropy of the electron fluxes reflects the anisotropy of the SW electrons. In some cases the tailward electrons are not only mirrored earthward fluxes but an additional source earthward of the observations is present. The positive spacecraft potential plays a substantial role in modifying the observed electron distributions.

Advances in Space Research, 2002

Presented are two cases when AMEI-2 instrument aboard INTERBALL-1 measures simultaneously He ++ a... more Presented are two cases when AMEI-2 instrument aboard INTERBALL-1 measures simultaneously He ++ and O + ions in near Earth magnetospheric boundary regions, connected to the cusp/cleft region. Data show that ionospheric ions could be accelerated to several keV by different mechanisms.

Advances in Space Research, 2006

We present and discuss observations of a region in the high-latitude near-Earth outer magnetosphe... more We present and discuss observations of a region in the high-latitude near-Earth outer magnetosphere when over a distance of 9R E -from GSM [0.83R E , 1.6R E , 8.5R E ] to [À0.957R E , 10.175R E , 12.738R E ] -Interball-1 observed multiple alternative changes in plasma characteristics: hot plasma sheet population is replaced by a region of mixed magnetosheath -plasma sheet population with the presence of ionospheric ions and vice versa. In the ÔmixedÕ region, both ion populations were nearly stagnant, their velocity rarely exceeded 50 km/s and plasma-sheet electrons were absent. Most of the time interplanetary magnetic field (IMF) clock angle was less than 90°, rotating to more than 270°at the end of the interval, IMF B x being positive and dominating. A flux transfer event was registered near the magnetopause. Plasma characteristics suggest that observations took place at the high-latitude boundary of the near-Earth plasma sheet on closed field lines. We suggest that the mixed regions are formed on filed lines first reconnected to the magnetosheath magnetic field, then draped and convected duskward and tailward and secondary reconnected and closed.