Christos Katsavrias

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Christos verified their affiliation via an institutional email.

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• PhD Space physics; MSc Astrophysics; BSc Physics
• Research Associate at National and Kapodistrian University of Athens

Context. Periodic density structures (PDSs) are a type of solar wind mesoscale structure characterised by quasi-periodic variations in the density of the solar wind ranging from a few minutes to a few hours. They are trains of advected density structures with radial length scales of L R ≈ 100 − 10 000 Mm. Analysis of case studies shows that PDSs ca...

Motivated by the need for more accurate radiation environment modeling, this study focuses on identifying and analyzing the drivers behind the sub-relativistic electron flux variations in the inner magnetosphere. We utilize electron flux data between 1 and 500 keV from the Hope and MagEIS instruments on board the RBSP satellites, as well as from th...

A polytropic process describes the transition of a fluid from one state to another through a specific relationship between the fluid density and temperature, and the value of the polytropic index that governs this relationship determines the heat transfer and the effective degrees of freedom of this specific process. In this paper, we investigate i...

Shock-generated transients, such as hot flow anomalies (HFAs), upstream of planetary bow shocks, play a critical role in electron acceleration. Using multimission data from NASA’s Magnetospheric Multiscale and ESA’s Cluster missions, we demonstrate the transmission of HFAs through Earth’s quasi-parallel bow shock, accelerating electrons to relativi...

Shock-generated transients, such as hot flow anomalies (HFAs), upstream of planetary bow shocks, play a critical role in electron acceleration. Using multi-mission data from NASA's Magnetospheric Multiscale (MMS) and ESA's Cluster missions, we demonstrate the transmission of HFAs through Earth's quasi-parallel bow shock, associated with acceleratio...

Context. A polytropic process describes the transition of a fluid from one state to another through a specific relationship between the fluid density and temperature, while the value of the polytropic index that governs this relationship determines the heat transfer and the effective degrees of freedom of that specific process. Aims. In this paper...

Developing an automated pipeline for solar-wind condition prediction upstream of Earth is an important step for transitioning from space weather research to operation. We develop a prototype pipeline called “Helio1D” to model ambient solar wind conditions comprising temporal profiles of wind speed, density, temperature, and tangential magnetic fiel...

Periodic density structures (PDSs) are quasiperiodic variations of solar wind density ranging from a few minutes to a few hours. PDSs advect with the solar wind and have radial length scales ( L x ) of tens to several thousand megameters, thus belonging to the class of “mesoscale structures.” Current interplanetary multispacecraft observations are...

Context. In recent years, mesoscales have gained scientific interest because they have been determined to be important in a broad range of phenomena throughout heliophysics. The solar wind mesoscale structures include periodic density structures (PDSs), which are quasi-periodic increases in the density of the solar wind that range from a few minute...

Plain Language Summary The Sun is an active star at the origin of several charged particle emissions. Some of these particles interact with the Earth's magnetic field and contribute in dynamically populating the so‐called radiation belts. The radiation belts are a region in the near‐Earth space where high energy charged particles can remain trapped...

In this paper, we present the SafeSpace prototype for a safety warning system, dedicated to the electron radiation-belt-induced internal charging hazard aboard spacecraft. The space weather tool relies on a synergy of physical models associated in a chain that covers the whole Sun–interplanetary-space–Earth's inner magnetosphere medium. With the pr...

Our current capability of space weather prediction in the Earth's radiation belts is limited to only an hour in advance using the real-time solar wind monitoring at the Lagrangian L1 point. To mitigate the impacts of space weather on telecommunication satellites, several frameworks were proposed to advance the lead time of the prediction. We develo...

In this paper, we present the SafeSpace prototype for a safety warning system, dedicated to the electron-radiation-belt induced internal charging hazard, aboard spacecraft. The space weather tool relies on a synergy of physical models associated in a chain that covers the whole Sun-interplanetary space-Earth's inner magnetosphere medium. With the p...

