Modeling Jupiter's decametric modulation lanes
Modeling Jupiter's decametric modulation lanes
复制标题
模拟木星的十进制调制通道
DOI：
10.1029/96ja03960
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发表时间：
1997
影响因子：
--
通讯作者：
Thomas D. Can
中科院分区：
文献类型：
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作者：
K. Imai;Liyun Wang;Thomas D. Can
木星十米波射电频谱中的调制通道是由Riihimaa [1968]发现的。我们已经开发了一个模型的机制，负责其生产的自由参数已被调整，以提供一个非常密切的配合与观察。在我们的模型中，由增强或耗尽等离子体密度的场对准柱组成的网格状干涉屏位于靠近地球下点经度的木卫一轨道附近。柱间距通常约为140 km。当从激发的磁通量管底部附近发射的频率分量带穿过屏幕时，不同的频率会产生方向略有不同的干涉图案。这组干涉图样与木星的共转导致了观测到的动态光谱的倾斜调制通道。新的计算结果表明：（1）Io-B和Io-A辐射主要来自北方半球，而Io-C辐射主要来自南半球;（2）Io-B假设的空锥发射光束的半角度通常为60°，变化几度，（3）在同一时刻，在通过Io的通量管前面的无线电发射的先前激发的通量管的赤道超前角变化较大，Io-B的典型值为50°。来自与木卫一无关的发射的调制通道也被成功地模拟出来，在这种情况下，假设是一些能量源，而不是与木卫一直接相遇，激发了包含发射射电源的通量管。非Io-A的L壳值定义不太清楚，但肯定在4和7之间。对Io-B和Io-A的通道调制深度的灵敏测量表明，干涉屏柱的衰减时间与木星的自转周期具有相同的数量级。尽管约2 s的主要调制通道周期性指示沿增加的经度方向沿着70 km的Io-B源宽度的上限，但在至少一种情况下存在的更精细结构表明上限仅为20 km。
The modulation lanes in Jupiter's decametric radio spectra were discovered by Riihimaa [1968]. We have developed a model for the mechanism responsible for their production in which the free parameters have been adjusted to provide a very close fit with the observations. In our model, a grid-like interference screen composed of field-aligned columns of enhanced or depleted plasma density is located near Io's orbit close to the longitude of the sub-Earth point. The column spacing is typically about 140 km. As a band of frequency components emitted from near the foot of an excited tube of magnetic flux passes through the screen, interference patterns of slightly different orientations are produced by the different frequencies. The corotation of this set of interference patterns with Jupiter results in the sloping modulation lanes of the observed dynamic spectrum. Newly calculated results indicate that (1) the Io-B and Io-A radiations are emitted from the northern hemisphere, while that from Io-C comes mainly from the southern hemisphere, (2) the half-angle of the assumed hollow-cone emission beam for Io-B is typically 60°, with a variation of a few degrees, and (3) the equatorial lead angle of the radio-emitting previously excited flux tube ahead of the flux tube through Io at the same instant is more variable, 50° being a typical value for Io-B. Modulation lanes from Io-unrelated emission were also successfully modeled, the assumption in this case being that some source of energy other than a direct encounter with Io excited the flux tube containing the emitting radio source. The L shell value for non-Io-A was less clearly defined but was definitely between 4 and 7. Sensitive measurements of the lane modulation depths for Io-B and Io-A indicated that the decay time for the columns of the interference screen is of the same order of magnitude as Jupiter's rotation period. Although the predominant modulation lane periodicity of about 2 s indicates an upper limit on Io-B source width of 70 km along the direction of increasing longitude, finer structure that was present in at least one case suggests an upper limit of only 20 km.