A statistical study of proton precipitation onto the Martian upper atmosphere:Mars Express observations

Due to the small size of the Martian magnetic pile-up region, especially at the subsolar point, heated protons with high enough energy can penetrate the induced magnetosphere boundary without being backscattered, i.e., they precipitate. We present a statistical study of the downgoing ~ keV proton fluxes measured in the Martian ionosphere by the Analyzer of Space Plasma and Energetic Atoms experiment onboard the Mars Express spacecraft. We find that on the dayside, the events of proton penetration occur during 3% of the observation time; the precipitation is an intermittent phenomenon. The proton events carry on average ~0.2% of the incident solar wind flux. Therefore, the induced magnetosphere is an effective shield against the magnetosheath protons. The events are more frequent during fast solar wind conditions than during slow solar wind conditions. The sporadic proton penetration is thought to be caused by transient increases in the magnetosheath temperature. The precipitating flux is higher on the dayside than on the nightside, and its spatial deposition is controlled by the solar wind convective electric field. The largest crustal magnetic anomalies tend to decrease the proton precipitation in the southern hemisphere. The particle and energy fluxes vary in the range 10^4–10^6 cm^–2 s^–1 and 10^7–10^9 eVcm^–2 s^–1, respectively. The corresponding heating for the dayside atmosphere is on average negligible compared to the solar extreme ultraviolet heating, although the intermittent penetration may cause local ionization. The net precipitating proton particle flux input to the dayside ionosphere is estimated as 1.2 · 10^21 s^–1

Hybrid simulations of the proton precipitation patterns onto the upper atmosphere of Mars

We study the dependence of proton precipitation patterns onto the Martian upper atmosphere on altitude, proton energy, proton origin, and in a lesser extent, solar zenith angle, using the HYB-Mars model, a 3D quasineutral hybrid model. We find that the flux of precipitating protons has a strong altitude dependence: on the dayside, the flux of precipitating protons decreases substantially when the altitude over Mars decreases. We also find that the contribution of exospheric protons to the deposition is significant and its spatial distribution is not identical to that of the solar wind protons. In addition, the low energy proton population comes mainly from the newborn planetary protons. The energized pick-up protons and solar wind protons contribute to the higher energy proton population. The study also confirms that the proton precipitation is highly asymmetric with respect to the direction of the convection electric field in the solar wind. The study implies that the Martian induced magnetosphere protects the upper atmosphere effectively against proton precipitation

Reduced proton and alpha particle precipitation at Mars during solar wind pressure pulses:Mars Express results

We performed a statistical study of downward moving protons and alpha particles of ~keV energy (assumed to be of solar wind origin) inside the Martian induced magnetosphere from July 2006 to July 2010. Ion and electron data are from the Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) package on board Mars Express. We investigated the solar wind ion entry into the ionosphere, excluding intervals of low-altitude magnetosheath encounters. The study compares periods of quiet solar wind conditions and periods of solar wind pressure pulses, including interplanetary coronal mass ejections and corotating interaction regions. The solar wind ion precipitation appears localized and/or intermittent, consistent with previous measurements. Precipitation events are less frequent, and the precipitating fluxes do not increase during pressure pulse encounters. During pressure pulses, the occurrence frequency of observed proton precipitation events is reduced by a factor of ~3, and for He^2+ events the occurrence frequency is reduced by a factor of ~2. One explanation is that during pressure pulse periods, the mass loading of the solar wind plasma increases due to a deeper penetration of the interplanetary magnetic flux tubes into the ionosphere. The associated decrease of the solar wind speed thus increases the pileup of the interplanetary magnetic field on the dayside of the planet. The magnetic barrier becomes thicker in terms of solar wind ion gyroradii, causing the observed reduction of H^+/He^2+ precipitations