Radial diffusion is one of the dominant physical mechanisms driving acceleration and loss of electrons in the outer radiation belt. Therefore, the accurate estimation of radial diffusion coefficients (DLL) is crucial for detailed radiation belt modeling. In recent years several semi‐empirical (SE) models have been developed for the estimation of ra...

In this paper, we present a new method to compute rapidly, wave particle interaction induced pitch angle and momentum diffusion coefficients. Those terms are normally obtained by the numerical solving of equations based on the quasi‐linear theory. However, this bulk resolution leads to a high computational cost, preventing the integration of plasma...

During July to October of 2019, a sequence of isolated Corotating Interaction Regions (CIRs) impacted the magnetosphere, for four consecutive solar rotations, without any interposed Interplanetary Coronal Mass Ejections. Even though the series of CIRs resulted in relatively weak geomagnetic storms, the net effect of the outer radiation belt during...

Radial diffusion has been established as one of the most important mechanisms contributing to both the acceleration and loss of relativistic electrons in the outer radiation belt, as well as to the supply of particles to the inner radiation belt. In the framework of the “SafeSpace” project, we have used 9 years (2011–2019) of multi-point magnetic a...

Geospace disturbances refer collectively to the variations of the geomagnetic field and the trapped particle populations in the near-Earth space. These are the result of transient and recurrent solar activity, which consequently drives the variable solar wind. They may appear in multiple timescales, from sub-seconds to days, months and years. Wavel...

The Earth's outer radiation belt response to geospace disturbances is extremely variable spanning from a few hours to several months. In addition, the numerous physical mechanisms, which control this response depend on the electron energy, the timescale, and the various types of geospace disturbances. As a consequence, various models that currently...

Radial diffusion has been established as one of the most important mechanisms contributing to both the acceleration and loss of relativistic electrons in the outer radiation belt. In the framework of the SafeSpace project we have used 9 years (2011–2019) of multi-point magnetic and electric field measurements from THEMIS A, D and E satellites to cr...

We report observations of a magnetosheath jet followed by a period of decelerated background plasma. During this period, THEMIS‐A magnetometer showed abrupt disturbances which, in the wavelet spectrum, appeared as prominent and irregular pulsations in two frequency bands (7.6–9.2 and 12–17 mHz) within the Pi2 range. The observations suggest—for the...

Accurate measurements of trapped energetic electron fluxes are of major importance for the studies of the complex nature of radiation belts and the characterization of space radiation environment. The harmonization of measurements between different instruments increases the accuracy of scientific studies and the reliability of data‐driven models th...

Electron variability at geosynchronous orbit (GEO) plays a key role in satellite operations especially concerning the low energies which can lead to surface charging effects on spacecraft. In this work, we use 9 years (2011–2019) of electron measurements from GOES‐13, 14 and 15 satellites to study the evolution of electron fluxes with respect to va...

The nature of the semi-annual variation in the relativistic electron fluxes in the Earth's outer radiation belt is investigated using Van Allen Probes (MagEIS and REPT) and Geostationary Operational Environmental Satellite Energetic Particle Sensor (GOES/EPS) data during solar cycle 24. We perform wavelet and cross-wavelet analysis in a broad energ...

The nature of the semi-annual variation in the relativistic electron fluxes in the Earth's outer radiation belt is investigated using Van Allen Probes (MagEIS and REPT) and GOES (EPS) data during solar cycle 24. We perform wavelet and cross-wavelet analysis in a broad energy and spatial range of electron fluxes and examine their phase relationship...

We perform a superposed epoch analysis on two groups of selected geospace disturbance events, emerging from single and isolated interplanetary drivers, and resulting in either the enhancement or the depletion of the average relativistic electron Phase Space Density (PSD). We investigate the occurrence of behavioural/temporal patterns of solar wind...

