Search

This paper describes a new way of determining the high-latitude solar rotation rate statistically from simultaneous observations of many polar faculae. In this experiment, I extracted frames from a movie made previously from flat-fielded images obtained in the 6767 A continuum during February 1997-1998 and used those frames to construct space-time maps from high-latitude slices of the favorably oriented south polar cap. These maps show an array of slanted tracks whose average slope indicates the east-west speed of faculae at that latitude, Ls. When the slopes are measured and plotted as a function of latitude, they show relatively little scatter 0.01-02 km/s from a straight line whose zero-speed extension passes through the Sun's south pole. This means that the speed, v(Ls), and the latitudinal radius, R cos(Ls), approach 0 at the same rate, so that their ratio gives a nearly constant synodic rotation rate 8.6 deg/day surrounding the Sun's south pole. A few measurements of the unfavorably oriented north polar cap are consistent with these measurements near the south pole., Comment: 13 pages, 8 figures

This paper uses wavelet transforms to look for the rotational frequencies of the Sun's mean line-of-sight magnetic field. For a sufficiently high wavelet frequency, the spectra of the dipole, quadrupole, and hexapole field components each show a time-dependent fine structure with periods in the range of 26.5-30 days and their harmonics. These maps confirm that a large enhancement of 30-day power occurred in the dipole field during 1989-1990, as recorded previously using Fourier techniques (Sheeley 2022). Also, during some years the maps show power at 26.5 days (or its harmonics), that is clearly distinguishable from the 26.9-27.0 day rotation period at the Sun's equator. In at least one case, the 26.5-day period was a wave phenomenon caused by the systematic eruption of active regions at progressively more western locations in the Carrington coordinate system, as if the flux were emerging from a fixed longitude in a faster rotating subsurface layer. Based on previous studies of the mean field (Sheeley et al 1985, Sheeley & DeVore 1986, Sheeley 2022), I conclude that the enhanced wavelet patterns in this paper are regions where magnetic flux is emerging in configurations that strengthen the Sun's horizontal dipole, quadrupole, and hexapole fields, and (in the case of the more slowly rotating patterns) where this flux is being transported to mid-latitudes whose rotation periods are in the range 28-30 days., Comment: 15 pages, 3 figures, 4 appendices version 2 corrects equation references in Appendices C and D. Also, references to unavailable video streaming have been removed, and a typo is fixed

We regard the Sun-as-a-star magnetic field (i.e. the mean field) as a filter for the spherical harmonic components of the photospheric field, and calculate the transmission coefficients of this filter. The coefficients for each harmonic, $Y_{l}^{m}$, are listed in three tables according to their dependence on $B_{0}$, the observer's latitude in the star's polar coordinate system. These coefficients are used to interpret the 46-yr sequence of daily mean-field measurements at the Wilcox Solar Observatory. We find that the non-axisymmetric part of the field originates in the $Y_{1}^{1}$, $Y_{2}^{2}$, and a combination of the $Y_{3}^{3}$ and $Y_{3}^{1}$ harmonic components. The axisymmetric part of the field originates in $Y_{2}^{0}$ plus a $B_{0}$-dependent combination of the $Y_{1}^{0}$ and $Y_{3}^{0}$ components. The power spectrum of the field has peaks at frequencies corresponding to the ~27-day synodic equatorial rotation period and its second and third harmonics. Each of these peaks has fine structure on its low-frequency side, indicating magnetic patterns that rotate slowly under the influence of differential rotation and meridional flow. The sidebands of the fundamental mode resolve into peaks corresponding to periods of ~28.5 and ~30 days, which tend to occur at the start of sunspot maximum, whereas the ~27-day period tends to occur toward the end of sunspot maximum. We expect similar rotational sidebands to occur in magnetic observations of other Sun-like stars and to be a useful complement to asteroseismology studies of convection and magnetic fields in those stars., Comment: 27 pages, 16 figures

This paper describes a mathematical model for the spread of a virus through an isolated population of a given size. The model uses three, color-coded components, called molecules (red for infected and still contagious; green for infected, but no longer contagious; and blue for uninfected). In retrospect, the model turns out to be a digital analogue for the well-known SIR model of Kermac and McKendrick (1927). In our RGB model, the number of accumulated infections goes through three phases, beginning at a very low level, then changing to a transition ramp of rapid growth, and ending in a plateau of final values. Consequently, the differential change or growth rate begins at 0, rises to a peak corresponding to the maximum slope of the transition ramp, and then falls back to 0. The properties of these time variations, including the slope, duration, and height of the transition ramp, and the width and height of the infection rate, depend on a single parameter - the time that a red molecule is contagious divided by the average time between collisions of the molecules. Various temporal milestones, including the starting time of the transition ramp, the time that the accumulating number of infections obtains its maximum slope, and the location of the peak of the infection rate depend on the size of the population in addition to the contagious lifetime ratio. Explicit formulas for these quantities are derived and summarized. Finally, Appendix E has been added to describe the effect of vaccinations., Comment: 86 pages, 44 figures

Although the Sun's polar magnetic fields are thought to provide important clues for understanding the 11-year sunspot cycle, including the observed variations of its amplitude and period, the current database of high-quality polar-field measurements spans relatively few sunspot cycles. In this paper we address this deficiency by consolidating Mount Wilson Observatory polar faculae data from four data reduction campaigns, validating it through a comparison with facular data counted automatically from MDI intensitygrams, and calibrating it against polar field measurements taken by the Wilcox Solar Observatory and average polar field and total polar flux calculated using MDI line-of-sight magnetograms. Our results show that the consolidated polar facular measurements are in excellent agreement with both polar field and polar flux estimates, making them an ideal proxy to study the evolution of the polar magnetic field. Additionally, we combine this database with sunspot area measurements to study the role of the polar magnetic flux in the evolution of the heliospheric magnetic field (HMF). We find that there is a strong correlation between HMF and polar flux at solar minimum and that, taken together, polar flux and sunspot area are better at explaining the evolution of the HMF during the last century than sunspot area alone., Comment: 14 pages, 17 figures

Perhaps the most compelling evidence for the role of magnetic reconnection in solar flares comes from the supra-arcade downflows that have been observed above many post-flare loop arcades. These downflows are thought to be related to highly non-potential field lines that have reconnected and are propagating away from the current sheet. We present new observations of supra-arcade downflows taken with the Atmospheric Imagining Assembly (AIA) on the \textit{Solar Dynamics Observatory} (\textit{SDO}). The morphology and dynamics of the downflows observed with AIA provide new evidence for the role of magnetic reconnection in solar flares. With these new observations we are able to measure downflows originating at much larger heights than in previous studies. We find, however, that the initial velocities measured here ($\sim$144\,km s$^{-1}$) are well below the Alfv{\'e}n speed expected in the lower corona, and consistent with previous results. We also find no evidence that the downflows brighten with time, as would be expected from chromospheric evaporation. These observations suggest that simple two-dimensional models cannot explain the detailed observations of solar flares., Comment: Movies are available http://tcrb.nrl.navy.mil/~hwarren/temp/papers/inflows/ in QuickTime format