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.     

Physical implications of discrepancy between summer and winter PC indices observed in the course of magnetospheric substorms

The PC index based on a statistically justified relationship between the polar cap magnetic activity and the interplanetary electric field E_KL has been derived as a value standardized for the E_KL intensity regardless of season, UT and hemisphere. As a result, the summer and winter PC indices are consistent with one another under ordinary conditions. Discrepancies between the summer and winter PC indices arising in the course of magnetospheric substorms are analyzed in this paper. It is argued that the channel of enhanced conductivity, formed in the auroral oval owing to intense auroral particle precipitation, strongly improves the conditions for closure of the Region 1 field-aligned currents in the winter dark polar region but only trivially affects the conditions of the Region 1 FAC closure in the summer sunlit ionosphere. Since the coefficients describing the relationship between E_KL and the polar cap magnetic activity were derived for statistically justified (i.e., mean) conditions, their application to such abnormal situation, as intense field-aligned currents in the winter dark polar region, leads to overestimation of the winter PC index. The summer and winter PC indices level off as soon as the intense auroral particle precipitation terminates and the auroral ionosphere in the winter and summer polar caps returns to the ordinary (statistically justified) state.     

Detection Performance of a Mean-Level Threshold

The problem of detecting signals in nonstationary clutter is met by presenting a mean-level or adaptive threshold which adjusts to the changing background level. Such a threshold performs better than a fixed threshold that must be set for the highest amplitude clutter. However, the mean-level threshold does not perform as well for stationary noise as a fixed threshold set at the proper value. One measure of effectiveness of an adaptive threshold is its performance in stationary noise (compared to the optimum fixed threshold) for a specified speed of response. For the mean-level threshold, a simple mathematical solution is found for the detection probability when the noise is stationary and the signal scintillates rapidly. The performance is evaluated for a wide range of mean-level-threshold time constants and for several false-alarm probabilities. The results are presented graphically. As an example, the mean-level threshold suffers 3 dB in detectability (equivalent signal-to-noise ratio) in the presence of stationary noise as compared to the optimum fixed threshold for 50-percent probability of detection, false-alarm probability of 10-8, and an adjustment time of 15 times the signal duration.     

Cosmic Rays and Earth – A Summary

Cosmic rays provide a diagnostic tool to analyze processes in interplanetary space and at the Sun. Cosmic rays also directly affect the terrestrial environment and serve as indicators of solar variability and non anthropogenic climatic changes on Earth at present and in the distant past. After the invention of the neutron monitor by John A. Simpson in 1948, an international network of cosmic ray detectors developed in a cooperative effort to examine temporal and spatial variations in our space environment. The resulting datasets represent the longest continuous, high time resolution series of particle radiation measurement in space science. At present, the neutron monitor network is complemented by spacecraft instrumentation to study solar-terrestrial correlated phenomena. This revised version was published online in August 2006 with corrections to the Cover Date.     

Multi-station observation of ionospheric disturbance of March 9 2012 and comparison with IRI-model

The magnetic storm of 9 March 2012 is a single step intense storm (Dst = −143 nT) whose main phase begins around 0100 UT and lasted for almost 11 h. The increases in NmF2 recorded 33% and 67% incidence respectively during the main and the recovery phase of the storm at the stations considered. The increase in hmF2 occurred concurrently with the increase in thickness parameter B0 between 0000 and 1100 UT, and a simultaneous decrease in the shape parameter B1 for the entire mid-latitude stations. Generally, B1 responded to the storm with a decrease away from the quiet day average, and decreased simultaneously with the increase in NmF2. B0 displays higher variability magnitude during daytime than the nighttime period. The occasional differences in the response of the ionospheric parameters to the storm event are attributed to longitudinal differences. Variation in hmF2 and NmF2 is projected to change in B1, but the rationale behind this effect on B1 is still not known and therefore left open. The two IRI options over-estimate the observed values with that of URSI higher than CCIR. The over-estimation was higher during the nighttime than the daytime for NmF2 response for the mid-latitude stations and the reverse for the equatorial station. A fairer fit of the model with the observed for all parameters over Jicamarca suggests that equatorial regions are better represented on the model. Extensive study of B1 and B0 is recommended to arrive at a better performance of IRI.     