He^2+ transport in the Martian upper atmosphere with an induced magnetic field

Solar wind helium may be a significant source of neutral helium in the Martian atmosphere. The precipitating particles also transfer mass, energy, and momentum. To investigate the transport of He^2+ in the upper atmosphere of Mars, we have applied the direct simulation Monte Carlo method to solve the kinetic equation. We calculate the upward He, He^+, and He^2+ fluxes, resulting from energy spectra of the downgoing He^2+ observed below 500 km altitude by the Analyzer of Space Plasmas and Energetic Atoms 3 instrument onboard Mars Express. The particle flux of the downward moving He^2+ ions was 1–2 × 10^6 cm^–2 s^–1, and the energy flux is equal to 9–10 × 10^–3 erg cm^–2 s^–1. The calculations of the upward flux have been made for the Martian atmosphere during solar minimum. It was found, that if the induced magnetic field is not introduced in the simulations the precipitating He^2+ ions are not backscattered at all by the Martian upper atmosphere. If we include a 20 nT horizontal magnetic field, a typical field measured by Mars Global Surveyor in the altitude range of 85–500 km, we find that up to 30%–40% of the energy flux of the precipitating He^2+ ions is backscattered depending on the velocity distribution of the precipitating particles. We thus conclude that the induced magnetic field plays a crucial role in the transport of charged particles in the upper atmosphere of Mars and, therefore, that it determines the energy deposition of the solar wind

Proton and hydrogen atoms transport in the Martian upper atmosphere with an induced magnetic field

We have applied the Direct Simulation Monte Carlo method to solve the kinetic equation for the H/H^+ transport in the upper Martian atmosphere. We calculate the upward H and H^+ fluxes, values that can be measured, and the altitude profile of the energy deposition to be used to understand the energy balance in the Martian atmosphere. The calculations of the upward flux have been made for the Martian atmosphere during solar minimum. We use an energy spectrum of the down moving protons in the altitude range 355–437 km adopted from the Mars Express Analyzer of Space Plasma and Energetic Atoms measurements in the range 700 eV–20 keV. The particle and energy fluxes of the downward moving protons were equal to 3.0 × 10^6 cm^−2 s^−1 and 1.4 × 10^−2 erg cm^−2 s^−1. It was found that 22% of particle flux and 12% of the energy flux of the precipitating protons is backscattered by the Martian upper atmosphere, if no induced magnetic field is taken into account in the simulations. If we include a 20 nT horizontal magnetic field, a typical field measured by Mars Global Surveyor in the altitude range of 85–500 km, we find that up to 40%–50% of the energy flux of the precipitating protons is backscattered depending on the velocity distribution of the precipitating protons. We thus conclude that the induced magnetic field plays a crucial role in the transport of charged particles in the upper atmosphere of Mars and, therefore, that it determines the energy deposition of the solar wind

A case study of proton precipitation at Mars:Mars Express observations and hybrid simulations

Using the data from the Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) experiment on board Mars Express and hybrid simulations, we have investigated the entry of protons into the Martian induced magnetosphere. We discuss one orbit on the dayside with observations of significant proton fluxes at altitudes down to 260 km on 27 February 2004. The protons observed below the induced magnetosphere boundary at an altitude of less than 700 km have energies of a few keV, travel downward, and precipitate onto the atmosphere. The measured energy flux and particle flux are 10^8–10^9 eV cm^−2 s^−1 and 10^5–10^6 H^+ cm^−2 s^−1, respectively. The proton precipitation occurs because the Martian magnetosheath is small with respect to the heated proton gyroradius in the subsolar region. The data suggest that the precipitation is not permanent but may occur when there are transient increases in the magnetosheath proton temperature. The higher-energy protons penetrate deeper because of their larger gyroradii. The proton entry into the induced magnetosphere is simulated using a hybrid code. A simulation using a fast solar wind as input can reproduce the high energies of the observed precipitating protons. The model shows that the precipitating protons originate from both the solar wind and the planetary exosphere. The precipitation extends over a few thousand kilometers along the orbit of the spacecraft. The proton precipitation does not necessarily correlate with the crustal magnetic anomalies

