Vol 59, No 8 (2019)

The paper presents atmospheric coupling physics through identifying a few significant features imprinted on the ionosphere by certain unique seismic environments when a number of successive cluster of earthquakes ranging from 7.1 to 8.2 magnitudes occurred within about two weeks period, over the East-West Pacific zone covering 150° E to 70° W. Amongst the cases considered here are earthquakes of Chile Apr. 1, 2014 (M = 8.2) and Apr. 3, 2014 (M = 7.7), New Guinea Apr. 11, 2014 (M = 7.1) and Solomon Islands 13.04.2014 (M = 7.6). The main data source for the study is Global TEC with supplementary inputs from GPS observations taken at Guwahati (26° N, 92° E), an Appleton anomaly crest region. A few EQ events with epicenters in and around this anomaly zone are also taken in the study to focus on the seismic induced density features like Earthquake time Equatorial Anomaly (EEA) and Earthquake time Equatorial Anomaly Crest (EEAC) developed over the belt. Such anomalous modifications in TEC resulting to growths of EEA and EEAC covering Solomon Islands—New Guinea extending up to Chile along the fault lines for more than a month, are significant observations brought out in the paper. The GPS TEC data from Gauhati University are utilized in identifying the epicentre position through anomalous appearance of satellites beyond the Line Of Sight (LOS) observation. Finally, the seasonal role on enhancing the seismic induced E-field coupled by mutual interactive EQ preparatory effects of the three major events as well as in enhancement of EQ time radon emission through fault is invoked in explanation to the anomalous density features.

Discrete spectra of frequencies at 8, 14, 20, 26, … Hz are generated by electromagnetic emission from lightning sources and can be regarded as excitation of AC global circuit. These electromagnetic emissions originating within the Earth-ionosphere waveguide occur in the ULF, ELF and VLF frequency ranges. These include Schuman Resonances (SR), ELF-VLF sferics, sprites etc. During 1990s and later, the scenario with these sub-ionospheric ELF SR waves changed and several new aspects emerged. The SR power varies with respect to the receiver position and the lightning centers, commonly referred as source-observer distance. Both electric and magnetic components of SR intensity vary with the spatial shifts of the thunderstorm regions under El-Niño and La-Niña conditions. The magnitude of the lightning in the lower atmospheric region varies with time of the day. The electromagnetic waves thus generated at SR frequencies resonate due to multiple reflections in the Earth-ionosphere cavity. The total signal may be dependent on the waves from the different lightning sources. In this context, different groups of researchers throughout the globe are working and published few interesting results. In this work, few results of different observatories are discussed. Also, an attempt was made to detect experimentally the discrete signals at Kolkata (Lat. 22.56° N, Long. 88.5° E) from the year 1999. Some frequency changes in the peak values are observed in the recorded data which may be attributed to uncertainty arising from spatial distribution of lightning sources exciting the Schuman Resonance modes. Some of those results are also presented in this paper.

The kinetic theory is particularly suitable and convenient to calculate the collision parameters in the ionospheric medium. In this study, the mean free path (λ) and total collision numbers (Z₁₂) for the O⁺ + N₂ → NO⁺ + N reaction occurring in the ionospheric F region were calculated separately on geomagnetically quiet and disturbed days over Istanbul, Turkey. The relationship between geomagnetic Dst, solar IMF-Bz indices and the obtained results (λ and Z₁₂) by kinetic theory were investigated by the statistical multiple regression model. As a result of the investigation, it was seen that Dst and IMF-Bz are related to the mean free path and the total collision number on all days. It was found that IMF-Bz has a positive effect on the mean free path and the total collision number, and has a greater effect on λ and Z₁₂ than Dst in all conditions. For both parameters, it was observed that the effect of Dst and IMF-Bz on quiet days was more than on disturbed days. Therefore, it can be argued that the mean free path decreases on disturbed days, especially during nighttime.

