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Summary The systematic change in the phase of the first harmonic of the low-latitude DS field of magnetic storms determined by Chapman (1952) and Sugiura & Chapman (1960) is interpreted as being due to westward drift of protons in a partial ring current. It is shown that to account for the statistical average phase shift of the DS field the average energy of the protons must be about 10 ke V.

We report on our observation of pulse-like electromagnetic signals in the frequency range 1∼10 kHz that we associate with earthquakes. The severest difficulty in separating earthquake-associated VLF signals from those originating in lightning discharges stems from the circumstance that the latter signals are overwhelming in number compared with the former. While claims have often been made of observation of electromagnetic signals in association with earthquakes, most of the claims, excepting a few, heavily rely on temporal correlation. By means of simple instrumentation and data processing software, our method by and large enables us to isolate VLF signals whose direction of arrival is well focussed at the epicenter direction. In this preliminary report we present several examples that positively demonstrate the existence of a class of VLF signals having a peak frequency of occurrence 1∼4 days prior to earthquakes of Magnitude 4∼6. With an accumulation of experience the technique described in this paper would seem to offer a promising approach towards earthquake prediction.

Using data from the polar orbiting Dynamic Explorer (DE) −1 and −2 satellites and a ground-based station, we investigated electron precipitation phenomena accompanying Pc 5 pulsations. DE-2 observed oscillatory disturbances in the magnetic and electric fields in the upper ionosphere at the geomagnetic footprint of the high altitude region in which transverse Pc 5 pulsations were detected by DE-1. DE-2 observed electrons precipitating into the ionosphere with energies of several keV to several tens of keV. These electrons were accelerated in the direction of the ambient magnetic field. When Pc 5 pulsations in the H-component and periodic variations of cosmic radio noise absorption (CNA pulsations) were observed at Syowa Station, DE-2 which was in geomagnetic conjunction with Syowa Station also observed oscillatory disturbances in the magnetic and electric fields. These oscillatory disturbances are caused by small-scale field-aligned currents each with width of 0.5°–1.4° invariant latitude. This suggests that Pc 5 pulsations have a small-scale resonance structure in the radial direction. The resonance structure has a small scale comparable to the ion acoustic gyroradius, then kinetic Alfven waves having electric fields parallel to the ambient magnetic field can arise. The parallel electric field generates a field-aligned potential drop of about 3–5 kV. Electrons accelerated by these kinetic Alfven waves would cause CNA pulsations, the phase of which leads that of the H-component of the Pc 5 pulsations by 90° in the southern hemisphere. This is consistent with the observations at Syowa Station.

We present a new global magnetospheric index that measures the intensity of the Earth's ring current through energetic neutral atoms (ENAs). We have named it the Global Energetic Neutral Index (GENI), and it is derived from ENA measurements obtained by the Imaging Proton Spectrometer (IPS), part of the Comprehensive Energetic Particle and Pitch Angle Distribution (CEPPAD) experiment on the POLAR satellite. GENI provides a simple orbit-independent global sum of ENAs measured with IPS. Actual ENA measurements for the same magnetospheric state look different when seen from different points in the POLAR orbit. In addition, the instrument is sensitive to weak ion populations in the polar cap, as well as cosmic rays. We have devised a method for removing the effects of cosmic rays and weak ion fluxes, in order to produce an image of “pure” ENA counts. We then devised a method of normalizing the ENA measurements to remove the orbital bias effect. The normalized data were then used to produce the GENI. We show, both experimentally and theoretically the approximate proportionality between the GENI and the Dst index. In addition we discuss possible implications of this relation. Owing to the high sensitivity of IPS to ENAs, we can use these data to explore the ENA/Dst relationship not only during all phases of moderate geomagnetic storms, but also during quiescent ring current periods.

Three-dimensional magnetic field structure in the inner magnetosphere is statistically analyzed using data obtained by the DE-1 magnetometer. The main results are as follows: (1) The magnetic field structure of the rotational pattern associated with an eastward current is clearly seen in the dayside equatorial region at geocentric distances around 2.5R e but not on the nightside. The current density is approximately 0.0.5μ A/m 2 , and does not show any clear dependence on geomagnetic disturbance, but shows a solar activity dependence which possibly suggests that a substantial part of the closure of the eastward current is through the dayside mid-latitude ionosphere. (2) The azimuthal component of the magnetic field associated with field-aligned currents is seen in the low-latitude magnetosphere. The intensity of this component is about 5 to 10 nT, and has a dependence on geomagnetic activity. (3) Compared with the currently available magnetospheric models, the observed inner magnetospheric magnetic fields have much more complex structures than the models indicate. The necessity of including the field-aligned current system and an eastward current in the models is evident. (4) A noon-midnight asymmetry of the magnetic structure is clearly seen, particularly in the southward component associated with the ring current. The asymmetry is much larger in this meridian than that in the dawn-dusk meridian. This is in contrast with the asymmetry observed on the ground or by low-altitude satellites over the ionosphere.

The paper introduces an angular parameter, termed alpha, which represents the angular difference between the observed, or model, field and the internal model field. The study discusses why this parameter is chosen and demonstrates its usefulness by applying it to both observations and models. In certain areas alpha is more sensitive than delta-B (the difference between the magnitude of the observed magnetic field and that of the earth's internal field calculated from a spherical harmonic expansion) in expressing magnetospheric field distortions. It is recommended to use both alpha and delta-B in comparing models with observations.

