A classification of dayside auroral forms and activities as a function of interplanetary magnetic field orientation

Details A classification of dayside auroral forms and activities as a function of interplanetary magnetic field orientation A classification of dayside auroral forms and activities as a function of interplanetary magnetic field orientation

Oct 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998jgr...10323325s&link_type=abstract

Journal of Geophysical Research, Volume 103, Issue A10, p. 23325-23346

Physics

76

Interplanetary Physics: Interplanetary Magnetic Fields, Ionosphere: Auroral Ionosphere, Magnetospheric Physics: Auroral Phenomena, Magnetospheric Physics: Solar Wind/Magnetosphere Interactions

Scientific paper

We present a classification of auroral forms in the dayside high-latitude ionosphere, based on ground observations from Svalbard. Having sorted the different auroral forms by magnetic local time (MLT) and morphological and optical spectral characteristics, we then study them as a function of the orientation of the interplanetary magnetic field (IMF). We find that the IMF clock angle θ is a good parameter with which to order the different dayside auroras. This is illustrated by two case examples covering the whole dayside: (1) the 4-hour-long passage of the sheath region of the January 10-11, 1997, magnetic cloud and (2) a 10-hour-long interval on January 12, 1997, during passage of the corotating stream overtaking the cloud. A variety of IMF conditions were realized. We identify the following three auroral configurations in the cusp region and the IMF clock angle regimes in which they occur: (1) In the clock angle range θ<45° there are auroral bands located at high latitudes (~78°-79° magnetic latitude (MLAT)), (2) For θ within ~45°-90°, auroral bands are simultaneously present at high and low (<75°MLAT) latitudes, (3) For θ>~90° the high-latitude aurora disappears, and only the low-latitude forms remain. These latter forms manifest themselves as quasiperiodic sequences of moving bands or band fragments within ~73°-78°MLAT (called poleward moving auroral forms) or quasi-steady auroral bands with east-west moving forms at low latitudes (<73°MLAT). Strong asymmetries in auroral forms and motions are related to the east-west component (By) of the IMF. The above auroral configurations are discussed in terms of current knowledge on particle precipitation, IMF-related, field-aligned currents, and corresponding modes of solar wind-magnetosphere coupling. We find that the time history of the basic magnetopause coupling modes is manifested in the dayside aurora. We identify candidate auroral signatures of both quasi-steady and pulsed reconnection processes occurring at either low or high magnetopause latitudes. Additional auroral forms in the dawn and dusk sectors are discussed in terms of processes in a closed magnetospheric model, such as the Kelvin-Helmholtz instability.

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