Geomagnetism and Aeronomy

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First Results from VLF Observations during the Transarctica 2019 Polar Expedition

Sun, 03/01/2020 - 00:00
Abstract

The first results are presented for observations of the VLF emissions (1–15 kHz) conducted at polar latitudes during the expedition Transarctica 2019, which was organized by the Arctic and Antarctic Research Institute. The observations were conducted onboard the Akademik Treshnikov vessel with highly sensitive equipment developed at the Polar Geophysical Institute. Bursts of the VLF emission of the auroral hiss type were registered on 13 of the 26 observational days. These bursts were simultaneously observed at Barentsburg Observatory, which is ~600 km to the west and ~160 km to the south. However, these bursts were not registered at lower auroral latitudes at the same meridian at Lovozero Observatory or at a Finnish station, Kannuslehto. One of the most typical cases, the auroral VLF hiss of April 11, 2019, is considered in detail. It is concluded that the region of the exit of the studied auroral hiss from the ionosphere to the Earth’s surface was local and limited in latitude.

Station-Ring Method in the Study of Cosmic-Ray Variations: 2. Examples of Its Use

Sun, 03/01/2020 - 00:00
Abstract

The station-ring method makes it possible to isolate and study the specific angular distributions of cosmic-ray variations that are poorly described by the sum of the first spherical harmonics. Examples of the use of the station-ring method are given and described in detail. The application of the method to study precursors of Forbush effects and the behavior of cosmic rays inside the perturbations of the solar wind is shown.

A New Method for Research on Magnetically Oriented Ionospheric Inhomogeneities using a Program of Radio-System Determination

Sun, 03/01/2020 - 00:00
Abstract

The work proposes methods for the study of artificial, magnetically oriented, ionosphere inhomogeneities and for its practical implementation. The developed approach makes it possible to determine the most probable longitudinal sizes and distances comparable with the wavelength of heat radiation between inhomogeneities along and across the Earth’s magnetic field, as well as the speed and direction of their movement. The method uses a software-defined radio system, which enables the remote performance of the necessary measurements. The results of observations in experiments on the formation of magnetically oriented artificial inhomogeneities at Arecibo Observatory are presented. They confirm that the topology of magnetically oriented ionospheric inhomogeneities can be determined based on the proposed method.

Estimation of Solar Activity Impact on the Outgoing Infrared-Radiation Flux

Sun, 03/01/2020 - 00:00
Abstract

A parameterization of the mechanism of solar activity impact on the Earth’s troposphere developed by the authors is proposed for a model of outgoing longwave radiation, based on the integral transmission function. The PC-index of geomagnetic activity, which was developed to monitor the polar cap magnetic activity and reflects the affect of the interplanetary electric field on the magnetosphere, was used as the indicator of solar activity. Based on data from NCEP/NCAR reanalysis, we calculated. The integrated transmission function and outgoing longwave flux for periods of increased and decreased solar activity. Correlation analysis of the calculated radiation characteristics with temperature in the 925- to 700-hPa layer showed that the inclusion of solar activity leads to higher correlation between the radiation characteristics and temperature. Comparison of the calculation results with temperature changes confirmed that the proposed parameterization can be used to include impacts of solar activity in numerical models with the integral transmission function to calculate outgoing longwave radiation.

Analytical Description of the Near Planetary Bow Shock Based on Gas-Dynamic and Magneto-Gas–Dynamic Modeling for the Magnetic Field Parallel and Perpendicular to the Plasma Flow

Sun, 03/01/2020 - 00:00
Abstract

An analytical semiempirical model of the bow shock based on theoretical MGD calculations, accurate analytical solutions, and experimental data continues to be developed. The model parameters have a clear physical meaning. For cases in which the magnetic field of the solar wind is directed along its velocity or is perpendicular to the velocity vector, analytical expressions that allow calculating the parameters of the bow shock—the distance to the subsolar point, the radius of the curvature, and the bluntness at the subsolar point—are obtained via renormalization of the previously developed detailed gas-dynamic model. For the case in which the magnetic field vector is perpendicular to the solar wind velocity vector, it is shown that it is sufficient for an analytical description of the bow shock surface to approximate its parameters in two perpendicular planes.

