ALBERT

Beschreibung: We present a time-of-flight mass spectrometer design for the measurement of ions in the ~30 keV to 10 MeV range for protons (up to ~40 MeV and ~150 MeV for He and heavy ions, respectively) and ~30 keV to 1 MeV range for electrons, covering half of the sky with 80 apertures. The instrument, known as the “Mushroom”, owing to its shape, solves the field of view problem for magnetospheric and heliospheric missions that employ three-axis stabilized spacecraft, yet still require extended angular coverage; the Mushroom is also compatible with a spinning spacecraft. The most important new feature of the Mushroom is the method through which uncomplicated electrostatic optics and clean position sensing combine to permit many apertures to fit into a compact, low-mass sensor head (or wedge), several of which (ideally eight) compose a full instrument. Most of the sensor head's volume is an empty, equipotential region, resulting in the modest 250 g mass of each ten-aperture wedge. The Mushroom is capable of separating ion species across most of its energy range and angular field of view. For example, separation of the neighboring 3 He and 4 He isotopes is excellent; the full-width/half-maximum mass resolution has been measured to be 0.24 amu to 0.32 amu, respectively. Converting this to a Gaussian width σ m in mass m this represents a σ m / m mass resolution better than 0.04. This separation is highly desirable for the flight program for which the first Mushroom was built, the Solar Probe Plus mission. More generally we estimate the mass resolution to be σ m / m  ≈ 0.1, but this is energy, mass, and angularly dependent. We also discuss the solid-state detector stack capability, which extends the energy range of protons and helium, with composition, to ~100 MeV.

Beschreibung: We present a precise measurement of downward-going albedo proton fluxes for kinetic energy above ~ 70 MeV performed by the PAMELA experiment at an altitude between 350 and 610 km. On the basis of a trajectory tracing simulation, the analyzed protons were classified into quasi-trapped, concentrating in the magnetic equatorial region, and un-trapped spreading over all latitudes, including both short-lived (precipitating) and long-lived (pseudo-trapped) components. In addition, features of the penumbra region around the geomagnetic cutoff were investigated in detail. PAMELA results significantly improve the characterization of the high energy albedo proton populations at low Earth orbits.

Beschreibung: [1]  The observed γ -ray fluence distribution of Terrestrial Gamma-ray Flashes (TGFs) detected by the Fermi Gamma-ray Burst Monitor (GBM) is altered by instrumental effects. We perform corrections for deadtime, pulse pile-up and detection efficiency in a model independent manner. A sample of 106 GBM TGFs is selected to include both TGFs which triggered GBM and weaker TGFs found using an offline search. Detector deadtime and pulse pile-up lower the observed fluence of each TGF and the detection efficiency causes weaker TGFs to have a lower probability of detection than brighter TGFs. Monte Carlo simulations are performed in each case to correct for these effects. The corrected fluence distribution is well fit with a power-law of index α  = –2.20 ± 0.13. This is consistent with previous estimates using other techniques. Neither a high-fluence cut-off nor a low-fluence limit is found. The fluence distribution is also expressed in units of TGF hour –1  km –2 versus photons cm –2 per TGF.

Beschreibung: The MMS mission was designed to make observations in the very small electron diffusion region (EDR), where magnetic reconnection takes place. From a data set of over 4500 magnetopause crossings obtained in the first phase of the mission, MMS had encounters near or within 12 EDRs. These 12 events and associated magnetopause crossings are considered as a group to determine if they span the widest possible range of external and internal conditions (i.e, in the solar wind and magnetosphere). In addition, observations from MMS are used to determine if there are multiple X-lines present and also to provide information on X-line location relative to the spacecraft. These 12 events represent nearly the widest possible range of conditions at the dayside magnetopause. They occur over a wide range of local times and magnetic shear angles between the magnetosheath and magnetospheric magnetic fields. Most show evidence for multiple reconnection sites.

Beschreibung: The Gamma-ray Burst Monitor (GBM) on board the Fermi Gamma-ray Space Telescope has triggered on over 300 Terrestrial Gamma-ray Flashes (TGFs) since its launch in June 2008. With 14 detectors, GBM collects on average ~ 100 counts per triggered TGF, enabling unprecedented studies of the time profiles of TGFs. Here we present the first rigorous analysis of the temporal properties of a large sample of TGFs (278), including the distributions of the rise and fall time of the individual pulses and their durations. A variety of time profiles are observed with 19% of TGFs having multiple pulses separated in time and 31 clear cases of partially overlapping pulses. The effect of instrumental dead time and pulse pile-up on the temporal properties are also presented. As the observed gamma-ray pulse structure is representative of the electron flux at the source, TGF pulse parameters are critical to distinguish between relativistic feedback discharge and lightning leader models. We show that at least 67% of TGFs at satellite altitudes are significantly asymmetric. For the asymmetric pulses, the rise times are almost always shorter than the fall times. Those which are not are consistent with statistical fluctuations. The median rise time for asymmetric pulses is ~ 3 times shorter than for symmetric pulses while their fall times are comparable. The asymmetric shapes observed are consistent with the Relativistic Feedback Discharge (RFD) model when Compton scattering of photons between the source and Fermi isincluded and instrumental effects are taken into account.

