Solar Wind Parameters and Its Geoefficiency During Minimums of Four Solar Cycles

Recently a number of publications have appeared on the long and deep minimum in cycle 23 of solar activity. This interest is due to the fact that it turned out to be the longest and deepest in terms of the number of sunspots in the entire era of space exploration. The features of the minimum of cycle 23 of solar activity and the beginning of cycle 24 made it possible to assume that in the coming decades, a minimum of solar activity similar to the Dalton or Maunder minimum, leading to a global change in the earth's climate, may occur. Such assumptions make a detailed study of the influence of the minimum of solar cycle 23 on the parameters of the solar wind and the interplanetary magnetic field, as well as a comparison of this influence with similar manifestations in the three previous cycles very urgent. The work carried out statistical processing and analysis of data available in print and on the Internet on the indices of solar activity (W and F10.7), on geomagnetic activity, as well as on the parameters of the solar wind and interplanetary field. In contrast to other similar studies, when choosing time intervals for all cycles, only one — 12 months was used, which made it possible to exclude annual and semi-annual variations in solar wind parameters. For the considered minima of solar activity, the geoeffectiveness of the disturbed fluxes ICME, CIR, and Sheath was considered. A monotonic and very significant decrease in the geoeffectiveness of the ICME streams was found. Data processing on the hourly average values of the solar wind parameters at the minima of geomagnetic activity for 4 cycles confirmed the significant difference between cycle 23 and the previous ones in the behavior of the magnetic field. The cycle-by-cycle decrease in the geoeffectiveness of coronal ejections discussed in the press deserves a more detailed analysis using extensive data on magnetic activity indices.

Deep Minimum and a Vortex for Positronium Formation in Low-Energy Positron-Helium Collisions

We find a zero in the positronium formation scattering amplitude and a deep minimum in the logarithm of the corresponding differential cross section for positron–helium collisions for an energy just above the positronium formation threshold. Corresponding to the zero, there is a vortex in the extended velocity field that is associated with this amplitude when one treats both the magnitude of the momentum of the incident positron and the angle of the scattered positronium as independent variables. Using the complex Kohn variational method, we determine accurately two-channel K-matrices for positron–helium collisions in the Ore gap. We fit these K-matrices using both polynomials and the Watanabe and Greene’s multichannel effective range theory taking into account explicitly the polarization potential in the Ps-He+ channel. Using the fitted K-matrices we determine the extended velocity field and show that it rotates anticlockwise around the zero in the positronium formation scattering amplitude. We find that there is a valley in the logarithm of the positronium formation differential cross section that includes the deep minimum and also a minimum in the forward direction.

Spectroscopic evidence for a large spot on the dimming Betelgeuse

During October 2019 and March 2020, the luminous red supergiant Betelgeuse demonstrated an unusually deep minimum of its brightness. It became fainter by more than one magnitude and this is the most significant dimming observed in the recent decades. While the reason for the dimming is debated, pre-phase of supernova explosion, obscuring dust, or changes in the photosphere of the star were suggested scenarios. Here, we present spectroscopic studies of Betelgeuse using high-resolution and high signal-to-noise ratio near-infrared spectra obtained at Weihai Observatory on four epochs in 2020 covering the phases of during and after dimming. We show that the dimming episode is caused by the dropping of its effective temperature by at least 170 K on 2020 January 31, that can be attributed to the emergence of a large dark spot on the surface of the star.

Changes in Atlantic major hurricane frequency since the late-19th century

Atlantic hurricanes are a major hazard to life and property, and a topic of intense scientific interest. Historical changes in observing practices limit the utility of century-scale records of Atlantic major hurricane frequency. To evaluate past changes in frequency, we have here developed a homogenization method for Atlantic hurricane and major hurricane frequency over 1851–2019. We find that recorded century-scale increases in Atlantic hurricane and major hurricane frequency, and associated decrease in USA hurricanes strike fraction, are consistent with changes in observing practices and not likely a true climate trend. After homogenization, increases in basin-wide hurricane and major hurricane activity since the 1970s are not part of a century-scale increase, but a recovery from a deep minimum in the 1960s–1980s. We suggest internal (e.g., Atlantic multidecadal) climate variability and aerosol-induced mid-to-late-20th century major hurricane frequency reductions have probably masked century-scale greenhouse-gas warming contributions to North Atlantic major hurricane frequency.

Linking Solar Minimum, Space Weather, and Night Sky Brightness

New observations indicate previously unrecognized significant sources of night sky brightness variations, not involving corresponding changes in the Sun's EUV flux , occur during deep solar minimum. Our data was taken at 5 sites spanning more than 8,500 km during the deep minimum of Solar Cycle 24 into the beginning of Solar Cycle 25. It shows; 1) Semi-annual night sky brightness variations are produced by interactions between the Earth's magnetic field and the interplanetary magnetic field. 2) Solar wind plasma streams from solar coronal holes produce major night sky brightness increase events. 3) Some night sky brightness events are relatively local. Others extend at least 8,500 km along the Earth's surface. 4) It is plausible, terrestrial night airglow and geomagnetic indices have similar responses to the solar energy input into Earth's magnetosphere. Our empirical results contribute to a quantitative basis for understanding and predicting night sky brightness variations. They are applicable in astronomical, space weather, light pollution, biological, and recreational studies.