Solar Radio Bursts Associated with Standing Shock Waves

Sun, 03/01/2020 - 00:00
Abstract

A number of phenomena with radio bursts in the decimeter and centimeter wavelength ranges similar to type-II bursts in the meter range have been considered. In all phenomena, the radio bursts are characterized by the cessation of frequency drift and its reversal. Analysis of all of the available data on relevant bursts provides evidence of termination shocks with particle accelerations in their fronts. This is confirmed by the generation of new sources of hard X-ray radiation and the radio emission of fast bursts (spikes), fibers, and zebra structures. The sources of drift stripes with a drift turn are located either between the burst loop and the lower shock wave or between the lower and upper shock waves. Estimates of the critical Mach number for common parameters of the burst plasma indicated that the values (Mcr = 1.1–1.3) can easily be observed in the given phenomena and that the radiation can be associated with the Buneman instability. The conditions necessary for the generation of observed electromagnetic radiation bursts can be provided in helmet-shaped magnetic structures in the solar corona.

Effect of Geomagnetic Field on Motion of Passive Conductive Satellites

Sun, 03/01/2020 - 00:00
Abstract

In this paper we analyze theoretically the effect of geomagnetic field on rotation of passive conductive satellites of a spherical shape such as Russian-Australian satellite WESTPAC or Russian satellite Larets. The main cause of this effect is the generation of eddy currents and satellite magnetic moment, which interact with the Earth’s magnetic field. The analytical solutions have been derived for orbital and intrinsic magnetic moments of satellite, which result from a translatory motion of an Earth-orbiting satellite and from a satellite spin around axes passing through its center of mass. An arbitrary relation between skin layer depth and satellite radius is assumed. Both a torque acting on satellite in geomagnetic field and the changes in its angular velocity are derived. The satellite orbiting the Earth in a circular orbit with an arbitrary tilt of the orbital plane is studied having regard to rotation of the vector of geomagnetic dipole moment. A characteristic time it takes for the angular velocity of the satellite to decrease exponentially is estimated. Peculiarities of residual irregular vibrations of the satellite angular velocity are examined.

Spatial and Temporal Characteristics of Subrelativistic Electron Fluxes in the Near-Earth Space from the Vernov Satellite Data

Sun, 03/01/2020 - 00:00
Abstract

The spatial distribution and dynamics of subrelativistic electron fluxes (from tens to hundreds of keV) were studied in a space experiment onboard the Vernov satellite. A joint analysis of the experimental data from the Vernov and POES satellites was carried out. Maps of the global distribution of electron fluxes with energies from hundreds keV to MeV in the near-Earth space were obtained, as well as their distribution over drift shells, local time, and geomagnetic longitude. It is shown that significant electron fluxes of subrelativistic energies exist in drift shells with a McIlwain parameter of L < 1.5. The measured longitudinal distribution of electron fluxes in these drift shells indicates that the observed fluxes are “tied” to the shells, and the inhomogeneities of the longitudinal distribution are caused by the features of the configuration of the magnetic field in the satellite orbits.

Frequency Dependence of the Wave Field Power Parameters for Limiting Single-Hop Radio Paths in Low Solar Activity Conditions

Sun, 03/01/2020 - 00:00
Abstract

This paper considers the possibility of the deep trough formation in the integral amplitude–frequency dependence of the wave field at the classical limiting paths of a single-hop ionospheric radio waves propagation under conditions of low solar activity. Calculations based on the global ionospheric model with both standard (IRI) and alternative dynamic (IRI + GDMF2) representations of the F2 layer of the ionosphere are compared with the experimental results of multifrequency oblique ionospheric sounding (OIS). It is shown that it is fundamentally possible to use the model to describe this feature based on the energy parameters of the radiation transfer problem in the ionosphere.

Influence of Oxygen Ions on the Structure of the Thin Current Sheet in the Earth’s Magnetotail

