Outline of the Global Aurora Dynamics Campaign, carried out from December 20, 1985 to February 3, 1986, is briefly described. Some of the initial results are reviewed in connection with other campaign papers of this issue. Importance and effectiveness of multi-station network observation are emphasized for obtaining spatio-temporal information of the upper atmosphere phenomena such as auroral activities and magnetic field perturbations. The network observation is useful especially for studying the global propagation of ULF waves, global dynamics of auroras, and consistent relationships among electric currents, conductivity distributions and electric fields. It is shown that the multi-station network is also greatly efficient to increase the possibilities of studying the relationships between in situ measurements of the magnetospheric plasma parameters by satellites and ground observations of precipitation particles and field variations along the common magnetic field lines.

View full abstract

Auroral activities on January 7, 1986, are examined with all-sky video data obtained at multiple stations. It is shown that a poleward expansion front of an expansion aurora usually consists of many northwestward protrusions which develop and decay here and there during the course of the auroral expansion. Developments of characteristic auroral protrusions are compared with magnetic field changes on the ground. The result shows that the developments of large magnetic field deflections on the ground are most likely due to enhancements of local westward electrojets associated with counterclockwise vortex currents around developing auroral protrusions in the night sector. The developments of auroral protrusions are also related to magnetic field changes at the synchronous satellites, GOES 5 and 6, conjugate with the auroral forms. Characteristic changes of magnetic field occur at GOES 5 and 6 concurrently with developments of auroral protrusions around respective magnetic footpoints of the satellites. Auroral structures within or in the vicinity of auroral protrusions are likely interlinked with the field-aligned currents around the conjugate synchronous satellites.

View full abstract

High sensitive TV observations of auroras were made together with ULF and VLF measurements at Ny Ålesund (75.4°, 131.4° geomagnetic coordinates), Svalbard in December-January, 1984-85 and 1985-86, in order to examine characteristics of dayside auroras and associated upper atmosphere phenomena. In this report we will discuss relationships between impulsive pulsation bursts in the Pc1 range and auroral displays near the dayside cusp region. The cusp region is characterized by the appearance of Pi-like bursts during daytime. These bursts have an enhancement band in the frequency of 0.3-0.8Hz. Pulsation bursts in the Pc1 range are often associated with occurrence of poleward moving auroras. Poleward drifts of auroral forms generally last for 1-3 minutes over spatial extent of 100-300km at ionospheric level. Poleward drifts of luminosity occasionally show a quasi-periodic repetition in a time scale of several minutes. One-to-one correspondence is often noted between the enhancement band in the Pc1 range and poleward movements of auroras having a duration of several minutes. Implication of these results is discussed in relation to observations of flux transfer events near the magnetopause.

View full abstract

It is found that the occurrence and luminosity of diffuse auroras, including pulsating auroras, in the dawn sector show space-time variations synchronized with geomagnetic Pc5 pulsations. The activation region of aurora (not auroral structure) quasi-periodically propagates towards the northwest. The observed propagation velocities at the ionospheric level are about 1km/s northward and about 15km/s westward, respectively. These velocities are in good agreement with the phase velocities of Pc5 pulsations previously measured by radars and by ground networks of geomagnetic field observations. Oscillations in drifts of auroral patches generally in the east-west direction are found to be synchronized with the Pc5 pulsations. The observations suggest that the ground Pc5 pulsations do not necessarily reflect the HM wave structures in the magnetosphere, but the wave nature could be inferred from a close examination of the relationships between the ground magnetic pulsations and concurrent auroral dynamics.

View full abstract

Bright auroral forms several hundreds of km in spatial extent were observed repeatedly (a few to about 15min, periodicity) in the premidnight hours, following auroral breakups. The auroral forms drifted towards the northwest or the southwest, and were related to the magnetic field fluctuations on the ground in a similar period range. The leading front of the drifting auroral form has a discrete auroral (vortexchain) feature. After the passage of discrete forms pulsating aurora appears. From the comparison with magnetic field perturbations at the geosynchronous orbit satellites GOES 5 and GOES 6, these auroral forms are likely to correspond to the depression of the magnetic total intensity. A possible source of these bright auroral forms is hot plasmas injected from the plasma sheet. The concurrent magnetic pulsations, here called Ps5, would be produced by the fluctuating electric field and conductivity in the ionosphere due to the electron precipitation into the auroral forms. Hot plasma clouds, quasi-periodically injected during the course of a substorm, are related to the auroral and magnetic field pulsations. A steep injection front of hot plasma in the magnetosphere is likely related to discrete auroras at the ionosphere.

