The theta aurora

摘要: The theta aurora is a remarkable configuration of auroral and polar cap luminosities for which generally sun-aligned transpolar arc extends contiguously from the dayside to nightside sectors oval. Four individual occurrences over earth's northern hemisphere are examined in detail with global imaging instrumentation on board high-altitude, polar-orbiting spacecraft DE 1. Simultaneous measurements fields plasmas this high-altitude its low-altitude, companion, 2, order establish an overview phenomena associated appearance aurora. For these series observations, two general states found corresponding (1) bright, well-developed (2) dim or absent arc. During periods relatively bright plasma convection region sunward. Elsewhere antisunward. pattern zones suggestive existence four cells convection. Field-aligned electron acceleration into atmosphere field-aligned current sheets present plasmas. This precipitation rest region. exhibit similar densities ion compositions relative those observed simultaneously poleward zone include hot H+, He++, O+ ions thus both ionospheric solar wind origins. Principal remainder H+ indicating access magnetosheath ions. Low-energy electrons identified source also dominant thermal flowing upward ionosphere. These heated along magnetic flux tubes within Pairs oppositely directed occur magnitudes currents carried by accelerated potential. Funnel-shaped hiss broadband electrostatic noise presence Energetic employed show that field lines threading oval probably closed. In contrast, accessibility indicates regions characterized topology connected directly interplanetary medium. Thus overall character appears be very latter currently thought magnetically mapped boundary layer sheet magnetotail, namely, high-speed beams currents. When at initial stages brightening, there severe change luminosities, electric fields, no longer signature simple four-cell pattern. Plasma turbulent sunward cap. Remarkably, ions, unique arc, still examples presented here. However, ionosphere displays complex system arcs glows almost entire Similarly, occurrence acceleration, noise, widespread Outside position primary composition indicative direct magnetosheath. implies magnetospheric topology. dynamics magnetosphere during actively contested issue. comprehensive, correlated observations here intended provide foundation future theoretical interpretive efforts.