The research field of solar-terrestrial physics (STP), with a long and varied history, has undergone in the last fifteen years a minor revolution in understanding as well as in the number of active participants. These changes in the field in the last two decades have come about to a large extent because of the advent in several nations of space programs using rocket and satellite technology and because. of the large amounts of research money that were made available for these programs.

Interactions between Pc5 pulsations and particles are investigated with the magnetic field data obtained by the DE-1 polar orbiting satellite and the precipitating electron data from the DMSP satellites. We found geomagnetic conjunction events of DE-1 and DMSP in which these satellites respectively observed Pc5 pulsations and particle precipitation approximately on the same geomagnetic field lines. The invariant latitude ranges for the observations of Pc5 and precipitation of 3 keV electrons were almost the same. A statistical study also showed that the region of the central plasma sheet obtained by P. T. NEWELL and C.-I. MENG (J. Geophys. Res., 99,273,1994) falls in the region of the occurrence of transverse Pc5 pulsations. The precipitation of electrons having energies greater than 3 keV was investigated. It is shown that there are differences in the characteristics of 30 keV electron precipitation between the cases in which pulsations were observed and those in which pulsations were not observed. These results suggest that electrons are modulated by transverse Pc5 pulsations.

The DE 2 satellite observed electric field fluctuations on the topside of the nighttime midlatitude ionosphere. They extended several hundred kilometers in the latitudinal direction with wavelengths of several tens of kilometers, and their amplitudes were a few millivolts per meter. Such fluctuations were often observed at magnetically conjugate points in the northern and southern hemispheres. These electric field fluctuations are perpendicular to the geomagnetic field. They are not accompanied by any significant plasma depletion or electron temperature variations. Magnetic field fluctuations are sometimes observed simultaneously with electric field fluctuations. We interpret that these fluctuations are caused by field-aligned currents which flow from the ionosphere in one hemisphere to the conjugate point in the other hemisphere. The power spectrum of these midlatitude electric field fluctuations follows a power law of the form Power α ƒ −n, with the spectral index n of 3.5 to 4.5, which is steeper than that of the electric field fluctuations in the high-latitude ionosphere or in the equatorial ionosphere. This phenomenon may be related to other ionospheric phenomena, for example, the F region field-aligned irregularities or spread-F, observed by ground-based methods such as the MU radar, but the relationship is not clear.

Using the magnetic field data obtained by the DE-1 polar orbiting satellite, statistical characteristics of transverse Pc5 pulsations in the inner magnetosphere are examined. The occurrence distribution is found to have a strong dawn/dusk asymmetry. The occurrence is most frequent in the region around 72° invariant latitude (ILAT) between 0800 and 1000MLT. The distribution shifts to lower ILAT both in the early morning and in the afternoon sectors. Our results are generally consistent with the occurrence distributions obtained by previous studies except for appreciable differences in the local time of the peak occurrence. The dependence of the transverse Pc5 occurrence on solar wind velocity is also investigated. Results show that the higher the solar wind velocity, the more frequent the Pc5 occurrence. This fact suggests that the energy source of these Pc5's is in the Kelvin-Helmholtz instability (KHI) on the magnetopause. To explain the strong dawn/dusk asymmetry, the dependence of the Pc5 occurrence on the angle between the solar wind velocity and the IMF in the ecliptic plane is investigated. It is found that this angle controls the magnetic local time of Pc5 appearance when the solar wind velocity is small. This dependence may be explained by the low threshold of KHI due to an influence of a quasi-parallel bow shock.

The global solar ultraviolet-B (UV-B: 290-320 nm) irradiance has been measured by a newly designed band-spectral solar UV-B radiometer at Tokai University, Hiratsuka (35°N, 139°E), Japan from October 1990 to April 1994. The global solar total (Total: 300-3300 nm) irradiance has also been measured by a pyranometer. When the seasonal variation is removed by taking 12-month moving averages, an increase at an average rate of 3.4% per year is found in the monthly averages of daily integrated global solar UV-B irradiance. In contrast, the monthly averages of daily integrated global solar Total irradiance remained nearly constant throughout the same period. The existence of a linear trend over the above time period is confirmed by a statistical method different from the analysis of the moving averages, using the global solar UV-B irradiance normalized by dividing it by the global solar Total irradiance. Corresponding to the increase in the global solar UV-B irradiance, a decrease is found in the total ozone amount measured at Tateno (35°N, 140°E), offering supportive evidence for a direct link between these two parameters

There is generally high correlation between the orthogonal magnetic and electric field perturbations on the ionospheric field-aligned current region based on observations by polar orbiting satellites. The ratio between the magnetic and electric field perturbations, ⊿B_z/μ_oE_x, has a scale-length dependence : the ratio ⊿B_z/μ_oE_x decreases with decreasing scale length. B. FORGET et al.(J. Geophys. Res., 96,1843,1991) explained this scale-length dependence using a static model. In this paper, we compare the ratio ⊿B_z/μ_oE_x observed by the DE-2 satellite for various spatial scales with the effective Pedersen conductivity Σ_ calculated by the method of FORGET et al. The results show that in many cases this model can adequately explain the observed scale-length dependence. However, cases exist in which the difference, ⊿B_z/μ_oE_x-Σ_, decreases at about 0.25-1.0s in temporal scales (2-8km in spatial scales). This behavior is explained as being due to Alfven waves.