Beschreibung: The presence of ionospheric disturbances associated with Sumatra 2004 tsunami that propagated ahead of tsunami itself has previously been identified. However their origin remains unresolved till date. Focusing on their origin mechanism, we document these ionospheric disturbances referred as Ahead of tsunami Travelling Ionospheric Disturbances (ATIDs). Using TEC data from GPS Aided GEO Augmented Navigation (GAGAN) GPS receivers located near the Indian east coast, we first confirm the ATIDs presence in TEC that appear ~90 minutes ahead of the arrival of tsunami at the Indian east coast. We propose here a simulation study based on Tsunami-Atmospheric-Ionospheric coupling that considers tsunamigenic Acoustic Gravity Waves (AGWs) to excite these disturbances. We explain the ATIDs generation based on the dissipation of transverse mode of the primary AGWs. The simulation corroborates the excitation of ATIDs with characteristics similar to the observations. Therefore, we offer an alternative theoretical tool to monitor the offshore ATIDs where observations are either rare or not available and could be potentially important for the tsunami early warning.

Beschreibung: Magnetic influences increase in importance in the solar atmosphere from the photosphere out into the corona, yet our ability to routinely measure magnetic fields in the outer solar atmosphere is lacking. We describe the scientific objectives and capabilities of the COronal Solar Magnetism Observatory (COSMO), a proposed synoptic facility designed to measure magnetic fields and plasma properties in the large-scale solar atmosphere. COSMO comprises a suite of three instruments chosen to enable the study of the solar atmosphere as a coupled system: 1) a coronagraph with a 1.5-m aperture to measure the magnetic field, temperature, density and dynamics of the corona; 2) an instrument for diagnostics of chromospheric and prominence magnetic fields and plasma properties; and 3) a white-light K-coronagraph to measure the density structure and dynamics of the corona and coronal mass ejections. COSMO will provide a unique combination of magnetic field, density, temperature and velocity observations in the corona and chromosphere that have the potential to transform our understanding of fundamental physical processes in the solar atmosphere and their role in the origins of solar variability and space weather.

Beschreibung: We study the formation process of an oxygen torus during the 12-15 November 2012 magnetic storm, using the magnetic field and plasma wave data obtained by Van Allen Probes. We estimate the local plasma mass density ( ρ L ) and the local electron number density ( n e L ) from the resonant frequencies of standing Alfvén waves and the upper hybrid resonance band. The average ion mass ( M ) can be calculated by M ∼ ρ L / n e L under the assumption of quasi-neutrality of plasma. During the storm recovery phase, both Probe-A and Probe-B observe the oxygen torus at L =3.0-4.0 and L =3.7-4.5, respectively, on the morning side. The oxygen torus has M =4.5-8 amu and extends around the plasmapause that is identified at L ∼3.2-3.9. We find that during the initial phase, M is 4-7 amu throughout the plasma tough and remains at ∼1 amu in the plasmasphere, implying that ionospheric O + ions are supplied into the inner magnetosphere already in the initial phase of the magnetic storm. Numerical calculation under a decrease of the convection electric field reveals that some of thermal O + ions distributed throughout the plasma trough are trapped within the expanded plasmasphere, whereas some of them drift around the plasmapause on the dawnside. This creates the oxygen torus spreading near the plasmapause, which is consistent with the Van Allen Probes observations. We conclude that the oxygen torus identified in this study favors the formation scenario of supplying O + in the inner magnetosphere during the initial phase and subsequent drift during the recovery phase.

Beschreibung: Magnetic reconnection, as one important energy dissipation process in plasmas, has been extensively studied in the past several decades. Magnetic reconnection occurring in the downstream of a primary X-line is referred to as secondary reconnection. In this paper, we used kinetic simulations to investigate the secondary reconnection in detail. We found that secondary reconnection is reversed by the compression caused by the outflowing jet originating from the primary reconnection site, which results in the erosion of the magnetic island between the two X lines within ~3 ω ci −1 . We show the observational signatures expected in electromagnetic fields and plasma measurements in the Earth Magnetotail, associated with this mechanism. These simulation results could be applied to interpret the signatures associated with the evolution of earthward magnetic islands in the Earth's magnetotail.

Beschreibung: We test the utility of the OII 83.4 nm emission feature as a measure of ionospheric parameters. Observed with the Remote Atmospheric and Ionospheric Detection System (RAIDS) Extreme Ultraviolet Spectrograph on the International Space Station (ISS), limb profiles of 83.4 nm emissions are compared to predicted dayglow emission profiles from a theoretical model incorporating ground-based electron density profiles measured by the Millstone Hill radar and parameterized by a best-fit Chapman-α function. Observations and models are compared for periods of conjunction between Millstone Hill and the RAIDS fields-of-view. These RAIDS observations show distinct differences in topside morphology between two days, 15 January and 10 March 2010, closely matching the forward model morphology and demonstrating that 83.4 nm emission is sensitive to changes in the ionospheric density profile from the 340 km altitude of the ISS during solar minimum. We find no significant difference between 83.4 nm emission profiles modeled assuming a constant scale height Chapman-α best-fit to the ISR measurements and those assuming varying scale height.