Solar Wind Helium Abundance Heralds Solar Cycle Onset

We study the solar wind helium-to-hydrogen abundance's ( A He ) relationship to solar cycle onset. Using OMNI/Lo data, we show that A He increases prior to sunspot number (SSN) minima. We also identify a rapid depletion and recovery in A He that occurs directly prior to cycle onset. This A He Shutoff happens at approximately the same time across solar wind speeds ( v sw ) and the time between successive A He shutoffs is typically on the order of the corresponding solar cycle length. In contrast to A He 's v sw -dependent phase lag with respect to SSN (Alterman and Kasper, 2019), A He Shutoff's concurrence across v sw likely implies it is independent of solar wind acceleration and driven by a mechanism near or below the photosphere. Using Brightpoint (BP) measurements to provide context, we infer that this shutoff is likely related to the overlap of adjacent solar cycles and the equatorial flux cancelation of the older, extended solar cycle during solar minima.

A Study of Variation of the 11-yr Solar Cycle before the onset of the Spoerer Minimum based on Annually measured 14C Content in tree Rings

ABSTRACTProxy-based observations of solar activity in the past have revealed long-term variations, such as the Gleissberg cycle (~88 yr), de Vries cycle (~200 yr), and the Hallstatt cycle (~2000 yr). Such long-term variations of solar activity sometimes cause the disappearance of sunspots for several decades. Currently, solar activity is becoming weaker, and there is a possibility that another long-term sunspot minimum could occur. However, the detailed mechanism of the weakening in solar activity is unknown, and the prediction of solar activity is ambiguous. In this study, we investigate the transitions of solar cycle length before the onset of the Spoerer Minimum, the longest grand minimum in the past 2000 yr. We measured the 14C content in an asunaro tree (Thujopsis dolabrata) excavated at Shimokita Peninsula from 1368–1420 CE using the compact AMS system at Yamagata University. It is found that the solar cycle lengthened to be 14–16 yr from 2 cycles before the onset of the Spoerer Minimum.

Modelling solar cycle length based on Poincaré maps for Lorenz-type equations

Two systems of Lorenz-type equations modelling solar magnetic activity are studied: Firstly a low order dynamic system in which the toroidal and poloidal fields are represented by x- and y-coordinates respectively, and the hydrodynamical information is given by the z coordinate. Secondly a complex generalization of the three ordinary differential equations studied by Lorenz. By studying the Poincaré map we give numerical evidence that the flow has an attractor with fractal structure. The period is defined as the time needed for a point on a hyperplane to return to the hyperplane again. The periods are distributed in an interval. For large values of the Dynamo number there is a long tail toward long periods and other interesting comet-like features. These general relations found for periods can further be physically interpreted with improved helioseismic estimates of the parameters used by the dynamical systems. Solar Dynamic Observatory is expected to offer such improved measurements.