Poleward moving auroral forms (PMAFs) revisited: responses of aurorae, plasma convection and Birkeland currents in the pre- and postnoon sectors under positive and negative IMF IBsuby/sub/I conditions

摘要

Using five case studies, weinvestigate the dynamical evolution of daysideauroral precipitation in relation to plasma convection,classifying it by theIMF B_y component and position with respect to noon.Auroral observations were madeby meridian scanning photometers(MSPs) and an all-sky camera (ASC) in Ny ?lesund,Svalbard at 76° MLAT, while the spatial structure of the ionosphericplasma convection is inferred from SuperDARN radarsand ion drift observations from spacecraft in polar orbit.The IMF configuration of major interest here is one pointing southwardand with a dominant east-westcomponent. Our emphasis is on the auroral phenomenon of PMAFs(poleward moving auroral forms), whichare ionospheric signaturesof pulsed reconnection at the magnetopause.We distinguish betweenPMAFs/prenoon and PMAFs/postnoon. These two activities are found to beseparatedby an auroral form around noon with attenuated emission at 630.0 nm.We document for the first time that this "midday gap aurora"appears in the form of a midday auroral brighteningsequence (MABS).We study the PMAF activity consisting of aninitial brightening phase and the later stages ofPMAF evolutionin relation to plasma convection cells, flow vorticity,and precipitation boundaries in the prenoon and postnoon sectorsfor both B_y polarities.Flow channels (PIFs) associated with PMAFsare strengthened by polarization effects at auroral boundaries.Addressing the implications of our proposed, extended perspective on daysideauroral morphology under southeast/west IMFfor M-I coupling associated with pulsedmagnetopause reconnection (FTEs),we draw inferences on the MLT-dependent geoeffectiveness(Birkeland current/auroral intensity) of magnetopauseFTEs (subsolar region versusflanks).