Desarrollo de la Antártica

Takesí Nagata / THE ADVANCEMENT OF SCIENTIFIC RESEARCH ••• magnetO'spheric plasma mO'tiO'n finally results in an plasma instabi– lity in the anti-sO'lar side (night-side) magnetO'sphere, electrO'ns and prO'tons there ibeing accelerated~by tlhe instability effect tO' precipita te intO' the earth's polar atmO'sphere along the geomagnetic fieId lines. This is an onset of t:he auroral flare expansion phase. The time du– ration of the growth phase is generalIy 1 '-' 2 hours. The onset of the expansiO'n phase is characterized by a) a sudden brightning O'f the electron auroral is near the midnight, which ra– pidly moves ,poleward and fO'nns an electrO'n aurO'ral bulge, the newly formed auroral bulge rapidly expanding pO'leward and wcst– ward (where theexpansion velocity is abO'ut 1 kmjsec), and b) a sudden brightning prO'ton aurora in the post·midnight sectO'r. During 10 '-' 30 minutes after the expansion phase O'nset, the electrO'n aurO'– ral bulge further expa,nds westward a!nd poleward. In !!he area which has been swept by tlhe expanding electron aurora, the proton auroral belt which was previously shifted equatorward, retums pO'le– ward. In the dusk sector, the bridghtness oi prO'ton aurora is greatly increased and this prO'ton aurO'ral belt expands equatorward. ,1 '-' 2 hO'urs after rhe expansion phase onset, the poleward and westward expansiO'n O'f tlhe electrO'n aurO'ra is stO'pped, and the equatorward expanded proton aurO'ral belt in the evening sectO'r begins tO' retum poleward. This is the recoveryphase of an auroral fiare. It has heen physically c1arified that these movements O'f electrO'n and prO'ton auro– ral belts are caused by the electronand proton mavements in mag– netosplhere due tO' the magnetospheric plasma folw instability. ii. Polar Magnetic substonn It is observed in the case of an auroral fiare that intense electric eu– rrents fIow along the lines oi geomagnetic field and the auroral zone iO'nO'sphere, thus prO'ducing a polar magnetic substonn. Westward elec– trie currents fIow along a bright arc of the electron aurO'ra, resulting in a negative magnetic bay O'n the ground. Along a band O'f !he pro– ton aurora, on the otiber hand, eastward electric currents flow and consequently the currents are assO'ciated with a pO'sitive magnetic bay on the ground. HistO'rically, studies on these magnetic bay phe– nomena were tihe initiatiO'n O'f researches of the magnetospheric subs– torms including a,uroral fiares. iii. Other polar substO'rm phenO'mena Fig. 12 schematically illustrates an example of simuJtaneous magnetic, ionospheric and VLF substonn phenO'mena wlhich are assO'ciated with 111