The magnetic field and plasma data from 47 passes of DE-2 are used to study the IMF By-dependent distribution of field-aligned currents in the cleft region. It is proposed that the low-latitude cleft current (LCC) region is not an extension of the region 1 or region 2 current system and that a pair of LCCs and high-latitude cleft currents (HCCs) constitutes the cleft field-aligned current regime. The proposed pair of cleft field-aligned currents is explained with a qualitative model in which this pair of currents is generated on open field lines that have just been reconnected on the dayside magnetopause. The electric fields are transmitted along the field lines to the ionosphere, creating a poleward electric field and a pair of field-aligned currents when By is positive; the pair of field-aligned currents consists of a downward current at lower latitudes and an upward current at higher latitudes. In the By negative case, the model explains the reversal of the field-aligned current direction in the LCC and HCC regions.

The universal time (UT) variation in the ap index for the years 1932-1956 and 1957-1986 is analyzed. Results are compared with the UT variation in the Dst index and with that in the rate of energy input into the ring current estimated from the Dst index. It is found that the UT variation of the ap index does not agree with that of the Dst index, but is in agreement with the UT variation in the rate of energy input into the ring current. Results on the seasonal variation of the ap index indicate that the UT variation has mostly a minimum around 1030 UT for different seasons, though the average values have features similar to the well-known semiannual variation in geomagnetic activity. The averaged ap values and the numbers of events of the ap greater than 30, 50, or 100 reach a minimum around 1030 UT or during the UT time interval 0900-1200. These values are anti-correlated with the UT variation of the magnetic flux that would occupy the nightside auroral oval approximated by offset circles in corrected geomagnetic coordinate system. The modulation of E × B drift speed in the magnetosphere by the UT variation of the oval magnetic flux could be the source of the UT variation in the ap and the Dst index.

A new waterproof broadband UVB radiometer was designed to monitor biologically active solar UVB (290-320 nm) irradiance at ground level. Using this radiometer, solar UVB irradiance has been measured, together with UVA (320-400 nm) and Total (300-3300 nm) solar irradiances, for two years from October 1990 to September 1992. The global UVB solar irradiance shows clear seasonal changes, i.e., approximately by factors of 4 and 2 for the ratios of summer to winter and equinox to winter, respectively. In contrast, the seasonal variations in global UVA and Total are very similar and moderate in amplitude, and the corresponding ratios are about 1.7 and 1.3, respectively. Moreover, it is shown that the seasonal variation in the daily global UVB and that in the killing efficiency of sunlight for bacteriophage T1 have a similar pattern. For UVB and Total irradiances, the diffuse component was separately recorded. The monthly average ratio of the diffuse to the global (direct + diffuse) in UVB is persistently high, being about 80% throughout the year. The monthly average ratio of the diffuse to the global in Total solar irradiance was about 50% for the same period. Based on the present observation we found the 24-month average ratios of monthly global UVB/UVA/Total solar irradiance to be 0.14/4.1/100. Increases in the diffuse Total irradiance and in the global UVB irradiance, coupled with a decrease in the global Total irradiance, observed from November 1991 to February 1992 are interpreted as being an influence of the June 1991 eruption of Mt. Pinatubo.

著者人数：15名, Accepted: 1993-06-16, 資料番号: SA1001258000

We have derived on a test basis a geomagnetic index by using presently available data in the southern polar cap. Observatories used here are Scott Base, Dumont d'Urville, Vostok and Mirny. To derive disturbance fields a base value of each station for each month is first calculated using a moving average method, and this base value is subtracted from hourly data from the station in that month. Then after a coordinate transformation the largest and smallest values are selected from the four stations, respectively in the same way as the AU and AL indices are derived, and we call them the polar cap AU and AL indices. The difference between these values gives the polar cap AE index, and we derived these indices for the H and D components and T, the total force of the geomagnetic field for the years 1966 (near solar activity minimum) and 1980 (near solar activity maximum). The results of the variation of the disturbance fields from the four stations show a clear diurnal and seasonal variation depending on distribution of the stations and the ionospheric conductivities in the southern polar cap. We find the highest correlation between the polar cap AE indices and the AE, AU, and AL indices in the local winter, and the correlation decreases in the local summer due to the increase of the ionospheric conductivity in the polar cap caused by solar UV radiation. The relationship between the IMF B_y component and the polar cap AU index during local summer seems to be quadratic. The results indicate that both positive and negative B_y increase the value of the polar cap AU index due to enhancement of the B_y dependent currents in the polar cap.

Results are presented of the first ground-satellite correlation study of ion cyclotron wave events inside geosynchronous orbit. Several intervals are found during which waves at the same frequency were observed simultaneously by the DE 1 Goddard Space Flight Center Fluxgate Magnetometer and by the Air Force Geophysics Laboratory Magnetometer Network. This represents about 33 percent of the intervals during which waves were seen on the ground and DE 1 was in a favorable location (near the geomagnetic equator around L = 4.6) to observe the wave generation region. Three of seven simultaneous events showed a positive correlation when a detailed correlation analysis was performed. Peaks in the the cross-correlation function occurred at delays of 30-100 s and are interpreted as the group delay time of signals from space to the ground station. The small number of events seen in space during conjunction intervals results from the satellite's path missing the source region.

