Physics of auroral phenomena : proceedings of the 40th annual seminar, Apatity, 13-17 March, 2017 / [ed. board: N. V. Semenova, A. G. Yahnin]. - Апатиты : Издательство Кольского научного центра РАН, 2017. - 143 с. : ил., табл.

THEMIS SPACE-GROUND OBSERVATIONS IN MIDNIGHT SECTOR DURING THE SUBSTORM RECOVERY PHASE T.V. Kozelova, B.V. Kozelov (Polar Geophysical Institute, Murmansk region, Russia) Abstract. We report a case study of substorm recovery phase on 14 November 2014 in the interval 20:30-23:00 UT using data from THEMIS-D satellite located in the midnight sector (-2300-0030 MLT) magnetosphere at 6.5-9.25 Re. The substorm recovery phase of interest was not just a decline of previous disturbances, but include also a new intense substorm intensification in the midnight sector of the auroral oval. This new auroral activation presents the eastward expanding auroral (EEA) structures occurred precisely after the substorm intensification onset and concentrated to the midnight sector of the auroral oval. We show that these EEA structures were observed in diffuse aurora, formed the undulations on the poleward edge of the diffuse aurora similar to of omega bands. The pulsating aurora was observed after the passage o f the EEA structures. Rapid poleward expansion of the poleward diffuse region boundary coincided with the occurrence o f Pi2 pulsations in the ionosphere and with the large-scale dipolarization and the particle injections in the near-Eart plasma sheet of the magnetosphere at -7.2 Re. Besides, the THEMIS-D reveals the quasiperiodic variations o f electrostatic ELF wave intensity at frequency of <100 Hz coincided with the DC electric field variation. At the moments o f more small-scale local dipolarizations, the low-energy electron flux (0.1-3 keV) bursts occur simultaneously with the ELF wave intensity enhancements. 1. Substorm evolution The substorm of 14 November 2014 (Kp=3+) began near Amderma (AMD) at - 18:05 UT. The #=-500 nT was minimal at - 18:50 UT. After -19 UT, during the substorm decay phase, the magnetic pulsations (30-40 min periodicity) in the Ps6 wave band were observed from AMD to Tromso (TRO). During this recovery phase in 20:30- 22:30 UT interval, when the initial substorm expansive phase decreases, a new substorm disturbance initiated in the midnight sector. In this paper we focus on the changes occur both in the ionosphere and in the magnetosphere in the midnight sector during this substorm decay phase in 20:30-22:30 UT interval, when three auroral substorm activations A l, A2 and A3 occur above the Kola Peninsula. We used the auroral data from Apatity all-sky camera and the data observed by the THEMIS-D satellite (THD). In this interval, the THD location changes from L= 9.25 to £=6.5 and MLT from 23.9 to 0.5. Activations A l and A2. Fig.l shows the map of ground-based stations, the projections of the auroras and the THD satellite footprints along magnetic field-line during the activation Al at 21:15-21:40 UT. From this figure one can see that the auroral activity propagated westward from AMD to APT-LOZ-SOD and presents the weak auroral activity o f pseudo-breakup type. Before the activation onset a weak azimuthal auroral arc was located in the APT zenith (21:09:30 UT), accompanied by auroral activity to the north. We analyze auroral activity occurring at most equatorward arc at the latitude - 67.7°. At the moment -21:16 UT, the arc bifurcated, then its equatorward part moved to lower latitudes and northward part expanded to the north (to LOZ). The moment ?i=21:20 UT, when the Pi2-like pulsations o f the magnetic field occur at the LOZ, was associated with the substorm activation Al onset. After t\ the bulgingform o f weak aurora appears at longitudes 28° - 36°. Western edge of this form reached the longitude 28° at - 21:33 UT. At -2 1 :36 UT, the northward border of the bulging auroral form has the maximum latitude (~ 68.7° at LOP). The auroral activity inside this weak bulging form has been neglected and then after -21:36 UT, the western part o f this auroral form quickly faded. At the interval 21:45-21:55 UT new very weak auroral activity A2 occurs poleward the APT. The moment <2=21:52 UT was the activation A2 onset. Other details of its development cannot be easily distinguished. This activity was classified also as weak auroral pseudo-breakup. On the whole, one can say that during two initial activations Al and A2 the small ground-based magnetic disturbances dH >0 were observed at the longitudes from AMD to AND and they were just a decline of previous disturbances, associated with the substorm near AMD at - 18:05 UT. During the activation A l, the footprints o f the THD were mapped in the field of view of Apatity all-sky camera and were located northward equatorial-most arc. Before -21:33 UT, the THD was located westward expanded bulging aurora and at - 21:33—21:36 UT the THD observed the passage of western edge of activation Al. Activation A3. Fig. 2 shows the auroral dynamics during the activation A3 at 22:15-22:35 UT. A clear auroral arc appear from the west along the 67.8° latitude at -22:20 UT. After 22:20 UT the auroral emission expanded northward and eastward over APT. The moment b = 22:23 UT, when the Pi2-like pulsations of the magnetic field occur at the LOZ, was associated with the substorm activation A3 onset. This onset begins westward the APT (possibly near the AND-TRO) and was more intense than the Al and A2. During the activation A3, more intense ground-based magnetic disturbances dH <0 were observed at the longitudes LOZ-AND, which associated with intensified westward auroral electrojet. “Physics o f Auroral Phenomena", Proc. XL Annual Seminar, Apatity, pp. 30-33, 2017 © Polar Geophysical Institute, 2017 30 Polar Geophysical Institute