Measurements of quasi-static electric fields between 3 and 7 Earth radii on GEOS-1

Quasi-static electric fields have been measured with two spherical probes supported by cable booms providing a baseline of 42 m for the measurement. The performance of the experiment is outlined to demonstrate that electric fields can be measured with accuracies of ±0.7 mV m^-1 and ±1.0 mV m^-1 in the dawn-dusk and satellite-sun directions respectively. These uncertainties can be considerably reduced under favourable plasma conditions. Examples of typical observations are described.

1. The average electric field is always characterized by an irregular structure with time scales 0.5–5 min and with amplitudes of a few mV m^-1.
2. During substorms dawn-dusk electric fields up to 20–30 mV m^-1 have been observed over intervals of 30–60 s.
3. Oscillating electric fields with peak-to-peak amplitudes up to 10 mV m^-1 and periods of 3–10 min have been observed following magnetospheric disturbances.

The observations are discussed in terms of plasma motions and possible spatial scale sizes of the phenomena, standing magnetospheric wave modes and electrostatic potentials.     

Auroral Substorms: Search for Processes Causing the Expansion Phase in Terms of the Electric Current Approach

Auroral substorms are mostly manifestations of dissipative processes of electromagnetic energy. Thus, we consider a sequence of processes consisting of the power supply (dynamo), transmission (currents/circuits) and dissipations (auroral substorms-the end product), namely the electric current line approach. This work confirms quantitatively that after accumulating magnetic energy during the growth phase, the magnetosphere unloads the stored magnetic energy impulsively in order to stabilize itself. This work is based on our result that substorms are caused by two current systems, the directly driven (DD) current system and the unloading system (UL). The most crucial finding in this work is the identification of the UL (unloading) current system which is responsible for the expansion phase. A very tentative sequence of the processes leading to the expansion phase (the generation of the UL current system) is suggested for future discussions.

1. (1)
   The solar wind-magnetosphere dynamo enhances significantly the plasma sheet current when its power is increased above \(10^{18}~\mbox{erg}/\mbox{s}\) (\(10^{11}\) w).
    
2. (2)
   The magnetosphere accumulates magnetic energy during the growth phase, because the ionosphere cannot dissipate the increasing power because of a low conductivity. As a result, the magnetosphere is inflated, accumulating magnetic energy.
    
3. (3)
   When the power reaches \(3\mbox{--}5\times 10^{18}~\mbox{erg}/\mbox{s}\) (\(3\mbox{--}5\times 10^{11}\) w) for about one hour and the stored magnetic energy reaches \(3\mbox{--}5\times10^{22}\) ergs (\(10^{15}\) J), the magnetosphere begins to develop perturbations caused by current instabilities (the current density \({\approx}3\times 10^{-12}~\mbox{A}/\mbox{cm}^{2}\) and the total current \({\approx}10^{6}~\mbox{A}\) at 6 Re). As a result, the plasma sheet current is reduced.
    
4. (4)
   The magnetosphere is thus deflated. The current reduction causes \(\partial B/\partial t > 0\) in the main body of the magnetosphere, producing an earthward electric field. As it is transmitted to the ionosphere, it becomes equatorward-directed electric field which drives both Pedersen and Hall currents and thus generates the UL current system.
    
5. (5)
   A significant part of the magnetic energy is accumulated in the main body of the magnetosphere (the inner plasma sheet) between 4 Re and 10 Re, because the power (Poynting flux \([ \boldsymbol{E} \times \boldsymbol{B} ])\) is mainly directed toward this region which can hold the substorm energy.
    
6. (6)
   The substorm intensity depends on the location of the energy accumulation (between 4 Re and 10 Re), the closer the location to the earth, the more intense substorms becomes, because the capacity of holding the energy is higher at closer distances. The convective flow toward the earth brings both the ring current and the plasma sheet current closer when the dynamo power becomes higher.
    

This proposed sequence is not necessarily new. Individual processes involved have been considered by many, but the electric current approach can bring them together systematically and provide some new quantitative insights.

