On the association of quiet-time Pi2 pulsations with IMF variations

The association of quiet-time Pi2 pulsations with the variations of the interplanetary magnetic field (IMF) has been examined by using three reported events, occurring during extremely quiet intervals, of which the first was on 10 March 1997, the second 27 December 1997, and the third 11 May 1999. For the first event, the onset time of ground Pi2s maps to the IMF structure bearing a variation cycle of north-to-south and north again as seen by Wind in the upstream region and Geotail in the magnetosheath. Likewise, the second and the third events have respectively, four and three recurrent turnings propagating to the Earth sensed by multiple satellites. The comparison of geomagnetic perturbations, auroral brightenings, and energetic particle data in the magnetotail with the IMF observations shows successive substorm-like activations accompanied by ground Pi2 onsets. For a clear variation cycle, the first Pi2 burst appears 36 ± 8 min after southward turning of the IMF and the second one follows14 ± 4 min after a northward turning. Moreover, ground Pi2 onsets recur under low IMF clock angle conditions. These observational results can be interpreted with the prevailing models of externally triggered substorm. But the solar wind coupling to the magnetosphere under quiet conditions proceeds in a less efficient way than under substorm time conditions. Consequently, we suggest that recurrent quiet-time Pi2s can be associated with IMF variations and their cause can be the same as those for substorm times.     

Bursts of geomagnetic pulsations in the frequency range 0.2-5 Hz excited by large changes of the solar wind pressure

We present the results of studying the magnetospheres’s response to sharp changes of the solar wind flow (pressure) based on observations of variations of the ions flux of the solar wind onboard the Inreball-1 satellite and of geomagnetic pulsations (the data of two mid-latitude observatories and one auroral observatory are used). It is demonstrated that, when changes of flow runs into the magnetosphere, in some cases short (duration ~ < 5 min) bursts of geomagnetic pulsations are excited in the frequency range Δf~ 0.2–5 Hz. The bursts of two types are observed: noise bursts without frequency changes and wide-band ones with changing frequency during the burst. A comparison is made of various properties of these bursts generated by pressure changes at constant velocity of the solar wind and by pressure changes on the fronts of interplanetary shock waves at different directions of the vertical component of the interplanetary magnetic field.     

ESA’s process for the identification and assessment of high-risk conjunction events

ESA’s Space Debris Office provides an operational service for the assessment of collision risks of ESA satellites. Currently, the ENVISAT and ERS-2 missions in low Earth orbits are covered by this service. If an upcoming high-risk conjunction event is predicted based on analysis of Two-Line Element (TLE) data from the US Space Surveillance Network, then independent tracking data of the potential high-risk conjunction object are acquired to improve the knowledge of its orbit. This improved knowledge and the associated small error covariances derived from the orbit determination process scale down the position error ellipsoid at the conjunction epoch. Hence, for the same miss-distance, in most cases an avoidance manoeuvre can be suppressed with an acceptable residual risk.     

Mathematical modeling of cruciform parachute deployment

A problem of cruciform parachute deployment is considered. The process of deployment is simulated using the present-day numerical methods in the continuum mechanics, that is, the method of concentrated masses and the method of vortex frames. The calculation results are compared with the experimental data.     

The high-latitude ionosphere structure on 22 March, 1979 magnetic storm from multi-satellite and ground-based observation

Variations in the high-latitude ionosphere structure during March 22, 1979 geomagnetic storm are examined. Electron density Ne and temperature Te from the Cosmos-900 satellite, NmF2, Ne and He⁺ from the ISS-b satellite, precipitation of soft electrons from the Intercosmos-19 satellite, and the global picture of the auroral electron precipitation from the DMSP, TIROS and P78 satellites are used. These multi-satellite databases allow us to investigate the storm-time variations in the locations of the following ionospheric structures: the day-time cusp, the equatorial boundary of the diffuse auroral precipitation (DPB), the main ionospheric trough (MIT), the day-time trough, the ring ionospheric trough (RIT) and the light ions trough (LIT). The variations in NmF2, Ne, He⁺ and Te in the high-latitude ionosphere for the different local time sectors are analyzed also. The features of the high-latitude ionospheric response to a strong magnetic storm are described.     

Time variations of cosmic-ray helium isotopes with BESS-Polar I

The Balloon-borne Experiment with a Superconducting Spectrometer (BESS) is configured with a solenoidal superconducting magnet and a suite of precision particle detectors, including time-of-flight hodoscopes based on plastic scintillators, a silica-aerogel Cherenkov detector, and a high resolution tracking system with a central jet-type drift chamber. The charges of incident particles are determined from energy losses in the scintillators. Their magnetic rigidities (momentum/charge) are measured by reconstructing each particle trajectory in the magnetic field, and their velocities are obtained by using the time-of-flight system. Together, these measurements can accurately identify helium isotopes among the incoming cosmic-ray helium nuclei up to energies in the GeV per nucleon region. The BESS-Polar I instrument flew for 8.5 days over Antarctica from December 13th to December 21st, 2004. Its long-duration flight and large geometric acceptance allow the time variations of isotopic fluxes to be studied for the first time. The time variations of helium isotope fluxes are presented here for rigidities from 1.2 to 2.5 GV and results are compared to previously reported proton data and neutron monitor data.     