The solar activity at different latitudes is analyzed based on daily observations at Kodaikanal, Mount Wilson, Sacramento Peak, and Meudon observatories in the CaIIK line. Activity elements of various sizes, from the elements of the chromospheric network to the flocculi, are identified. A joint database of observation results that provides information on solar activity for 1905–2018 is created. Bright elements at middle and high latitudes are distinguished in the CaIIK line in daily images, in addition to the low-latitude activity that accompanies the appearance of sunspots. The activity can be represented as a single process that begins at high latitudes during the decline phase of the previous solar cycle and continues at low latitudes as sunspot activity. The activity-drift pattern is studied for Cycles 14–24. It is more consistent with the hypothesis of an extended solar cycle than the concept of two activity waves from the midlatitudes to poles and equator obtained from the processing of faculae in white light.

The longitudinal asymmetry of the photospheric magnetic field distribution is studied based on data from the Kitt Peak National Solar Observatory (synoptic maps for 1976–2016). Vector summation is used to weaken the effect of a stochastic component uniformly distributed along the longitude and to emphasize the stable nonaxisymmetric field component. Distributions of magnetic fields with different strength are considered: strong (B > 50 G), weak (B < 5 G), and medium (50 > B > 5 G). It is shown that the longitudinal asymmetry in all the groups of fields varies in phase with the 11-year solar cycle. The asymmetry of the strong and medium fields varies in phase with the magnetic fluxes of these fields, whereas that of weak fields is in antiphase with the flux of the weak fields. The longitudinal distributions of the strong and medium magnetic fields resemble each other in shape: the distribution maximum is located at a longitude of ~180° during the ascent–maximum period of the solar cycle and at a longitude of ~0°/360° during the decrease–minimum period. Weak fields show the opposite picture: their distribution maximum is always located at the longitude of the strong and medium field minimum.

Paleoclimatic data from a sequence of argillite deposits of the Gowganda Formation located in the Mississagi River Valley (southern Ontario Province, Canada) covering a time interval of 256 years with a time resolution of one year are studied to research possible variations of the Earth’s climate in the Paleoproterozoic (~2 Ga ago). The following quasi-periodic variations have been found via the construction of a combined spectral periodogram: 3, 5, 11, 14, 29, and 75 years (at significance levels of the respective estimated values of magnitudes ranging from 2σ to 4σ). This may indicate the possible influence of solar activity on climate changes in the geological past.

According to a model of sunspot dissipation through a thin boundary layer between the sunspot magnetic flux tube and the surrounding medium, the rate of decrease in the sunspot area must slow as the spot size decreases until it reaches a critical threshold at which the linear law of sunspot dissipation gives way to a nonlinear one. This theoretically predicted effect is confirmed with SOHO/MDI data, which have a high spatial and temporal resolution in comparison with ground-based observations. This work confirms the dissipation slowdown effect in small sunspots. It is reported that the nonlinear dissipation phase derived from discrete receiver (charge-coupled device, CCD) data is somewhat flatter and more diffuse than that derived from continuous radiation receiver data (photographic plates).

It is known that the form of the 11-year solar-activity cycle can be approximately described by its amplitude A and the arrangement of three characteristic moments: the moment of the minimum (T_min), maximum (T_max), and the subsequent minimum (T_min2). According to the classical Waldmeier rule, there is an anticorrelation between the maximum activity value (amplitude) of cycle A and the duration of its ascending branch T_max – T_min, while the correlation between A and the length of the downward branch of the cycle T_min2 – T_max is much lower. Following Waldmeier, the moment T_V can be entered near the end of the downward branch of the cycle, in which the activity falls within a certain (low) specified level V. The relationship between the length of the corresponding phase of cycle T_V – T_max and the amplitude of this cycle is quite strong. We demonstrate that this connection, which can be called the “second Waldmeier rule,” agrees well with the fact that the downward branch of the cycle has a universal appearance. Thus, one parameter, its value is at the maximum, is enough for an approximate qualitative description of the form of a single 11-year cycle that takes into account the two Waldmeier rules.

