By -dependent convection patterns during northward interplanetary magnetic field
By -dependent convection patterns during northward interplanetary magnetic field
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DOI：
10.1029/ja089ia11p09753
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发表时间：
1984-11
影响因子：
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通讯作者：
T. Potemra;L. Zanetti;P. Bythrow;A. Lui;T. Iijima
中科院分区：
文献类型：
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作者：
T. Potemra;L. Zanetti;P. Bythrow;A. Lui;T. Iijima
在向北的行星际磁场(IMF)期间，对极地日侧区域的Birkeland电流、电场和极光形态的观测可以统一起来，以符合IMF主要按分量排序的一致对流模式。在弱IMF by期间，两个极地对流单体对称地位于正午-午夜子午线的两侧，如先前报道的那样，在极地上空产生向阳对流。当IMF by变得显著正(负)时，黎明(黄昏)对流单体在北极冰盖上扩张，而另一个单体收缩。在南极帽中，是黄昏(黎明)细胞在膨胀。在强对流期间，该单体的膨胀使极地地区出现一个单一的对流单体。在“坍塌”环流区形成了一个大的对流流动梯度，在那里统计地观察到了向北BZ(NBZ)Birkland电流系统的反转、反太阳的极地电离层电流和最强的极帽电场。我们认为，这个对流梯度区还与太阳向北的弧线和西塔极光的跨极地弧线有关，这两个弧线是在极地地区向北移动时观察到的。本文提出的对流型与反平行合并模式是一致的。在反平行合并模式中，IMF与北上IMF间隔期尾叶的地磁线合并。在尾部产生的对流将等离子体从等离子体片带到尾部。这一过程分割了叶的开放场线，并在极冠中产生了与西塔极光的跨极弧相关联的闭合场线区域。
Observations of Birkeland currents, electric fields, and auroral forms in the dayside polar regions during periods of northward interplanetary magnetic field (IMF) can be unified to fit into consistent convection patterns ordered principally by the IMF By component. During periods of weak IMF By, two polar convection cells are symmetrically located on either side of the noon-midnight meridian, producing sunward convection over the pole, as previously reported. As the IMF By becomes significantly positive (negative), the dawn (dusk) convection cell expands across the northern polar cap, whereas the other cell shrinks. In the southern polar cap it is the dusk (dawn) cell which expands. During strong By this cell expansion gives the appearance of a single convection cell in the polar region. At the “collapsed” cell a large convective flow gradient is developed where reversal of the northward Bz (NBZ) Birkeland current system, antisunward polar ionospheric current, and the most intense polar cap electric fields are statistically observed. We suggest that this convection gradient region is also associated with sun-aligned arcs and the transpolar arc of the theta aurora, which are observed in the polar regions during northward IMF. The convection patterns proposed here are consistent with the antiparallel merging model in which the IMF merges with the geomagnetic field lines in the tail lobe during northward IMF intervals. The resulting convection in the tail brings plasma from the plasma sheet to the tail. This process divides the open field lines of the lobes and produces an area of closed field lines in the polar cap associated with the transpolar arc of the theta aurora.