Difficulties in the study of cosmic radio noise absorption at 30 MHz using riometer at low latitude station,Kolhapur (Lat-16.8°N,Long-74.25°E)

A dual dipole antenna has been installed at low latitude station Kolhapur (Geographic 16.8°N, 74.25°E), Maharashtra, India for the study of cosmic radio noise absorption using Solid State Riometer (which operates at 30 MHz) during pre phase of 24th solar maxima. The aim for this type of study over Kolhapur was to know the response of lower (D region) ionosphere over low latitude by cosmic radio noise absorption using riometer technique during quite period as well as sudden ionospheric disturbances (SID). The observations are being taken for 3 years. Two different sites (∼40 km away from each other) were used for the installation of riometer equipment assuming minimum local noise. It is found that solar noise to cosmic radio noise hence resulting in signal saturation. The night time signal is relatively free of interference but sometimes local noise is responsible for spike-like signatures. Hence it is concluded that Kolhapur (a low latitude station) is not suitable for the study of cosmic radio noise absorption on 30 MHz with riometer and dual dipole antenna. Proper choice for operating frequency of riometer and antenna gain is suggested for low latitude use of this technique for ionospheric deviative and nondeviative absorption studies.     

Short-arc tracklet association for geostationary objects

Measurement association and initial orbit determination is a fundamental task when building up a database of space objects. This paper proposes an efficient and robust method to determine the orbit using the available information of two tracklets, i.e. their line-of-sights and their derivatives. The approach works with a boundary-value formulation to represent hypothesized orbital states and uses an optimization scheme to find the best fitting orbits. The method is assessed and compared to an initial-value formulation using a measurement set taken by the Zimmerwald Small Aperture Robotic Telescope of the Astronomical Institute at the University of Bern. False associations of closely spaced objects on similar orbits cannot be completely eliminated due to the short duration of the measurement arcs. However, the presented approach uses the available information optimally and the overall association performance and robustness is very promising. The boundary-value optimization takes only around 2% of computational time when compared to optimization approaches using an initial-value formulation. The full potential of the method in terms of run-time is additionally illustrated by comparing it to other published association methods.     

Langley method applied in study of aerosol optical depth in the Brazilian semiarid region using 500, 670 and 870 nm bands for sun photometer calibration

Due to the high costs of commercial monitoring instruments, a portable sun photometer was developed at INPE/CRN laboratories, operating in four bands, with two bands in the visible spectrum and two in near infrared. The instrument calibration process is performed by applying the classical Langley method. Application of the Langley’s methodology requires a site with high optical stability during the measurements, which is usually found in high altitudes. However, far from being an ideal site, Harrison et al. (1994) report success with applying the Langley method to some data for a site in Boulder, Colorado. Recently, Liu et al. (2011) show that low elevation sites, far away from urban and industrial centers can provide a stable optical depth, similar to high altitudes. In this study we investigated the feasibility of applying the methodology in the semiarid region of northeastern Brazil, far away from pollution areas with low altitudes, for sun photometer calibration. We investigated optical depth stability using two periods of measurements in the year during dry season in austral summer. The first one was in December when the native vegetation naturally dries, losing all its leaves and the second one was in September in the middle of the dry season when the vegetation is still with leaves. The data were distributed during four days in December 2012 and four days in September 2013 totaling eleven half days of collections between mornings and afternoons and by means of fitted line to the data V₀ values were found. Despite the high correlation between the collected data and the fitted line, the study showed a variation between the values of V₀ greater than allowed for sun photometer calibration. The lowest V₀ variation reached in this experiment with values lower than 3% for the bands 500, 670 and 870 nm are displayed in tables. The results indicate that the site needs to be better characterized with studies in more favorable periods, soon after the rainy season.     

Time-dependent stresses in a beam under a load moving along its surface

We studied the time-dependent processes in a beam under the action of the load that is normal to its surface and moves with the constant velocity. It was found that the maximum stresses are realized in the fixed beam section at different moments of time depending on the travel speed of external load. With increasing the load movement velocity, the maximum stresses in the region of beam clamping are reduced, while the levels of local normal and shear stresses in the limits of its action increase more significantly approaching to the limiting values in accordance to the known experimental fact that at high rates the beam failure is caused by shear stresses.