Energy‐flux relationship in the FUV Jovian aurora deduced from HST‐STIS spectral observations
Energy‐flux relationship in the FUV Jovian aurora deduced from HST‐STIS spectral observations
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从 HST-STIS 光谱观测推导出 FUV 木星极光的能量通量关系
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发表时间：
2004
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影响因子：
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通讯作者：
A. Grard
中科院分区：
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作者：
J. Gustin;J. Gérard;D. Grodent;S. Cowley;J. Clarke;A. Grard
[1]自1997年以来，利用哈勃空间望远镜上的空间望远镜成像光谱仪（STIS）以低光谱分辨率对木星极光进行了远紫外光谱观测。光谱分辨率与STIS狭缝沿着的强度变化相结合，提供了关于降水极光电子能量通量和平均电子能量的纬向变化的信息，由此还可以推断大气顶部的电子流密度。据发现，平均电子能量与主椭圆谎言在30-200 keV的范围内，并显示出增加的趋势与沉淀能通量。电流密度在0.04-0.4 μA m−2之间，与先前的估计一致，并且与能通量呈正相关。观测到的极光时间积分能量通量和主椭圆中的电子能量之间的关系与奈特的场向电流理论所预期的关系是相容的。当电子温度Te = 2.5 keV，源密度N = 0.003 cm−3时，观测数据和奈特曲线之间的最佳一致性是在旅行者号飞越赤道平面时观测到的数值范围内。没有系统的依赖性的电子能量与磁当地时间被发现，但上午部门约0800 MLT表现出更大的变化比其他地区的椭圆形。对时间标记数据的分析表明，主要的椭圆形能通量通常在几分钟的观测间隔内稳定地变化，平均电子能量通常经历相关的变化，使得电流密度保持相对恒定。它表明，这些整体性能也与骑士的极光电子加速理论与磁场对齐的电流，从它推断，观察到的时间变化往往是由于磁层的“源”电子参数的缓慢变化中存在的近稳定的磁层电离层耦合电流是一致的。相比之下，在极地地区的时间积分的排放量被发现与类似的平均电子能量的主要椭圆形，但通常较小的能量通量和电流密度。压力平衡参数先进，这表明，这些排放量的光明必须与极光加速机制，也许类似于在主椭圆操作，而它仍然可能是较弱的排放量可能会导致从准各向同性热磁层电子源的降水。
[1] Far ultraviolet spectral observations of the Jovian aurora have been made since 1997 with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope at low spectral resolution. The combination of the spectral resolution with the intensity variation along the STIS slit provides information on the latitudinal variation of the precipitating auroral electron energy flux and the mean electron energy, from which the electron current density at the top of the atmosphere can also be deduced. It is found that the mean electron energies associated with the main oval lie in the range 30–200 keV and show a tendency to increase with the precipitating energy flux. The current densities lie in the range ∼0.04–0.4 μA m−2, consistent with previous estimates, and are also positively correlated with the energy flux. The observed relationship between the auroral time-integrated energy fluxes and the electron energies in the main oval is compatible with that expected from Knight's theory of field-aligned currents. The best agreement between the observed data and the Knight curves is obtained for an electron temperature of Te = 2.5 keV and a source density N = 0.003 cm−3, that is within the range of values observed in the equatorial plane during the Voyager flybys. No systematic dependence of the electron energy with magnetic local time is found, but the morning sector around 0800 MLT shows greater variability than other regions of the oval. Analysis of time-tagged data shows that the main oval energy flux usually varies steadily over the several minute intervals of observation and that the mean electron energy usually undergoes correlated variations such that the current density remains relatively constant. It is shown that these overall properties are also consistent with Knight's theory of auroral electron acceleration associated with field-aligned current flow, from which it is inferred that the temporal variations observed are often due to slow changes in the magnetospheric “source” electron parameters in the presence of near-steady magnetosphere-ionosphere coupling currents. By contrast, time-integrated emissions in the polar region are found to be associated with similar mean electron energies to the main oval but with typically smaller energy fluxes and current densities. Pressure balance arguments are advanced, which indicate that the brighter of these emissions must be associated with an auroral acceleration mechanism perhaps similar to that operative in the main oval, while it remains possible that the weaker emissions could result from precipitation from a quasi-isotropic hot magnetospheric electron source.