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At least 55 records · Page 3Linked to original sources
arXiv2013

Simulation of the dynamics in the magnetotail current sheet

The dynamics in the magnetosphere current sheet was simulated following transformations to the rectangular NxM array of cells (cellular automaton) originally proposed by Koselov and Koselova (2002). The magnetosphere part of the modeling system was organized as a rectangular arrangement of cells with a stored energy, a local redistribution of the energy will exist when a value threshold is exceeded in one of the cells. We assume that the threshold value in each cell depends on external control parameter which influences the long boundaries of the rectangular array (40x80). The model dynamics controlled by the z-component of the interplanetary magnetic field (Bz) as well as analogies between the model transient processes and the observed substorm auroral activations are discussed. The Bz correspond to temporary windows of the solar wind for a group of magnetic clouds and plasmoids. The model simulates organized patterns in the energy distribution. The function of distribution of probability (or PDF) of the size of the avalanches have a power-law form, showing evidences of a system with Self-Organized Criticality (SOC). The occurrence of big avalanches in the model is related with the activation of some intense magnetic substorm. The arrival to the terrestrial magnetopause of a solar wind with Bz negative is a fundamental condition of occurrence of magnetic substorms. While more negative it is the Bz IMF component bigger it is the value of the AE index and trigger a strong magnetic substorm.

physics.space-ph↗
arXiv2013

The Unfolding of the Spectra of Low Energy Galactic Cosmic Ray H and He Nuclei as the Voyager 1 Spacecraft Exits the Region of Heliospheric Modulation

This paper describes the unfolding of the solar modulated galactic cosmic ray H and He nuclei spectra beyond ~105 AU in the heliosheath. Between 2008.0 and 2012.3 when Voyager 1 went from about 105 to 120.5 AU the spectral intensities of these two components between about 30 and 500 MeV/nuc unfolded (increased) in a manner consistent with an average modulation potential decrease ~5 MV per AU as described by a Parker like cosmic ray transport in the heliosphere where the overall modulation is described by a modulation potential in MV. Between 120.5 and 121.7 AU, however, as a result of two sudden intensity increases starting on May 8th and August 25th, 2012, this modulation potential decreased by ~80 MV and spectra resembling possible local interstellar spectra for H and He were revealed. Considering these spectra to be the local interstellar spectra would imply that almost 1/3 of the total modulation potential of about 270 MV required to explain the spectra of these components observed at the Earth must occur in just a 1 AU radial interval in the outer heliosheath. As a result about ~80% of the total modulation potential observed at the Earth at this time occurs in the heliosheath itself. The remaining 20% of the total modulation occurs inside the heliospheric termination shock. The details of these intensity changes and their description by a simple modulation model are discussed.

physics.space-ph↗
arXiv2013

A Comparison of the Galactic Cosmic Ray H, He and C/O Nuclei Spectra Measured Between ~5 and 500 MeV/nuc Beyond 122 AU at Voyager 1 with the Predictions of a Diffusion Model for Propagation in the Galaxy

After the disappearance of lower energy heliospheric particles at Voyager 1 starting on August 25th, 2012, spectra of H, He and C/O nuclei were revealed that resembled those to be expected for galactic cosmic rays. These spectra had intensity peaks in the range of 30-60 MeV, decreasing at both lower energies down to a few MeV and at higher energies up to several hundred MeV. We have modeled the propagation of these particles in the galaxy using an updated Leaky Box Diffusion model which determines the spectra of these components from ~2 MeV to >200 GeV. The key parameters used in the model are a galactic input spectrum ~P^-2.24, the same for all components and independent of rigidity, and a diffusion coefficient that is ~P^0.5 above a lower rigidity and increases ~beta^-1.0 below a lower rigidity ~0.56 GV. These same parameters also fit the high energy H and He data from ~10-200 GeV/nuc from the PAMELA and BESS experiments. The new Voyager spectra for all three nuclei are thus consistent with rigidity spectra ~P^-2.24 from the lowest energies to at least 100 GeV. Deviations from this spectrum can reasonably be attributed to propagation effects. Some deviations between the calculated and newly observed spectra are noted, however, below ~30 MeV/nuc, particularly for C/O nuclei, that could be significant regarding the propagation and sources of these particles.

physics.space-ph↗
arXiv2013

Calculations of the Propagated LIS Electron Spectrum Which Describe the Cosmic Ray Electron Spectrum below ~100 MeV Measured Beyond 122 AU at Voyager 1 and its Relationship to the PAMELA Electron Spectrum above 200 MeV