View full abstract

Short period geomagnetic pulsations called IPDP (intervals of pulsations of diminishing periods) are investigated, using ground data obtained at 35 campaign stations in the northern polar region. Comparison of the frequency-time (f-t) spectrograms of data from the stations shows that the internal structures of f-t pattern of IPDP pulsations vary with a small separation between stations. The variability of the internal structures suggests that “an IPDP event” consists of many discrete wave packets each of which comes from individual sources. Spatial-temporal developments of IPDP wave power are also examined. The two-dimensional distribution of IPDP power is both highly structured in space, suggesting presence of discrete source regions, and also highly variable with time, indicating characteristic dynamic features of the source regions. The source regions are located in the dusk half of the magnetosphere in a range of L value from 4 to 10. Three types of dynamics of the source regions are found; 1) fast westward motion consistent with magnetic-drift velocity of 60-70keV protons in the magnetosphere, 2) quasi-stationary sources, which are almost stationary in the magnetospheric frame for periods longer than 10 minutes, 3) evolution of the IPDP region toward the night and earthward with increase in center frequency. When the westward moving sources arrive at the location of the stationary sources, they merge with them and do not go further westward beyond the stationary sources. These time developments of the IPDP source regions comprehensively explain most of the IPDP characteristics so far obtained from observations in a limited area. Not only well-defined IPDP's but also IPDP-like events with small and slower frequency rise were observed in high latitudes associated with concurrent magnetic field depressions at synchronous orbit and with positive magnetic bays. For both, the magnetic field depression is probably due to hot plasma injection into the evening sector, although clear substorm onsets were only identified for well-defined IPDP's. The occurrence rate of IPDP events monitored within the semi-global coverage of the network was once every six days or 20 percent in hourly occurrence in the dusk sector, more than twice the previously reported rate. The occurrence rate of IPDP is still much smaller than that of substorms. The small occurrence shows that IPDP events are not caused by every “plasma injection” associated with substorms.

View full abstract

Fluxgate magnetometers with accurate timing data logger were set up at two equatorial stations (Garoua/Maroua and Huancayo), and also at a middle latitude station (Kuju). The phase of Pi2 waves is compared among these stations. It is found that
1) Pi2 pulsations in low and equatorial latitudes are linearly polarized approximately along the magnetic meridian,
2) phase difference of the H component of Pi2 waves at different stations is much less than 1/10 of the pulsation period despite a large longitudinal separation (-90°) of the stations, showing the so-called azimuthal wave number, m, to be much less than unity and
3) phase difference of the D component at different stations is variable.

View full abstract

Equatorial Pc pulsations, having periods from 30 to 100sec and amplitude up to several nT, were studied by making use of the fluxgate magnetometer data obtained at Huancayo (0.8°N, 335.6°E in geomagnetic coordinates), Peru during the period from December 5, 1985 to January 5, 1986. Diurnal change of polarization parameters (orientation angle of the major axis and ellipticity) in the H-D plane were investigated. The following results were obtained.
1) Pulsations are linearly polarized. The ellipticities lie between +0.3 and -0.3.
2) orientation angle of the principal axis of variation vectors shows a diurnal variation. It deviates westward from the north for the local time 6-7h. The deviation angle of the major axis from the north occasionally amounts to 60 degrees. A small eastward deviation is also seen in the local time 15-17h. Around 17h a westward turning tendency is noted. During the other time of day, it remains in the north-south direction.
It is suggested that the changes in the D component which bring about the deviation of the orientation angle from the north could locally be produced through an east-west non-uniformity of the ionospheric conductivity distribution.

View full abstract