The existence of a sharp break in the power spectrum of AE at about 5 hours is demonstrated. Several possible explanations of the nonlinear response of AE to the IMF Bs driver are briefly discussed, including: variable ionospheric conductivity (increasing with Bs) for the high frequency regime, and several AE saturation mechanisms for the low frequency regime.

The Akebono (EXOS-D) satellite carries triaxial fluxgate and search coil magnetometers with sensors mounted on 5- and 3-m masts, respectively. The fluxgate magnetometer has four automatically switchable ranges from ±1024 to ±65536nT (full scale), and resolutions commensurate with a 16-bit A/D converter in each range (0.031 to 2nT). The rate of sampling is 32 vectors per second. The triaxial search coil magnetometer has a frequency response up to 800Hz. Signals in the frequency range higher than 100Hz are used for VLF plasma wave experiments (KIMURA et al., 1990), while signals less than 100Hz are used for magnetic field experiments.After the 3- and 5-m masts were extended on March 7 and 8, 1989, respectively, both the magnetometers are operating continuously. Intense small-scale field-aligned currents embedded in the large-scale field-aligned current system were always observed at 1-2 Re altitudes in all local time regions. The region 0 currents which flow in the poleward region adjacent to the region 1 currents were also frequently observed. The search coil magnetometer measured ion cyclotron waves at 1-2 Re altitudes near the equator.

Dynamics Explorer 2 observed a highly structured plasma convection in the dawn sector of the high-latitude ionosphere on October 25, 1981. Analyzing the magnetic and electric field and plasma data for the event, we have clarified the relation between the electric field variations and the plasmas. There is a region of spiky electric field variations that create a highly structured convection. This region of spiky electric field variations generally coincides with a region having source electrons of low temperature (roughly 60–100 eV) and high density (roughly 1-5 cm−3, sometimes much higher). Ions having energies of several hundred to several kilo electron volts precipitate in the region of the spiky electric field variations. Results of the analysis also suggest that the highly structured plasma drift is detached from the dayside reverse convection, that is, sunward flow at the highest latitudes and antisunward flow at lower latitudes. Thus our results do not agree with some of the previous studies which suggested that the structured plasma convection is a continuation of the dayside convection that has become irregular near the nightside edge and that its source region is the plasma sheet. We suggest that the source for the highly structured convection lies in the distant low-latitude boundary layer, and propose a source electric field configuration.

The characteristics of the large-scale electrodynamic parameters, field-aligned currents (FACs), electric fields, and electron precipitation, which are associated with auroral substorm events in the nighttime sector, have been obtained through a unique analysis which places the ionospheric measurements of these parameters into the context of a generic substorm determined from global auroral images. A generic bulge-type auroral emission region has been deduced from auroral images taken by the Dynamics Explorer 1 (DE 1) satellite during a number of isolated substorms, and the form has been divided into six sectors, based on the peculiar emission characteristics in each sector: west of bulge, surge horn, surge, middle surge, eastern bulge, and east of bulge. By comparing the location of passes of the Dynamics Explorer 2 (DE 2) satellite to the simultaneously obtained auroral images, each pass is placed onto the generic aurora. The organization of DE 2 data in this way has systematically clarified peculiar characteristics in the electrodynamic parameters. An upward net current mainly appears in the surge, with little net current in the surge horn and the west of bulge. The downward net current is distributed over wide longitudinal regions from the eastern bulge to the east of bulge. Near the poleward boundary of the expanding auroral bulge, a pair of oppositely directed FAC sheets is observed, with the downward FAC on the poleward side. This downward FAC and most of the upward FAC in the surge and the middle surge are assoc iated with narrow, intense antisunwqard convection, corresponding to an equatorward directed spikelike electric field. This pair of currents decreases in amplitude and latitudinal width toward dusk in the surge and the west of bulge, and the region 1 and 2 FACs become embedded in the sunward convection region. The upward FAC region associated with the spikelike field on the poleward edge of the bulge coincides well with intense electron precipitation and aurora appearing in this western and poleward protion of the bulge. The convection reversal is sharp in the west of bulge and surge horn sectors, and near the high-latitude boundary of the upward region 1, with a near stagnation region often extending over a large interval of latitude. In the eastern bulge and east of bulge sectors, the region 1 and 2 FACs are located in the sunward convection region, while a spikelike electric field occasionally appears poleward of the aurora but usually not associated with a pair of FAC sheets. In the eastern bulge, magnetic field data show complicated FAC distributions which correspond to current segments and filamentary currents.

