Multispacecraft observation of magnetic cloud erosion by magnetic reconnection during propagation
Multispacecraft observation of magnetic cloud erosion by magnetic reconnection during propagation
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DOI：
10.1029/2012ja017624
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发表时间：
2012-09-07
影响因子：
2.8
通讯作者：
Galvin, A. B.
中科院分区：
文献类型：
--
作者：
Ruffenach, A.;Lavraud, B.;Galvin, A. B.
在传播过程中，磁云（MC）与它们的环境相互作用，特别是可能与周围的太阳风重新连接，侵蚀掉其初始磁通量的一部分。在这里，我们定量分析这样的相互作用，使用组合，多点观测同一MC通量绳STEREO A，B，ACE，风和THEMIS在2007年11月19日至20日。观测MC磁绳内的方位磁通量不平衡被认为是由于其前边界处的磁重联引起的侵蚀。本研究增加了这样的分析，预计从这个侵蚀过程中的一个大的签名集。(1)在相距甚远的点上对同一MC进行方位角通量不平衡的比较，排除了MC腿交叉作为通量不平衡估计偏差的来源。(2)使用不同的方法，相关的误差和参数分析表明，只有一个意想不到的大误差MC轴方向可以解释方位磁通不平衡。(3)在所有航天器的MC前端都观察到了重连特征，这与正在进行的侵蚀过程相一致。(4)超热电子的签名表明，MC的尾部有一个不同的大尺度磁拓扑结构，正如预期的那样。在ACE和STEREO A处估计的方位磁通量侵蚀分别对应于传播时MC侵蚀之前推断的初始方位磁通量的44%和49%。在过境期间，相应的平均重连率估计在0.12-0.22 mV/m的范围内，这表明大部分侵蚀发生在日光层的内部。未来的研究应该量化这种侵蚀过程对地质效益的影响。
During propagation, Magnetic Clouds (MC) interact with their environment and, in particular, may reconnect with the solar wind around it, eroding away part of its initial magnetic flux. Here we quantitatively analyze such an interaction using combined, multipoint observations of the same MC flux rope by STEREO A, B, ACE, WIND and THEMIS on November 19-20, 2007. Observation of azimuthal magnetic flux imbalance inside a MC flux rope has been argued to stem from erosion due to magnetic reconnection at its front boundary. The present study adds to such analysis a large set of signatures expected from this erosion process. (1) Comparison of azimuthal flux imbalance for the same MC at widely separated points precludes the crossing of the MC leg as a source of bias in flux imbalance estimates. (2) The use of different methods, associated errors and parametric analyses show that only an unexpectedly large error in MC axis orientation could explain the azimuthal flux imbalance. (3) Reconnection signatures are observed at the MC front at all spacecraft, consistent with an ongoing erosion process. (4) Signatures in suprathermal electrons suggest that the trailing part of the MC has a different large-scale magnetic topology, as expected. The azimuthal magnetic flux erosion estimated at ACE and STEREO A corresponds respectively to 44% and 49% of the inferred initial azimuthal magnetic flux before MC erosion upon propagation. The corresponding average reconnection rate during transit is estimated to be in the range 0.12-0.22 mV/m, suggesting most of the erosion occurs in the inner parts of the heliosphere. Future studies ought to quantify the influence of such an erosion process on geo-effectiveness.