No Arabic abstract
In March and August/September 1995, February 1996, and in March-April 1998, observations of the inhomogeneous structure of the high-latitude ionosphere were carried out at Norilsk (geomagnetic latitude and longitude are 64.2 N and 160.4 E, and L=5.2). Small-scale irregularities (with the lifetime of several seconds,and the spatial scale less than 5-7 km), and medium-size wave irregularities(with the period of 10-50 min, and the horizontal size of tens and hundreds of kilometres) of the ionospheric F layer were investigated under different geophysical conditions. A total of 300 hours of observations was recorded, including 250 reflections from the F2 layer, and the other reflections from the sporadic E layer. The diurnal variations of inhomogeneous structure parameters in March and April is obtained. Dependence of some ionospheric irregularity parameters on geomagnetic activity is presented.
Saturns ionosphere is produced when the otherwise neutral atmosphere is exposed to a flow of energetic charged particles or solar radiation. At low latitudes the latter should result in a weak planet-wide glow in infrared (IR), corresponding to the planets uniform illumination by the Sun. The observed low-latitude ionospheric electron density is lower and the temperature higher than predicted by models. A planet-ring magnetic connection has been previously suggested in which an influx of water from the rings could explain the lower than expected electron densities in Saturns atmosphere. Here we report the detection of a pattern of features, extending across a broad latitude band from ~25 to 60 degrees, that is superposed on the lower latitude background glow, with peaks in emission that map along the planets magnetic field lines to gaps in Saturns rings. This pattern implies the transfer of charged water products from the ring-plane to the ionosphere, revealing the influx on a global scale, flooding between 30 to 43% of the planets upper-atmospheric surface. This ring `rain plays a fundamental role in modulating ionospheric emissions and suppressing electron densities.
We are currently measuring the dissolution kinetics of albite feldspar at 100 deg C in the presence of high levels of dissolved CO_2 (pCO_2 = 9 MPa) as a function of the saturation state of the feldspar (Gibbs free energy of reaction, Delta G). The experiments are conducted using a flow through reactor, thereby allowing the dissolution reactions to occur at a fixed pH and at constant, but variable saturation states. Preliminary results indicate that at far-from-equilibrium conditions, the dissolution kinetics of albite are defined by a rate plateau, with R approx 5.0 x 10^{-10} mol m^{-2} s^{-1} at -70 < Delta G < -40 kJ mol^{-1}. At Delta G > -40 kJ mol^{-1}, the rates decrease sharply, revealing a strong inverse relation between the dissolution rate and free energy. Based on the experiments carried out to date, the dissolution rate-free energy data correspond to a highly non-linear and sigmoidal relation, in accord with recent studies.
Using the geomagnetic storm of July 15, 2000 as an example, we investigated the dependence of GPS navigation system performance on the nightside at mid-latitudes on the level of geomagnetic disturbance. The investigation was based on the data from the global GPS system available through the Internet. It was shown that the number of GPS phase slips increases with the increasing level of disturbance and that there is a good correlation between the rate of Dst-variation and the frequency of slips. It was further shown that the relative frequency of slips has also a clearly pronounced aspect dependence. Phase slips of the GPS signal can be caused by the scattering from small-scale irregularities of the ionospheric E-layer. Phase slip characteristics are indicative of Farley-Buneman instabilities as a plausible physical mechanism that is responsible for the formation of geomagnetic field-aligned irregularities. Using simultaneous measurements of backscatter signal characteristics from the Irkutsk incoherent scatter radar and existing models for such irregularities, we estimated the order of magnitude of the expected phase fluctuations of the GPS signal at a few degrees.
We analyzed 44 passes of the MAVEN spacecraft through the magnetosphere, arranged by the angle between electric field vector and the projection of spacecraft position radius vector in the YZ plane in MSE coordinate system (${theta}$ E ). All passes were divided into 3 angular sectors near 0{deg}, 90{deg} and 180{deg} ${theta}$ E angles in order to estimate the role of IMF direction in plasma and magnetic properties of dayside Martian magnetosphere. The time interval chosen was from January 17 through February 4, 2016 when MAVEN was crossing the dayside magnetosphere at SZA ~ 70{deg}. Magnetosphere as the region with prevailing energetic planetary ions is always found between the magnetosheath and the ionosphere. 3 angular sectors of dayside interaction region in MSE coordinate system with different orientation of the solar wind electric field vector E = -1/c V x B showed that for each sector one can find specific profiles of the magnetosheath, the magnetic barrier and the magnetosphere. Plume ions originate in the northern MSE sector where motion electric field is directed from the planet. This electric field ejects magnetospheric ions leading to dilution of magnetospheric heavy ions population, and this effect is seen in some magnetospheric profiles. Magnetic barrier forms in front of the magnetosphere, and relative magnetic field magnitudes in these two domains vary. The average height of the boundary with ionosphere is ~530 km and the average height of the magnetopause is ~730 km. We discuss the implications of the observed magnetosphere structure to the planetary ions loss mechanism.
The X-ray emission of gamma-ray bursts (GRBs) is often characterized by an initial steep decay, followed by a nearly constant emission phase (so called plateau) which can extend up to thousands of seconds. While the steep decay is usually interpreted as the tail of the prompt gamma-ray flash, the long-lasting plateau is commonly associated to the emission from the external shock sustained by energy injection from a long lasting central engine. A recent study proposed an alternative interpretation, ascribing both the steep decay and the plateau to high-latitude emission (HLE) from a structured jet whose energy and bulk Lorentz factor depend on the angular distance from the jet symmetry axis. In this work we expand over this idea and explore more realistic conditions: (a) the finite duration of the prompt emission, (b) the angular dependence of the optical depth and (c) the lightcurve dependence on the observer viewing angle. We find that, when viewed highly off-axis, the structured jet HLE lightcurve is smoothly decaying with no clear distinction between the steep and flat phase, as opposed to the on-axis case. For a realistic choice of physical parameters, the effects of a latitude-dependent Thomson opacity and finite duration of the emission have a marginal effect on the overall lightcurve evolution. We discuss the possible HLE of GW170817, showing that the emission would have faded away long before the first Swift-XRT observations. Finally, we discuss the prospects for the detection of HLE from off-axis GRBs by present and future wide-field X-ray telescopes and X-ray surveys, such as eROSITA and the mission concept THESEUS.