Solar Cycle Variability in Coronal Holes and Their Effects on Solar Wind Sources

Abstract

Various upstream spacecraft have now observed the solar wind conditions affecting the Earth since the 1970s, covering over four solar activity cycles. These measurements provide a long term picture of the related patterns in large scale incident plasma and magnetic field parameters of interest for both interpreting cycles in geospace effects, and understanding how the Sun controls our space environment. This paper focuses on the latter, in part to provide context at the start of the new solar cycle 25, and toward establishing connections between the 1 AU ecliptic solar wind behavior and the unprecedented near‐Sun measurements of heliospheric features on Parker Solar Probe and Solar Orbiter. Magnetograph data‐based potential field source surface models provide a basic picture of how the solar wind sources, including those that give rise to corotating high speed streams in the ecliptic, have changed since the beginning of the record of regular solar wind measurements. In particular, they suggest the contributions from low to mid latitude coronal holes dominate the observed cycles (21–24), especially the weaker cycles (23 and 24), impacting upstream measurement interpretations, modeling, and forecasting considerations. For example, recurring features are affected by differential rotation of the Sun's surface field, which through its effects on the corona, can produce solar wind streams reappearing at ∼25–30 days intervals instead of at the canonical 27.3 days Carrington rotation rate. In addition, the conditions that lead to the corotating stream structure that can dominate periods of low solar activity are seen to be more complicated than suggested by the simple concepts of early studies. The overall results illustrate where in the cycles well‐defined, long‐lived large scale structures can be expected, and the advantages of synoptic displays of 1 AU solar wind parameters for anticipating timings of recurring features.

Whole Heliosphere and Planetary Interactions (WHPI): The Big Picture on Solar Cycle Minima

“…The effects of differential rotation (faster solar rotation at equator than higher latitudes) can be seen in the drift of the equatorial portion of both coronal holes to the right (the equator rotates prograde relative to the synoptic Carrington rate of 27.3 days; see discussion in Luhmann et al. (2022)) (right column) Solar wind at Earth versus time (top) and related wavelet (bottom) showing periodic solar wind 7–9 day forcing. Data from https://omniweb.gsfc.nasa.gov/.…”

“…The level of participation increased with its expanded scope, encompassing Sun to solar wind to planetary magnetospheres and atmospheres. The articles accompanying this introduction (Allen et al, 2023;Badman et al, 2023;Bregou et al, 2022;Gasperini et al, 2023;Hewins et al, 2023;Hudson et al, 2021;Lloveras et al, 2022;Luhmann et al, 2022;Mlynczak et al, 2022;Palmerio et al, 2022;Riley et al, 2022;Varela et al, 2022;Younas et al, 2022) represent the beginnings of analyses that are likely to continue for years to come.…”

“…Riley et al (2022) did a statistical comparison of the three solar minima and found, as was the case with the polar magnetic fields, that the WHPI solar wind properties lay in between those of WSM and WHI. Luhmann et al (2022, a paper in this collection) determined the sources of solar wind velocity measured in the ecliptic from global coronal magnetic models and found that low-to-mid latitude open fields (as opposed to polar open fields) were the primary source of solar wind measured at the Earth, in particular during the extended minima of WHI and WHPI. Thus, to summarize, coronal magnetic field and solar wind observations indicate that WHPI was similar to WHI in its length and magnetic complexity, but demonstrated at least a "partial recovery" of solar dipole dominance and solar wind density and velocity.…”

Forward‐Looking Study of Solar Maximum Impact in 2025: Effects of Satellite Navigation Failure on Aviation Network Operation in the Greater Bay Area, China

“…To the best of our knowledge, only a few studies have evaluated the effects of space weather on aviation by systematically considering space weather, satellite navigation, and ATM together. In previous studies, Solar activity has shown an 11-year cycle (Luhmann et al, 2022;Swiger et al, 2022). The annual mean total sunspot number since 1900 is illustrated in Figure 1.…”

Global MHD Simulations of the Time-dependent Corona

“…As such, changes in the average shape and structure of the corona in time have often been characterized in a variety of models on CR-to-CR basis, ranging from simple potential field source surface (PFSS) extrapolations to full magnetohydrodynamic (MHD) calculations. In this modeling paradigm, successive monthly "snapshots" of the corona are computed separately, with each calculation for a given CR being fully independent of the previous case (e.g., Riley et al 2006;Luhmann et al 2022).…”