Using the Dynamics Explorer (DE) 2 magnetic and electric field and plasma data, B(sub y)- controlled convection and field-aligned currents in the midnight sector for northward interplanetary magnetic field (IMF) are examined. The results of an analysis of the electric field data show that when IMF is stable and when its magnitude is large, a coherent B(sub y)-controlled convection exists near the midnight auroral oval in the ionosphere having adequate conductivities. When B(sub y) is negative, the convection consists of a westward (eastward) plasma flow at the lower latitudes and an eastward (westward) plasma flow at the higher latitudes in the midnight sector in the northern (southern) ionosphere. When B(sub y) is positive, the flow directions are reversed. The distribution of the field-aligned currents associated with the B(sub y)-controlled convection, in most cases, shows a three-sheet structure. In accordance with the convection the directions of the three sheets are dependent on the sign of B(sub y). The location of disappearance of the precipitating intense electrons having energies of a few keV is close to the convection reversal surface. However, the more detailed relationship between the electron precipitation boundary and the convection reversal surface depends on the case. In some cases the precipitating electrons extend beyond the convection reversal surface, and in others the poleward boundary terminates at a latitude lower than the reversal surface. Previous studies suggest that the poleward boundary of the electrons having energies of a few keV is not necessarily coincident with an open/closed bounary. Thus the open/closed boundary may be at a latitude higher than the poleward boundary of the electron precipitation, or it may be at a latitude lower than the poleward boundary of the electron precipitation. We discuss relationships between the open/closed boundary and the convection reversal surface. When as a possible choice we adopt a view that the open/closed boundary agrees with the convection reversal surface, we can explain qualitatively the configuration of the B(sub y)-controlled convection on the open and close field line regions by proposing a mapping modified in accordance with IMF B(sub y).

Fujii et al. (1994) obtained characteristics of the electrodynamic parameters, that is, field-aligned currents, electric fields, and electron precipitation, which are associted with auroral substorm events in the nighttime sector, through a unique analysis that places the ionospheric measurements of these parameters into the context of a generic substorm determined from global auroral images. In this paper we investigate in considerably more detail the characteristics of the field-aligned currents using data from the same set of passes as the previuos study. We show for the first time that the net upward field-aligned currents throughout the surge and surge horn are sufficient to account for most if not all of the converging currents of the auroral electrojets. Current densities are largest in the surge and surge horn. Current region continuity does not appear to exist across the substorm bulge region. Much of the auroral substorm field-aligned current is composed of filamentary currents and finite current segments at large angles to each other. The westward electrojet may contain large gradients in intensity both in local time and latitude due to sets of localized field-aligned currents. The net downward current for several hours to the west of the surge is insufficient to account for the eastward electrojet, consistent with the concept that this electrojet originates primarily on the dayside. Our pattern of field-aligned currents associated with the surge has common features and also differs significantly from the patterns previously derived from data from radars and ground-based magnetometer arrays. Our pattern is considerably more complex, probably due to the much higher resolution in latitude of the satellite data. It is also larger in area, since our average substorm is much larger than those pertaining to the previous patterns, giving a substorm wedge considerably wider than that obtained from the radar and array data.

The relation between electron temperature enhancement and large amplitude Pc 1 wave injections in the upper ionosphere is investigated using the data obtained by the Dynamics Explorer 2 spacecraft. Results can be summarized as follows: (1) The region of the temperature enhancement coincides with that of the wave injection which is latitudinally very narrow (less than 100 km) in comparison with the wavelength along the ambient magnetic field (several hundred kilometers). (2) The duration of the wave injection (or the temperature enhancement) seems to be less than a few hours even under quiet geomagnetic conditions, and/or the injection seems to be very localized, not only latitudinally, but also longitudinally. (3) The appearance and the magnitude of temperature enhancement depend on both the wave amplitude and the satellite altitude. (4) Two of the 22 events that were analyzed show a clear enhancement of low-energy electron flux (5 to 30 eV) at the wave injection, and the flux is field-aligned both downward and upward. The region of the temperature enhancement coincides with that of the downward electron flux. From these results, it is suggested that the temperature enhancement which accompanies large-amplitude waves with Pc 1 pulsation frequencies (0.2 to 5 Hz) is caused by the direct acceleration of thermal electrons at low altitudes by the parallel electric field (0.01 to 0.001 mV/m) of the ion-cyclotron waves (kinetic Alfven waves) having an oblique wave normal.

The satellite-observed high correlations between magnetic and electric field perturbations in the high-latitude field-aligned current regions are investigated by examining the dependence of the relationship between Delta-B and E on spatial scale, using the electric and magnetic field data obtained by DE 2 in the polar regions. The results are compared with the Pedersen conductivity inferred from the international reference ionosphere model and the Alfven wave velocity calculated from the in situ ion density and magnetic field measurements.

Accepted: 1992-01-10, 資料番号: SA1001251000

Results are presented of a detailed analysis of plasma and field measurements taken close in time by the DE 1 and DE 2 satellites during the September 6, 1982 magnetic storm. High-altitude data show that, during the storm, the DE 1 satellite entered the magnetosheath by crossing a magnetopause with a large normal magnetic field component, and data from DE 2 show a well-defined cusp current system occurring on open magnetic field lines. The interactions of the solar wind/IMF with the magnetosphere low-altitude signatures of the magnetopause that most adequately explain the high-altitude observations of DE 1 and the near-earth cusp observations of DE 2 are considered, and the relationship between the measurements made by the two satellites are discussed.

