Sun, Weather, and Climate

This book introduces the general field of Sun-weather/climate relationships, that is, apparent weather and climate responses to solar activity, and provides theoretical and experimental suggestions for further research to identify and investigate the unknown causal mechanisms. It is directed to researchers active in the atmospheric and space sciences who wish to expand their background for meeting the challenge of this newly emerging field and to students who desire a general background in the several disciplinary areas of the field. In the 200-year history of Sun-weather studies, a large body of information has accumulated. Even though the reported results have sometimes been confused, disjointed, and contradictory, there has emerged a growing belief that there are connections between changes on the Sun and changes in the lower atmosphere. There is, however, a deplorable lack of acceptable physical mechanisms to explain those probable connections, and this has prevented widespread acceptance of the reality of solar activity effects on the weather and climate. The discovery of viable mechanisms will strengthen the scientific basis of Sun-weather relationships and may lead to improved predictions of weather and climate. It is obvious that improved predictions would have a profound impact on several crucial societal problems, especially in the areas of global food production and utilization of solar energy for man's needs. This book reviews the correlations between solar activity and weather and climate reported in historical and contemporary literature, addresses the physical linking mechanisms, and suggests experimental concepts for future investigations of such mechanisms. It is our intention to fill a gap in the literature by combining a review of the nature and quality of existing correlations with the basic physics underlying the various scientific disciplines required to pursue studies of physical linking mechanisms. We emphasize the multidisciplinary nature of the subject while providing a basic background in each of the various areas thought to play a role in coupling processes. In following this approach, we hope to acquaint meteorologists with solar and geophysical phenomena, solar physicists with terrestrial atmospheric processes, and so on, thereby stimulating the cross fertilization we believe is necessary for further progress in Sun-weather studies.

This work reviews both long and short-term meteorological variations related to solar activity and the few physical linking mechanisms that have been suggested to explain the relationships. Several new mechanisms are postulated with varying degrees of completeness to supplement those already reported in the literature. Physical background material is provided where appropriate to assist the reader in grasping the concepts presented.

The book also examines some experimental concepts useful for investigating physical links between solar variability and meteorological responses. The rationale for this objective is that, despite the vast literature supporting a probable connection between the two phenomena, there is considerable disbelief for such a connection. This disbelief seems to be based principally on the fact that no plausible physical mechanisms have been identified to explain how the relatively minor fluctuations in solar energy output can influence or drive the vastly more energetic meteorological processes. If linking mechanisms can be identified, the subject of Sun-weather relationships will be on much firmer ground, and improved predictions of climatic trends and weather changes may in fact become possible.

From these few introductory remarks it can be appreciated that the subject we address is truly multidisciplinary. It will be seen in subsequent pages that even the present modest effort touches on solar physics, magnetospheric physics, atmospheric physics and chemistry, atmospheric electricity, cosmic rays, geomagnetism, and meteorology. To gain new insights into Sun-weather relationships we believe it is necessary to combine the extant knowledge of all these disciplines and interpret that knowledge in new ways. We do not claim to do that here, but we do attempt to bring together, and in some cases simply point out, the essential ingredients required.

In that spirit, the characteristics of solar variables and solar energy sources suggested to be related to weather and climate fluctuations are discussed in chapter 2. Included are galactic cosmic rays and geomagnetic activity, since variations in the intensity of these phenomena are related to solar activity, and both have been observed to be correlated with weather changes.

Long-term climatic trends and their association with solar activity are examined in chapter 3. In some cases it has been noted that correlations between meteorological phenomena and the sunspot cycle may persist for several cycles and then break down or even reverse sign. These peculiarities may be indicative of a fortuitous correlation between unrelated variables, or they may point toward an as yet undiscovered key to an undefined link between two seemingly independent variables that are in fact related. Because of these two important possibilities, a separate section (3.3) is devoted to such breakdowns and reversals.

Short-term correlations between meteorological parameters and transient solar phenomena, such as solar flares and solar magnetic sector boundaries, are treated in chapter 4. Correlations between weather changes and magnetic activity as an indicator of solar variability are included in this chapter.

In chapter 5, the possibility that observed correlations between magnetic activity and weather phenomena are unrelated to solar activity is examined briefly. The heart of the problem, that is, the physical processes and mechanisms that produce the observed correlations, is addressed in chapter 6. Here the discussion must be speculatory and in some cases naive, because no hypotheses have been proven that explain the physical links to couple solar variations to the troposphere.

A summary of the highlights of Sun-weather relationships and an extensive table of reported correlations are given in chapter 7. This narrative summary can be read first to gain an overview of the subject.

The principal weather and climate factors that affect man and his activities are summarized in chapter 8, along with an argument for a continuation and intensification of Sun-weather research. Meteorological and solar-related measurement parameters required in such future research are also summarized in this chapter, and some experimental guidelines for searching out physical linking mechanisms are suggested. Following this final chapter, a comprehensive list of references is collected.

Basic physical properties of the atmosphere (temperature, pressure, density) up to 50 km, along with conversion factors for pressure units are given in appendix A. Acronyms, abbreviations, units, and symbols used in the text are collected in appendix B.