Two-Component Aurora

It is well known that the auroral electrojet consists of two basic components: one is the direct-driven component and the other is the loading-unloading component. The former is associated with a convection enhancement caused by southward interplanetary magnetic field (IMF), while the latter is related to a sudden energy release from the tail onto the polar ionosphere. By examining Polar UltraViolet Imager auroral images at the 160-180 nm N₂ Lyman-Birge-Hopfield emission band, we find that the auroral dynamics during substorms shows a similar two-component feature. A pair of auroras (one on the dawnside and the other on the duskside) appear first. The Wind solar wind data show that they are associated with the southward IMF during the growth phase of substorms. A substorm occurs some time later, adding an additional aurora in the midnight sector. As the substorm continuously increases the strength, the substorm aurora connects with both the duskside and dawnside auroras, forming a well-defined crescent-shape aurora. In this presentation we will show examples of such auroral images and discuss their physical implication. "agu01fall.txt" 30 lines, 1267 characters