The ACRIM data in the context of stellar variability

The Active Cavity Radiometer Irradiance Monitor (ACRIM) total-irradiance data from the Solar Maximum Mission have given a first comprehensive view of solar variability in the stellar sense. Five types of solar variability have been identified thus far. These have small amplitudes, less than a few tenths of one percent, and are at levels generally not yet detectable on other stars. The possible stellar analogs are interesting physically, and in particular may help us to understand solar behavior on longer time scales. The ACRIM data is described from the stellar point of view. The present state of stellar time-series photometry is discussed

Scientific tradeoffs in pinhole/occulter facility accommodation

The Pinhole/Occulter Facility (P/OF) consists of state-of-the-art instruments for the study of particle acceleration in the solar corona, and uses a large structure to obtain very high angular resolution. P/OF has been studied in the past as an attached payload for the Space Shuttle, and has been the subject of study by a NASA Science Working Group (P/OFSWG). Appendix A lists various technical studies and reports carried out under the auspices of P/OFSWG and the Program Development Office of NASA Marshall Space Flight Center. Under the rationalization of NASA flight opportunities following the Challenger disaster, and the beginning of the Space Station Freedom program, the sortie-mode deployment of P/OF seemed less efficient and desirable. Thus, NASA decided to reconsider P/OF for deployment on the Space Station Freedom. The technical studies for this deployment continue at the present and will evolve as our knowledge of Space Station architecture and capabilities increase. MSFC contracted with Teledyne Brown Engineering for these technical studies

Solar flare build-up and release

Flares and coronal mass ejections should follow a pattern of build-up and release, with the build-up phase understood as the gradual addition of stress to the coronal magnetic field. Recently Hudson (Mon. Not. Roy. Astron. Soc. 491, 4435, 2020) presented observational evidence for this pattern in two isolated active regions from 1997 and 2006, finding a correlation between the waiting time after the event, and the event magnitude. In this article we systematically search for related evidence in the largest 14 active regions of Solar Cycle 24, chosen as those with peak sunspot area exceeding 1000 millionths of the solar hemisphere (MSH). The smallest of these regions, NOAA 12673, produced the exceptional flares SOL2017-09-06 and SOL2017-09-10. None of these regions showed significant correlations of waiting times and flare magnitudes, although two hinted at such an interval-size relationship. Correlations thus appear to be non-existent or intermittent, depending on presently unknown conditions

The Unpredictability of the Most Energetic Solar Events

Observations over the past two solar cycles show a highly irregular pattern of occurrence for major solar flares, gamma-ray events, and solar energetic particle (SEP) fluences. Such phenomena do not appear to follow the direct indices of solar magnetic activity, such as the sunspot number. I show that this results from the non-Poisson occurrence for the most energetic events. This Letter also points out a particularly striking example of this irregularity in a comparison between the declining phases of the recent two solar cycles (1993-1995 and 2004-2006, respectively) and traces it through the radiated energies of the flares, the associated SEP fluences, and the sunspot areas. These factors suggest that processes in the solar interior involved with the supply of magnetic flux up to the surface of the Sun have strong correlations in space and time, leading to a complex occurrence pattern that is presently unpredictable on timescales longer than active region lifetimes (weeks) and not correlated well with the solar cycle itself.Comment: 4 page