The new Voyager measurements of cosmic ray electrons between 6-60 MeV beyond 122 AU are very sensitive indicators of cosmic ray propagation and acceleration in the galaxy at a very low modulation level. Using a Monte Carlo diffusion model with a source spectrum with a single spectral index of -2.2 at all energies we are able to fit this observed Voyager spectrum and the contemporary PAMELA electron spectrum over an energy range from 6 MeV to ~200 GeV. This spectrum has a break in it but this break is due to propagation effects, not changes in the primary spectrum. This break is gradual, starting at > 2 GeV where the spectrum is ~E^-3.2 and continuing down to ~100 MeV or below where the spectrum becomes ~E^-1.5. At the higher energies the loss terms due to synchrotron radiation and inverse Compton effects which are ~E^2.0 steepen the exponent of the source spectrum by 1.0. At lower energies, these terms become unimportant and the loss is governed by diffusion and escape from the galaxy. A diffusion term which is proportional to beta^-1 below ~0.32 GV (which also fit the H and He spectra measured at Voyager) and has a value = 3x1028 cm^2 x s^-1 at 1 GV and a boundary at +/-1 Kpc will fit the Voyager or other similar spectra at low energies.

physics.space-ph↗
arXiv2013

Simultaneous Analysis of Recurrent Jovian Electron Increases and Galactic Cosmic Ray Decreases

The transport environment for particles in the heliosphere, e.g. galactic cosmic rays (GCRs) and MeV electrons (including those originating from Jupiters magnetosphere), is defined by the solar wind flow and the structure of the embedded heliospheric magnetic field. Solar wind structures, such as co-rotating interaction regions (CIR), can result in periodically modulation of both particles species. A detailed analysis of this recurrent Jovian electron events and galactic cosmic ray decreases measured by SOHO EPHIN is presented here, showing clearly a change of phase between both phenomena during the cause of the years 2007 and 2008. This effect can be explained by the change of difference in heliolongitude between the Earth and Jupiter, which is of central importance for the propagation of Jovian electrons. Furthermore, the data can be ordered such that the 27-day Jovian electron variation vanishes in the sector which does not connect the Earth with Jupiter magnetically using observed solar wind speeds.

astro-ph.HE↗
arXiv2013

Mode-locked Lasers Applied to Deflecting a Near Earth Object on Collision Course with Earth

We consider synchronized trains of sub-picosecond pulses generated by mode-locked lasers applied to deflection of near Earth objects (NEO) on collision course with Earth. Our method is designed to avoid a predicted collision of the NEO with Earth by at least the diameter of Earth. We estimate deflecting a 10,000 MT NEO, such as the asteroid which struck Earth near Chelyabinsk, Russia to be feasible within several months using average power in the ten kilowatt range. We see this deflection method as scalable to larger NEO to a degree not possible using continuous laser systems.

physics.space-ph↗
arXiv2013

Establishment of the new Ecuadorian solar physics phenomena division

Crucial physical phenomena occur in the equatorial atmosphere and ionosphere, which are currently understudied and poorly understood. Then, scientific campaigns for monitoring equatorial region are required, which will provide the data for analyzing and creating adequate models. Ecuador is located in strategic geographical position where these studies can be performed, providing data for the scientific community working for understanding the nature of these physical systems. The Quito Astronomical Observatory of National Polytechnic School is working in this direction, promoting research in Space Sciences for studying the equatorial zone. With the participation and valuable collaboration of international initiatives like AWESOME, MAGDAS, SAVNET and CALLISTO, the Quito Observatory is creating a new space physics division on the basis of the International Space Weather Initiative. In this contribution, the aforementioned initiative is presented inviting leaders from others scientific projects to deploy their instruments and to join us giving the necessary support for the creation of this new strategic research center.

astro-ph.IM↗
arXiv2013

First Magdas Equipment In Ecuador

The Magnetic Data Acquisition System (MAGDAS) was installed in the protected Jerusalem Park in Malchingui-Ecuador in October of 2012, under the joint collaboration between Kyushu University of Japan and the Quito Astronomical Observatory of the National Polytechnic School of Ecuador. In this paper, we describe the installation process and present the preliminary data obtained with the MAGDAS equipment. The behavior of the four components, D, H, Z and F allow us to see the importance of having the Ecuador station where the magnetic field has not been systematically measured before, in valuable contribution to study of the equatorial atmosphere.

physics.space-ph↗
arXiv2013

Fast magnetosonic modes of cylindrical magnetotail

FMS modes are studied in the model of the magnetotail as a cylinder with plasma sheet. The presence of the plasma sheet leads to a significant modification of the modes existing in the magnetotail in the form of a cylinder with no plasma sheet. Azimuthal scales of the FMS modes differ significantly between the lobes and the plasma sheet. The azimuthal scale in the plasma sheet is much smaller than that in the magnetotail lobes. FMS waves with certain parameters are strongly reflected from the boundary between the lobes and the plasma sheet and are very weak in the plasma sheet.

