TEMPORAL AND SPATIAL VARIABILITY OF AURORAL FORMS IN THE 10-14 MLT SECTOR - RELATIONSHIP TO PLASMA CONVECTION AND SOLAR WIND-MAGNETOSPHERE COUPLING

Ground-based observations of dayside auroral forms and magnetic pertur bations in the arctic sectors of Svalbard and Greenland, in combinatio n with the high-resolution measurements of ionospheric ion drift and t emperature by the EISCAT radar, are used to study temporal/spatial str uctures of cusp-type auroral forms in relation to convection. Large-sc ale patterns of equivalent convection in the dayside polar ionosphere are derived from the magnetic observations in Greenland and Svalbard. This information is used to estimate the ionospheric convection patter n in the vicinity of the cusp/cleft aurora. The reported observations, covering the period 0700-1130 UT, on January 11, 1993, are separated into four intervals according to the observed characteristics of the a urora and ionospheric convection. The morphology and intensity of the aurora are very different in quiet and disturbed intervals. A latitudi nally narrow zone of intense and dynamical 630.0 nm emission equatorwa rd of 75 degrees MLAT, was observed during periods of enhanced antisun ward convection in the cusp region. This (type 1 cusp aurora) is consi dered to be the signature of plasma entry via magnetopause reconnectio n at low magnetopause latitudes, i.e. the low-latitude boundary layer (LLB I,). Another zone of weak 630.0 nm emission (type 2 cusp aurora) was observed to extend up to high latitudes (similar to 79 degrees MLA T) during relatively quiet magnetic conditions, when indications of re verse (sunward) convection was observed in the dayside polar cap. This is postulated to be a signature of merging between a northward direct ed IMF (B-z > 0) and the geomagnetic field poleward of the cusp. The c oexistence of type 1 and 2 auroras was observed under intermediate cir cumstances. The optical observations from Svalbard and Greenland were also used to determine the temporal and spatial evolution of type 1 au roral forms, i.e. poleward-moving auroral events occurring in the vici nity of a rotational convection reversal in the early post-noon sector . Each event appeared as a local brightening at the equatorward bounda ry of the pre-existing type 1 cusp aurora, followed by poleward and ea stward expansions of luminosity. The auroral events were associated wi th poleward-moving surges of enhanced ionospheric convection and F-lay er ion temperature as observed by the EISCAT radar in Tromso. The EISC AT ion flow data in combination with the auroral observations show str ong evidence for plasma flow across the open/closed field line boundar y.