Study of Long-Duration Flares and Associated Chromospheric and Coronal Ejections in Solar Cycles 23 and 24

Geomagnetism and Aeronomy - A statistical study of long-duration (long-duration event, LDE) flares in the soft X-ray (SXR) range for solar cycles 23 and 24 is carried out. Graphs of the dependence...     

Reconstruction of the Parameters of the Lower Midlatitude Ionosphere in M- and X-Class Solar Flares

Geomagnetism and Aeronomy - The paper presents the results of the reconstruction of the effective height h' and the slope of the profile β of the electron concentration in the D layer of...     

Cyclic Variations,Magnetic Morphology,and Complexity of Active Regions in Solar Cycles 23 and 24

Geomagnetism and Aeronomy - In this paper, 2046 active regions of solar cycle 23 and 1507 active regions of solar cycle 24 observed during the period from May 1996 to December 2018 have been...     

Solar Activity Indices for Ionospheric Parameters in the 23rd and 24th Cycles

Geomagnetism and Aeronomy - Characteristics of changes in the solar activity indices (the flux of the solar radio emission at a wavelength of 10.7 cm F and the new version of the relative sunspot...     

24th Cycle of Solar Activity: Geoefficiency of Flares

Geomagnetism and Aeronomy - Various aspects of the of geoefficiency of solar-activity phenomena, such as flares and coronal mass ejections (CMEs), are considered. The number of geoefficient events...     

Solar-Activity Indices for the Ionosphere in Cycles 23 and 24: the Form of Cycles

Geomagnetism and Aeronomy - Analysis of the features of the form of low solar cycles 23 and 24 for the solar-activity indices (F is the solar radio flux at a wavelength of 10.7 cm, Rz and Ri are...     

Flux Variations in Lines of Solar EUV Radiation beyond Flares in Cycle 24

Geomagnetism and Aeronomy - Studies in the extreme ultraviolet (EUV) and X-ray ranges of the solar spectrum are important due to the active role of radiation of these ranges in the formation of the...     

Complexity in Sequences of Solar Flares and Earthquakes

In this paper the statistical properties of solar flares and earthquakes are compared by analyzing the energy distributions, the time series of energies and interevent times, and, above all, the distributions of interevent times per se. It is shown that the two phenomena have different statistics of scaling, and even the same phenomenon, when observed in different periods or at different locations, is characterized by different statistics that cannot be uniformly rescaled onto a single, universal curve. The results indicate apparent complexity of impulsive energy release processes, which neither follow a common behaviour nor could be attributed to a universal physical mechanism.     

Formation Conditions and Energetics of Solar Nanoflares

The energy potential of solar nanoflares is estimated with a new approach proposed by the author. This approach is based on the drift mechanism for the formation of a dense loop structure in the magnetic field of a bipolar source. The densification process is assumed to proceed until the appearance of unmagnetized protons. These protons produce a current that heats the loop structure. The presence of bipolar sources is associated with local amplification of the background magnetic field by mesogranulation cells. The calculations conducted with the proposed model, which take into account observational data, yield a nanoflare energy range of 10²⁴–10²⁶ erg. The same estimates are obtained from the observed emission of nanoflare radiation. This fact is evidence, on the one hand, that the proposed model is adequate to the given process and, on the other hand, that there are no significant fluxes of the energy of this process as thermal conductivity and nonthermal particle beams. This situation is characterized by a maximum possible nanoflare energy release at a level of ≈10²⁷ erg during the mesogranule lifetime (≈10⁴ s), which yields an intensity of the energy flux of ≈10⁵ erg/s cm². This flux is insufficient to heat even the quiet regions of solar corona.     

Computation of Composite Mg II Core-to-Wing Ratio for Solar Cycle 22 and 23

Geomagnetism and Aeronomy - The Mg II core-to-wing ratio (c/w ratio) data is used to derive the solar extreme UV emission which brings a vital role in the creation of the Earth’s ionosphere...     

2006年12月系列太阳耀斑事件的近地响应分析

利用几种不同空间位置空间天气观测数据对2006年12月系列太阳耀斑近地空间天气效应进行多方位分析,结果表明,该系列耀斑都伴随不同程度日冕物质抛射CME和高速太阳风,首轮耀斑产生超过600 km/s高速太阳风,12月6日通过L1点并持续到12月12日,12月14日次轮耀斑产生900 km/s太阳风高速流,该股高速太阳风引发12月15日地磁场特大磁暴。ACE数据显示,12月6、14、15日IMF南向分量长时间超过5 nT,14～15日有4 h以上超过10 nT,NOAA SEC发布的全球地磁综合KP指数15日超过8。磁暴期间华南地区30 min平均TEC最大值波动幅度达到10TECU或20%,表明发生了较大电离层暴。     

Oscillations of the Microwave Emission of Solar Active Region 12673 before Flares

Geomagnetism and Aeronomy - We present a study of quasi-periodic pulsations in the microwave emission from solar active region (AR) NOAA 12673, which produced the strongest flares of the 24th solar...     