Sun, 03/01/2020 - 00:00
Abstract

During geomagnetic substorms, the current sheet in the Earth’s magnetotail can transversely reduce in thickness from a few radii of the Earth (RE) to one to several proton gyroradii, 250–2000 km. It is the key structure in which the energy of the magnetic field is stored and later released due to the development of instability and magnetic reconnection during the substorm period. Despite its small thickness, the thin current sheet has a complex multiscale structure with a hierarchy of embedded layers that determines its properties. During substorms, single-charged oxygen ions enter the Earth’s magnetotail from the ionosphere and their concentrations can be comparable to those of protons. The interaction of oxygen ions with the current sheet, which results in changes in its structure and properties, is not well studied. The self-consistent profiles of the magnetic field, current densities, and plasma in the multicomponent magnetotail plasma are analyzed in a wide range of system parameters within the hybrid model of the quasi-equilibrium current sheet. It is shown that the current sheet is a multiscale structure embedded in a wide plasma layer. The increase in the concentration of oxygen ions in the current sheet leads to its thickening and formation of additional embedded scale. At the same time, breaks characterizing the transition from the oxygen-ion dominated region in the current sheet to the proton- and electron-dominated region appear on the profiles of the magnetic field and current density. The amplitude of the current density of such an embedded layer decreases in proportion to the concentration of oxygen ions. The dependence of the embedding parameter on relative concentrations of heavy ions, as well as their thermal and drift velocities, is studied.

Experimental Global Forecasts of Atmospheric Parameters Based on Experimental Technology that Takes into Account Ozone Photochemistry (FOROZ Model)

Sun, 03/01/2020 - 00:00
Abstract

The results of numerical seasonal forecasts of temperature calculated with two interactive global numerical models, the CHARM photochemical model (0–90 km) of the Central Aerological Observatory (CAO) and the seasonal forecast model PLAV of the Hydrometeorological Centre/Institute of Numerical Mathematics of the Russian Academy of Sciences (0–30 km), are presented. The wind and temperature fields above 30 km were linked with the CAO ARM general circulation model. The forecast results are compared with reanalysis data. The calculations show that the new combined model (Forecast with Ozone, FOROZ) is stable under numerical scenarios. The seasonal forecast temperature fields of the PLAV model and the combined FOROZ model with reanalysis data are close in the lower troposphere and differ in the stratosphere. The combined FOROZ model improves the temperature forecast for the upper troposphere and stratosphere.

Detection of Large Fluctuations in Ozone Content in the Middle Atmosphere during Sudden Stratospheric Warmings and Subpolar Latitudes of the Arctic

Sun, 03/01/2020 - 00:00
Abstract

The results of microwave radiometry studies of the ozone-content dynamics in the middle atmosphere above Peterhof during stratospheric warmings of two winters, 2015–2016 and 2016–2017, are presented. Ground-based observations employed mobile microwave ozone-measuring instrument (operating frequency is 110.8 GHz). The vertical ozone distribution in the altitude range of 22–60 km is estimated. The results are compared to satellite-borne data on the total ozone content, to vertical profiles of the ozone and temperature in the middle atmosphere, and to data from an ozone-measuring sounder. In the middle atmosphere above Peterhof, there have been significant variations (by several times) in the ozone content at heights of 40–60 km due to minor stratospheric warming.

Variations in the Structure of the Equatorial Anomaly during the Summer Solstice according to the Interkosmos-19 Satellite

Sun, 03/01/2020 - 00:00
Abstract

Changes in the structure of the summer equatorial anomaly of electron density with local time and longitude at high solar activity are considered in detail according to topside sounding data from the Interkosmos-19 satellite. It is shown that the equatorial anomaly starts to develop from ~0800 LT, when the winter (southern) crest is formed. The summer (northern) crest is ~2 h behind in development. It is formed at the background of a low latitudinal foF2 maximum. In the daytime, the northern crest is ~3° farther from the geomagnetic equator than the southern one. The crest position changes greatly with longitude. A local maximum is observed in the development of the equatorial anomaly at 1400 LT. It is particularly pronounced in the Eastern Hemisphere. The foF2 value above the geomagnetic equator and anomaly intensity change with longitude at 1200–1400 LT according to the changes in the vertical plasma drift W. A local minimum is observed in the development of the equatorial anomaly at 1800 LT. The anomaly intensity then increases to a maximum 1.5–2.0 h after the evening peak in W. Longitudinal foF2 variations and the anomaly intensity in the interval 2000–2200 LT are also associated with W variations. The anomaly intensity decreases after the maximum, and the crests decrease in magnitude and move toward the equator. The foF2 maxima in the crest region of the anomaly after midnight, conversely, are farther away from the geomagnetic equator, which seems to be due to the action of the neutral wind. The equatorial anomaly has almost decayed by 0400 LT and does not manifest itself as a structure from 0500 to 0700 LT. Therefore, the well-expressed equatorial anomaly is observed from 1200 to 2400 LT at high solar activity.

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