The equatorward cutoff of ion and electron precipitation in relation to the evening region 2 field-aligned current during isolated substorms has been investigated using the magnetic field and plasma data obtained from the Dynamics Explorer 2 satellite. The equatorward boundaries of the region 2 currents relative to those of central plasma sheet (CPS) electron precipitation are determined predominantly by magnetic local time and subsequently change with substorm phases. With approaching midnight, the equatorward boundary of CPS electron precipitation extends toward and eventually equatorward of that of the region 2 current. On the other hand, the equatorward boundary of the region 2 current coincides well with that of 10-20 keV ion precipitation during the whole course of substorms. It is proposed that these ions originate in the so-called Alfven layer and that the location of this inner boundary determines the lower latitude boundary of the region 2 current.

Almost 1 year of IMP 8 interplanetary magnetic field and plasma data (days 1-312, 1979) have been examined to determine the interplanetary causes of geomagnetic AE activity. The nature of the interplanetary medium (Alfvenic or non-Alfvenic) and the B(s) correlation with AE were examined over 12-hour increments throughout the study. It is found that Alfvenic wave intervals are present over 60 percent of the time, and the southward component of the Alfven waves is well correlated with AE (average peak correlation coefficient 0.62), with a median lag of 43 min. From this statistical study, no major differences in the magnetospheric response to Alfvenic and non-Alfvenic intervals were obvious. The high-intensity long-duration continuous AE activity (HILDCAA) events discussed previously by Tsurutani and Gonzales (1987) are demonstrated to be caused by the southward components of the Alfven waves, presumably through the process of magnetic reconnection.

A 74-nT sudden commencement on July 13, 1982, was observed in the magnetosphere, with instruments on the Dynamics Explorer 1 satellite. Inbound, near L = 4.5, the satellite was located at 1524 magnetic local time and 20 deg magnetic latitude. The sudden commmencement established a strong, east-west oscillation, with 100-s period, which was observed in the magnetic field, the electric field, and the plasma flow velocity records. There was also a compressional component of this 100-s oscillation and a rapidly damped 300-s compressional pulsation. The compressional oscillations may be an evidence of cavity resonances, excited by the sudden commencement. The cavity waves may, in turn, couple to toroidal waves in field line resonance at the satellite location. In addition, the sudden commencement caused the onset of waves with frequencies from 0.1 up to at least 0.5 Hz. The observations are compared with similar reports from earlier pulsations related to sudden commencements.

Studies of Birkeland current systems have been conducted primarily with low altitude satellite magnetometer data whereas electrojet current signatures have been usually analyzed with data from ground-based magnetometer chains. However, the Magsat magnetometer data set allows magnetic disturbances due to both field-aligned and electrojet currents to be examined simultaneously. This is mainly due to Magsat's approximately 400 km altitude, thus providing data closer to the electrojet current system than has been previously available from satellite measurements. Of additional importance are the superior accuracy, both in sensitivity and altitude, of the magnetic field measurements obtained by Magsat and last, but not least, the availability of an accurate magnetic field model of the concurrent epoch (based on the Magsat data set) that allows one to obtain a better baseline than previous models. The aforementioned points are emphasized and both Birkeland and electrojet currents have been analyzed in a case study for November 13, 1979.

A study of the data from the high-latitude North American IMS network of magnetic stations suggests that there is a component in substorm perturbations that corotates with the earth. It is as yet not certain whether the existence of this component stems from the corotation of a part of the magnetospheric plasma involved in the substorm mechanism or if it is a 'phase change' resulting from the control of the substorm manifestations by the earth's main magnetic field which is not axially symmetric. There are other geophysical phenomena showing a persistence of longitudinal variations corotating with the earth. These phenomena are of significance for a better understanding of ionosphere-magnetosphere coupling.

Magnetic field observations of four dayside pulsation events detected near the equatorial plasmapause region on August 23, 24, September 30, and October 10, 1982 are examined. The wave characteristics and the magnetic components of the pulsation events obtained from DE-1 satellite data and ground data from Siple, Antarctica are described and compared. The pulsations displayed similar complex wave structures; long period transverse waves greater than 100 s are the fundamental mode oscillations of magnetic shells and short period waves of 20-40 s are superimposed on them. It is observed that wave bursts are present in all frequency ranges. The relationship between eigenperiod and the magnetic shell is studied.

From the magnetic and electric field observations on the DE-2 satellite it is deduced that the perturbation magnetic field and the electric field in the field-aligned current regions are, as a rule, orthogonal to each other and are highly correlated. This deduction is equivalent to the statement that the Poynting vector calculated from these magnetic and electric field components is equal to the ionospheric energy dissipation and that the height-integrated Hall current is divergence free. The state described is interpreted as a frequently prevailing mode of the magnetosphere-ionosphere coupling involving field-aligned currents.

From the Triad magnetometer observation of a step-like level shift in the east-west component of the magnetic field at 800 km altitude, the existence of a net current flowing into or away from the ionosphere in a current layer was inferred. The current direction is toward the ionosphere on the morning side and away from it on the afternoon side. The field aligned currents observed by Triad are considered as being an important element in the electro-dynamical coupling between the distant magnetosphere and the ionosphere. The current density integrated over the thickness of the layer increases with increasing magnetic activity, but the relation between the current density and Kp in individual cases is not a simple linear relation. An extrapolation of the statistical relation to Kp = 0 indicates existence of a sheet current of order 0.1 amp/m even at extremely quiet times. During periods of higher magnetic activity an integrated current of approximately 1 amp/m and average current density of order 0.000001 amp/sq m are observed. The location and the latitudinal width of the field aligned current layer carrying the net current very roughly agree with those of the region of high electron intensities in the trapping boundary.

