Kaylene Scherer

Kaylene Scherer
Moraine Park Technical College · Nursing Program

About

163
Publications
5,834
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1,915
Citations
Citations since 2017
22 Research Items
728 Citations
2017201820192020202120222023050100150
2017201820192020202120222023050100150
2017201820192020202120222023050100150
2017201820192020202120222023050100150

Publications

Publications (163)
Article
Full-text available
Luminous blue variable type stars are massive O-type stars which show variable outflow parameters. These stars can also undergo eruptions where a large amount of mass is ejected in a very short duration. The astrospheres of these stars are modelled using a magnetohydrodynamic model including the effect of radiative cooling. The variation in outflow...
Article
Full-text available
Context. Given their uniqueness, the Ulysses data can still provide us with valuable new clues about the properties of plasma populations in the solar wind, and especially about their variations with heliographic coordinates. In the context of kinetic waves and instabilities in the solar wind plasma, the electron temperature anisotropy plays a cruc...
Article
Full-text available
Context. State of the art simulations of astrospheres are modelled using three-dimensional (3D) magnetohydrodynamics (MHD). An astrospheric interaction of a stellar wind (SW) with its surrounding interstellar medium (ISM) can only generate a bow shock if the speed of the interstellar inflow is higher than the fast magnetosonic speed. Aims. The diff...
Preprint
Full-text available
Context. State of the art simulations of astrospheres are modelled using three-dimensional (3D) magnetohydrodynamics (MHD). An astrospheric interaction of a stellar wind (SW) with its surrounding interstellar medium (ISM) can only generate a bow shock if the speed of the interstellar inflow is higher than the fast magnetosonic speed. Aims. The diff...
Article
Context. In heliospheric plasmas, such as the solar wind and planetary magnetospheres, the transport of energy and particles is governed by various fluxes (e.g., heat flux, particle flux, current flow) triggered by different forces, electromagnetic fields, and gradients in density or temperature. In the outer corona and at relatively low heliocentr...
Article
Context. While the shapes of many observed bow shocks can be reproduced by simple astrosphere models, more elaborate approaches have recently been used to explain differing observable structures. Aims. By placing perturbations of an otherwise homogeneous interstellar medium in front of the astrospheric bow shock of the runaway blue supergiant λ Cep...
Article
Observations in space plasmas reveal particle velocity distributions out of thermal equilibrium, with anisotropies (e.g., parallel drifts or/and different temperatures, T∥ - parallel and T⊥ - perpendicular, with respect to the background magnetic field), and multiple quasithermal and suprathermal populations with different properties. The recently...
Article
In the literature different so-called κ-distribution functions are discussed to fit and model the velocity (or energy) distributions of solar wind species, pickup ions, or magnetospheric particles. Here, we introduce a generalized (isotropic) κ-distribution as a ‘cookbook’, which admits as special cases, or ‘recipes’, all the other known versions o...
Article
Full-text available
The interpretation of recent observations of bow shocks around O-stars and the creation of corresponding models require a detailed understanding of the associated (magneto-)hydrodynamic structures. We base our study on 3D numerical (magneto-)hydrodynamical models, which are analysed using the dynamically relevant parameters, in particular, the (mag...
Preprint
Full-text available
Three-dimensional models of astrospheres have recently become of interest. However, comparisons between these models and observations are non-trivial because of the two-dimensional nature of observations. By projecting selected physical values of three-dimensional models of astrospheres onto the surface of a sphere that is centred on a virtual all-...
Preprint
Full-text available
The interpretation of recent observations of bow shocks around O-stars and the creation of corresponding models require a detailed understanding of the associated (magneto-)hydrodynamic structures. We base our study on three-dimensional numerical magneto-)hydrodynamical models, which are analyzed using the dynamically relevant parameters, in partic...
Article
Full-text available
Context. Three-dimensional models of astrospheres have recently become of interest. However, comparisons between these models and observations are non-trivial because of the two-dimensional nature of observations. Aims. By projecting selected physical values of three-dimensional models of astrospheres onto the surface of a sphere that is centred on...
Article
So-called κ -distributions are widely invoked in the analysis of nonequilibrium plasmas from space, although a general macroscopic parametrization as known for Maxwellian plasmas near thermal equilibrium is prevented by the diverging moments of order l ≥ 2 κ − 1. To overcome this critical limitation, recently novel regularized κ -distributions ( RK...
Article
Full-text available
Solar wind electrons are observed to be distributed in velocity space such that they can be empirically fitted with the κ-distribution. Among physical processes that are responsible for the generation of the observed electron distribution is the asymptotically steady-state Langmuir turbulence and the suprathermal electron distribution function asso...