     

Substorm aspects of magnetic pulsations

The different types of magnetic pulsations occurring during magnetospheric substorms are analysed into the concept of polar substorms recently described in detail by Akasofu (1968). Special attention is thus paid, to the simultaneous occurrence of different types of micropulsations at different places around the earth, during the development of a substorm. Time lags between the appearance of micropulsations and other geophysical effects of the substorm are of fundamental importance in this respect. Relationships between the occurrence or spectral shape of micropulsations and the state of the magnetosphere, as determined by satellite measurements are also of interest. Recent theoretical studies about the origin of these micropulsations are reviewed: natural h.m. emissions are directly linked to the thermal plasma density, the high energetic particle fluxes and pitch angle distributions in the far magnetosphere (L 5–8). We can thus expect to be able to deduce some information about the changes of these quantities during substorms. New semi-quantitative work is reported, which tries to interpret the repetitive structure of SIP events in terms of thickness of the magnetospheric tail, and the frequency drift of IPDP's in terms of magnetospheric electric fields. The present knowledge about absorption and dispersion of hydromagnetic waves through the ionosphere or inside the submagneto-ionospheric guide is also stated, because not taking these effects into account could lead to misinterpretation of the data.     

Dynamic phenomena in the visible layers of sunspots

The empirical properties of the various dynamic phenomena are reviewed and interrelated with emphasis on recent observational results. The topics covered are:

1. Introduction
2. Aperiodic Phenomena
3. Externally Driven Phenomena
4. Umbral Flares
5. Inverse Evershed Flow
6. Internally Driven Phenomena
7. Penumbra
8. Penumbral Grains
9. Evershed Flow
10. Umbra
11. Umbral Dots
12. Inhomogeneity of the Umbral Magnetic Field
13. Umbral Turbulence
14. Oscillations and Waves
15. Chromosphere
16. Umbra: Oscillations and Flashes
17. Penumbra: Running Waves and Dark Puffs
18. Photosphere
19. Overview

It is proposed from the observations that umbral dots and penumbral grains are essentially the same phenomenon, and that the observational goal of highest priority with respect to both the origin of the periodic phenomena and the problem of the missing heat flux is to better determine the nature of these elementary bright features.     

Ion Acceleration and Outflow from Mars and Venus: An Overview

Solar wind forcing of Mars and Venus results in outflow and escape of ionospheric ions. Observations show that the replenishment of ionospheric ions starts in the dayside at low altitudes (??300?C800 km), ions moving at a low velocity (5?C10 km/s) in the direction of the external/ magnetosheath flow. At high altitudes, in the inner magnetosheath and in the central tail, ions may be accelerated up to keV energies. However, the dominating energization and outflow process, applicable for the inner magnetosphere of Mars and Venus, leads to outflow at energies ??5?C20 eV. The aim of this overview is to analyze ion acceleration processes associated with the outflow and escape of ionospheric ions from Mars and Venus. Qualitatively, ion acceleration may be divided in two categories:

1. Modest ion acceleration, leading to bulk outflow and/or return flow (circulation).
2. Acceleration to well over escape velocity, up into the keV range.

In the first category we find a processes denoted ??planetary wind??, the result of e.g. ambipolar diffusion, wave enhanced planetary wind, and mass-loaded ion pickup. In the second category we find ion pickup, current sheet acceleration, wave acceleration, and parallel electric fields, the latter above Martian crustal magnetic field regions. Both categories involve mass loading. Highly mass-loaded ion energization may lead to a low-velocity bulk flow??A consequence of energy and momentum conservation. It is therefore not self-evident what group, or what processes are connected with the low-energy outflow of ionospheric ions from Mars. Experimental and theoretical findings on ionospheric ion acceleration and outflow from Mars and Venus are discussed in this report.     