Meteor Phenomena and Bodies

Meteoroids can be observed at collision with the Earth's atmosphere as meteors. Different methods of observing meteors are presented: besides the traditional counts of individual events, exact methods yield also data on the geometry of the atmospheric trajectory; on the dynamics and ablation of the body in the atmosphere; on radiation; on the spectral distribution of radiation; on ionization; on accompanying sounds; and also data on orbits. Theoretical models of meteoroid interaction with the atmosphere are given and applied to observational data. Attention is paid to radar observations; to spectroscopic observations; to experiments with artificial meteors and to different types of meteor sounds. The proposed composition and structure of meteoroids as well as their orbits link them to meteorites, asteroids and comets. Meteor streams can be observed as meteor showers and storms. The rate of influx of meteoroids of different sizes onto Earth is presented and potential hazards discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Comparison of GPS TEC variations with IRI-2007 TEC prediction at equatorial latitudes during a low solar activity (2009–2011) phase over the Kenyan region

This work presents an analysis of the Total Electron Content (TEC) derived from the International GNSS Service (IGS) receivers at Malindi (mal2: 2.9^oS, 40.1^oE, dip −26.813^o), Kasarani (rcmn: 36.89^oE, 1.2^oS, dip −23.970^o), Eldoret (moiu: 35.3^oE, 0.3^oN, dip −21.037^o) and GPS-SCINDA (36.8^oE, 1.3^oS, dip −24.117^o) receiver located in Nairobi for the period 2009–2011. The diurnal, monthly and seasonal variations of the GPS derived TEC (GPS-TEC) and effects of space weather on TEC are compared with TEC from the 2007 International Reference Ionosphere model (IRI-TEC) using the NeQuick option for the topside electron density. The diurnal peaks in GPS-TEC is maximum during equinoctial months (March, April, October) and in December and minimum in June solstice months (May, June, July). The variability in GPS-TEC is minimal in all seasons between 0:00 and 04:00 UT and maximum near noon between 10:00 and 14:00 UT. Significant variability in TEC at post sunset hours after 16:00 UT (19:00 LT) has been noted in all the seasons except in June solstice. The TEC variability of the post sunset hours is associated with the occurrence of the ionization anomaly crest which enhances nighttime TEC over this region. A comparison between the GPS-TEC and IRI-TEC indicates that both the model and observation depicts a similar trend in the monthly and seasonal variations. However seasonal averages show that IRI-TEC values are higher than the GPS-TEC. The IRI-TEC also depicts a double peak in diurnal values unlike the GPS-TEC. This overestimation which is primarily during daytime hours could be due to the model overestimation of the equatorial anomaly effect on levels of ionospheric ionization over the low latitude regions. The IRI-TEC also does not show any response to geomagnetic activity, despite the STORM option being selected in the model; the IRI model generally remains smooth and underestimates TEC during a storm. The GPS-TEC variability indicated by standard deviation seasonal averages has been presented as a basis for extending the IRI-model to accommodate TEC-variability.     

Numerical simulation of formation of cyclone vortex flows in the intratropical zone of convergence and their early detection

Mechanisms of formation of cyclonic vortices in the tropical atmosphere of the Earth are investigated in the intratropical zone of convergence using numerical simulation made with the complete system of equations of gas dynamics taking into account transport of infrared radiation, phase transitions of water vapor into microdrops of water and ice particles, and sedimentation of these drops and ice particles in the field of gravity force. Observational data on the structure of dominant air streams, which are formed in the intratropical zone of convergence over the North Atlantic in the periods of its highest thermodynamic intensity and instability, are used in the initial and boundary conditions of the model. Formation of cyclonic vortex flows is obtained numerically at sufficiently strong bending of the intratropical zone of convergence. The results of numerical modeling are compared with the data of satellite microwave monitoring: global radio thermal fields of the Earth from the electronic collection GLOBAL-Field allowing one to study the structure of atmospheric motions in a wide range of space-time scales.