We perform a superposed epoch analysis on two groups of selected geospace disturbance events, emerging from single and isolated interplanetary drivers, and resulting in either the enhancement or the depletion of the average relativistic electron Phase Space Density (PSD). We investigate the occurrence of behavioural/temporal patterns of solar wind...

We report observations of energetic electron flux and phase space density to show that a relatively weak magnetic storm with Sym‐Hmin≈−50 nT, resulted in a relativistic and ultrarelativistic electron enhancement of two orders of magnitude similar to the St. Patrick's event of 2015, an extreme storm with Sym‐Hmin≈−235 nT. This enhancement appeared a...

Electrons in the outer Van Allen (radiation) belt occasionally reach relativistic energies, turning them into a potential hazard for spacecraft operating in geospace. Such electrons have secured the reputation of satellite killers and play a prominent role in space weather. The flux of these electrons can vary over time scales of years (related to...

We investigate the response of the outer Van Allen belt electrons to various types of solar wind and magnetospheric disturbances. We use electron phase space density calculations as well as concurrent Pc5 and chorus wave activity observations in the outer belt during the Van Allen Probes era to compare 20 electron enhancement and 8 depletion events...

We report observations of energetic electron flux and Phase Space Density (PSD) to show that a relatively weak magnetic storm with $Sym-H_{min} \approx -50 $nT, resulted in a relativistic and ultra--relativistic electron enhancement of two orders of magnitude similar to the St. Patrick's event of 2015, an extreme storm with $Sym-H_{min} \approx -23...

We investigate the response of the outer Van Allen belt electrons to various types of solar wind and magnetospheric disturbances. We use electron phase space density (PSD) calculations as well as concurrent Pc5 and chorus wave activity observations in the outer belt during the Van Allen Probes era to compare 20 electron enhancement and 8 depletion...

Key Points: • Long-lasting multi-MeV electron enhancement during a period of a relatively weak geomagnetic storm not recorded in GEO. • Electron seed population was accelerated to relativistic energies by the enhanced chorus waves. • Relativistic electrons were further accelerated up to 10 MeV by inward diffusion Abstract We report observations of...

Key Points: • The number of events with PSD enhancements is L and µ-dependent. • Loss, as a combined effect of magnetopause shadowing and outward diffusion, is a common feature in both depletion and enhancement events. • The synergy of enhanced seed population and chorus activity is what distinguishes relativistic electrons enhancements from deplet...

Electrons in the outer Van Allen (radiation) belt occasionally reach relativistic energies, turning them into a potential hazard for spacecraft operating in geospace. Such electrons have secured the reputation of satellite killers and thus a prominent role in space weather. The flux of these electrons can vary over timescales of years (related to t...

Transient and recurrent solar activity drive geomagnetic disturbances; these are quantified (amongst others) by DST, AE indices time-series. Transient disturbances are related to the Interplanetary Coronal Mass Ejections (ICMEs) while recurrent disturbances are related to corotating interaction regions (CIR). We study the relationship of the geomag...

Transient and recurrent solar activity drive geomagnetic disturbances; these are quantified (among others) by DST, AE indices time-series. Transient disturbances are related to the Interplanetary Coronal Mass Ejections (ICMEs) while recurrent disturbances are related to co-rotating interaction regions (CIR). We study the relationship of the geomagn...

We investigate the effect of magnetic disturbances on the ring current buildup and the dynamics of the current systems in the inner geospace by means of numerical simulations of ion orbits during enhanced magnetospheric activity. For this purpose, we developed a particle-tracing model that solves for the ion motion in a dynamic geomagnetic field an...

During the interval 2012 March 7–11 the geospace experienced a barrage of intense space weather phenomena including the second largest geomagnetic storm of solar cycle 24 so far. Significant ultra-low-frequency wave enhancements and relativistic-electron dropouts in the radiation belts, as well as strong energetic-electron injection events in the m...