physics.space-ph↗
arXiv2013

Time-dependent cosmic ray modulation in the outer heliosphere: Signatures of a heliospheric asymmetry and model predictions along Voyager 1 and 2 trajectories

A two-dimensional, time-dependent numerical model is used to calculate the modulation of cosmic rays in the heliosphere. Computations are compared to spacecraft observations in the inner and outer heliosphere. It is shown that the model produces cosmic ray proton intensities compatible to different spacecraft observations on a global scale, at Earth and along both Voyager spacecraft trajectories. The study reveals that when the same modulation parameters, which resulted in compatible intensities along Voyager 1, were assumed along the Voyager 2 trajectory, the model failed to reproduce the observations. The study also found that any change in diffusion parameters alone could not reproduce the cosmic ray observations along Voyager 2 so that changes to the heliospheric geometry were necessary i.e the computed intensities along both Voyager trajectories suggest that the heliosphere is asymmetric. Furthermore, $E >$ 70 MeV and 133-242 MeV proton intensities along Voyager 1 and 2 trajectories are predicted from end of 2012 onwards. It is shown that the computed intensities along Voyager 1 increase with an almost constant rate up to the heliopause. However, the model shows that Voyager 2 is still under the influence of temporal solar activity changes because of its relatively large distance to the heliopause. Along the Voyager 2 trajectory, the intensities remained generally constant for some time and should soon start to increase steadily.

astro-ph.HE↗
arXiv2013

Hypermodular Distributed Solar Power Satellites -- Exploring a Technology Option for Near-Term LEO Demonstration and GLPO Full-Scale Plants

This paper presents a new and innovative design for scaleable space solar power systems based on satellite self-assembly and microwave spatial power combination. Lower system cost of utility-scale space solar power is achieved by independence of yet-to-be-built in-space assembly and transportation infrastructure. Using current and expected near-term technology, this study explores a design for near-term space solar power low-Earth orbit demonstrators and for mid-term utility-scale power plants in geosynchronous Laplace plane orbits. High-level economic considerations in the context of current and expected future launch costs are given as well.

physics.space-ph↗
arXiv2013

Finding the Force -- Consistent Particle Seeding for Satellite Aerodynamics

When calculating satellite trajectories in low-earth orbit, engineers need to adequately estimate aerodynamic forces. But to this day, obtaining the drag acting on the complicated shapes of modern spacecraft suffers from many sources of error. While part of the problem is the uncertain density in the upper atmosphere, this works focuses on improving the modeling of interacting rarified gases and satellite surfaces. The only numerical approach that currently captures effects in this flow regime---like self-shadowing and multiple molecular reflections---is known as test-particle Monte Carlo. This method executes a ray-tracing algorithm to follow particles that pass through a control volume containing the spacecraft and accumulates the momentum transfer to the body surfaces. Statistical fluctuations inherent in the approach demand particle numbers in the order of millions, often making this scheme too costly to be practical. This work presents a parallel test-particle Monte Carlo method that takes advantage of both GPUs and multi-core CPUs. The speed at which this model can run with millions of particles allowed exploring a regime where a flaw in the model's initial particle seeding was revealed. Our new model introduces an analytical fix based on seeding the calculation with an initial distribution of particles at the boundary of a spherical control volume and computing the integral for the correct number flux. This work includes verification of the proposed model using analytical solutions for several simple geometries and demonstrates uses for studying aero-stabilization of the Phobos-Grunt Martian probe and pose-estimation for the ICESat mission.

physics.comp-ph↗
arXiv2017

Acceleration of galactic electrons at the solar wind termination shock and Voyager 1 observations

Diffusive shock acceleration (DSA), as an acceleration process for Galactic electrons at the solar wind termination shock (TS), is investigated with a comprehensive numerical model which incorporates shock-acceleration, particle drifts and other major modulation processes in the heliosphere. It is known from our previous work that the efficiency of DSA depends on the shape of electron spectra incident on the TS, which in turn depends on the spectral shape of the very local interstellar spectrum. Modulation processes also influence the efficiency of DSA. We find that TS accelerated electrons can make contributions throughout the heliosphere to intensity levels, especially at lower energies. An interesting result is that increases caused by DSA at the TS are comparable in magnitude to electron intensity enhancements observed by Voyager 1 ahead of the TS crossing. These intensity increases are large enough to account for observed intensity peaks, and thus supports the view that DSA is involved in their production. Additionally, the energy spectra observed by Voyager 1 throughout the heliosheath are reproduced satisfactorily, as well as the PAMELA spectrum at Earth at higher energies. We also find that an increase in the rigidity dependence of the diffusion coefficients for these low-energy electrons seems required to reproduce the spectral shape of observed modulated spectra in the heliosheath at kinetic energy E < ~ 4 MeV. This is different from intermediate energies where rigidity independent diffusion explains observations satisfactory.

