Study of Momentum Diffusion with the Effect of Adiabatic Focusing

The momentum diffusion of charged energetic particles is an important mechanism of the transport process in astrophysics, the physics of fusion devices, and laboratory plasmas. In addition to the momentum diffusion term for a uniform field, we obtain an additional momentum diffusion term due to the focusing effect of the large-scale magnetic field. After evaluating the coefficient of the additional momentum diffusion term, we find that it is determined by the sign of the focusing characteristic length and the cross helicity of the turbulent magnetic field. Furthermore, by deriving the mean momentum change rate contributed from the additional momentum diffusion term, we identify that the focused field provides an additional momentum loss or gain process.

Uniting The Sun’s Hale Magnetic Cycle and ‘Extended Solar Cycle’ Paradigms

Through meticulous daily observation of the Sun’s large-scale magnetic field the Wilcox Solar Observatory has catalogued two magnetic (Hale) cycles of solar activity. Those two (∼22-year long) Hale cycles have yielded four (∼11-year long) sunspot cycles-21 through 24. Recent research has highlighted the persistence of the “Extended Solar Cycle” (ESC) and its connection to the fundamental Hale Cycle-albeit through a host of proxies resulting from image analysis of the solar photosphere, chromosphere and corona. This Letter presents, for the first time, a direct mapping between the ESC, the Sun’s toroidal magnetic field evolution of the Hale Cycle. As Sunspot Cycle 25 begins to accelerate its growth, interest in mapping the Hale and Extended cycles could not be higher given potential predictive capability that synoptic scale observations can provide.

Subcritical dynamo and hysteresis in a Babcock-Leighton type kinematic dynamo model

In the Sun and Sun-like stars, it is believed that cycles of the large-scale magnetic field are produced due to the existence of differential rotation and helicity in the plasma flows in their convection zones (CZs). Hence, it is expected that for each star, there is a critical dynamo number for the operation of a large-scale dynamo. As a star slows down, it is expected that the large-scale dynamo ceases to operate above a critical rotation period. In our study, we explore the possibility of the operation of the dynamo in the subcritical region using the Babcock–Leighton type kinematic dynamo model. In some parameter regimes, we find that the dynamo shows hysteresis behavior, i.e., two dynamo solutions are possible depending on the initial parameters—decaying solution if starting with weak field and strong oscillatory solution (subcritical dynamo) when starting with a strong field. However, under large fluctuations in the dynamo parameter, the subcritical dynamo mode is unstable in some parameter regimes. Therefore, our study supports the possible existence of subcritical dynamo in some stars which was previously demonstrated in a mean-field dynamo model with distributed α and MHD turbulent dynamo simulations.

Dependence of the velocity changes of secular variations on the position of observatory and time

According to the data of world observatories net secular variations of geomagnetic fields from internal and outer sources have been studied. Averaged 3-year data have been used for this purpose. Procedure of calculations of secular variations from internal and outer sources according to observatories data has been submitted. 1979 has been chosen as a zero level for accounting secular variations from outer sources because the sign of the large-scale magnetic field has changed this year. It has been shown that the value of secular variations from outer sources is different for different regions and increases with the growth of the latitude of magnetic observatory. Maximal values of secular variations are observed in the northern polar cap as well as at the longitudes of the eastern focus of secular variation. It has been shown that at the DIK, CSS, TIK observatories secular variations have maximal values. Groups of observatories have been segregated with symmetric and asymmetric changes of secular variation comparing to 1979. Symmetric changes of secular variation during two Hail’s cycles are observed at the observatories in circumpolar area (ALE, NAL, BJN), in auroral and middle latitudes. Maximal asymmetry of secular variation is observed at the observatories GDH, BLC, FCC, as well as at certain subauroral observatories and the regions with raised seismic activity. Secular variation from outer sources depends on the value of the large scale magnetic field of the Sun. The value of secular variation from the inner sources has been modulated by the outer sources and depends on special features of underlying surfaces of the observatories, induction currents in particular.

Spacecraft Reveal New Details of Magnetic Reconnection

Energetic electrons are accelerated directly by magnetic reconnections and can act as tracers of large-scale magnetic field conditions.

The magnetic helicity density patterns from non-axisymmetric solar dynamo

We study the helicity density patterns which can result from the emerging bipolar regions. Using the relevant dynamo model and the magnetic helicity conservation law we find that the helicity density patterns around the bipolar regions depend on the configuration of the ambient large-scale magnetic field, and in general they show a quadrupole distribution. The position of this pattern relative to the equator can depend on the tilt of the bipolar region. We compute the time–latitude diagrams of the helicity density evolution. The longitudinally averaged effect of the bipolar regions shows two bands of sign for the density distributions in each hemisphere. Similar helicity density patterns are provided by the helicity density flux from the emerging bipolar regions subjected to surface differential rotation.