Article
Full-text available
In classical thermodynamics the entropy is an extensive quantity, i.e., the sum of the entropies of two subsystems in equilibrium with each other is equal to the entropy of the full system consisting of the two subsystems. The extensitivity of entropy has been questioned in the context of a theoretical foundation for the so-called κ distributions,...
Preprint
Full-text available
In classical thermodynamics the entropy is an extensive quantity, i.e.\ the sum of the entropies of two subsystems in equilibrium with each other is equal to the entropy of the full system consisting of the two subsystems. The extensitivity of entropy has been questioned in the context of a theoretical foundation for the so-called $\kappa$-distribu...
Article
Full-text available
Context. While several studies have investigated large-scale cluster winds resulting from an intra-cluster interaction of multiple stellar winds, as yet they have not provided details of the bordering flows inside a given cluster. Aims. The present work explores the principal structure of the combined flow resulting from the interaction of multiple...
Article
For various plasma applications the so-called (non-relativistic) $\kappa$-distribution is widely used to reproduce and interpret the suprathermal particle populations exhibiting a power-law distribution in velocity or energy. Despite its reputation the standard $\kappa$-distribution as a concept is still disputable, mainly due to the velocity momen...
Article
Full-text available
The Voyager plasma observations show that the physics of the heliosheath is rather complex and that the temperature derived from observation particularly differs from expectations. To explain this fact, the temperature in the heliosheath should be based on κ distributions instead of Maxwellians because the former allows for much higher temperature....
Article
The study addresses the question of the origin of low-energy electrons measured by Voyager 1 in the multi-keV range in the inner heliosheath. It intends to demonstrate that the observed keV-fluxes of electrons are consistent with their transmission through the termination shock under the influence of the associated electrostatic field. A power-law...
Article
Full-text available
This paper summarizes the results obtained by the team "Heliosheath Processes and the Structure of the Heliopause: Modeling Energetic Particles, Cosmic Rays, and Magnetic Fields" supported by the International Space Science Institute in Bern, Switzerland. We focus on the physical processes occurring in the outer heliosphere, especially at its bound...
Article
Full-text available
Simulations of astrospheres around hot and cool stars have recently move into the focus of scientific research. We describe here the differences between the astrospheres around hot and cool stars. While those around the former are huge (on pc scales) because of their high stellar wind momentum flow, those around cool stars are on a AU scale and the...
Article
Full-text available
The Interstellar Boundary Explorer (IBEX) spacecraft maps the neutral atom fluxes across the whole sky. Thereby it is indirectly mapping the structure of the outer heliosphere and the (very) local interstellar medium. A particularly interesting feature in the IBEX-Hi all-sky maps of the differential flux of Energetic Neutral Atoms (ENAs) in the 0.7...
Article
Full-text available
The study aims at a derivation of generalized Rankine-Hugonoit relations, especially that for the entropy, for the case of different upstream/downstream polytropic indices and their implications. We discuss the solar/stellar wind interaction with the interstellar medium for different polytropic indices and concentrate on the case when the polytropi...
Article
Full-text available
We extend a two-component model for the evolution of fluctuations in the solar wind plasma so that it is fully three-dimensional (3D) and also coupled self-consistently to the large-scale magnetohydrodynamic (MHD) equations describing the background solar wind. The two classes of fluctuations considered are a high-frequency parallel-propagating wav...
Article
The evolution of the solar wind proton distribution function along the plasma flow downstream of the heliospheric termination shock is studied. Starting from a kinetic phase space transport equation valid in the bulk frame of the plasma flow that takes into account convective changes, cooling, velocity diffusion, and charge exchange-induced injecti...
Article
Full-text available
Huge astrospheres or stellar wind bubbles influence the propagation of cosmic rays at energies up to the TeV range and can act as small-scale sinks decreasing the cosmic ray flux. We model such a sink (in 2D) by a sphere of radius 10 pc embedded within a sphere of a radius of 1 kpc. The cosmic ray flux is calculated by means of backward stochastic...
Article
Full-text available
The interaction between a supersonic stellar wind and a (super-)sonic interstellar wind has recently been viewed with new interest. We here first give an overview of the modeling, which includes the heliosphere as an example of a special astrosphere. Then we concentrate on the shock structures of fluid models, especially of hydrodynamic (HD) models...
Article
Full-text available
Global models of the heliosphere and its interaction with the local interstellar medium have evolved to fit spacecraft observations since the beginning of their development. It is now understood that neutral hydrogen plays a very important role in the modification of the shape and location of the heliopause. Comparisons of simulations to observatio...