Aurora Observations from the Principality of Transylvania from the 16th to the 18th Century CE

We focused on the period from about 1500 CE to 1800 CE and present a compilation of 78 different auroral sightings for the period from the geographical area of the former Principality of Transylvania, then part of the Kingdom of Hungary, and we give source quotations in English translation. Of the 78 potential aurorae, 23 are missing from the catalog of Rethly and Berkes (1963) and are introduced here for the first time into the scientific discourse on past solar activity. The region of Transylvania located around 46° northern latitude is a good geographical indicator for an auroral oval extending unusually far towards the Equator. The reports of seven celestial phenomena from Transylvania during the period of the Maunder minimum (1645 – 1715), which are considered genuine northern lights at a medium to very high probability level, suggest that even during this time of greatly reduced solar activity, aurorae penetrated down to near 45° latitude. Three of these potential aurorae, however, fall within the 18th century, when the Sun was already recovering from the deep minimum phase. Comparing the distribution of potential auroral sightings in Transylvania from the 16th to the 18th century clearly shows, in comparison with other aurora catalogs and with reconstructed solar activity, that high selectivity due to the historical-source situation (incomplete chronicles, lost reports, and lack of scientific interest on the part of chroniclers) makes statements about actual long-term distributions almost impossible. Furthermore, the catalog of Rethly and Berkes is shown to be rather incomplete and to contain several doubtful entries.

Changes in Atlantic Major Hurricane Frequency Since the Late-19th Century

Atlantic hurricanes are a major hazard to life and property1,2,3, and a topic of intense scientific interest4,5,6. Historical changes in observing practices limit the utility of century-scale records of Atlantic major hurricane frequency7-13. To evaluate past changes in frequency, we have here developed a homogenization method for Atlantic hurricane and major hurricane frequency over 1851-2019. We find that recorded century-scale increases in Atlantic hurricane and major hurricane frequency, and associated decrease in USA hurricanes strike fraction, are consistent with changes in observing practices and not likely a true climate trend. After homogenization, increases in basin-wide hurricane and major hurricane activity since the 1970s14-15 are not part of a century-scale increase, but a recovery from a deep minimum in the 1960s-1980s. These results support the notion that internal climate variability and aerosol-induced mid-to-late-20th century major hurricane frequency reductions16-24 have probably masked century-scale greenhouse-gas warming contributions to North Atlantic major hurricane frequency.

Secular Variations of Inclination of the Geomagnetic Field in SE Poland Between 1200 and 1800 AD

A set of brick samples from 26 historical buildings in SE Poland was taken for archeomagnetic study. As a result of this study, the secular variations of inclination of the geomagnetic field from 1200 to 1800 AD were defined for SE Poland. The course of them is approximately the same as obtained in other parts of Europe. The only remarkable difference is a more rapid and deeper drop of inclination noted in SE Poland at the end of the 18th century. The regional curve of secular variations of inclination for SE Poland differs substantially from the coeval curve defined earlier for N Poland (Gdańsk) in their segments dated at the first half of the 18th century, where a deep minimum of inclination was disclosed in the bricks from N Poland only. The reuse of medieval bricks for the construction of objects giving this minimum or later secondary heating of original bricks can be a reason for the difference observed. Further archeomagnetic studies of the bricks of the last millennium are necessary in SE Poland to eliminate the gaps and uncertainties in the regional curve of secular variations of inclination.

Два вида структуры плазменного канала в импульсном разряде высокого давления в цезии

Simulation of the pulse-periodic high pressure cesium discharge is performed on the basis of equations of radiative gas dynamics. It is shown that in the discharge it is possible to implement two different types of structure of the plasma channel. At the beginning of the current pulse, the plasma discharge channel has a centered structure. At the same time, most of the plasma is concentrated near the discharge axis. The concentration of charged particles decreases along the radius.Then, if the current amplitude is large enough, during the plasma heating process, a transformation from the centered to the shell structure of the channel occurs. In this case, most of the plasma is concentrated on the periphery of the discharge and its concentration increases along the radius from the axis to the walls of the tube. It is shown that the transition from one channel structure to another occurs at a time when the specific heat capacity of the plasma near the axis reaches a deep minimum corresponding to a completely single ionized e-i plasma.

Dynamic and Static Properties of Aqueous NaCl Solutions at 25°C as a Function of NaCl Concentration: A Molecular Dynamics Simulation Study

We present the result of molecular dynamics (MD) simulations to calculate the molar conductivity Λ m = λ N a + + λ C l − of NaCl in SPC/E water at 25°C as a function of NaCl concentration (c) using Ewald sums employing a velocity Verlet algorithm. It is found that the MD result for Λm with Ewald sum parameter κ = 0.10 Å−1 gives the closest one to the experimental data and that the obtained radial distribution functions g i i (r) with κ = 0.10 Å−1 show a dramatic change with a very deep minimum of g NaCl (r) and, as a result, sharp maxima of g NaNa (r) and g ClCl (r) at the distance 9.95 Å, which indicates a characteristic of ionic atmosphere, the basis of the Debye–Hückel theory of ionic solutions. The static and dynamic properties of NaCl (aq) solutions are analyzed in terms of radial distribution functions, hydration numbers, coordination numbers around Na+ and Cl−, residence times of water around Na+ and Cl−, water diffusion, and ion-ion electrostatic energies to explain the behavior of the molar conductivity Λm of NaCl obtained from our MD simulations.