TWILIGHT
TWILIGHT A STUDY IN ATMOSPHERIC OPTICS Georgii Vladimirovich Rozenberg Deputy Director Institute of Physics of the Atmosphere Academy of Sciences of the USSR With a Preface by J. V. Dave National Center for Atmospheric Research Authorized translation from the Russian by Richard B. Rodman Harvard College Observatory Springer Science+Business Media, LLC 1966
The Russian language text was published by the State Press for Physicomathematical Literature in Moscow in 1963. TWILIGHT SUMERKI CyMepKH rcopauit BAaiJUMUP06U'l Poacu6epB Library of Congress Catalog Card Number 65-11345 1966 Springer Science+ Business Media New York Originally published by Plenum Press in 1966 A Division of Plenum Publishing Corporation 227 West 17 Street, New York, N..10011 All rights reserved No part of this publication may be reproduced in any form without written permission from the publisher ISBN 978-1-4899-6176-1 ISBN 978-1-4899-6353-6 (ebook) DOI 10.1007/978-1-4899-6353-6
FOREWORD The first phase of the passive sounding of the planetary atmosphere can be considered as a sort of pioneering" in which some sweeping claims are made on the basis of rather meager observational material and theoretical understanding. This helps to attract well-qualified persons from other scientific disciplines such as applied mathematics and classical physics. This in turn creates newer and stronger controversies which demand direct sounding of the atmosphere. As a result, more experimental physicists, engineers, and technologists appear on the scene, and the subject comes to the notice of the public and the government. At this stage, one would expect the passive sounding techniques to die a natural death. But this is not what has happened. On the contrary, history has shown that, in general, they have returned in a new role - either complementing the direct observations or exploring further unknowns on a much sounder basis. The idea of extracting information concerning the atmospheric structure from ground-based observations of the twilight sky is an old one. But little progress has been made because of the difficulty of obtaining reliable and absolute measurements and of understanding the process of radiation transfer in a nonhomogeneous, spherical atmosphere. Now, however, spacecraft provide many opportunities for observing twilight on our own and on other planets from various directions. Measurements can be made from the ground and also from orbiting and fly-by vehicles. In addition, the development of high-speed, electronic digital computers is bound to aid in the solution of the problems of radiative transfer. This treatise on twilight by Prof. G. V. Rozenberg appears at an opportune moment when young researchers are being attracted to this field. The book provides a good historical survey for these newcomers. Extensive citations by Prof. Rozenberg of twilight papers published in many countries clearly demonstrate the truly international appeal of the subject. Prof. Rozenberg has provided many references to Russian papers previously unfamiliar to most English-speaking scientists. The need has long existed for relating all these materials in one volume. This work by Prof. Rozenberg should prove extremely v
vi FOREWORD useful as a textbook for graduate students in atmospheric physics and as a reference book to persons already actively engaged in the field. J. V. Dave National Center for Atmospheric Research Boulder, Colorado February 1966
PREFACE TO THE RUSSIAN EDITION In this book the reader will find the twilight process treated as an optical phenomenon and as a tool for upper-atmosphere research. Our understanding of twilight has advanced considerably over the past 30 years. The acquisition mainly of descriptive material through rudimentary observing techniques has now given way to purposeful quantitative research which exploits every facility of modern experimental technology. And the frankly speculative arguments that had widely prevailed have been replaced by theory, developed in detail and tested experimentally, so that various aspects of the twilight phenomenon can now be treated from a rigorous mathematical standpoint to yield much valuable data on the structure of the atmosphere. But although these results have furnished a fairly comprehensive understanding of twilight, and have in fact established that the twilight method can be applied within certain limits for sounding the atmosphere, they remain scattered through papers in many different journals. It is therefore opportune now to collect the results and examine them from a unified viewpoint. The author has by no means attempted an exhaustive review of all twilight research - of the earlier work in particular. This book aims to outline the current status of the problem. Considerable space is devoted to ideas that the author has developed in recent years at the Atmospheric OptiCS Laboratory of the Institute of Atmospheric PhysiCS, USSR Academy of Sciences. He has often reported this material verbally and much of it has been incorporated in published papers, but the results are here presented for the first time in complete form, together with certain data from experimental studies of the twilight sky conducted at the Atmospheric Optics Laboratory over the past few years. As is customary, omission of references to the literature indicates that the material is original. G. V. R. vii
BIOGRAPHICAL NOTE Professor Georgii Vladimirovich Rozenberg, Doctor of Physical and Mathematical Sciences, has been Chief of the Section on Atmospheric Optics of the Institute of Physics of the Atmosphere, Academy of Sciences of the USSR, since 1956. His field of specialization is theoretical and experimental investigations in the field of the optics of nonhomogeneous media. His principal studies relate to the theory of light propagation in a scattering medium (general formulation of the transfer equation with allowance for the effects of polarization of light, the optical properties of thick layers of a scattering medfum, spectroscopic study of dispersive media), experimental and theoretical investigations of polarization effects during the scattering of light. and experimental and theoretical investigations in atmospheric optics (especially the development of optical methods for investigating the atmosphere and interference phenomena in thin films). Born in Smolensk in 1914. he holds degrees in optics and theoretical physics from Moscow State University. Initially. he worked at the Physics Institute. Academy of Sciences. under Professor G. S. Landsberg. From 1946 to 1961. he was senior scientific editor of the journal Uspekhi FizicheskikhNauk (Soviet Physics - Uspekhi). Professor G. V. Ro~enberg is the author of two other books: "Optika tonkosloinykh pokrytii" (Optics of Thin Films), published in 1958; and ftprozhektornyi luch v atmosfere- (Searchlights in the Atmosphere), publislied in collaboration with a group of specialists in 1960. viii
CONTENTS Introduction..... 1 CHAPTER I. Survey of Observational Results... 5 1. Some Properties of the Daytime Sky... 5 2. The Twilight Phenomenon. 17 3. Spectrophotometry of the Twilight Sky. 23 4. Polarimetry of the Twilight Sky. 46 CHAPTER II. Structure and Optics of the Atmosphere.. 59 1. Some Structural Properties of the Atmosphere.. 59 2. Basic Optical Properties of a Turbid Medium 77 3. Atmospheric Optics. 99 CHAPTER III. Principles of the Twilight Theory 125 1. The Geometry of Sunlight 125 2. Single Scattering of Sunlight by the Atmosphere. 151 3. The Air-Mass Problem. 155 4. Anomalous Transparency and the Reversal Effect. 165 5. Attenuation of the S un at Twilight 179 CHAPTER IV. The Anatomy of Twilight Phenomena. 199 1. A First Approximation 199 2. The Twilight Layer and Twilight Ray 202 3. Twilight Phases and the Effective Shadow Boundary 209 4. Atmospheric Inhomogeneities and the Logarithmic Brightness Gradient 219 5. Dispersion in Effective Shadow Heights and the Color of the Twilight Sky. 236 6. Multiple Scattering..... 249 7. Deep Twilight and Nightfall 271 CHAPTER V. The Inverse Theory: Twilight Sounding of the Mesosphere 275 1. Formulation of the Problem............ 275 ix