Article
Full-text available
Cosmic rays passing through large astrospheres can be efficiently cooled inside these "cavities" in the interstellar medium. Moreover, the energy spectra of these energetic particles are already modulated in front of the astrospherical bow shocks. We study the cosmic ray flux in and around lambda Cephei as an example for an astrosphere. The large-s...
Article
It is well known that (pick-up) ions in the inner heliosphere do not maintain Maxwellian distributions but tend to non-equilibrium distributions with extended suprathermal tails. Such states have been classified as quasi-equilibria which in many cases can well be described by so-called κ-distributions. With the present study we start out from a pha...
Article
Full-text available
Context. A new hypothesis is offered to explain the so-called ribbon feature appearing in the all-sky flux maps of energetic neutral atoms presently observed with the IBEX spacecraft, namely that the ribbon is a consequence of inhomogeneities in the local interstellar medium. Aims: The study aims at a detailed presentation of this hypothesis and i...
Article
In the heliosphere, especially in the inner heliosheath, mass-, momentum-, and energy loading induced by the ionization of neutral interstellar species plays an important, but for some species, especially Helium, an underestimated role. We discuss the implementation of charge exchange and electron impact processes for interstellar neutral Hydrogen...
Article
Recently it has been discussed whether a bow shock ahead of the heliospheric stagnation region does exist or not. This discussion was triggered by measurements indicating that the Alfv\'en speed and that of fast magnetosonic waves are higher than the flow speed of the local interstellar medium (LISM) relative to the heliosphere and resulted in the...
Article
Full-text available
Maps of the radial magnetic field at a heliocentric distance of 10 solar radii are used as boundary conditions in the MHD code CRONOS to simulate a three-dimensional inner-heliospheric solar wind emanating from the rotating Sun out to 1 AU. The input data for the magnetic field are the result of solar surface flux transport modeling using observati...
Article
Full-text available
Results from a newly developed hybrid cosmic ray (CR) modulation model are presented. In this approach, the transport of CRs is computed by incorporating the plasma flow from a magnetohydrodynamic model for the heliospheric environment, resulting in representative CR transport. The model is applied to the modulation of CRs beyond the heliopause (HP...
Article
Full-text available
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...
Chapter
During recent years it became evident that the climate of the Earth is not only determined by terrestrial, in particular anthropogenic influences, but also by external parameters. An open question is still whether the solar radiation or the cosmic rays are the main agents regarding the external climate driving. An answer to this question requires q...
Article
Full-text available
Galactic transport models for cosmic rays involve the diffusive motion of these particles in the interstellar medium. Due to the large-scale structured galactic magnetic field this diffusion is anisotropic with respect to the local field direction. We included this transport effect along with continuous loss processes in a quantitative model of gal...
Chapter
The interaction of the solar wind with the surrounding interstellar medium (ISM) forms a cavity in the ISM. This cavity is called the heliosphere (influence sphere) of the Sun. Numerical models were developed using hydrodynamic (HD) and magneto-hydrodynamic (MHD) equations to simulate the interaction of the different fluids in the heliosphere. Thes...
Article
In the context of heliospheric cosmic ray transport following the well-known Parker Transport Equation approach, it is a long standing and well-established paradigm to treat the spatial diffusion of energetic particles by employing a tensorial quantity for the diffusion, i.e. using different diffusion coefficients along and perpendicular to the mag...
Article
Most of the large-scale models of the heliosphere include for the coupling of the neutral hydrogen gas and the proton plasma the charge exchange process and the photoionization, but only a few also consider explicitly the electron impact process. Here we will briefly review the characteristics of all of these ionization processes and will especiall...
Article
It has recently been discussed that two of the paradigms in modeling the transport of galactic cosmic rays -- namely that the modulation boundary is identical with the heliopause and that the local interstellar spectra are identical to the galactic cosmic ray spectra -- have to be revised. Theoretical findings imply that the modulation is, due to t...
Article
Full-text available
One paradigm concerning galactic cosmic ray energy spectra is that they are created in violent events, like supernova explosions. Recently, we have demonstrated that Sun-like stars can contribute to the lower energy range of the cosmic ray proton spectrum, by creating so-called anomalous cosmic rays (ACRs). The seed population of the latter are the...
Article
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The spatial diffusion of cosmic rays in turbulent magnetic fields can, in the most general case, be fully anisotropic, i.e. one has to distinguish three diffusion axes in a local, field-aligned frame. We reexamine the transformation for the diffusion tensor from this local to a global frame, in which the Parker transport equation for energetic part...