The arc-polarized Alfvén waves observed in the near-Earth region of the heliosphere are studied with instruments of the WIND spacecraft in 1995–2011. Statistical distributions of the parameters characterizing the duration, amplitude, and nature of the variations in the magnetic field during the studied events are considered. The orientation of the polarization planes of Alfvén waves is studied and found to be nonrandom in nature and associated with the presence of two distinct directions (axes), which are inclined at angles of ~40° to the plane of the heliographic equator.

The paper studies the dynamics of the distribution of the index of the north–south asymmetry of the sunspot number for the phase of the 11-year cycle, from cycle to cycle, for the period 1874–2012. The used method of expansion over natural orthogonal functions makes it possible to estimate the contribution of different harmonics. It is shown that the contribution of the first harmonic of the decomposition varies from cycle to cycle from 25 to 45% and that the contribution of the first three harmonics is more than 70%. The correlation coefficient for the annual values of the north–south asymmetry of the sunspot number in the cycle and the corresponding values of the first time component of the decomposition varies from cycle to cycle, from 0.9 or higher. It is shown that the north–south asymmetry of the sunspot number is determined mainly by the periodic shift of the cyclic curves of the northern and southern hemispheres relative to each other. This ensures the appearance in the spectrum of 11-, 40-, and 80-year variations in the index of the north–south asymmetry of harmonics.

The evolution of the magnetic configuration in the solar corona is studied. The curvature of the K-corona helmets obtained from an analytical approximation of the geometry of the helmet axis was used as an indicator of the configuration change. The period of minimum solar activity was analyzed with solar eclipse materials. As a result of the analysis, the dependence of the curvature value on the latitude of the position of the helmet base and the phase of the solar cycle has been obtained. It has been established that this dependence is different for the period of solar-activity growth (the beginning of the cycle) and its decline. It was found that there is a sharp decrease in the curvature to almost zero at the beginning of the solar cycle. During the decline of the 23rd cycle and at the beginning of the 24th cycle, the change of the curvature of the helmets differs from the trend of the previous solar cycles. The apparent reason for this is a change in the conditions of the generation of the solar magnetic field. The found latitudinal–phase dependences of the curvature of the coronal helmets indicate a difference in the coronal magnetic configuration during periods of decline and increase in solar activity, as well as a sharp reorganization of the configuration at the beginning of the new solar cycle.

The study analyzes the millimeter emission of a solar flare on April 2, 2017, observed by the Bauman Moscow State Technical University telescope RT-7.5. Based on the flare atmosphere model proposed by Machado et al. (1980) we inferred the emission contribution function of the source and determined its main characteristics. The results show that the subterahertz emission is formed in a thin, chromospheric layer with a thickness of about 10 km with a plasma temperature of ~10⁵ K. The proposed homogeneous model of the layer makes it possible to explain the observed spectral features. The obtained results suggest the chromospheric source heating with heat fluxes generated in the overlying flare areas.

A multi-wavelength study and simulation is conducted for the solar flare SOL2014-09-23T23:11. GOES-class M2.5. Radio (Nobeyama Radioheliograph) and X-ray (Reuven Ramaty High Energy Solar Spectroscopic Imager) maps and energy spectra are studied, including their temporal and spatial evolution, with the superposition of radiation sources on the magnetic field structure. For the first time, a simulation of accelerated electrons transport in several characteristic magnetic structures of a flare arcade simultaneously is conducted. Accelerated electron injection functions, which depend on the space along the magnetic loop, pitch angle, and energy, are fitted to reconcile observations with the simulation results such that the calculated radiation parameters are consistent with the observed brightness distributions of hard X‑rays in the range of 28–135 keV and gyrosynchrotron radiation of 17 and 35 GHz. The energy spectrum of the electron beam corresponds in this case to one- and two-power law functions with spectral indices in the ranges δ₁ ≈ 4–5 and δ₂ ≈ 2.0–2.4 and spectrum break energy E_br ≈ 240–320 keV, depending on the specific magnetic structure. The pitch-angle distribution of accelerated electrons is essentially an anisotropic electron flux with an divergence angle of ~80° from the magnetic looptops towards the footpoint with a dominant hard X-ray source.