Augmented Empirical Models of Plasmaspheric Density and Electric Field Using IMAGE and CLUSTER Data

Empirical models for the plasma densities in the inner magnetosphere, including plasmasphere and polar magnetosphere, have been in the past derived from in situ measurements. Such empirical models, however, are still in their initial phase compared to magnetospheric magnetic field models. Recent studies using data from CRRES, Polar, and Image have significantly improved empirical models for inner-magnetospheric plasma and mass densities. Comprehensive electric field models in the magnetosphere have been developed using radar and in situ observations at low altitude orbits. To use these models at high altitudes one needs to rely strongly on the assumption of equipotential magnetic field lines. Direct measurements of the electric field by the Cluster mission have been used to derive an equatorial electric field model in which reliance on the equipotential assumption is less. In this paper we review the recent progress in developing empirical models of plasma densities and electric fields in the inner magnetosphere with emphasis on the achievements from the Image and Cluster missions. Recent results from other satellites are also discussed when they are relevant.     

Evolution of the Moon: The 1974 model

The geology of the decade of Apollo and Luna probably will become one of the fundamental turning points in the history of all science. For the first time, the scientists of the Earth have been presented with the opportunity to interpret their home planet through the direct investigations of another. Mankind can be proud and take heart in this fact. The interpretive evolution of the Moon can be divided now into seven major stages beginning sometime near the end of the formation of the solar system. These stages and their approximate durations in time are as follows:

1. The Beginning — 4.6 billion years ago.
2. The Melted Shell — 4.6–4.4 billion years ago.
3. The Cratered Highlands — 4.4–4.1 billion years ago.
4. The Large Basins — 4.1–3.9 billion years ago.
5. The Light-colored Plains — 3.9–3.8 billion years ago.
6. The Basaltic Maria — 3.8–3.0 (?) billion years ago.
7. The Quiet Crust — 3.0 (?) billion years ago to the present.

The Apollo and Luna explorations that permit us to study these stages of evolution each have contributed in progressive and significant ways. Through them we now can look with new insight into the early differentiation of the Earth, the nature of the Earth's protocrust, the influence of the formation of large impact basins in that crust, the effects of early partial melting of the protomantle and possibly the earliest stages of the breakup of the protocrust into continents and ocean basins.     

Solar wind interaction with comets

The planned missions to Comet Halley, which will arrive at the nearest space of the Sun in 1986, have recently revived interest in studying solar wind interaction with comets. Several unsolved problems exist and the most urgent of them are as follows:

1. The character of the solar wind interaction with comets: bow shocks and contact surface formation near comets; similarities and differences of solar- wind interaction with comets and with Venus. The differences are probably associated with a great extension of neutral atmospheres of comets (due to a practical lack of cometary gravitation) and the ‘loading’ of the solar wind flux by cometary ions during the interaction.
2. The anomalous ionization in cometary heads.
3. The problem of the anamalously high accelerations of ions in the plasma tails of comets.
4. The variability of plasma structures observed in cometary tails.

     

The atmosphere of Venus

The investigations of Venus take a special position in planetary researches. It was just the atmosphere of Venus where first measurements in situ were carried out by means of the equipment delivered by a space probe (Venera 4, 1967). Venus appeared to be the first neighbor planet whose surface had been seen by us in the direct nearness made possible by means of the phototelevision device (Venera 9 and Venera 10, 1975). The reasons for the high interest in this planet are very simple. This planet is like the Earth by its mass, size and amount of energy obtained from the Sun and at the same time it differs sharply by the character of its atmosphere and climate. We hope that the investigations of Venus will lead us to define more precisely the idea of complex physical and physical-chemical processes which rule the evolution of planetary atmospheres. We hope to learn to forecast this evolution and maybe, in the far future, to control it. The last expeditions to Venus carried out in 1978 — American (Pioneer-Venus) and Soviet (Venera 11 and 12) — brought much news and it is interesting to sum up the results just now. The contents of this review are:

1. The planet Venus — basic astronomical data.
2. Chemical composition.
3. Temperature, pressure, density (from 0 to 100 km).
4. Clouds.
5. Thermal regime and greenhouse effect.
6. Dynamics.
7. Chemical processes.
8. Upper atmosphere.
9. Origin and evolution.
10. Problems for future studies

Here we have attempted to review the data published up to 1979 and partly in 1980. The list of references is not exhaustive. Publications of special issues of magazines and collected articles concerning separate space expeditions became traditional last time. The results obtained on the Soviet space probes Venera 9, 10 (the first publications) are collected in the special issues of Kosmicheskie issledovanija (14, Nos. 5, 6, 1975), analogous material about Venera 11, 12 is given at Pis'ma Astron. Zh. (5, Nos. 1 and 5, 1978), and in Kosmicheskie issledovanija (16, No. 5, 1979). The results of Pioneer-Venus mission are represented in two Science issues (203, No. 4382; 205, No. 4401) and special issue of J. Geophys. Res. (1980). We shall mention some articles to the same topic among previous surveys: (Moroz, 1971; Sagan, 1971; Marov, 1972; Hunten et al., 1977; Hoffman et al., 1977) and also the books by Kuzmin and Marov (1974) and Kondrat'ev (1977). Some useful information in the part of ground-based observations may be found in the older sources (for example, Sharonov, 1965; Moroz, 1967). For briefness we shall use as a rule the abbreviations of space missions names: V4 instead of Venera 4, M10 instead of Mariner 10 and so on. The first artificial satellites of Venus in the world (orbiters Venera 9 and 10) we shall mark as V9-O, V10-O unlike the descent probes V9, V10. Fly-by modules of Venera 11 and Venera 12 we shall mark as V11-F and V12-F. Pioneers descent probes — Large (Sounder), Day, Night and North — will be marked as P-L, P-D, P-Ni, P-No, orbiter as P-O, and bus as P-B.     

The Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) NASA Mission-of-Opportunity

Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) is a NASA Explorer Mission-of-Opportunity to stereoscopically image the Earth’s magnetosphere for the first time. TWINS extends our understanding of magnetospheric structure and processes by providing simultaneous Energetic Neutral Atom (ENA) imaging from two widely separated locations. TWINS observes ENAs from 1–100 keV with high angular (～4°×4°) and time (～1-minute) resolution. The TWINS Ly-α monitor measures the geocoronal hydrogen density to aid in ENA analysis while environmental sensors provide contemporaneous measurements of the local charged particle environments. By imaging ENAs with identical instruments from two widely spaced, high-altitude, high-inclination spacecraft, TWINS enables three-dimensional visualization of the large-scale structures and dynamics within the magnetosphere for the first time. This “instrument paper” documents the TWINS design, construction, calibration, and initial results. Finally, the appendix of this paper describes and documents the Southwest Research Institute (SwRI) instrument calibration facility; this facility was used for all TWINS instrument-level calibrations.     

Energy coupling between the solar wind and the magnetosphere

This paper describes in detail how we are led to the first approximation expression for the solar wind-magnetosphere energy coupling function , which correlates well with the total energy consumption rate U _T of the magnetosphere. It is shown that is the primary factor which controls the time development of magnetospheric substorms and storms. The finding of this particular expression indicates how the solar wind couples its energy to the magnetosphere; the solar wind and the magnetosphere constitute a dynamo. In fact, the power P generated by the dynamo can be identified as by using a dimensional analysis. Furthermore, the finding of indicates that the magnetosphere is closer to a directly driven system than to an unloading system which stores the generated energy before converting it to substorm and storm energies. Therefore, the finding of and its implications have considerably advanced and improved our understanding of magnetospheric processes. The finding of has also led us to a few specific future problems in understanding relationships between solar activity and magnetospheric disturbances, such as a study of distortion of the solar current disk and the accompanying changes of . It is also pointed out that one of the first tasks in the energy coupling study is an improvement of the total energy consumption rate U _T of the magnetosphere. Specific steps to be taken in this study are suggested.     

