Reconfiguration and closure of lobe flux by reconnection during northward IMF: possible evidence for signatures in cusp/cleft auroral emissions

[摘要] Observations are presented of the response ofthe dayside cusp/cleft aurora to changes in both the clock and elevation anglesof the interplanetary magnetic field (IMF) vector, as monitored by the WINDspacecraft. The auroral observations are made in 630 nm light at the wintersolstice near magnetic noon, using an all-sky camera and a meridian-scanningphotometer on the island of Spitsbergen. The dominant change was the response toa northward turning of the IMF which caused a poleward retreat of the daysideaurora. A second, higher-latitude band of aurora was seen to form following thenorthward turning, which is interpreted as the effect of lobe reconnection whichreconfigures open flux. We suggest that this was made possible in the winterhemisphere, despite the effect of the Earth's dipole tilt, by a relatively largenegative X component of the IMF. A series of five events then formed in thepoleward band and these propagated in a southwestward direction and faded at theequatorward edge of the lower-latitude band as it migrated poleward. It is shownthat the auroral observations are consistent with overdraped lobe flux beinggenerated by lobe reconnection in the winter hemisphere and subsequently beingre-closed by lobe reconnection in the summer hemisphere. We propose that thebalance between the reconnection rates at these two sites is modulated by theIMF elevation angle, such that when the IMF points more directly northward, thesummer lobe reconnection site dominates, re-closing all overdraped lobe flux andeventually becoming disconnected from the Northern Hemisphere.

Key words. Magnetospheric physics (magnetopause · cuspand boundary layers; solar-wind-magnetosphere interactions) · Space plasmaphysics (magnetic reconnection)

[学科分类] 地球科学(综合)