. " i Sun, Climate »v \!i> ;V:.;^'* ;- '• National Aeronautics and Space Administration NASA SP-426 Sun, Weather, and Climate John R. Herman and Richard A. Goldberg Scientific and Technical Information Branch 1978 NATIONAL AERONAUTICS AND SPACE ADMINISTRATION Washington, D.C. Library of Congress Cataloging in Publication Data Herman, John R Sun, weather, and climate. (NASA SP ; 426) Includes indexes. Supt. of Docs. no. : NAS 1.21:426 1. Solar activity. 2. Weather. 3. Climatology. I. Goldberg, Richard A., joint author. II. Title. III. Series: United States. National Aeronautics and Space Administration. NASA SP ; 426. QC883.2.S6H47 551.5 78-606053 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 (Paper cover) Stock Number 033-000-00747-7 Foreword "A growing mass of evidence suggests that transient events on the Sun affect our weather and long-term variations of the Sun's energy output affect our climate. Solar terrestrial exploration can help estab- lish the physical cause and effect relationships between solar stimuli and terrestrial responses. When these relationships are understood, science will have an essential tool for weather and climate predic- tion." This paragraph, written by Robert D. Chapman as part of a proposal for a five-year plan for Solar Terrestrial Programs in the National Aeronautics and Space Administration, is an indication of the present status of Sun-weather/climate investigations. The literature on this subject covers a period of more than 100 years, and many distinguished scientists have contributed. Never- theless, until very recently, Sun-weather/climate investigations have not been taken very seriously by many scientists. In the last few years, compelling (but not absolutely conclusive) evidence for correlations between solar variations and the area of tropospheric cyclones has helped to make this subject suitable for serious studies. Almost every large solar-terrestrial symposium now includes at least one session on Sun-weather/climate investigations. This book is particularly welcome at a time at which many astron- omers, space scientists, geophysicists, and meteorologists are entering the field of Sun-weather/climate investigation. The subject is an example par excellence of an interdisciplinary endeavor in which any single scientist is not likely to have professional competence throughout the entire range of relevant subject matter. The literature on the subject is often confusing and contradictory and of highly variable quality. This book provides an excellent opportunity for a scientist consid- ering this new field to get an overall view of the present status of the subject in its many disciplinary aspects. The existing correlations pro- vide a strong suggestion that some physical mechanism exists linking the variable Sun and the weather and climate, but the details of such a mechanism or mechanisms are quite unknown at present. Several attractive possibilities are described in the book. in SUN, WEATHER. AND CLIMATE It seems likely that Sun-weather/climate investigations will occupy an increasingly prominent role in the coming decade, and the publication of this book should give a significant impetus to these efforts. John M. Wilcox Stanford University IV Preface 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 litera- ture, addresses the physical linking mechanisms, and suggests experi- mental 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 SUN, WEATHER, AND CLIMATE atmospheric processes, and so on, thereby stimulating the cross fer- tilization we believe is necessary for further progress in Sun-weather studies. In providing a reasonably comprehensive review of reported corre- lations, we have applied appropriate critiques when possible; how- ever, in several cases the statistical significance is difficult to assess. Other correlations have been omitted because we believe they are faulty. The correlations are divided into two basic categories, long and short term, to correspond to climate and weather relationships, respectively. Sufficient quantities of the various types have been re- tained to reflect the true flavor of the Sun-weather field at this time. Correlations with other phenomena, such as apparent lunar and tropospheric influences on geomagnetic activity, are included to demonstrate how relationships with solar activity might be masked by competing effects. The book covers some of the more recent suggestions concerning causal processes and provides examples of explanations for short-, intermediate-, and long-term relationships between solar activity and weather and climate. The coverage is not meant to be comprehen- sive, but rather a sampling of the ideas now emerging in this field. The last part of the book briefly discusses a general outline for experi- mental procedures to investigate possible mechanisms. More detailed plans have been proposed, but at the present stage of evolution, we feel that this book should guide rather than specify. This is especially true in view of the rapid progress now being made in the field —pro- gress that is certain to make obsolete many of the current suggestions. Intertwined throughout the book are numerous discussions of basic physical processes, definitions, and geophysical phenomena, intro- duced when they are appropriate and relevant to the relationships and/or mechanisms under discussion. In addition, an introduction to the many geophysical and solar-related phenomena and indices used for discussion of the correlations is given early in the book. Although it may appear that the treatment is favorably oriented to the Sun-weather field, we have attempted to be objective while main- taining an agnostic attitude. In our opinion, there is no conclusive evidence for or against the relationships at this time. We do feel, however, that the hard statistical evidence that has emerged recently is more than fortuitous and justifies a strong research effort to search for, identify, and study the unidentified physical coupling processes that may be responsible for the observed correlations. VI PREFACE In a multidisciplinary effort of this kind, we cannot be experts in all fields, and we have therefore drawn freely on the advice, com- ments, and suggestions of numerous colleagues who gave willingly of their time to help us clarify our thinking. Any errors and mis- interpretations in the book are our responsibility. We are especially indebted to Dr. Ray Wexler, Dr. John M. Wilcox, Dr. S. J. Bauer, and Dr. Leif Svalgaard for reading several complete drafts and revisions and offering constructive criticism. Others who read complete drafts and contributed helpful comments include Dr. George C. Reid, Dr. James Barcus, Dr. Rudolf Penn- dorf, Dr. Kaichi Maeda, Dr. Eldon Ferguson, and Dr. A. Ebel. We greatly appreciate the help on various portions of the manu- script given by Mr. Ernest Hilsenrath, Dr. Kenneth Schatten, Dr. Leslie C. Hale, Dr. Masahisa Sugiura, and Dr. Roger E. Olson. Helpful advice and comments were also received from Dr. Bruce Guenther, Dr. Walter Orr Roberts, and Dr. T. Matsuno. With par- ticular pleasure we thank Dr. Donald F. Heath, Mr. William E. Ban- deen, and Dr. David Atlas for their support of work leading to this book and their encouragement to publish it. John R. Herman Radio Sciences Co. and Richard A. Goldberg NASA Goddard Space Flight Center November 1977 vn Page Intentionally Left Blank Table of Contents 1 Introduction 1 2 Solar-Related