Electric Fields and Magnetic Fields in the Plasmasphere: A Perspective From CLUSTER and IMAGE

The electric field and magnetic field are basic quantities in the plasmasphere measured since the 1960s. In this review, we first recall conventional wisdom and remaining problems from ground-based whistler measurements. Then we show scientific results from Cluster and Image, which are specifically made possible by newly introduced features on these spacecraft, as follows. 1. In situ electric field measurements using artificial electron beams are successfully used to identify electric fields originating from various sources. 2. Global electric fields are derived from sequences of plasmaspheric images, revealing how the inner magnetospheric electric field responds to the southward interplanetary magnetic fields and storms/substorms. 3. Understanding of sub-auroral polarization stream (SAPS) or sub-auroral ion drifts (SAID) are advanced through analysis of a combination of magnetospheric and ionospheric measurements from Cluster, Image, and DMSP. 4. Data from multiple spacecraft have been used to estimate magnetic gradients for the first time.     

Why space physics needs to go beyond the MHD box

Magnetohydrodynamic (MHD) theory has been used in space physics for more than forty years, yet many important questions about space plasmas remain unanswered. We still do not understand how the solar wind is accelerated, how mass, momentum and energy are transported into the magnetosphere and what mechanisms initiate substorms. Questions have been raised from the beginning of the space era whether MHD theory can describe correctly space plasmas that are collisionless and rarely in thermal equilibrium. Ideal MHD fluids do not induce electromotive force, hence they lose the capability to interact electromagnetically. No currents and magnetic fields are generated, rendering ideal MHD theory not very useful for space plasmas. Observations from the plasma sheet are used as examples to show how collisionless plasmas behave. Interpreting these observations using MHD and ideal MHD concepts can lead to misleading conclusions. Notably, the bursty bulk flows (BBF) with large mean velocities left(〈 v 〉≥400 km s right) that have been interpreted previously as E×B flows are shown to involve much more complicated physics. The sources of these nonvanishing 〈 v 〉 events, while still not known, are intimately related to mechanisms that create large phase space gradients that include beams and acceleration of ions to MeV energies. The distributions of these nonvanishing 〈 v 〉 events are associated with large amplitude variations of the magnetic field at frequencies up to and exceeding the local Larmor frequency where MHD theory is not valid. Understanding collisionless plasma dynamics such as substorms in the plasma sheet requires the self-consistency that only kinetic theory can provide. Kinetic modeling is still undergoing continual development with many studies limited to one and two dimensions, but there is urgent need to improve these models as more and more data show kinetic physics is fundamentally important. Only then will we be able to make progress and obtain a correct picture of how collisionless plasmas work in space.     

Particle code simulations with injected particles

As problems we are interested in become more complex, we often find our simulations stretching the limits of available computer resources. For example, an interesting problem is simulation of dissipation processes in sub-critical collisionless shocks. To simulate this system our simulation box must contain the shock and its upstream and downstream regions over the entire length of a run. If the shock moves with any appreciable speed the box must then be considerably larger than the shock thickness making it hard to resolve the shock front itself with a reasonable number of grid points. A solution to this problem is to run the simulation in the frame of reference of the shock. Particles are injected upstream of the shock and leave the simulation box downstream. With the shock stationary in the simulation box, we only need to contain enough of the up and downstream regions for the fields, etc., to settle down and separate the shock from the box boundaries. In this tutorial we consider some basic algorithms used in a practical particle injection code, such as the two dimensional WAVE code used at Los Alamos. We will try to present these ideas in a simple format general enough to be easily included in any particle code. Topics covered are:

1. Smoothly Injecting Particles.
2. Generating the Distribution Functions.
3. Time Dependent Injection Density.
4. Boundary Conditions on Fields and Particles.

