The time dynamics of the cosmic ray distribution function in a magnetic cloud is calculated. The magnetic cloud has the form of a torus segment with the force‐free magnetic field structure at the ...initial moment. The subsequent propagation of the magnetic cloud in interplanetary space is determined by inertial description. The magnetic field is determined by the frozen‐in condition. When calculating the particle distribution function, the electromagnetic field of the magnetic cloud is taken into account, with the scattering of particles not being taken into account. Relations between the particle distribution function and its three moments (particle density and unidirectional and bidirectional anisotropies) are derived. It is established that cosmic ray losses at the regions connecting the magnetic cloud with the Sun determine the amplitude of the second step of Forbush decrease. The time dependence of the Forbush decrease characteristics on magnetic cloud type is determined. The calculation results of the particle density and unidirectional anisotropy generally correspond to measurements. The referred results show a prominent role of the magnetic field structure in the time dynamics of the Forbush decrease.
Key Points
The time dynamics of the cosmic ray distribution function in a toroidal magnetic cloud is calculated
Relation between the particle distribution function and its three moments is derived
The time dependence of the Forbush decrease characteristics on magnetic cloud type is determined
A theory of the formation of Forbush decrease in a magnetic cloud is presented. It is found that the formation mechanism is the energy loss of cosmic rays in a magnetic cloud represented as a moving ...magnetic loop with a helical field. The Forbush decrease amplitude, the components of the vector, and tensor anisotropies are calculated along the path of the magnetic cloud passing Earth. It is shown that the Forbush decrease characteristics depend on the following magnetic cloud parameters: magnetic field strength, the helical field structure, velocity and the velocity gradient, and geometric dimensions. It is found that the Forbush decrease characteristics mainly depend on the magnetic field strength and the state of the global helical structure of the field.
The paper presents the results of the staff of ShICRA SB RAS on cosmic ray research over the past two decades. A brief description of the current state and prospects for further development of the ...experimental base for recording cosmic rays, methods for processing experimental data, and scientific research of various phenomena of heliospheric modulation of galactic and solar cosmic rays are presented.
We calculate cosmic ray intensity using the model of the Forbush decrease formation in a magnetic cloud by the electromagnetic mechanism for three events. The properties of the Forbush decrease are ...determined by solving the Boltzmann kinetic equation without particle scattering. At the initial time, the magnetic cloud has the shape of a torus, for which geometric parameters such as velocity, velocity gradient, cross-sectional area, and angular dimensions are specified. The kinematic model determines the subsequent propagation of the cloud in interplanetary space. The magnetic field properties and the type of helical structure near the Sun are based on the Miller and Turner toroidal model. In interplanetary space, magnetic field components are determined by the frozen-in condition. The model properties of the velocity, velocity gradient, magnetic field components, and characteristics of the Forbush decrease roughly agree with measurements in three events. There are no free parameters in the Forbush decrease formation model.
We report on the specific properties of O- and OH-terminated Ti3C2Tx nanosheets contributing the permeance of MXene membranes with sorption type selectivity. Thin MXene selective layers on porous ...support demonstrated separation factor for NH3/H2 pair over 50 with ammonia permeance up to 5.0 m3(STP)∙m−2∙bar−1∙h−1 facilitated for humid medium and separation factor for H2O/N2 over 1000 with water permeance over 30 m3(STP)∙m−2∙bar−1∙h−1 close to P0(H2O). According to QCM and GIWAXS studies, high permeance and selectivity of membranes towards ammonia and water vapors are attributed both to ultimate sorption capacity for “basic” vapors and condensation-induced expansion of the interlayer space. Sorption capacity of MXene over 0.045 g∙g(MXene)−1 at 0.3P0 for both NH3 and H2O, significantly exceeds the sorption capacity for permanent gases. Calculations of the diffusion coefficient suggest labyrinthine transport of vapors. For permanent gases no variation of diffusion coefficients was observed with feed pressure, indicating Knudsen diffusion mechanism. Diffusion coefficient of strongly absorbed gases significantly increases with pressure. According to GIWAXS the effect was attributed to the increase of the interlayer distance with saturation of membrane with vapors and reduction of activation barriers for hopping diffusion. Demonstrated characteristics of Ti3C2Tx nanosheets makes it a promising candidate for developing of ammonia selective membranes for Haber-Bosch process membrane extractors.
