Corr. member Peter Velinov, Bulgarian Academy of Sciences, Sofia
Corr. member Georgi Nestorov, Bulgarian Academy of Sciences, Sofia
Prof. DSc Lev Dorman, IZMIRAN Russian AS, Moscov/Tel Aviv University, Israel


This is the first monography in the world which investigates and takes an all-round view ofimportant problem of cosmic ray interaction with the ionosphere and atmosphere.

This international monograph deals with the investigations made by the authors on the influence of cosmic rays of galactic and solar origin and of the corspuscular fluxes on the lower and middle ionosphere. This is a comparatively new and promising branch of the currently buoyantly developing complex science of solar-terrestrial influences. The methods of analysing the interactions between cosmic rays and the upper atmosphere, as described in the monograph, make it possible to pass from measurable parameters to numerical evaluations of a number of quantities in the Earth's environment, which is based on the high of the ionosphere to space phenomena. On the other hand, the analysis of the variations and disturbances of solar and galactic origin provide the possibility of numerical determination of certain basic parameters of the lower ionosphere and the examination of their important influence on the propagation of radio waves.

The monograph is divided into seven chapters.

Chapter One contains a brief historical review of the discovery of the ionosphere, of cosmic rays, and the emergence of the problem of the inter - action between them. The more important results of this problem and its state are reviewed. The cosmic ray layer that lies in the lowest part of the D-region and is created by cosmic rays is defined, and the tasks and aims of the monograph are formulated which border on the physics of the ionosphere, the physics of cosmic rays and atomic physics.

That is why the Second Chapter contains basic information about cosmic rays, the upper atmosphere and their interaction, as necessary for the elaboration of the entire problem. The variations of cosmic rays, the methods of their investigation, their classification, as well as some data about the atmosphere at the height of the cosmic ray layer are briefly discussed.

The basic interaction between cosmic rays and the upper atmosphere is discussed, and it is demonstrated that in the region of the cosmic ray layer (50 - 90 km) the nuclear interactions may be neglected in a first approxi - mation, and that the electromagnetic interactions remain as the most important ones. The basic principles and the formulae about the ionization losses of charged particles are presented.

On their basis a number of expressions are worked out in Chapter Three about the electron production rate q(h) of the galactic cosmic rays in the lower ionosphere, with calculation of the profiles q(h) for different geomagnetic latitudes during the summer and winter seasons, under maximum and minimum solar activity. Formulae are derived for the ionisation capacity of cosmic rays, as well as a survey is made of the planetary distribution of q(h) and of the energy balance of the cosmic ray layer. An equation for the q(h) variations is obtained, on the basis of which they are classified into three classes which are analogous to the cosmic ray variations: First Class - variations of atmospheric origin, Second Class - variations of magnetospheric origin, Third Class - variations of cosmic origin. The concept of effective geomagnetic rigidity is introduced and the effect of penumbra of the cosmic rays at the height of the cosmic ray layer examined.

The electron production rate in the cosmic ray layer under the influence of secondary cosmic rays is calculated.

Chapter Four examines the physico-chemical processes in the lower ionosphere, presenting the main ionisation processes, the charge transfer, the ion-atomic exchange and neutralisation in accordance with the contemporary concepts about the composition of the upper atmosphere. Equations are derived for the electron balance, for the negative ion-electron ratio l and for the effective recombination coefficient α’. On that basis the height distribution and the temporary variations of the most important cosmic ray layer parameter - the electron density N(h) - are examined. The role of the cosmic ray layer at Sunrise is shown, and it is established that cosmic ray ionisation in the upper atmosphere together with the quick variations of the factor l under the action of solar radiation in the optic spectrum have their influence on the structure and of the entire D-region at Sunrise.

This analysis has been checked on the basis of data about the ionospheric absorption L of long waves. A relation is found between the variations of q(h) and L, from which it follows that the absorption of radio waves comes as an indicator for the variations and disturbances in the cosmic ray layer. The behaviour of the cosmic ray layer during the main corpuscular and electromagnetic disturbances is examined. Modulation effects - Forbush effects (decrease of the cosmic ray intensity during geomagnetic storms) - and the 27-day variations in the cosmic ray layer, connected with the 27-day modulation of solar activity and generation effects - the influence of the solar cosmic rays upon the lower ionosphere are put in the group of the first. Disturbances during solar flares and the behaviour of the cosmic ray layer during Sun eclipses are related to the electromagnetic disturbances. Certain concrete cases are interpreted upon examining all these problems, and the relevant quantitative evaluations of the essential parameters are made.

In Chapter Five the ionisation of the solar cosmic rays in the ionosphere is examined. At the beginning the effect of the relativistic solar cosmic rays is considered, which influence the cosmic ray layer of the whole planet. A more complicated and important problem here is the influence of the non-relativistic solar cosmic rays on the polar ionosphere (the polar cap absorption (PCA) event). After a brief report on the state of this problem, a number of approximate solutions for q(h)-profiles are given, as well as solutions based on the range-energy ratio. After that the exact formulae for q(h) are derived from the different kinds of solar particles, account being also taken of the sphericity of the Earth. The influence of the solar cosmic rays' parameters and theEarth's environment on the q(h)-profiles is investigated, too.

The solutions for q(h) for a different pitch angle distribution of the particles in the upper hemisphere are given: completely anisotropic (at the starting moment of the PCA-effect), a general case and an isotropic penetration of the solar cosmic rays which embraces the larger part of PCA. Some of the other factors of the solar cosmic rays - as the spectrum, composition, time variations are also discussed, as well as factors of the Earth's environment - the atmospheric, geomagnetic and electric cut-off, which influence the q(h)-distribution. At the end of Chapter Five analytical and numerical solutions are given for the dissipation of the particle energy in the polar atmosphere.

In the Sixth Chapter the electronic concentration N(h) and the absorption of radio waves as a result of the solar cosmic rays penetration are reviewed. An analysis is also made of a number of individual cases of proton flare. The comparison of the additional rate of electronic production, calculated by two independent methods - by means of data from the ionospheric absorption, and from the cosmic rays, shows satisfactory coincidence. The coefficient of the losses ψ = α’(1+l) in the lower ionosphere is determined by using data of the ionospheric disturbances during PCA. The profiles of electron concentration N(h) and of radio-wave absorption are calculated for different spectra of the solar cosmic rays, both model and real ones - as obtained at the analysis of separate PCA-effects. Here the expected values of absorption harmonise well with the experiment. At the end of the Sixth Chapter a method is presented for determining the parameters of the solar cosmic rays by ionospheric data, i. e., a solution of the reverse task, this being of essential practical significance.

The Seventh Chapter examines the influence of the softer corpuscular radiations upon the lower ionosphere of middle latitudes. The ionisation of the corpuscular fluxes in the night ionosphere at heights of under 90 km (D-region) and in the region of 90 - 120 km (E-layer) is analysed.

A study is made of the influence of the corpuscular fluxes during geomagnetic disturbances under day conditions and of the development of ionisation processes on height - from the upper to the lower ionosphere. The behaviour of processes within the cycle of solar activity is shown.

The role of the corpuscular fluxes in the lower ionosphere under calm circumstances is shown, when they determine the initial ionisation at Sunrise. At the end a number of practical results are presented from the study of radio communications in a broad frequency range.