(Flux and Charge Conservation)     

A strategy for investigation of the outer solar system

The requirements of systematic exploration of the outer solar system have been intensively studied by a Science Advisory Group (SAG) of consulting scientists for the National Aeronautics and Space Administration (NASA). Comets and Asteroids were excluded from this study, as a separate group is planning missions to these bodies. This paper and accompanying articles on specific related scientific subjects written by members of the SAG, summarize the findings and recommendations of this group. These recommendations should not be interpreted as official NASA policy. Following some general introductory remarks, a brief sketch is given of the development and current status of scientific missions to the inner planets by the U.S. and the U.S.S.R. With this perspective, the development of the U.S. program for investigation of the outer solar system is described. The scientific focus of outer solar system exploration has been studied in detail. The relationship of the outer planetary bodies to one another and to the inner planets, as parts in a unified solar system evolved from a primitive solar nebula, is emphasized. Deductions from outer solar system investigations regarding the conditions of the solar nebula at the time of planetary formation have been considered. Investigations have been proposed that are relevant to studies of the atmospheric structure and dynamics, internal structure of the planets, satellite composition and morphology, and planetary and interplanetary fields and energetic particles. The mission type and sequence required to conduct a systematic exploration of the outer solar system has been developed. Technological rationales for the suggested missions are discussed in general terms. The existing NASA program for outer solar system exploration is comprised of four missions:

1. Pioneer 10 fly-by mission to Jupiter and beyond, currently underway, with launch on 3 March 1972;
2. Pioneer G, intended for a similar mission with planned launch 2–22 April 1973; and
3. Two Mariner Jupiter/Saturn fly-bys in 1977, with experiment selection scheduled for late 1972 and detailed engineering design during 1972–74.

The Science Advisory Group advocates that detailed mission planning be undertaken on the following additional missions for launches during the late 1970's and early 1980's. Together with existing plans, these would provide a balanced, effective exploration program.

1. 1976 Pioneer Jupiter/Out-of-Ecliptic (One Mission)
2. 1979 Mariner Jupiter/Uranus Fly-bys (Two Missions)
3. 1979 Pioneer Entry Probe to Saturn 1980 Pioneer Entry Probe to Uranus via Saturn Fly-by (Three Missions)
4. 1981/1982 Mariner Jupiter Orbiter (Two Missions).

     

A Multiscale Model for Substorms

Most substorm researchers assume substorms to be caused by a unique large-scale process. However, a critical evaluation of substorm observations indicates that a new paradigm is needed to understand the substorm phenomenon and the magnetospheric dynamics in general. It is proposed here that substorms involve a number of physical processes covering over a wide range of spatial and temporal scales. Potential candidates include the kinetic or shear ballooning instability, the Kelvin-Helmholtz instability, the cross-field current instability, the tearing instability, and magnetic reconnection. An observational constraint on the qualified process for substorm onset is that it must be associated with magnetic field lines of auroral arcs since substorm onsets start with brightening of a pre-existing auroral arc. Which particular process dominates in a given substorm depends on the present and past states of the magnetosphere as well as the external solar wind. The magnetosphere is almost perpetually driven by the solar wind to be near a critical point and in a metastable state. Magnetospheric disturbances occur sporadically in multiple localized sites. A substorm is realized when the combined effect of these localized disturbances become global in extent, much like the system-wide activity in a sandpile or avalanche model.     

The magnetogram inversion technique: Applications to the problem of magnetospheric substorms