Using magnetic data from the North American IMS network at high latitudes, Pi 3 pulsations are analysed for a period of 4 1 2 continuously-disturbed days. The data were obtained from 13 stations in the Alaska and Fort Churchill meridional chains and in the east-west chain along the auroral zone. In the past, Pi 3 pulsations associated with substorms have been classified into two sub-categories, Pi p and Ps 6. However, we find that Pi 3's which have longer periods than Pi p and which are different from Ps 6 are more commonly observed than these two special types. Power spectra, coherence and phase differences are compared among the stations. Results show that noticeable differences for latitudinal dependence of period and amplitude exist among midnight, morning and late-evening Pi 3 pulsations. Results for Pi 3 occurring near midnight indicate that the periods at which the power spectral density is a maximum are longest, and the amplitude largest, near the center of the westward auroral electrojet. On the other hand, for Pi 3 pulsations occurring in the morning, the periods at which the power spectral density is a maximum are longest, and the amplitude largest, near the poleward edge of the westward electrojet. Furthermore, for Pi 3 pulsations occurring in the late evening, their periods are longer and their amplitudes larger near both the Harang discontinuity and the poleward edge of the westward electrojet than near its center. Correlations between pairs of adjoining stations are better in the polar cap than at auroral latitudes. It is also found from hodograms that the sense of polarization often varies from one station to another for the same event, and that the time duration in which the same rotational sense is maintained is shorter near midnight than in the morning and late evening. It is suggested that the source regions of the morning and late-evening Pi 3's lie on the electrojet boundaries; that is at the Harang discontinuity (in the evening) and at the poleward edge of the westward electrojet (in the morning and evening). The generation of midnight Pi 3 pulsations, centered at a location within the westward auroral electrojet appears to be associated directly with the generation of that electrojet.

By a spherical harmonic expansion of the magnetic potential the geomagnetic Sq variation is shown to have peak-to-peak amplitudes of a few tens of nanotesla at 400 km altitude. It is shown, in particular, that for harmonics of degree n up to about 4, with which Sq can be well represented, the vertical component of the magnetic field at altitudes to about 400 km is virtually the same as on the ground. Even though the NASA's Magnetic Field Satellite (Magsat), scheduled for launch in September 1979, is planned to be placed in a twilight sun-synchronous orbit, Sq over certain areas of the earth can be of comparable magnitude as magnetic anomalies of geological origin sought in the data. Due consideration should be given to Sq as well as to the effects from magnetospheric sources in analyzing the Magsat data. The Sq effect is expected to be large during the period of Magsat operation which is near the predicted solar maximum.

The first degree external spherical harmonic coefficients are obtained for each year of a 12-year period centered at 1958.5, using annual mean values of X, Y, and Z components from 54 magnetic observatories. Values of the coefficient g01e of the zonal first degree harmonic clearly show a solar cycle variation. The peak-to-peak amplitude of the variation is approximately 29 nT, which is consistent with values obtained earlier by first filtering data to retain only those variations having periods near the solar cycle and then subjecting the filtered data to a spherical harmonic analysis. The variation in g01e is found to correlate extremely well with the annual mean Dst, index and with the annual number of days having Ap≥60. Based on statistics of the mean square successive difference, an explanation is presented why the obtained solar cycle variation in g01e, which is very much smaller in magnitude than the standard deviations calculated by the conventional method, is statistically meaningful. The determined absolute (not relative) values of g01e are in agreement, within several nanotesla, with the expectation from a theoretical model of solar wind compression of the magnetosphere and an analysis of the Dst index.

Initial results of the electric and magnetic field observations from the DE-2 satellite show a remarkably good correlation between the north-south component of the electric field and the east-west component of the magnetic field in many passes of the field-aligned current regions. For a dayside cusp pass on August 15, 1981 the coefficient of correlation between these components was 0.996. A preliminary inspection of the available data from the first 6 months of the DE operation indicates that the similarity between the electric and magnetic field signatures of the field-aligned currents is a commonly observed feature at all local times. This high correlation is interpreted to be an indication that the closure of the field-aligned current is essentially meridional. When the correlation between these components is not good, the closure current is likely to be flowing along the auroral belt. When the correlation between the electric and magnetic fields is high, it is possible to estimate the height-integrated Pedersen conductivity from the observed field components.

Using the OGO-5 fluxgate magnetometer data, the polar cap boundary is identified in the high altitude magnetosphere by a sudden transition from a dipolar field to a more tail like configuration. The basic pattern of the magnetic field variations observed during the satellite's traversal of the auroral belt is presented. This pattern shows the existence of a field aligned current layer on the equator side of the polar cap boundary. Currents flow in the opposite directions in the two field aligned current layers. The current directions in these layers as observed by OGO-5 in the high-altitude magnetosphere are the same as those observed at low altitudes by the polar orbiting TRIAD satellite. The magnetic field in the region where the lower latitude field aligned current layer is situated is essentially meridional. Thus the equatorial current closure of this current system must be via the equatorial current sheet. The two field aligned current systems, one at the polar cap boundary and the other on the low latitude side of the auroral belt, are coupled through the Pedersen current in the ionosphere.