Coronal Holes of Cycle 24 in Observations at the Solar Dynamics Observatory

Geomagnetism and Aeronomy - The dynamics of the areas of coronal holes and their localization on the Sun in solar cycle 24 and the minimum of cycles 24–25 were analyzed. The study is based on...     

Flares Unaccompanied by Interplanetary Coronal Mass Ejections and Solar Proton Events

Geomagnetism and Aeronomy - For a coronal mass ejection (CME) to occur, the magnetic pressure of the overlying layers must be lower than that of the underlying layers, and the corresponding...     

Diagnostic Analysis of the Solar Proton Flares of September 2017 by Their Radio Bursts

The powerful solar flares that occurred on September 4–10, 2017 are analyzed based on a quantitative diagnostics method for proton flares developed at the Institute of Terrestrial Magnetism, the Ionosphere and Radio-Wave Propagation (IZMIRAN) in the 1970–1980s. We show that the fluxes and energy spectra of the protons reached the Earth with the energies of tens of MeV qualitatively and quantitatively correspond to the intensity and frequency spectra of the microwave radio bursts in the range of 2.7–15.4 GHz. Specifically, the flare of September 4 with a peak radio flux S ~ 2000 sfu at the frequency f ~ 3 GHz (i.e., with the soft radio spectrum) was accompanied by a significant proton flux J (>10 MeV) ~100 pfu and a soft energy spectrum with the index γ ~3.0, while the strong flare on September 10 with S ~ 21000 sfu at f ~ 15 GHz (i.e., with the hard radio spectrum) led to a very intense proton event with J (>10 MeV) ~1000 pfu with a hard spectrum (γ ~ 1.4), including the ground level enhancement (GLE72). This is further evidence that microwave radio data can be successfully used in diagnostics of proton flares independently of a specific source of particle acceleration at the Sun, in particular, with the IZMIRAN method.     

Gamma Rays Generated in Nuclear Interactions of Protons Accelerated during Solar Flares

Geomagnetism and Aeronomy - The article considers 30 solar flare events during which the spectra of solar cosmic-ray (SCR) protons with energies above ~80 MeV were recorded in the course of the...     

Quasi-Periodic Hard X-Ray Pulsations in Solar Flares Based on RHESSI and Konus-Wind Data

Geomagnetism and Aeronomy - The results of the study of quasi-periodic hard X-ray pulsations in solar flares with respect to the spatial localization of emission sources based on data from the...     

Source characteristics of the deep Philippine earthquake cluster, 23 and 24 July 2010

We determine the rupture velocity, rupture area, stress drop and duration of four strong deep-focus earthquakes in the Philippines by back-projecting the teleseismic P waves. Four deep-focus earthquakes occurred in a totally consumed Molucca microplate; their focal depths were greater than 550 km and their moment magnitudes were between M _w 6.6 and M _w 7.6. By studying this deep-focus cluster, we are able to estimate the rupture velocity, rupture area and stress drop which would assist in constraining the physical mechanism for earthquakes deeper than 500 km. Since the Molucca microplate is totally consumed, little evidence is left on the surface for us to do research. This deep-focus cluster provides us the opportunity to reveal the properties of this totally consumed microplate by using seismic method for the first time. Four earthquakes in this deep-focus cluster all have multiple rupture subevents. The M _w 7.3 event ruptures in two subevents, the M _w 7.6 and M _w 7.4 events both have three subevents. The M _w 6.6 event has single peak on the amplitude as a function of time; however, its energy releases at two spatially separated areas. Our results show that this deep-focus cluster has a slow rupture velocity which is about 0.27 to 0.43 of the shear wave velocity, long-scaled duration, concentrated energy release area, and high stress drop. These source properties are similar to those of other deep earthquakes occurring in warm slabs and indicate that the totally consumed Molucca microplate possibly is a warm plate.     

Subsecond X-ray Spikes in Solar Flares: Kinematics of Acceleration and Transport of Accelerated Electrons

Geomagnetism and Aeronomy - Hard X-rays time structure of solar flares can be caused by the timing of electrons acceleration, the kinematics of their propagation in the flaring plasma, and possible...     

Energy Spectra and Time Delays of Hard X-Rays of Solar Flares in Konus-Wind and RHESSI Experiments

Geomagnetism and Aeronomy - This paper analyzes hard X-ray radiation of solar flares detected by Konus-Wind and RHESSI spacecrafts. X-ray quanta are measured using high energy, time (Konus-Wind),...