The magnetogram inversion technique (MIT) is based upon recordings of geomagnetic variations at the worldwide network of ground-based magnetometers. MIT ensures a calculation of a global spatial distribution of the electric field, currents and Joule heating in the ionosphere. Variant MIT-2 provides, additionally, continuous monitoring of the following parameters: Poynting vector flux from the solar wind into the magnetosphere (); power, both dissipated and accumulated in the magnetosphere; magnetic flux in the open tail; and the magnetotail length (l _T) (distance between the dayside and nightside neutral points in the Dungey model). Using MIT-2 and data of direct measurements in the solar wind, an analysis is made of a number of substorms, and a new scenario of substorms is suggested. The scenario includes the convection model, the model with a neutral line and the model of magnetosphere-ionosphere coupling (outside the current sheet), i.e., the three known models. A brief review is given of these and some other substorms models. A new element in the scenario is the strong positive feedback in the primary generator circuit, which ensures growth of the ratio = / _Aby an order of magnitude or more during the substorms. Here _Ais the Pointing vector flux in the Akasofu-Perrault approximation, i.e., without the feedback taken into account. The growth of during the substorm is caused only by the feedback effect. It is assumed that the feedback arises due to an elongation of the magnetotail, i.e., a growth of l _Tby a factor of (23) during the substorm.In the active phase of substorm, a part (the first active phase) has been identified, where the principal role in the energetics is played by the feedback mechanism and the external energy source (although the internal source plus reconnection inside the plasma sheet make a marked contribution). In the second active phase (expansion) the external generator (solar wind) is switched off, and the main role is now played by the internal energy source (the tail magnetic field and ionospheric wind energy).Models of DP-2 DP-1 transitions are also considered, as well as the magnetospheric substorm-solar flare analogy.     

A New Morphology of Solar Activity and Recurrent Geomagnetic Disturbances: The Late-Declining Phase of the Sunspot Cycle

Certain aspects of the Sun and resulting geomagnetic disturbances can be studied better on the source surface, an imaginary spherical surface of 3.5 solar radii, than on the photospheric surface. This paper presents evidence that the Sun exhibits one of the most fundamental aspects of activities most clearly during the late-declining phase of the sunspot cycle. It is the period when 27-day average values of the solar wind speed and of geomagnetic disturbances tend to be highest during the sunspot cycle. Important findings of this study on the late-declining phase of the sunspot cycle are the following:

1. By introducing a new coordinate system, modifying the Carrington coordinates, it is shown that various solar activity phenomena, solar flares, the brightest coronal regions, and also the lowest solar wind speed region, tend to concentrate in two quadrants, one around 90^° in longitude in the northern hemisphere (NE) and the other around 270^° in longitude in the southern hemisphere (SW). For this reason, the new coordinate system is referred to as the NESW coordinate system.
2. It is shown that the above results are closely related to the fact that the neutral line exhibits a single wave (sinusoidal or rectangular) in both the Carrington coordinates and the NESW coordinate system during the late-declining phase. The shift of the neutral line configuration during successive solar rotations during the late-declining phase causes longitudinal scatter of the location of solar flares with respect to the neutral line in a statistical study. The NESW coordinate system is designed to suppress the shift, so that the single wave location is fixed and thus a ‘nest’ of solar flares emerges in the NE and SW quadrants.
3. It is also shown that the single wave is the source of the double peak of the solar wind speed and two series of recurrent geomagnetic disturbances in each solar rotation, making the 27-day average solar wind and geomagnetic disturbances highest during the sunspot cycle. The double peak is a basic feature during the late-declining phase, but is obscured by several complexities which we identified in this paper; see item 8.
4. The single wave of the neutral line configuration can be approximated by three dipole fields, one which can be represented by a central dipole (parallel or anti-parallel to the rotation axis) and two hypothetical dipoles on the photosphere. This configuration is referred to as the triple dipole model.
5. The location of the two hypothetical photospheric dipoles coincide with the two active regions (solar flares, the brightest coronal region) and also the lowest solar wind speed region in the NESW coordinate system; the lowest solar wind regions are the cause of the valleys of the double peak of the solar wind speed.
6. The two hypothetical dipole fields actually do exist at the location of the two active regions in a coarse magnetic map (5 × 5^°). The two dipoles follow the Hale–Nicholson polarity law. Thus, they are real physical entities.
7. The apparent meridional rotation of the dipolar field on the source surface during the sunspot cycle results from combined changes of both the central dipole field and of the two photospheric dipoles, although the central dipole remains axially parallel or anti-parallel. Thus, the Sun has a general field that can be represented by an axially aligned dipole located at the center of the Sun throughout the sunspot cycle, except for the sunspot maximum period when the polarization reversal occurs.
8. The complexity of recurrent geomagnetic disturbances can also be understood by having the NESW coordinate system for various solar phenomena and the relative location of the earth with respect to the solar equatorial plane.
9. As the intensity of the two dipoles decreases toward the end of the sunspot cycle, the amplitude of the single wave decreases, and the neutral line tends to align with the heliographic equator.
10. The neutral line shows a double wave structure during certain epochs of the sunspot cycle. In such a situation, it can be considered that two NESW coordinate systems are present in one Carrington coordinate, resulting in four active regions.
11. The so-called classical “sector boundary” arises when the peaks (top and bottom) of the single wave reached 90^° in latitude in both hemispheres.
12. In summary: A study of the late-declining period of the sunspot cycle is very important compared with the sunspot maximum period. In the late-declining period, the Sun shows its activities in the simplest form. It is suggested that some of the basic features of solar activities and recurrent geomagnetic disturbances that have been studied by many researchers in the past can be synthesized in a simplest way by introducing the NESW coordinate system and the triple dipole model. There is a possibility that the basic results we learned during the late phase of the sunspot cycle can be applicable to the rest of the sunspot cycle.