Article
Two of the paradigms in modeling the transport of galactic cosmic rays are that the modulation boundary is the heliopause and that the local interstellar spectra are identical to the galactic cosmic ray spectra. Here we demonstrate, that the proton spectrum is already modulated, due to an altered interstellar diffusion coefficient in the outer heli...
Article
We discuss the energetic neutral atom (ENA) observations by HSTOF on SOHO. From mid 2003 the HSTOF field of view is restricted to the flanks of the heliosphere, away from the Voyager trajectories. To interpret the recent observations it is necessary to understand the processes shaping the energetic ion distributions in the inner heliosheath. We pre...
Article
Full-text available
Two of the paradigms in modeling the transport of galactic cosmic rays are that the modulation boundary is the heliopause and that the local interstellar spectra are identical to the galactic cosmic ray spectra. Here we demonstrate that the proton spectrum is already modulated due to an altered interstellar diffusion in the outer heliosheath as a c...
Article
Full-text available
In recent years one could witness tremendous progress regarding the physics of the transport of cosmic rays (CRs) in the heliosphere. This progress derives from both theoretical advances and new measurements from the outer boundary region of the heliosphere. At the same time theory and observations give new constraints on the local interstellar CR...
Article
Full-text available
In the description of cosmic ray transport based on a diffusion-convection equation, the spatial diffusion of energetic particles, in general, has to be treated by employing a tensorial quantity, i.e. using different diffusion strengths along and perpendicular to the magnetic field, respectively. This leads to results for the distribution function...
Article
Context. Heliospheric magnetic field configurations are relevant on a large scale for the transport of cosmic rays, especially for injecting possibly pre-accelerated particles into the Fermi-I acceleration process of cosmic rays. Aims: We compare four analytically described fields by calculating the scalar product between their vectors and the corr...
Article
Full-text available
Cosmogenic Isotopes are produced in the Earth's atmosphere due to the interaction of galactic cosmic rays with nuclei of atmospheric atoms. Among others, the 10Be concentration in ice cores depends on the galactic cosmic ray flux outside of the Earth's magnetosphere and provides therefore a unique tool to investigate the solar modulation over very...
Article
Full-text available
Context. The heliospheric current sheet is a plasma layer dividing the heliosphere into the regions of different magnetic field polarity. Since it is very thin compared to the size of the system, it is difficult to incorporate into the numerical models of the heliosphere. Because of the solar magnetic field reversals and the diverging and slowing d...
Article
Recharging of anomalous cosmic rays in the tail of the heliosphere produces high energetic ENAs (≈ 100 keV), as was observed with SOHO (Czechowski et al. 2001). Recently, we have shown that anomalous cosmic rays also penetrate into the outer heliosheath and even into the interstellar medium. Using our calulations and the Voyager observations at...
Article
The form of the field lines of the interplanetary magnetic field (IMF) is determined by the rotation of the Sun. In combination with the fact that the IMF is frozen into the solar wind, this leads to the well-known Parker spiral. While Parker's model has been verified by numerous in-situ measurements in the ecliptic plane, the question arises about...
Article
Hot Jupiters revolve around their host stars on very close orbits within a few days. This vicinity between star and planet leads to features unknown from the solar system, the most interesting of which is their magnetic interaction. The latter is manifested by a so-called hotspot in the stellar atmosphere moving across the stellar disk with the orb...
Article
Our hybrid BoPo code is able to handle a three species fluid, protons, hydrogen and pickup ions, as well as the kinetic description of energetic particles, i.e. galactic and anomalous cosmic rays (GCRs and ACRs). The boundary of the latter was, so far, the heliopause, beyond which the interstellar GCR spectra was assumed to be unperturbed and, more...
Article
From the presence of the 11-year Schwabe and the 22-year Hale period in numerous time series of climate indicators like tree rings, varves, precipitation, droughts or temperatures it has been concluded that solar activity has an influence on the terrestrial climate. While at present it is unclear, however, whether this influence is direct (solar) o...
Presentation
Galactic cosmic rays (GCRs) are high energy charged particles, mainly protons and doubly ionized helium, originating in the galaxy and striking the Earth from all directions. There are three lines of defends which protect humans on Earth against this radiation. While the inner two shields, the atmosphere and magnetosphere, protect us against cosmic...
Article
The transport of energetic particles in the heliosphere is usually described by the Parker trans-port equation including the physical processes of diffusion, drift, convection and adiabatic energy changes. The Ulysses spacecraft provides unique insight into the flux of MeV electrons at high latitudes. In this contribution, we compare our model resu...
