International Space Science Institute

About: International Space Science Institute is a nonprofit organization based out in Bern, Switzerland. It is known for research contribution in the topics: Solar wind & Comet. The organization has 120 authors who have published 858 publications receiving 25772 citations. The organization is also known as: ISSI.

Low-frequency electromagnetic waves and instabilities within the Martian bi-ion plasma

Abstract: The Martian environment is characterized by the presence of heavy (oxygen) ions of planetary origin which strongly influence the solar wind dynamics, including the bow shock structure and position and may cause additional plasma boundaries in the magnetosheath. In this paper the dispersion characteristics of low-frequency electromagnetic waves (LFEW) in the proton gyrofrequency range are studied. The excitation of these waves results from the relative motion between the solar wind protons and planetary heavy ions, which are considered as unmagnetized and, therefore, may act like a beam in the solar wind. The model takes into account the small extension of the Martian magnetosphere compared with the pickup gyroradius of an exospheric ion. From the dispersion analysis it was found that the most unstable waves with relatively high growth rates propagate oblique to the ambient magnetic field. For small propagation angle to the magnetic field these are right-hand polarized whistler waves in the solar wind frame, and due to Doppler shift they appear near to the proton cyclotron frequency as left-hand polarized waves in the beam (spacecraft) frame. We suggest that the sporadic LFEW emission as seen in the upstream region of Mars by Phobos-2 may indicate the existence of localized “heavy ion bunches” whose origin is relatively unclear, but a possible relation to the Martian moons cannot be excluded. Especially, the so-called Phobos events marked by spectral peaks around the proton cyclotron frequency may be interpreted as signatures of the solar wind interaction with a tenuous gas torus. A comparable situation is known from the AMPTE Ba and Li releases where during the late stages of the experiments an enhanced proton cyclotron emission was observed as well. Another important aspect of LFEW excitation is its role in proton deceleration and heating upstream the bow shock where turbulent processes may provide a strong momentum coupling between the solar wind and the newly generated ions of planetary origin.

First in‐situ analysis of dust devil tracks on Earth and their comparison with tracks on Mars

Abstract: In this study we report about the first in-situ analysis of terrestrial dust devil tracks (DDTs) observed in the Turpan depression desert in northwestern China. Passages of active dust devils remove a thin layer of fine grained material (< ∼63 μm), cleaning the upper surface of coarse sands (0.5–1 mm). This erosional process changes the photometric properties of the upper surface causing the albedo differences within the track to the surroundings. Measurements imply that a removal of an equivalent layer thickness of ∼2 μm is sufficient to form the dark dust devil tracks. Our terrestrial results are in agreement with the mechanism proposed by Greeley et al. (2005) for the formation of DDTs on Mars.

Space-Based Earth Observations for Disaster Risk Management

Abstract: As space-based Earth observations are delivering a growing amount and variety of data, the potential of this information to better support disaster risk management is coming into increased scrutiny. Disaster risk management actions are commonly divided into the different steps of the disaster management cycle, which include: prevention, to minimize future losses; preparedness and crisis management, often focused on saving lives; and post-crisis management aiming at re-establishing services supporting human activities. Based on a literature review and examples of studies in the area of coastal, hydro-meteorological and geohazards, this review examines how space-based Earth observations have addressed the needs for information in the area of disaster risk management so far. We show that efforts have essentially focused on hazard assessments or supporting crisis management, whereas a number of needs still remain partly fulfilled for vulnerability and exposure mapping, as well as adaptation planning. A promising way forward to maximize the impact of Earth observations includes multi-risk approaches, which mutualize the collection of time-evolving vulnerability and exposure data across different hazards. Opportunities exist as programmes such as the Copernicus Sentinels are now delivering Earth observations of an unprecedented quality, quantity and repetitiveness, as well as initiatives from the disaster risk science communities such as the development of observatories. We argue that, as a complement to this, more systematic efforts to (1) build capacity and (2) evaluate where space-based Earth observations can support disaster risk management would be useful to maximize its societal benefits.

Formation of phase lags at the cyclotron energies in the pulse profiles of magnetized, accreting neutron stars

Abstract: Context. Accretion-powered X-ray pulsars show highly energy-dependent and complex pulse-profile morphologies. Significant deviations from the average pulse profile can appear, in particular close to the cyclotron line energies. These deviations can be described as energy-dependent phase lags, that is, as energy-dependent shifts of main features in the pulse profile. Aims. Using a numerical study we explore the e ect of cyclotron resonant scattering on observable, energy-resolved pulse profiles. Methods. We generated the observable emission as a function of spin phase, using Monte Carlo simulations for cyclotron resonant scattering and a numerical ray-tracing routine accounting for general relativistic light-bending e ects on the intrinsic emission from the accretion columns. Results. We find strong changes in the pulse profile coincident with the cyclotron line energies. Features in the pulse profile vary strongly with respect to the average pulse profile with the observing geometry and shift and smear out in energy additionally when assuming a non-static plasma. Conclusions. We demonstrate how phase lags at the cyclotron energies arise as a consequence of the e ects of angular redistribution of X-rays by cyclotron resonance scattering in a strong magnetic field combined with relativistic e ects. We also show that phase lags are strongly dependent on the accretion geometry. These intrinsic e ects will in principle allow us to constrain a system’s accretion geometry.