Measurements made by the High Altitude Plasma Instrument on DE-1 have shown that intense upward electron beams with energies from about 20 eV to about 200 eV are a common feature of the region just equatorward of the morning-side polar cusp. Computations of the currents carried by these beams and by the precipitating cusp electrons show excellent agreement with the simultaneous DE-1 magnetometer measurements for both upward and downward Birkeland currents. The data indicate that cold ionospheric electrons, which carry the downward region-1 Birkeland currents on the morning side, are accelerated upward by potential drops of a few tens of eV at altitudes of several thousand kilometers. This acceleration process allows spacecraft above those altitudes to measure routinely the charge carriers of both downward and upward current systems.

The existence of highly correlated quasi-biennial variations in the geomagnetic field and in solar activity is demonstrated. The analysis uses a numerical filter technique applied to monthly averages of the geomagnetic horizontal component and of the Zurich relative sunspot number. Striking correlations are found between the quasi-biennial geomagnetic variations determined from several magnetic observatories located at widely different longitudes, indicating a worldwide nature of the obtained variation. The correlation coefficient between the filtered Dst index and the filtered relative sunspot number is found to be -0.79 at confidence level greater than 99% with a time-lag of 4 months, with solar activity preceding the Dst variation. The correlation between the unfiltered data of Dst and of the sunspot number is also high with a similar time-lag. Such a timelag has not been discussed in the literature, and a further study is required to establish the mode of sun-earth relationship that gives this time delay.

The orbit and payload of the AMPTE (active magnetospheric particle tracer explorer) Charge Composition Explorer (CCE) satellite, which provide an exellent opportunity for observing the geomagnetically trapped particle population in general and the earth's ring current in particular, are described. A global view of the September 4, 1984 geomagnetic storm is presented and the initial findings of the CCE investigators on the earth's ring current are given. It is shown that the CCE ring-current results pertain to an unusual asymmetric ring current and may not be applicable to a more typical ring-current development and decay.

Using the data obtained from the IMS North American magnetometer network stations at high latitudes, a motion picture was made by a computer technique, describing time changes of Pc5 and Pi3 magnetic pulsation vectors. Examples of pulsation characteristics derived from this presentation are regional polarization changes including shifts of polarization demarcation lines, changes in the extent of an active region and its movement with time.

Clear evidence for the existence of a quasi-biennial geomagnetic variation is shown by an analysis of annual averages of the horizontal (H) component of the geomagnetic field observed at five observatories. The analysis uses a numerical filter, which is equivalent to taking the second order time derivative of the time series. The cause for the variation is external to the earth because its amplitude depends on magnetic activity. The second order time derivative of H is well correlated with the corresponding time derivatives of the relative sunspot number and 10.7 cm solar flux. It is suggested that quasi-biennial oscillations observed in the geomagnetic field, cosmic rays, stratospheric zonal wind and temperature, total ozone, and other meteorological parameters could be produced by a common cause on the sun.

Results of a detailed examination of magnetic field residuals obtained from POGO satellite magnetometer data are presented which illustrate some problems which may be encountered in the reduction and analysis of Magsat data. Comparisons of field residuals determined from OGO 2, 4 and 6 data for the region between 270 and 290 deg E reveals significant differences between the satellite data sets which are related to differences in the residual field level on individual satellites, external field contamination and effects from ring current correction in the data reduction process. When a new map is prepared from OGO 2 and 4 satellite data by compensating for these factors, dramatic differences with the original map are noted, including the disappearance of a major positive anomaly and the better definition of various magnetic highs and lows. The new map is also noted to be more consistent with conventional airborne and marine magnetic measurements. The results thus demonstrate the necessity for the inspection of satellite data and the adequate removal of the external field signal prior to geological analysis.

Data from the DE-2 spacecraft are combined with data from the Magsat spacecraft and data from magnetic observatories and magnetic surveys to derive a geomagnetic field model for the period from May 1979 to May 1983. The model is an extension of the Goddard Space Flight Center (12/83) model. The model includes a solution for parameters representing the noncore field, or anomaly bias, at each observatory in the Project Magnet program. A table of these anomalies is presented. The results from this model are compared with those from the IGRF1980 (Peddie, 1982) and the IGRF1987 (Barraclough, 1987).

The determination of DS variation of magnetic storms as a function of storm time is critically examined. The regular changes in the phase angles of harmonics for DS, found by Yokouchi (1958), are attributed to irregular features that are not adequately averaged out. This apparently paradoxical circumstance is explained with an illustrative example.

The delta B distribution deduced from the Ogo 3 and 5 satellites shows large field depressions in the equatorial region inside the plasmasphere. On the basis of the delta B distribution, it is shown that what is usually considered the quiet-time ring current is an equatorial sheet current that is an extension of the neutral sheet current in the magnetospheric tail. The primary source of the large field reductions inside the plasmasphere is a population of protons with energies of 0.1-1 Mev initially detected by Davis and Williamson (1963) and Davis (1965) on Explorer 12, 14, and 15. Low-energy protons extensively measured on Ogo 3 by Frank (1967, 1971) are primarily responsible for the current near and outside the plasmapause.