Geomagnetism and Aeronomy最新文献

The paper presents the results of an analysis of observations of an eruptive prominence on the MFS and HSFA2 spectrographs of the Ondřejov Observatory (Astronomical Institute, Czech Republic) in the hydrogen, helium, and calcium lines. After spectral processing, the integral radiation fluxes in the lines were determined and the physical parameters of the plasma were calculated theoretically using a model in the absence of local thermodynamic equilibrium. Comparison of the observed and calculated values showed that the observed radiation fluxes in the lines can be explained in a model of stationary gas radiation taking into account the opacity in the spectral lines. To calculate the theoretical fluxes, in some cases, it was necessary to introduce radiation from several layers with different temperatures and heights. The calculated radiation fluxes agree with the observed ones to within 10%. As a result of the simulation, the main parameters of the plasma of the prominence were obtained: temperature, concentration, etc. The values of the radiation fluxes in the spectral lines are evidence of inhomogeneity of the emitting gas, and there may be regions next to each other with temperatures differing by an order of magnitude.

The results of correlation analysis of radon and air ion concentrations based on measurement data in an underground laboratory are presented. For pairs of pressure–radon and pressure–ion variables, a delayed pumping effect was revealed, similar to that previously observed for neutrons and gamma rays. A simple phenomenological model is presented to explain the results obtained. Within this model, the delay is caused by the gradual accumulation of radon in the room as atmospheric pressure decreases. The balance of the accumulation rate of radon, the time of its radioactive decay, and the characteristic time of pressure variations leads to an effective delay of 2 days between variations in atmospheric pressure and radon concentration. Correlation analysis for pressure–ion variables indicates that the air carrying radon into the laboratory already contains ions formed in soil pores. These ions make up approximately 21% of the total ions in the laboratory.

Ground-based observations of cosmic rays by the spectrographic global survey method were used to study the ground-level enhancement in cosmic ray intensity on August 24, 2002. Spectra of variations of primary cosmic rays and their anisotropy were obtained. Based on measurements from the GOES spacecraft and global network of cosmic ray stations, the differential rigidity spectra of accelerated particles in the vicinity of the Sun were calculated. The maximum rigidity to which solar particles were accelerated was estimated.

Disturbances in the lower ionosphere and in the region of the maximum of the ionospheric F2 layer during the eruption of Shiveluch volcano in April 2023 are analyzed based on data from ground-based magnetometers and GPS radio sounding of the ionosphere. The magnetic stations were located at distances of 455 (Paratunka) and 752 km (Magadan) from the volcano. The variations in the magnetic field and total electron content of the ionosphere were studied as characteristics of the ionospheric response to this event. Analysis of the measurements showed that the ionosphere was impacted by seismic Rayleigh waves and atmospheric acoustic-gravity waves generated by volcanic explosions. The energy of several explosions was estimated from the amplitude of the ionospheric signal in the total electron content.

The study analyzes the long-term average annual OH* temperature trend, the values of which were obtained from nighttime spectral measurements of hydroxyl airglow bands at Zvenigorod research station (56° N, 37° E) from 1957 to 2022. At present, this OH* temperature series, which reflects the thermal state of the mesopause region, is the longest in the world. On its basis, the linear trend and response of temperature to changes in solar activity are estimated both in general for the entire data set and for individual time intervals. In the first case, the trend was –0.23 ± 0.04 K/year. In the second case, the analysis showed a strong cooling in the mesopause region (–0.53 ± 0.34 K/yr) until the 1970s, which subsequently slowed to –0.14 ± 0.03 K/yr. Comparison of the results with other measurements and model calculations shows that the latter have lower trend values. It is suggested that the causes of the temperature trend, in addition to the increase in greenhouse gases, the main one being CO₂, can be due to long-term changes in the dynamics of the upper atmosphere.

This paper describes penumbra supersonic downflows (PSDs), which can be observed using the Hinode spectropolarimeter. The map obtained from red wing wavelengths at the half of line depth of the Fe I λ 6302 Å line makes it easy to detect these flows. They represent visible fragments of penumbral filaments as they turn sharply before entering the deep layers at the junction of the penumbra and the undisturbed photosphere. The PSD regions observed in this way are a part of the penumbral region where magnetic field lines bend relative to the plane parallel to the spectrometer’s aperture and experience polarity reversal of the longitudinal field. The polarity reversal zone is clearly visible on the map constructed from the values of signed net circular polarization (sNCP), i.e., the NCP values multiplied by the sign of the field. The region where the sNCP changes sign is characterized by elevated values of line-of-sight velocities, measured from the center of gravity of the circular polarization absolute value. In most cases, PSDs are observed on the limb side of the penumbra. On the side of the solar disk center, PSDs can be detected by other means, in particular, a map can be constructed from the positions of the centers of gravity of the red lobe in the linear polarization profile. Such a map also clearly shows the moat flow region.

