Creation and expansion of a magnetized plasma bubble for plasma propulsion

We discuss the coupled expansion of a plasma cloud and a neutral gas, both originating from a point-like source located in space and submitted to the action of an external flux of ionizing radiation. This problem is relevant to the artificial magnetospheric propulsion scheme for solar system exploration. We establish the relevant space and time scales for particle diffusion and plasma bubble formation. Emphasis is placed on the low ionization and high collisionallity of the plasma near the point source, leading to the existence of a small ionosphere surrounding the source, where (contrary to the more common views of this propulsion scheme) the ions are not magnetized. The possibility of direct plasma creation by an initial purely neutral gas release is also envisaged.     

Magnetic reconnection as a possible heating mechanism of the local high temperature protons within magnetic clouds

Magnetic clouds have the outstanding observational features of low proton temperature and plasma beta value, but numerous observations show that some magnetic clouds often have local high temperature phenomena. The local high temperature protons may be heated by magnetic reconnections within magnetic clouds. Here we take the magnetic cloud on 18–20 October 1995 as an example to discuss the possible heating mechanism. There is a famous protuberance in proton temperature between the front boundary and 11: 00 UT on 19 October 1995. Eight magnetic reconnection events were identified within the magnetic cloud, whose duration was less than 31 hours, and most of these reconnection events occurred within the proton temperature enhanced part of the magnetic cloud. Hence, it is possible for the local protons in the magnetic cloud to be heated by magnetic reconnections.     

Modeling the dynamics of a plasma bulge with a high specific energy in the upper atmosphere. 2. Numerical simulation and physical features of a large-scale plasma flow at its late development stage: A review

The results of three-dimensional calculations of a plasma flow caused by a cosmic nuclear explosion, performed in an MHD approximation, are presented. The main regularities and specific features of the development of a large-scale plasma flow have been analyzed for a later stage (up to several hundreds of seconds) depending on the altitude and plasma bulge energy.     

Optical observations of Io's neutral clouds and plasma torus

A review of ground-based optical observations of Io's neutral clouds and plasma torus is provided. The physical processes determining the spatial distribution and intensity of torus emissions are described with reference to a model based on Voyager spacecraft data. The model is then compared to ground-based observations. Inconsistencies and variations in torus conditions over long timescales are emphasized. Periodicities in the torus evident in Voyager and ground-based are critically discussed.Processes determining the spatial characteristics of the neutral clouds are discussed. Observations of the slow sodium cloud are compared to model calculations. Special attention is paid to recent observations of high velocity neutrals and species in the upper atmosphere of Io itself. The article concludes with suggestions for future observations and research.     

Guided waves in the plasma sheet and triggering of a substorm

A guided propagation of magnetoacoustic wave in the plasma sheet located between two lobes of the magnetotail is investigated. The dispersion equation for the wave and equation connecting a disturbance of plasma pressure inside the plasma sheet and amplitude of the plasma sheet boundary oscillations are obtained. For some value of plasma pressure disturbance, the displacement of the plasma sheet boundaries becomes of order of the half-thickness of the plasma sheet. In the case of symmetrical oscillations of the boundaries (“sausage-like” mode), it creates the favorable conditions for reconnection of the magnetic field lines in the magnetotail and may lead to triggering of a substorm. The magnetoacoustic wave may be generated by sudden impulse of the solar wind plasma pressure.     

Formation of a plasma antenna by an explosive action in the ionosphere

We have studied the radiative characteristics of the explosive action in the atmosphere. It has been shown that even a single explosive action produced simultaneously with a high-frequency (HF) discharge forms an effective plasma antenna. In the absence of an HF discharge, an explosive action with a specific arrangement of point explosions allows the generation of a convergent shockwave of pressure and magnetic field. As a result, a waveguiding disturbance of the background plasma is formed in the convergence region of the shockwave; given the simultaneous excitation of pulsed fields in the near-frontal region, this also leads to the formation of a plasma antenna at high altitudes.     