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•Acidic properties of OH groups on MXene surface determine affinity to “basic” gases.•NH3 sorption coefficient attains 52 mmol/(m3·Pa), drastically exceed sorption for other gases.•Membranes with Ti3C2Tx selective layer were obtained by spin-coating technique.•Selectivity for a NH3/H2 exceeds 50 with ammonia permeance up to 3.91 m3 m−2 bar−1∙h−1.•The increase of interlayer distance with MXene saturation with vapors was founded.
Oriented attachment of synthetic semiconductor nanocrystals is emerging as a route for obtaining new semiconductors that can have Dirac-type electronic bands such as graphene, but also strong ...spin-orbit coupling. The two-dimensional (2D) assembly geometry will require both atomic coherence and long-range periodicity of the superlattices. We show how the interfacial self-assembly and oriented attachment of nanocrystals results in 2D metal chalcogenide semiconductors with a honeycomb superlattice. We present an extensive atomic and nanoscale characterization of these systems using direct imaging and wave scattering methods. The honeycomb superlattices are atomically coherent and have an octahedral symmetry that is buckled; the nanocrystals occupy two parallel planes. Considerable necking and large-scale atomic motion occurred during the attachment process.
Measurements by the world network of neutron monitors during the period 1996–2018 31 are used to identify strong Forbush decreases (>5%) that meet the accepted criteria for event selection. ...Coordinated spatial distributions of solar wind parameters and drops in the density of cosmic rays are determined via epoch superimposition. It is established that contributions from the mechanisms of the formation of Forbush decreases differ greatly in two groups of events. This difference could be due to Forbush decreases forming in the front of one group and the peripheral part of the disturbance forming in the other group.
We assume that during the generation of solar cosmic rays in gradual events, the solar atmosphere has a limited spatial size due to the inhomogeneous distribution of the magnetic field turbulence ...level. For a limited solar atmosphere, the flux of relativistic particles injected into interplanetary space is calculated. The calculated flux is compared with the solar cosmic ray flux determined from the measurements of the worldwide network of ground-based neutron monitors on the April 15, 2001 event.
Magnetic clouds affect the intensity of galactic cosmic rays. The diffusion mechanism is usually used as the formation mechanism for Forbush decrease (FD) in a magnetic cloud (MC). An FD is an ...observed decrease in the cosmic ray intensity. There is a new theory of FD formation, in which the mechanism is the loss of particle energy in the electromagnetic field of a magnetic cloud. The shape of the FD spectrum is calculated for a wide range of particle energies in the 2004 July 27 event. According to the measurements of ground-based neutron monitors and muon telescopes, synchronous changes in the FD amplitude in time indicate that the FD is formed in a magnetic cloud for all energies. However, the calculated FD spectrum differs from the obtained one from measurements. The reasons for the difference can be: 1) the mechanism of formation is not the electromagnetic one; 2) the method for determining the FD spectrum, using the notion of mean or median energies, needs additional studies.
Based on the new mechanism, the Forbush decrease characteristics are calculated for eight magnetic cloud types. It is shown that the Forbush decrease amplitude does not depend on the magnetic cloud ...type, while the anisotropy strongly does. The Forbush decrease spectrum for (2–150 GV) rigidities is calculated for the first time. The Forbush decrease amplitude for low rigidities is ∼100%, which can be explained by a large number of forbidden particle trajectories. The Forbush decrease amplitude rapidly decreases for high rigidities due to the geometric condition. Comparing the calculated Forbush decrease characteristics with measurements for two events shows that the Forbush decrease amplitudes agree with the measurements quantitatively, and the anisotropies do qualitatively.
Key Points
Forbush decrease characteristics are calculated for eight magnetic cloud types
Forbush decrease spectrum depending on rigidity is calculated
Calculation results of the Forbush decrease characteristics agree with the measurements in two events
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