Article
Spatial diffusion of cosmic rays in weakly turbulent magnetic fields can be fully anisotropic. This is especially important for the transport of energetic electrons from Jupiter. In this case the local diffusion tensor has diagonal form with three distinct diffusion coefficients. Nondiagonal drift contributions can be included as well. Here, we wil...
Article
The interpretation of the SOHO observations of high energy ENAs (˜ 50-80 keV) are interpreted as the recharging of ACRs in the tail direction (Czechowski et al. 2001). Recently, we have improved our hybrid BoPo code to allow ACRs to penetrate into the outer heliosheath and even into the interstellar medium. With the help of Voyager observations at...
Poster
Ulysses launched on October 6, 1990 was turned off after 18 years of successful exploration of the 3 dimensional heliosphere on May, 30, 2009. On board the spacecraft the Kiel Electron Telescope determines the intensities of galactic cosmic ray electrons, protons, and alphas in the energy range from a few MeV/nucleon to a few GeV/nucleon. Measuring...
Article
Full-text available
During the latest Ulysses out-of-ecliptic orbit the solar wind density, pressure, and magnetic field strength have been the lowest ever observed in the history of space exploration. Since cosmic ray particles respond to the heliospheric magnetic field in the expanding solar wind and its turbulence, the weak heliospheric magnetic field as well as th...
Article
Because cosmic rays effect the production of cosmogenic isotopes and possibly the climate, we want to validtate the predictions of our PLANETOCOSMIC program concerning the ion-pair production. The PLANETOCOSMICS code is a Monte-Carlo based program which estimates the hadronic interaction of cosmic rays in the atmosphere and its electron production...
Article
Some theoretical as well as experimental studies based on ionosonde data suggest that climate change can also affect the upper layer of the ionosphere. Unfortunately, thee are several problems and uncertainties in determining the layer heights from ionosonde data, such that a precise determination of the F-layer height is difficult. With the EISCAT...
Article
Context. Anomalous cosmic rays are thought to be generated from pick-up ions that undergo Fermi-1 acceleration in the region close to the solar wind termination shock. This selective acceleration process depends on the efficiency at which upstream pick-up ions are injected into the first reflection mode, from where acceleration into higher energy a...
Article
The propagation of energetic particles in the heliosphere is described by the Parker transport equation. It includes the physical processes of diffusion, drift, convection and adiabatic energy changes. For the inner heliosphere the Jovian magnetosphere is the dominant source of energetic electrons. Therefore the so-called Jovian electrons are nearl...
Article
In recent years the variability of the cosmic ray flux has become one of the main issues not only for the interpretation of the abundances of cosmogenic isotopes in cosmochronic archives like, e.g., ice cores, but also for its potential impact on the terrestrial climate. It has been re-emphasized that the cosmic ray flux is not only varying due to...
Article
Galactic and anomalous cosmic-ray modulation in a dynamic realistic heliosphere is studied. We present the time evolution of cosmic-ray spectra from solar minima to maxima as computed by a newly developed hybrid model. This model consists of a hydrodynamic part to model the plasma flow of protons in the solar wind and in the LISM, neutral H atoms,...
Article
A brief discussion on the transport and acceleration of anomalous cosmic rays in the inner heliosheath is given with emphasis on stochastic acceleration and adiabatic heating of particles. Results from a numerical model is shown and compared to observations. We show that these acceleration processes play a major role in explaining Voyager 1 anomalo...
Article
Full-text available
Modeling of the global heliosphere seeks to investigate the interaction of the solar wind with the partially ionized local interstellar medium. Models that treat neutral hydrogen self-consistently and in great detail, together with the plasma, but that neglect magnetic fields, constitute a sub-category within global heliospheric models. There are s...
Article
The IBEX spacecraft, to be launched in July 2008, will measure the flux of energetic neutral hydrogen atoms (ENAs) that are produced by charge exchange in the outer heliosphere. The flux measurements and their comparison with model results will give insight into the nature of the ENA production region. In the energy range from 0.01 to 10 keV covere...
Article
We will discuss new theories describing the role of adiabating heating and stochastic acceleration of the anomalous proton component. We will present results of the propagation of the latter beyond the heliopause and its consequences regarding the measurements of the local interstellar proton spectrum (LIS). Furthermore, we will study a possible mo...
Article
A two-dimensional hydrodynamic model of the solar wind interaction with the local interstellar medium surrounding the solar system is used to study the heliosphere as a dynamic structure, including the effects of the solar cycle and short term variations in the solar wind observed by a range of spacecraft over the past 30 years. This dynamic model...