On Sunspot Modulated Temporal Modes of Variability

Abstract

It has recently been reported (Baker, 2024) that the average number of visible dark patches on the Sun's surface in August 2024 was higher than any other month since September 2001, a full 23-year period. The final count was more than twice as high as experts from the National Oceanic and Atmospheric Administration (NOAA) Space Weather Prediction Center (SWPC) in Boulder Colorado initially predicted it would be. There was an average of 215.5 daily sunspots on the Sun's surface during August. The number of black spots peppering the Sun's surface in August was the highest for almost 23 years, new data from the NOAA SWPC showed. The latest SWPC sunspot count was more than twice as high as their initial forecasts predicted and is taken as a clear sign that the Sun's explosive peak, or solar maximum, is likely well underway, and will be far more active than scientists initially thought. Sunspots are regions of the Sun's surface where surges of electromagnetic radiation break through the star's magnetic field, creating relatively cool patches that appear black to us thanks to an optical illusion. Along with the size and frequency of solar flares and coronal mass ejections, sunspot numbers indicate the progress of the Sun's roughly 11-year solar cycle. During the Sun's least active phase, or solar minimum, there are very few or occasionally no sunspots. For example, in late 2019, shortly before the start of the current solar cycle (Solar Cycle 25), there were 40 consecutive days with no visible sunspots. But as the sun's magnetic field gets entangled with itself and weakens, sunspot numbers quickly climb before peaking during solar maximum. During this active phase, the Sun's magnetic field eventually snaps and completely flips, which triggers a falling-off period of solar activity and a decrease in sunspots until the whole solar cycle is generally believed to restart. The last time the monthly sunspot number was this high was September 2001, during the solar maximum of Solar Cycle 23, when the average was 238.2. The number of sunspots peaked on August 8 2024, when up to 337 sunspots were observed on the Sun, which is the highest total in a 24-hour period since March 2001. These numbers indicate what some scientists have already suspected, that we have entered solar maximum. However, we can't be certain of this until long after sunspot numbers begin to drop again. In this study we harvest sunspot data from 24 prior solar cycles and employ a Hilbert-Huang Transform (Huang et al., 1999; Huang & Wu, 2007) to reveal sunspot activity consisting of internal modes of variability in excess of solely an 11-year cycle. We show that there are a suite of well-defined modes of sunspot variability, from multiple months, to multiple years to multiple decades, and centuries, which likely have important implications and consequences for conventional Earth atmospheric and oceanic weather, and also for the electromagnetic field of the Planet.