We report observations of electron Phase Space Density (PSD) dropout and evidence that supports the loss mechanism of magnetopause shadowing and outward radial diffusion during a nonstorm period characterized by persistently positive values of the SYM-H index. On 14 April 2013 an electron PSD dropout of 2 orders of magnitude was observed at the nig...

Geospace magnetic storms, driven by the solar wind, are associated with increases or decreases in the fluxes of relativistic electrons in the outer radiation belt. We examine the response of relativistic electrons to four intense magnetic storms, during which the minimum of the Dst index ranged from −105 to −387 nT, and compare these with concurren...

We present electron phase space density (PSD) calculations as well as concurrent Pc5 and chorus wave activity observations during two intense geomagnetic storms caused by interplanetary coronal mass ejections (ICMEs) resulting in contradicting net effect. We show that, during the 17 March 2013 storm, the coincident observation of chorus and relativ...

Broad Absorption Line Regions - BALR are composed of a number of successive independent absorbing density layers. Using the GR model, we analyze the UV Si IV ({\lambda}{\lambda}1393.755 - 1402.770), O IV ({\lambda}1401.156) and C IV ({\lambda}{\lambda}1548.187 - 1550.772) resonance lines in the spectra of a certain QSO and discuss the results conce...

Boad Absorption Line Regions - BALR are composed of a number of successive independent absorbing density layers. Using the GR model, we analyze the UV Si IV (1393.755 - 1402.770), O IV (1401.156) and C IV (1548.187 - 1550.772) resonance lines in the spectra of a certain QSO and discuss the results concerning its kinematic properties (rotational, ra...

The effects of the energetic phenomena of the Sun, flares and coronal mass ejections (CMEs) on the Earth’s ionosphere–magnetosphere, through the solar wind, are the sources of the geomagnetic disturbances and storms collectively known as Space Weather. The research on the influence of Space Weather on biological and physiological systems is open. I...

The sun as an oscillator produces frequencies which propagate in the heliosphere, via solar wind, to the terrestrial magnetosphere. We searched for those frequencies in the parameters of the near Earth solar plasma and the geomagnetic indices for the past four solar cycles. The solar wind parameters used in this work are the interplanetary magnetic...

Study of the solar and geomagnetic activity influence on the emergency proceedings in Greece, for selected months of solar cycle 23 and especially for the year 2005 is presented. We examined the time association between the magnetic storms (Dst geomagnetic index), daily numbers of solar flares and Coronal Mass Ejections (CMEs) with the emergency p...

We present the time distribution of a large number (7798) of Myocardial Infractions (MI) recorded at the General Hospital ‘St. Panteleimon’ of the city of Nikea (in Piraeus, Greece), during time interval 1997–2007. This data set consisted of 5160 NON‐STEACS (non‐ST) and 2638 STEACS (ST) infractions are examined along with the monthly numbers of sol...

In this paper we study the solar wind parameters during the 23rd solar cycle and the possible correlation between them. Those parameters’ data, which are Alfven Mach number, plasma beta, flow speed, proton density and temperature, dynamic pressure, average magnetic field, Bx and By, has been taken from OMNI 2. The first part of this project is ab...

Eruptive solar events as flares and coronal mass ejections (CMEs) occur during solar activ-ity periods. Energetic particles, fast solar wind plasma and electromagnetic radiation pass through interplanetary space, arrive on Earth's ionosphere-magnetosphere and produce various disturbances. It is well known the negative influence of geomagnetic subst...

Cosmological views of Democritus have been analyzed. Анализиран е космологичният светоглед на Демокрит.

Cosmological views of Democritus have been analyzed.

The purpose of this project is to study the behaviour of the solar wind parameters during the 23rd solar cycle and the possible correlation between them. The presented parameters are Alfven Mach number, plasma beta, flow speed, proton density and temperature, dynamic pressure, average magnetic field, Bx and By, and all data has been taken from OMNI...