Proton temperature anisotropies in the plasma environment of Venus

Velocity distribution functions (VDFs) are a key to understanding the interplay between particles and waves in a plasma. Any deviation from an isotropic Maxwellian distribution may be unstable and result in wave generation. Using data from the ion mass spectrometer IMA (Ion Mass Analyzer) and the magnetometer (MAG) onboard Venus Express, we study proton distributions in the plasma environment of Venus. We focus on the temperature anisotropy, that is, the ratio between the proton temperature perpendicular (T ⊥) and parallel (T ‖) to the background magnetic field. We calculate average values of T ⊥ and T ‖ for different spatial areas around Venus. In addition we present spatial maps of the average of the two temperatures and of their average ratio. Our results show that the proton distributions in the solar wind are quite isotropic, while at the bow shock stronger perpendicular than parallel heating makes the downstream VDFs slightly anisotropic (T ⊥/T ‖ > 1) and possibly unstable to generation of proton cyclotron waves or mirror mode waves. Both wave modes have previously been observed in Venus's magnetosheath. The perpendicular heating is strongest in the near-subsolar magnetosheath (T ⊥/T ‖≈3/2), which is also where mirror mode waves are most frequently observed. We believe that the mirror mode waves observed here are indeed generated by the anisotropy. In the magnetotail we observe planetary protons with largely isotropic VDFs, originating from Venus's ionosphere

Varför är populärkultur viktig i undervisningen? Buffy The Vampire Slayer som ett didaktiskt redskap för att arbeta med identitetsskapande och värdegrundsfrågor i gymnasiet

Uppsatsens syfte är att belysa varför populärkultur är viktigt i undervisningen. Detta undersöks genom tv-serien Buffy the Vampire Slayer (Buffy och vampyrerna) och hur den kan användas som didaktiskt verktyg, framför allt för värdegrundsfrågor. Huvudfrågan är hur Buffy kan användas som didaktiskt redskap för att utveckla gymnasieelevers förmåga att orientera sig och ta ställning i en mediestyrd vardag. Metoden är en kvalitativ textanalys och materialet tv-serien Buffy the Vampire Slayer, vilkens innehåll jämförs med gymnasiets läroplan 011 samt ämnesplaner. Flera exempel tas från Buffy in the Classroom: Essays on Teaching with the Slayer, red Jodie A. Kreider och Meghan K Winchell, och diskuteras utifrån Buffy-pedagogik och tidigare forskning. Forskning visar att populärkulturen bör ha en given plats i skolan, men också att pedagoger måste lära sig att använda den på andra sätt samt att kunskapsbristerna är stora. Uppsatsen bidrar med förslag på hur en tv-serie kan användas i undervisningen. Buffy är lämplig som didaktiskt verktyg då den är en ovanligt rik text. Den presenterar moraliska dilemman men utan att ge enkla svar, den är genreöverskridande, självreflekterande och laddad med referenser från populärkultur, kultur och samhälle. Undersökningen visar hur Buffy kan användas för att ge ett aktuellt och ungdomsorienterat perspektiv på skolans värdegrund. Exempel ges på hur läraren med Buffy som verktyg kan ta upp våld, jämställdhet, sex, identitet, mobbning, moral, beroende, medskapande och, nästan på köpet, mediemedvetenhet. Att använda en tv-serie ger eleverna möjlighet till identifikation och minskar deras passiva motstånd. Svåra ämnen kan diskuteras med mindre rädsla och krav, då de pratar utifrån rollfigurer, inte egna erfarenheter. I förlängningen visar exemplen hur andra populärkulturella företeelser, framför allt tv-serier – rörliga bilder – kan användas i undervisning. De lärare som inte kan eller vill använda Buffy kan överföra idéer och metoder till texter de själva har god kännedom om