physics.space-ph↗
arXiv2018

Cosmic Ray Electrons and Protons ~1 MeV - A 40 Year Study of Their Intensities from the Earth to the Heliopause and Beyond Into Local Interstellar Space by the CRS Experiment on Voyager 1

Studies on Voyager 1 using the CRS instrument have shown the presence of sub-MeV electrons in the interstellar medium beyond the heliopause. We believe that these electrons are the very low energy tail of the distribution of galactic GeV cosmic ray electrons produced in the galaxy. If so this observation places constraints on the origin and possible source distribution of these electrons in the galaxy. The intensities of these electrons as well as MeV protons and other higher energy electrons and nuclei have been followed outward from the Earth to beyond the heliopause during the 40 years of the Voyager mission. Among the other new features found in this study of the radial dependence of the electron intensity in the heliosphere are: 1. The heliosheath is a source of sub-MeV electrons as well as the already known anomalous cosmic rays of MeV and above, none of which appear to escape from the heliosphere because of an almost impenetrable heliopause at these lower energies; 2. Solar modulation effects are observed for these MeV electrons throughout the heliosphere. These modulation effects are particularly strong for electrons in the heliosheath and comprise over 90 percent of the observed intensity change of these electrons of 10-60 MeV between the Earth and the heliopause. Even for nuclei of 1 GV in rigidity, over 30 percent of the total intensity difference between the Earth and the LIM occurs in the heliosheath; 3. The 2 MeV protons studied here for the first time beyond the heliopause are also part of the low energy tail of the spectrum of galactic cosmic ray protons, similar to the tail noted above for sub MeV galactic cosmic ray electrons.

physics.space-ph↗
arXiv2021

Dodgeball -- Can a Satellite Avoid Being Hit by Debris?

Can a satellite dodge a collision with untracked orbiting debris? Can a satellite dodge collision with a tracked object, making only the avoidance manœuvers actually required to avoid collision, despite the uncertainties of predicted conjunctions? Satellite-borne radar may distinguish actual collision threats from the much greater number of near misses because an object on a collision course has constant bearing, which may be determined by interferometric detection of the radar return. A large constellation of such radars may enable the determination of the ephemerides of all cm-sized debris in LEO.

astro-ph.EP↗
arXiv2013

TEC evidence for near-equatorial energy deposition by 30-keV electrons in the topside ionosphere

Observations of energetic electrons (10 - 300 keV) by NOAA/POES and DMSP satellites at heights <1000 km during the period from 1999 to 2010 allowed finding abnormal intense fluxes of ~10^6 - 10^7 cm-2 s-1 sr-1 for quasi-trapped electrons appearing within the forbidden zone of low latitudes over the African, Indo-China, and Pacific regions. Extreme fluxes appeared often in the early morning and persisted for several hours during the maximum and recovery phase of geomagnetic storms. We analyzed nine storm-time events when extreme electron fluxes first appeared in the Eastern Hemisphere, then drifted further eastward toward the South-Atlantic Anomaly. Using the electron spectra, we estimated the possible ionization effect produced by quasi-trapped electrons in the topside ionosphere. The estimated ionization was found to be large enough to satisfy observed storm-time increases in the ionospheric total electron content determined for the same spatial and temporal ranges from global ionospheric maps. Additionally, extreme fluxes of quasi-trapped electrons were accompanied by the significant elevation of the low-latitude F-layer obtained from COSMIC/FORMOSAT-3 radio occultation measurements. We suggest that the storm-time ExB drift of energetic electrons from the inner radiation belt is an important driver of positive ionospheric storms within low-latitude and equatorial regions.

physics.space-ph↗
arXiv2012

Occurrence rate of extreme magnetic storms

Statistical analysis of occurrence rate of magnetic storms induced by different types of interplanetary drivers is made on the basis of OMNI data for period 1976-2000. Using our catalog of large scale types of solar wind streams we study storms induced by interplanetary coronal mass ejections (ICME) (separately magnetic clouds (MC) and Ejecta) and both types of compressed regions: corotating interaction regions (CIR) and Sheaths. For these types of drivers we calculate integral probabilities of storms with minimum Dst < -50, -70, -100, -150, and -200 nT. The highest probability in this interval of Dst is observed for MC, probabilities for other drivers are 3-10 times lower than for MC. Extrapolation of obtained results to extreme storms shows that such a magnetic storm as Carrington storm in 1859 with Dst = -1760 nT is observed on the Earth with frequency 1 event during ~500 year.

physics.space-ph↗