Numerical simulation of the interaction between two high-energy plasma bunches in the ionosphere

The 3D MHD algorithm developed by us has been adapted to modeling the interaction between two plasma bunches in the ionosphere, mainly in order to sufficiently correctly describe the physics of the interaction between two plasma regions with regard to the ionospheric inhomogeneity and the geomagnetic field action. Modeling has been performed for several versions of location of the plasma region centers.     

Modified theory of disturbances for stationary problems of a charged spherical body in a rarefied plasma

The modified theory of disturbances, which differs from the existent similar theory by the consideration of an additional term in disturbances of concentration and flux density of infinite plasma particles, has been developed for stationary problems of a charged spherical body in a rarefied plasma. It has been indicated that, in the simplest constant centrally symmetric field, the neglect of the above term results in a substantial error in the stationary disturbance of the concentration of infinite particles attracted by this field.     

Specific features of explosive plasma flows in the near-earth space

The analytical expressions for determining the deceleration region of plasma, produced during large-scale geophysical experiments of explosion type, and taking into account the effect of the rarefied ionosphere and geomagnetic field have been obtained. The possibility of the magnetosphere braking by plasma produced by a powerful explosion is analyzed. The simplified set of equations used to analyze the linear and non-linear stages of flute instability of explosive plasma expanding into the magnetic field has been obtained. The mass overflow between flutes and the viscous force is taken into account. The experimental studies of flute instability during laser plasma expansion into the magnetic field are theoretically substantiated. The mechanism explaining the formation of a jet stream and the main jet inclination of 11° with respect to the axis of symmetry has been proposed.     

Wave emission during a plasma density jump in the auroral zone of the topside ionosphere according to the APEX satellite data

The intensity of the wave emission in the 0.1–10 MHz band measured in the ionosphere (the APEX satellite experiment) has been presented. A jump of the plasma density and an increase in the emission intensity at a plasma frequency have been registered at altitudes of ～1300 km in the topside auroral ionosphere. The emission intensity in the whistler-mode band nonmonotonically increased along the satellite trajectory near the plasma jump wall. It has been indicated that waveguides could be formed near the wall during damping of electrostatic oscillations generated by precipitating electron fluxes. A spatially nonmonotonous separation of waveguides from the plasma inhomogeneity stretched along geomagnetic field lines is possible in this case.     

Dynamics of escape of high-energy electrons from a spherical plasma volume in the geomagnetic field

Using results of numerical modeling, the dynamics of escape of electrons, produced as a result beta-decay, to the external magnetic field from a spherical plasma volume with an expelled magnetic field is studied. The dependence of the fraction of escaped electrons on time and radius of the plasma volume has been obtained for two kinds of electron sources: a point isotropic source, located at the center of the sphere, and a volume isotropic source. It is shown that for a point source some part of electrons remains in the sphere, whereas for a volume source all electrons, at different values of the magnetic cavern radius, leave it at an identical relative escape rate.     

Equatorial plasma bubbles at altitudes of the topside ionosphere

A consistent patter, indicating that subtroughs in the He⁺ density and plasma bubbles can be considered as phenomena of the same origin, has been obtained within the scope of the existent model of equatorial plasma bubbles. The study has been performed based on the measurements of the ISS-b satellite, which flew during the period of high solar activity. The conclusion has been made based on a comparative analysis of the characteristics of subtroughs with the parameters of the known equatorial phenomena. (1) The similarity of the LT variations in the latitude of the minimums of subtroughs in the He⁺ density has been revealed. (2) It has been displayed that the variations in the averaged depth of subtroughs change from season to season similarly to the LT variations in the average velocity of the equatorial vertical plasma drift. (3) Good correlation (R = 0.67) between the occurrence probability of subtroughs and equatorial spread F statistics, constructed as the functions of LT and month, has been obtained. (4) The obtained velocity of the possible rise of plasma irregularities (observed as regions depleted in He⁺) is in good agreement with the ionosonde, satellite, and radar measurements of the equatorial plasma bubble velocities of the same period. (5) It has been indicated that plasma irregularities, reaching the altitudes of the topside ionosphere in the low-latitude and midlatitude regions during high solar activity, are most observable as depleted regions (subtroughs) of He⁺ density.     

