The quasi‐periodic DP 2 magnetic fluctuations (period of 30–40 min) appearing coherently at the auroral and equatorial latitudes during the day are analyzed based on the high time resolution magnetometer data recorded at the International Monitor for Auroral Geomagnetic Effects (IMAGE) stations in Scandinavia and at the Brazilian and African equatorial stations. It is shown that the correlation between the DP 2 magnetic fluctuations at both latitudes is excellent (correlation coefficient of 0.9). No discernible time shift has been found within the resolution of 25 s. The European incoherent scatter (EISCAT) radar observations in Scandinavia show that the DP 2 fluctuations at auroral latitudes are caused by an ionospheric Hall current which is controled by the convection electric field. The DP 2 fluctuations exhibit a strong decrease in magnitude with decreasing latitude, however, it is enhanced considerably at the dip equator with an amplitude comparable to that at the subauroral latitude. The considerable equatorial enhancement of the magnitude of the DP 2 fluctuations with an enhancement ratio of 4 is due to the concentration of the electric current along the highly conductive dayside equatorial ionosphere. These observational facts can be explained in terms of an ionospheric current which is generated by the magnetospheric electric field at the high latitude and extends to the equatorial ionosphere almost instantaneously. From the viewpoint of the electric field penetration, we conclude that the magnetospheric electric field penetrates to the equatorial ionosphere through the polar ionosphere almost instantaneously within the time resolution of 25 s. The nearly instantaneous propagation of the electric field to the equator can be explained primarily by a parallel plane transmission line model composed of the conductive Earth and ionosphere. In addition to our finding of the fast propagation of the DP 2 electric field, it is found that an impulsive magnetic change with a timescale of 100 s appears at the dayside dip equator with a time delay of about 10 s, which requires to include the effect of the high conductivity of the dayside equatorial ionosphere in future studies of the propagation model.

Abstract.Peculiarities of daytime and nighttime Pi 2 pulsations at the dip equator are examined by using multipoint measurements from the 210 ø magnetic meridian (MM) magnetometer network. We found that during daytime the amplitude of Pi 2 pulsations at the dip equator is enhanced, at the lower latitudes. Because the zonal ionospheric conductivity at the dip equator is much higher than that at the off-dip equator region, Pi 2 signals are expected to be distorted more effectively at the dip equator. The observations imply that the daytime and nighttime Pi 2 pulsations in the equatorial and low-latitude regions can be explained by invoking an instantaneous penetration of electric field variations from the nightside polar ionosphere to the dayside equatorial ionosphere, and a direct incidence of compressional oscillations from the nightside inner magnetosphere, respectively.

The spacial extent of the source region of Pc 1 geomagnetic pulsations is investigated with respect to several such events recorded simultaneously at thirteen stations in Canada. The investigation is based on amplitude distribution obtained through reduction of the data acquired with induction magnetometers at those stations.Propagation from the source region is not isotropic but tends to align with geomagnetic latitude and longitude. The spacial gradient of amplitude near the source region becomes as large as 10 dB/100 km. Left-hand polarization does not seem to be confined to the source region. Size of source regions is discussed.

The frequency of occurrence of pulsating auroras is statistically examined on the basis of all-sky TV data for 34 nights from five stations, in a range from 61.5 to 74.3" in geomagnetic latitude. The results are that: (I) occurrence probability of a pulsating aurora is 100% after 4 h in geomagnetic local time, (2) pulsating auroras occur in the morning hours along the auroral oval even when magnetic activity is as small as 00 5 K , 5 1, (3) pulsating auroras occur even in the evening when K,, increases to greater than 3-, (4) drift of pulsating auroras is westward in the evening while it is eastward in the morning hours. (5) the region ofpulsating auroras splits into two zones. 64 to 68' and 61 to 63' in geomagnetic latitude, after 4 h geomagnetic local time for K , from 20 to 3-, and the splitting also appears to exist for greater K , as evidenced by observation other than our auroral data. These results are discussed in relation to distributions of cold plasma irregularities and energetic electrons in the magnetosphere.On a fait une etude statistique de la frequence d'apparition des aurores pulsantes, sur la base des donnees TV plein ciel obtenues au cours de 34 nuits a cinq stations situees dans un intervalle de latitude geomagnetique allant de 61,5 B 71.3". Cette etude a donne les resultats suivants:(1) la probabilite d'apparition d'aurores pulsantes est 100% apres 4 h en temps geomagnetique local; (2) il se produit des aurores pulsantes durant les heures du matin le long de I'ovale auroral m2me lorsque I'activite magnetique est aussi faible que 00 5 K , 5 1; (3) il se produit des aurores pulsantes mime dans la soiree lorsque K , croit au delB de 3-; (4) la derive des aurores pulsantes se fait vers I'ouest le soir, alors qu'elle est vers I'est durant les heures du matin;(5) la region d'aurores pulsantes se separe en deux zones, 64 a 68" et 61 a 63" de latitude geomagnetique apres 4 h, temps geomagnetique local, pour K , entre 20 et 3-, et cette separation semble exister aussi pour des valeurs plus grandes de K,,, comme I'indiquent des observations autres que nos donnees aurorales. Ces resultats sont discutes en relation avec les distributions d'irregularites de plasma froid et d'electrons de haute energie dans la magnetosphkre.[Traduit par le journal]Can. J. Phys., 59, 1150 (1981) Introduction and that in the dawn auroral zone (5) indicates a A pulsating aurora is likely to be a visible primary importance of pulsating precipitation of manifestation of the pulsating precipitation of energetic electrons in pulsating auroras. Hence, magnetospheric electrons, and the pulsating pre-the study of the pulsating aurora can have an cipitation could be the result of wave-particle essential importance in understanding the plasma interactions in the magnetosphere. Even if some state in the magnetosphere. pulsating auroras originate from ionospheric proIn spite of their importance, pulsating auroras cesses (e.g., Deehr and Romick (1) and Luhmann have not been studied well enough, possibly be-(2)), modulation of precipit...

A good correlation was found between the very low frequency chorus and pulsating aurora observed at Park Site (L -4.4), Saskatchewan, Canada, during the recovery phase ofa substorrn on January 28, 1980. The activity of the chorus was low during the periods when the pulsating aurora was active over the station. However, seven chorus events were identified during that period and six of them showed one-to-one correlation with the brightening of a pulsating patch. The brightening of the patch leads chorus events by -0.1-0.2s. The corresponding patch detected by a low-light-level TV camera has anoval shape 75 krn in the north-south direction and 150krn in the east-west direction at the ionospheric altitudes. The energy of precipitated electrons was inferred to'lie between 20 and 90 keV. On a trouve une bonne correlation entre les observations de choeur frequence tres basse et d'aurore pulsante faites a Park Site ( L -4,4), Saskatchewan, Canada, durant la phase de retablissernent d'un sous-orage, le 28 janvier 1980. L'activite de choeur etait faible durant la periode d'activite d'aurore pulsante au-dessus de la station, rnais on a cependant identifie sept evenernents choraux durant cette ~eriode. et six d'entre eux etaient en correlation un a un avec I'augmentation de lurninosite d'une plage pulsante. Cette augmentation de IurninositC precede I'evenernent choral de-0.1-0,2 s. Laplage correspondantedetectee parune carnerade television pour faible flux lurnineux a la forrne d'un oval de 75 krn dans la direction nord-sud et de 150 krn dans la direction est-ouest, aux altitudes ionospheriques. On a estirne que I'energie des electrons precipites se situait entre 20 et 80 keV.