Short communication

, Volume: 10( 5) DOI: 10.37532/2320-6756.2022.10(5).279

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An Overview of the Planetary Theory of Solar Activity Variability

*Correspondence:

S. Mackowski
Executive Manager, Journal of Physics and Astronomy, UK
E-mail: physics.astronomy12@aol.com

Abstract

A summary of current knowledge of solar activity's long-term behaviour on a multi-millennial timescale, as rebuilt using the indirect proxy method, is presented here. The notion of solar activity is addressed, as well as an overview of the particular indices that are used to quantify various elements of changing solar activity, with a focus on sunspot number. Over long periods, only indirect proxies, such as the cosmogenic isotopes 14C and 10Be in natural stratified archives, can be used to derive quantitative information on previous solar activity (e.g., tree rings or ice cores).

Keywords

Solar variability; Adiabatic equilibrium; Galactic cosmic rays

Introduction

For centuries, Aristotle's view of the sun's perfection and constancy was a powerful belief and an official ideology of Christian and Muslim governments. However, as humans had already recognised before Aristotle's time, some little temporary changes in the sun can be seen with the naked eye. Although astronomers have known about "imperfect" spots on the sun since the early seventeenth century, it wasn't until the nineteenth century that they realised solar activity changes over the course of an 11-year solar cycle. Solar variability is manifested in a variety of ways, including the fact that the "solar constant," or total solar irradiance, TSI (the quantity of total incoming solar electromagnetic radiation in all wavelengths per unit area at the top of the atmosphere), is not constant. The sun appears to be far more sophisticated and active than a static hot plasma ball, having a wide range of nonstationary active processes that go beyond the adiabatic equilibrium predicted by the sun-as-star basic theory. In contrast to the so-called "calm" sun, such transient nonstationary (frequently eruptive) phenomena might be widely referred to as solar activity. The study of changeable solar activity, on the other hand, is not merely academic because it has a direct impact on the terrestrial environment. Despite the fact that changes in the sun are barely observable without the use of sophisticated scientific instruments, they have a significant impact on many parts of our life. The solar magnetic field, in particular, controls the heliosphere (a geographical region of about 200-300 astronomical units wide). As a result, the solar magnetic activity modulates Galactic Cosmic Rays (GCRs). Most characteristics that define solar phenomena include the solar activity cycle, which is a near-periodic change with a duration of around 11 years. Variation records, which were originally based on sunspot counts, demonstrate that this has been the case throughout history, even though sunspots were scarce during specific intervals lasting decades and more.

This proves that the Sun has a timing engine that appears to regulate or impact all elements of solar phenomena, as well as phenomena outside in the solar system that are influenced by the Sun. Because of the knowledge that solar events affect the Earth's space environment in ways that might be potentially destructive, understanding the solar activity cycle has advanced from a simply scientific interest to a practical need in recent decades. It is widely accepted that the Sun's timing engine produces a nearly periodic generation and evolution of magnetic fields in the solar interior and on the solar surface, and that the Sun's magnetic field is generated by a dynamo mechanism.

Without a doubt, our sun is a fluctuating star. Ground-based measurements of the sun at visible, infrared, and radio wavelengths over several decades have revealed cycles of around 11 years. Despite the relevance of these emissions for a wide range of solar, cometary, planetary, and terrestrial studies, little is known about solar variability at ultraviolet (UV) wavelengths. Because solar UV radiation with wavelengths less than 300 nm is absorbed by the earth's atmosphere, precise measurements are difficult, rare, and limited to two solar cycles.

The Sun, which is 4.6 billion years old, is a typical middle-aged G-type star. It's an active star, with short- to long-term changes in its radiative, electromagnetic, and particle emission due to its magnetic activity. Magnetic storms flares and Coronal Mass Ejections (CMEs) occur sometimes on the Sun, accompanied by strong radiation output, Solar Energetic Particles (SEPs), and magnetised plasma ejecta that disrupt planetary space habitats. While ground-based observations spanning four centuries have provided a good understanding of decadal to century-scale fluctuations in the solar magnetic cycle, and more recent space-based observations have uncovered subtle variations in solar radiation, constrained energetic processes such as flares and CMEs, and measured properties of the solar wind, observations of other Sun-like stars and exoplanetary systems are required to appreciate the full range of observables. Astrophysical data show that the Sun's activity and radiative output have fluctuated over time. Unfortunately, precise data is only available after 1978, i.e. after the satellite period. Looking at solar variability over such a short time frame only reveals a tiny range of solar forcing, such as 1 percent of total irradiance throughout an 11-year activity cycle. There are differing viewpoints on a multi-decadal irradiance pattern and a putative relationship between solar activity and cloud cover. Data collected during the next solar minimum could help answer both of these problems. Furthermore, the hypothetical impact of cosmic rays on cloud formation is poorly known, necessitating additional investigation. For times earlier to the last three decades, solar records are inherently incomplete.