Nonlinear modification of magnetospheric plasma under the action of the ULF-wave ponderomotive force on the dayside

Nonlinear modification of the plasma magnetospheric density near the dayside magnetospheric boundary, caused by the ponderomotive force induced by ULF geomagnetic pulsations, has been studied analytically and numerically. An expression for the ponderomotive force, which differs from the previous similar results, has been obtained. It has been indicated that the well-known Pitaevskii formula for magnetic moment is incomplete. The action of the ponderomotive, gravitational, and centrifugal forces on magnetospheric plasma modification in a two-dipole geomagnetic field according to the (Antonova and Shabanskii, 1968) model has been considered.     

Parameterizations of cloud feedback in a radiative-convective model

The effect of cloud feedback on the response of a radiative-convective model to a change in cloud model parameters, atmospheric CO₂ concentration, and solar constant has been studied using two different parameterization schemes. The method for simulating the vertical distribution of both cloud cover and cloud optical thickness, which depends on the relative humidity and on the saturation mixing ratio of water vapor, respectively, is the same in both approaches, but the schemes differ with respect to modeling the water vapor profile. In scheme I atmospheric water vapor is coupled to surface parameters, while in scheme II an explicit balance equation for water vapor in the individual atmospheric layers is used. For both models the combined effect of feedbacks due to variations in lapse rate, cloud cover, and cloud optical thickness results in different relationships between changes in surface temperature, planetary temperature, and cloud cover. Specifically, for a CO₂ doubling and a 2% increase in solar constant, in both models the surface warming is reduced by cloud feedback, in contrast to no feedback, with the greater reduction in scheme I as compared to that of scheme II.     

Analytical configurations of a force-free magnetic cylinder in the solar wind

The problem of a smooth field configuration, which should be an initial configuration in modeling (using the method of coarse particles) the problem of a stationary solar wind flow around a magnetic cloud in the case of a spatially two-dimensional statement (when a magnetic cloud is considered as a force-free magnetic cylinder with a finite radius) is considered. It has been indicated that such a statement is possible only when the magnetic field in the solar wind is parallel to the cylinder axis. The method for finding the magnetic field of a force-free cylinder with a finite radius, when some field component is specified and another component is determined based on this one (which makes it possible to construct fields with preassigned properties), has been proposed. The variant for constructing the initial field configuration in the transition region around a cylinder has been proposed. This variant makes it possible to gradually pass from homogeneous crossed fields in the solar wind to a force-free magnetic and zero electric fields within a cylinder, an electric field being potential and orthogonal to a magnetic field (in the reference system related to a magnetic cloud).     

Electrostatic radiation of plasma in the upper ionosphere in the inhomogeneous geomagnetic field

It has been indicated that the spectrum of electrostatic waves in the ionospheric plasma depends on the geophysical conditions and solar wind parameters. The wave field measurements in the frequency band 0.1–10 MHz in the topside ionosphere were used to analyze the electrostatic instabilities of the plasma electron content (the APEX satellite experiment). A change of the sign of one magnetic field component at the geomagnetic equator can result in the formation of the large-scale irregular plasma structure with a decay of the natural electrostatic oscillations and vortices in unstable plasma. The plasma particle polarization drift from the region of decay of electrostatic oscillations and vortices can cause large plasma density and temperature gradients across the geomagnetic field. New vortices can originate at these gradients. This mechanism of plasma vortex formation and decay can be important for mass and energy convection in the topside ionosphere.     