     

The SOHO concept and its realisation

The Solar and Heliospheric Observatory (SOHO) — a space observatory to be placed, in 1995, 1.5 Gm sunward from the Earth in a halo orbit around the L1 Lagrange point — will investigate:

the solar corona, its heating and expansion into the solar wind, by both studying the radiation emerging from the outer solar atmosphere and in-situ solar wind measurements near 1 AU, and

the structure and dynamics of the solar interior by the method of helioseismology.

The science policy evolution leading to this comprehensive observatory concept is described. SOHO's link to the space-plasma-physics mission CLUSTER — devoted to the three-dimensional study of small structures in the magnetosphere — within the Solar Terrestrial Science Programme (STSP) and the embedding of STSP in the much larger International Solar Terrestrial Physics (ISTP) Programme are cited as well. The scientific subjects to be addressed by SOHO are introduced, and their current status assessed. Subsequently, the measurements required to advance these subjects are stated quantitatively and the payload, which will actually perform these measurements, is presented. The mission design, comprising spacecraft, orbit, operations and the data and ground systems are described. The special efforts made to obtain a reliable radiometric calibration of the instruments observing the Sun in the extreme-ultraviolet and to achieve a stable sensitivity through extreme cleanliness of spacecraft and instruments are emphasized and substantiated.     

Hard rock cosmic ray archaeology

Recent examinations of extraterrestrial materials exposed to cosmic rays for different intervals of time during the geological history of the solar system have generated a wealth of new information on the history of cosmic radiation. This information relates to the temporal variations in

1. the flux and energy spectrum of low energy (solar) protons of ? 10 MeV kinetic energy;
2. the flux and energy spectrum of (solar) heavy nuclei of Z > 20 of kinetic energy, 0.5–10 MeV/n;
3. the integrated flux of protons and heavier nuclei of ? 0.5 GeV kinetic energy, and
4. the flux and energy spectrum of nuclei of Z > 20 of medium energy — 100–2000 MeV/n kinetic energy.

The above studies are entirely based on the natural detector method which utilises two principal cosmogenic effects observed in rocks, (i) isotopic changes and (ii) changes in the crystalline structure of rock constituents, due to cosmogenic interactions. The information available to date in the field of hard rock cosmic ray archaeology refers to meteorites and lunar rocks/soil. Additional information based on study of cosmogenic effects in man-made materials exposed to cosmic radiation in space is also discussed. It is shown that the natural detectors inspite of their extreme simplicity have begun to provide cosmic ray information in a very quantitative and precise manner comparable to the most sophisticated electronic particle detectors. The single handicap in using the hard rock detectors is however the uncertainty regarding their manner of exposure, geometry etc. At present, a variety of techniques are being used to study the evolutionary history of extraterrestrial materials and as this field grows, uncertainties in cosmic ray archaeology will correspondingly decrease.