MHD surface waves – a source of global magnetospheric modes (resonances)?

Various mechanisms have been proposed for explanation of the global magnetospheric modes whose frequency peaks are in the frequency range 1–4 mHz. Recent papers claim: basic characteristics of the 1–4 mHz activity events observed on ground give evidences for an existence of MHD surface mode excited on the Earth magnetopause. The discrete frequencies of such MHD surface wave modes suggest an emergence of standing wave structures along the magnetic field lines lying on the magnetopause. Such discrete frequencies of MHD surface waves on magnetopause however, are not stable, at all. Contrariwise, MHD surface wave modes supported by the two plasma boundaries – the magnetopause and the plasmapause, are in accordance with existing experimental facts: discrete set of almost stable frequencies, field amplitude peaks and positions, energy dissipation, and field distribution from high to low latitudes. Mechanisms of the global magnetospheric mode resonance are pointed out as well as tools for their identification and discrimination.     

Variations of geomagnetic cutoff rigidity in the southern hemisphere close to 70°W (South-Atlantic Anomaly and Antarctic zones) in the period 1975–2010

We report the existence of rapid variations in (effective) geomagnetic cutoff rigidity (Rc) between the equatorial and Antarctic zones adjacent to the Andes Mountains, revealed by the variation rate of geomagnetic cutoff rigidity (VRc) in the period 1975–2010. Our analysis is based on empirical records and theoretical models of the variations in cosmic rays and on the structure of geomagnetic fields. These have given us a different view of variations in Rc in time and space along the 70°W meridian, where secular variations in the geomagnetic field are strongly influenced by the proximity of the South Atlantic Magnetic Anomaly (SAMA), one of the most important characteristics of the terrestrial magnetic field that affects our planet, close from the equator to the 50°S parallel and from South America to South Africa. The VRc presents rapid changes in mid-latitudes where SAMA exerts its influence despite the existence of smooth changes in the geomagnetic field. This shows that these changes occur mainly in the spatial configuration, rather than in the temporal evolution of Rc. The analysis was performed using measurements from the Chilean Network of Cosmic Rays and Geomagnetism Observatories, equipped with BF-3 and latest generation He-3 neutron monitors, Fluxgate magnetometers, geomagnetic reference field (IGRF) and Tsyganenko 2001 model (just for completeness).     

Nonlinear filtering for sequential spacecraft attitude estimation with real data: Cubature Kalman Filter,Unscented Kalman Filter and Extended Kalman Filter

This article compares the attitude estimated by nonlinear estimator Cubature Kalman Filter with results obtained by the Extended Kalman Filter and Unscented Kalman Filter. Currently these estimators are the subject of great interest in attitude estimation problems, however, mostly the Extended Kalman Filter has been applied to real problems of this nature. In order to evaluate the behavior of the Extended Kalman Filter, Unscented Kalman Filter and Cubature Kalman Filter algorithms when submitted to realistic situations, this paper uses real data of sensors on-board the CBERS-2 remote sensing satellite (China Brazil Earth Resources Satellite). It is observed that, for the case studied in this article, the filters are very competitive and present advantages and disadvantages that should be dealt with according to the requirements of the problem.     

Monthly trends in temporal and spatial distribution of Ionospheric Irregularities across the African region during the descending phase of solar cycle 24

Ionospheric irregularities are well-known phenomena associated with ionospheric scintillation. These irregularities comprise steep electron density gradients in the equatorial F region some 1 to 2 h after sunset in regions close to the geomagnetic equator. Using the IGS network of GNSS receivers spread across the low-latitude region over the African sector, we present the monthly trends in ionospheric irregularity activity levels based on Rate of TEC Index (ROTI) during the declining phase of solar 24. The monthly trends are statistically represented by counts of the night time ROTI values exceeding a threshold of 0.4 TECU/min. A clear trend emerges on the irregularity occurrence across the African sector: during the first four months of the year, the irregularity occurrence is highly pronounced on the western side of the region. The irregularity occurrence then shifts to the eastern side during the months of May, June, July, and August. During the last four months of the year, the irregularity occurrence is again more intense on the western side of Africa than on the eastern side. The occurrence of irregularity structures on only one side of the region during a given night is an unusual feature reported here for the first time.     

Recent Advances in Understanding Particle Acceleration Processes in Solar Flares

We review basic theoretical concepts in particle acceleration, with particular emphasis on processes likely to occur in regions of magnetic reconnection. Several new developments are discussed, including detailed studies of reconnection in three-dimensional magnetic field configurations (e.g., current sheets, collapsing traps, separatrix regions) and stochastic acceleration in a turbulent environment. Fluid, test-particle, and particle-in-cell approaches are used and results compared. While these studies show considerable promise in accounting for the various observational manifestations of solar flares, they are limited by a number of factors, mostly relating to available computational power. Not the least of these issues is the need to explicitly incorporate the electrodynamic feedback of the accelerated particles themselves on the environment in which they are accelerated. A brief prognosis for future advancement is offered.     

Degradation of Signal-to-Noise Ratio Due to IF Filtering

A receiver for biphase modulated signals using an integrate-and-dump filter is optimum only if the IF filter bandwidth is infinite. Finite IF filter bandwidth results is a performance degradation. Using the predetection signal-to-noise ratio as the performance criterion, a lower bound on this quantity is determined as a function of the ratio (IF filter bandwidth)/(bit rate). The corresponding upper bound on the error probability is also presented.     

General Relativity Accuracy Test (GReAT): New configuration for the differential accelerometer

We presents the results of an activity concerning the test of the Einstein Weak Equivalence Principle with an accuracy of about 5 × 10⁻¹⁵. The experiment will be performed in an “Einstein elevator” using a differential accelerometer with a final sensitivity of about 10⁻¹⁴ g_⊕/Hz^1/2. The differential accelerometer is spun about an horizontal axis at a frequency in the range 0.5–1 Hz in order to modulate, during the free fall, the signal from a possible violation of the Equivalence Principle. In the paper the perturbing effects with the same signature of the possible violation are analyzed and constrained. The experimental results obtained in the laboratory with a first prototype of the differential accelerometer are discussed, comparing this results with those obtained using a new prototype.     

Insight into an Integration Algorithm

This paper develops, in a unique manner, a numeric algorithm for an integration and extrapolation scheme. The purpose of presenting it in this manner is to develop in the reader a complete understanding of how the algorithm is derived. It is also intended to give an insight into the limitations of the algorithm and to serve as a tool to derive additional integration schemes.     

Living plant systems: How robust are they in the absence of gravity?

The following hierarchical levels can be recognised in plant systems: cells, organs, organisms and gamodemes (interbreeding members of a community). Each level in this ‘living hierarchy’ is both defined and supported by a similar set of sub-systems. Within this framework of plant organization, two complementary questions are relevant for interpreting plant-oriented space experiments: 1) What role, if any, does gravity play in enabling the development of each organizational level? and 2) Does abnormal development in an altered gravity environment indicate sub-system inefficiency? Although a few representatives of the various organizational levels in plant systems have already been the subject of microgravity experiments in space laboratories—from cells in culture to gamodemes, the latter being found in some Closed Environment Life Support Systems—it would be of interest to investigate additional systems with respect to their response to microgravity. Recognition of the sub-systems at each level might be relevant not only for a more complete understanding of plant development but also for the successful cultivation and propagation of plants during long-term space flights and the establishment of plants in extra-terrestrial environments.