Effects of alternative cloud radiation parameterizations in a general circulation model

Using the National Center for Atmospheric Research (NCAR) general circulation model (CCM2), a suite of alternative cloud radiation parameterizations has been tested. Our methodology relies on perpetual July integrations driven by ±2 K sea surface temperature forcing. The tested parameterizations include relative humidity based clouds and versions of schemes involving a prognostic cloud water budget. We are especially interested in testing the effect of cloud optical thickness feedbacks on global climate sensitivity. All schemes exhibit negative cloud radiation feedbacks, i.e., cloud moderates the global warming. However, these negative net cloud radiation feedbacks consist of quite different shortwave and longwave components between a scheme with interactive cloud radiative properties and several schemes with specified cloud water paths. An increase in cloud water content in the warmer climate leads to optically thicker middle- and low-level clouds and in turn negative shortwave feedbacks for the interactive radiative scheme, while a decrease in cloud amount leads to a positive shortwave feedback for the other schemes. For the longwave feedbacks, a decrease in high effective cloudiness for the schemes without interactive radiative properties leads to a negative feedback, while no distinct changes in effective high cloudiness and the resulting feedback are exhibited for the scheme with interactive radiative properties. The resulting magnitude of negative net cloud radiation feed-back is largest for the scheme with interactive radiative properties. Even though the simulated values of cloud radiative forcing for the present climate using this method differ most from the observational data, the approach shows great promise for the future.     

Studying the Relationship between High-Latitude Geomagnetic Activity and Parameters of Interplanetary Magnetic Clouds with the Use of Artificial Neural Networks

The cause-and-effect relations of the dynamics of high-latitude geomagnetic activity (in terms of the AL index) and the type of the magnetic cloud of the solar wind are studied with the use of artificial neural networks. A recurrent neural network model has been created based on the search for the optimal physically coupled input and output parameters characterizing the action of a plasma flux belonging to a certain magnetic cloud type on the magnetosphere. It has been shown that, with IMF components as input parameters of neural networks with allowance for a 90-min prehistory, it is possible to retrieve the AL sequence with an accuracy to ~80%. The successful retrieval of the AL dynamics by the used data indicates the presence of a close nonlinear connection of the AL index with cloud parameters. The created neural network models can be applied with high efficiency to retrieve the AL index, both in periods of isolated magnetospheric substorms and in periods of the interaction between the Earth’s magnetosphere and magnetic clouds of different types. The developed model of AL index retrieval can be used to detect magnetic clouds.     

Magnetic field disturbance in magnetoactive plasma with a localized electrostatic field

Charged particle motion in magnetoactive plasma with an axially symmetric electrostatic field has been studied. It has been indicated that a difference between drift velocities of electrons and ions leads to a magnetic field disturbance. The equations for stationary magnetic field disturbances stretched along the magnetic field, which can be magnetic ducts for propagation of whistlers, have been obtained. The possibility of formation of such ducts by electrostatic fields from thunderstorm sources, penetrating into the ionosphere, has been estimated.     

A comparison of solar wind and ionospheric plasma contributions to the September 24–25, 1998 magnetic storm

We have used a global time-dependent magnetohydrodynamic (MHD) simulation of the magnetosphere and particle tracing calculations to determine the access of solar wind ions to the magnetosphere and the access of ionospheric O⁺ ions to the storm-time near-Earth plasma sheet and ring current during the September 24–25, 1998 magnetic storm. We found that both sources have access to the plasma sheet and ring current throughout the initial phase of the storm. Notably, the dawnside magnetosphere is magnetically open to the solar wind, allowing solar wind H⁺ ions direct access to the near-Earth plasma sheet and ring current. The supply of O⁺ ions from the dayside cusp to the plasma sheet varies because of changes in the solar wind dynamic pressure and in the interplanetary magnetic field (IMF). Most significantly, ionospheric O⁺ from the dayside cusp loses access to the plasma sheet and ring current soon after the southward turning of the IMF, but recovers after the reconfiguration of the magnetosphere following the passage of the magnetic cloud. On average, during the first 3 h after the sudden storm commencement (SSC), the number density of solar wind H⁺ ions is a factor of 2–5 larger than the number density of ionospheric O⁺ ions in the plasma sheet and ring current. However, by 04:00 UT, ∼4 h after the SSC, O⁺ becomes the dominant species in the ring current and carries more energy density than H⁺ ions in both the plasma sheet and ring current.