Interplanetary conditions: lessons from this minimum

Abstract

Abstract.Interplanetary conditions during the Cycle 23-24 minimum have attracted attention because they are noticeably different than those during other minima of the space age, exhibiting more solar wind stream interaction structures in addition to reduced mass fluxes and low magnetic field strengths. In this study we consider the differences in the solar wind source regions by applying Potential Field Source Surface models of the coronal magnetic field. In particular, we consider the large scale coronal field geometry that organizes the open field region locations and sizes, and the appearance of the helmet streamer structure that is another determiner of solar wind properties. The recent cycle minimum had an extraordinarily long entry phase (the decline of Cycle 23) that made it difficult to identify when the actual miminum arrived. In particular, the late 23 r d cycle was characterized by diminishing photospheric fields and complex coronal structures that took several extra years to simplify to its traditional dipolar solar minimum state. The nearly dipolar phase, when it arrived, had a duration somewhat shorter than those of the previous cycles. The fact that the corona maintained an appearance more like a solar maximum corona through most of the quiet transitional phase between Cycles 23 and 24 gave the impression of a much more complicated solar minimum solar wind structure in spite of the weaknesses of the mass flux and interplanetary field. The extent to which the Cycle 23-24 transition will affect Cycle 24, and/or represents what happens during weak cycles in general, remains to be seen.

Comparative analysis of extreme ultraviolet solar radiation proxies during minimum activity levels

“…Following the comparison of EUV levels between minimum periods, the superposed epoch analysis (Figure 3) clearly showed that the last two minima had lower EUV radiation levels than did the first two, together with a longer duration. This was already observed by several authors, especially in the case of min23-24 (Luhmann et al, 2012). In addition, each minimum was lower than the previous one, except MgII for the first two periods.…”

Interplanetary shocks and foreshocks observed by STEREO during 2007–2010

“…The number of shocks driven by SI was higher during the studied time interval, and this is related to the unusual configuration of the magnetic field in the solar corona during the extended minimum, which showed significant coronal holes at medium and low latitudes [ Luhmann et al ., ]. As the solar cycle evolves, the number of shocks driven by stream interaction does not vary much with 38 shocks observed by STEREO in the interval 2011–2012 (Blanco‐Cano et al, manuscript in preparation).…”