The influence of the effects of thermal conduction and heating/radiative losses on the propagation of acoustic waves in a rarefied high-temperature plasma is studied. A constant heating function is chosen, and an interpolation is used for the radiative-loss function, which is based on the values found by the CHIANTI 10 code. Waves are analyzed in a linear approximation based on the dispersion relation. The input parameters in the problem are the plasma temperature and density and the output parameters are the period of oscillations and their damping time. Conversely, having observational data on compression waves, one can pose the problem of finding the parameters of the coronal plasma from the oscillation parameters. The situations in which the effect of the misbalance between heating and losses can, along with thermal conductivity, play a significant role in wave damping are shown. The temperature ranges at which instability and aperiodic damping of acoustic oscillations are possible are determined.

The purpose of this work was to study maps of the temperature distribution in the corona above the NOAA active region (AR) 12 192 outside solar flares and during individual flare events of high X-ray classes as well as to determine the role of electric currents in heating the coronal matter. Data on the distribution of magnetic field vector components in the photosphere provided by the Helioseismic and Magnetic Imager (HMI) instrument on board the Solar Dynamics Observatory (SDO) are used to detect the large-scale electric current and calculate its magnitude. Photogeliograms of the solar corona in ultraviolet (UV) channels 131, 171, 193, and 211 Å provided by the Atmospheric Imaging Assembly (AIA/SDO) instrument are used to estimate the temperature in the corona above active regions (ARs). The following results have been obtained: (1) Outside the time of solar flares, a coronal structure with a temperature of 10 MK or more, which was observed for the entire time interval of AR monitoring and marked the location of a large-scale electric current channel at coronal heights, is detected in the central part above the studied AR. (2) The existence of the high-temperature coronal structure over a long time interval indicates a stationary mode of coronal matter heating due to the ohmic dissipation of large-scale electric currents. (3) It is shown that effective stationary heating of coronal matter by electric currents requires anomalous values of plasma conductivity (σ = 10¹⁰ s^–1) and filamentation of the current channel into elements with a cross section of the order of 10⁸ cm or less. (4) Heating of a coronal loop (loop system) with a cross section of 10⁸ cm and a length of 10¹⁰ cm to a temperature of 10 MK on time scales of a few hours can be implemented under the condition of anomalous plasma conductivity by an electric current in the corona of the order of 10⁹ A. (5) During solar flare events, a decrease (in percentage terms) in the role of electric currents in the processes of coronal matter heating and the activation of additional heating mechanisms are observed.

A comparative analysis of the evolution of the maximum magnetic field of sunspots, obtained at Mount Wilson Observatory (9033 measurements) and the spectral flux of radio emission at a frequency of 2.8 GHz (F_10.7) during the declining and minimum phase of solar cycle 24 (2014–2019), is carried out. An anomalous behavior of the magnetic field of sunspots with a strength of 1500 G or higher has been detected, which is characterized by even a slight increase in the sunspot magnetic field during the declining phase of the cycle, which is in a good agreement with the results of observations by the BST-2 telescope of the Crimean Astrophysical Observatory and with measurements of the areas of the biggest spot in a group according to the data of the Kislovodsk Mountain Astronomical Station. Despite a noticeable increase in the average values of the magnetic field from 2015 to 2017, no significant changes were found in the scatter diagram of the F_10.7 solar activity index and Wolf numbers. This indicates the decisive contribution to the index F_10.7 of the thermal bremsstrahlung mechanism of radio emission.

The lifetime of individual solar pores and sunspots is analyzed according to the data of the HMI/SDO space observatory observations in the 24th and 25th activity cycles. It is found that the lifetime of individual sunspots and pores T differs from the Gnevyshev–Waldmeier rule formulated for groups of sunspots. For regular sunspots, that is, spots with nuclei, there is a linear dependence on the maximum area S_mx: T_sp = –0.019(±0.2) + 0.027(±0.002)S_mx. For solar pores, the dependence of the lifetime on the area has a logarithmic form T_por = –0.24(±0.1) + 0.055(±0.014) log(S_mx). Possible mechanisms of disintegration of spots and pores are studied. The lifetime for regular spots is probably related to convective currents. It has been established that the average velocity of the matter flow, determined from observations of Doppler velocities, increases with a decrease in the area of sunspots. This can accelerate the decay rate of sunspots with a decrease in the area of sunspots. For solar pores, the lifetime can be determined by the heating mechanism.