Magnetopause reconnection rate estimates for Jupiter's magnetosphere based on interplanetary measurements at ~5AU
Magnetopause reconnection rate estimates for Jupiter's magnetosphere based on interplanetary measurements at ~5AU
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基于 ~5AU 行星际测量的木星磁层磁层顶重联率估计
DOI：
10.5194/angeo-24-393-2006
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发表时间：
2006
影响因子：
1.9
通讯作者：
D. McComas
中科院分区：
文献类型：
--
作者：
J. Nichols;S. Cowley;D. McComas
抽象。我们利用扩展的原位数据集，在Brice和Ionannouncement（1970）以及Kennel和Coroniti（1975，1977）大约30年前所做的简单数量级估计的基础上，首次对木星磁层顶重联率进行了定量估计。木星低纬度磁层顶（开放通量产生）重联电压是使用杰克曼等人（2004年）的算法估算的，该算法在地球上得到验证，以前应用于土星，现在适用于木星。高纬度（波瓣）磁层顶重联电压也是使用Gerard等人（2005年）的算法计算的，该算法以前也用于土星。我们使用的数据从木星探测器获得的时期，当它位于5AU附近和黄道面5°内（1992年1月至6月，1998年1月至8月，2004年4月至10月），沿着从卡西尼号飞船在2000/2001年飞越木星期间获得的数据。我们包括磁层压缩的影响，通过动态压力调制，并检查在整个木星的一天和一年的木星磁轴方向的变化的影响。所考虑的数据间隔代表太阳周期的不同阶段，因此我们也能够检查太阳周期依赖性。低纬度地区的整体平均重联电压估计约为230 kV，因此在一个太阳旋转过程中产生的平均开放通量约为500 GWb。因此，我们估计木星磁尾的平均时间，其中包含约300-500 GWb的开放通量，为约15-25天，对应的尾巴长度约3.8-6.5 Au。平均高纬度重联电压估计为~130千伏，与叶“搅拌”。然而，在这些平均值内，估计的电压经历相当大的变化。一般来说，低纬度重联电压呈现出约100 kV的“背景”，在每次太阳旋转期间，会被一个或两个显著的增强事件打断，其中电压升高到约1-3 MV。据估计，高纬度地区的电压约为这些值的一半。我们注意到，为了几MV的峰值是可比的潜在下降，由于在赤道磁层之间的20 RJ和磁层顶，这样，在这些期间磁层顶重连可能有一个显着的影响，否则旋转为主的磁层的次共转等离子体流。然而，尽管在每次太阳自转期间有这样的变化，但在每次太阳自转期间产生的开放通量的总量通常在该时期的总体平均值的两侧变化不到30%。各个数据时期的平均值在整个太阳周期内变化，从太阳活动最大时的每太阳旋转约600 GWb到太阳活动最小时的约400 GWb。此外，我们还表明，当木星自转轴时钟角也为正值时，具有正时钟角的IMF扇区有利于重联，反之亦然，尽管这种效应代表了对电压的一阶修正，而电压主要受到IMF的调制强度和方向。
Abstract. We make the first quantitative estimates of the magnetopause reconnection rate at Jupiter using extended in situ data sets, building on simple order of magnitude estimates made some thirty years ago by Brice and Ionannidis (1970) and Kennel and Coroniti (1975, 1977). The jovian low-latitude magnetopause (open flux production) reconnection voltage is estimated using the Jackman et al. (2004) algorithm, validated at Earth, previously applied to Saturn, and here adapted to Jupiter. The high-latitude (lobe) magnetopause reconnection voltage is similarly calculated using the related Gerard et al. (2005) algorithm, also previously used for Saturn. We employ data from the Ulysses spacecraft obtained during periods when it was located near 5AU and within 5° of the ecliptic plane (January to June 1992, January to August 1998, and April to October 2004), along with data from the Cassini spacecraft obtained during the Jupiter flyby in 2000/2001. We include the effect of magnetospheric compression through dynamic pressure modulation, and also examine the effect of variations in the direction of Jupiter's magnetic axis throughout the jovian day and year. The intervals of data considered represent different phases in the solar cycle, such that we are also able to examine solar cycle dependency. The overall average low-latitude reconnection voltage is estimated to be ~230 kV, such that the average amount of open flux created over one solar rotation is ~500 GWb. We thus estimate the average time to replenish Jupiter's magnetotail, which contains ~300-500 GWb of open flux, to be ~15-25 days, corresponding to a tail length of ~3.8-6.5 AU. The average high-latitude reconnection voltage is estimated to be ~130 kV, associated with lobe "stirring". Within these averages, however, the estimated voltages undergo considerable variation. Generally, the low-latitude reconnection voltage exhibits a "background" of ~100 kV that is punctuated by one or two significant enhancement events during each solar rotation, in which the voltage is elevated to ~1-3 MV. The high-latitude voltages are estimated to be about a half of these values. We note that the peak values of order a few MV are comparable to the potential drop due to sub-corotating plasma flows in the equatorial magnetosphere between ~20 RJ and the magnetopause, such that during these periods magnetopause reconnection may have a significant effect on the otherwise rotationally dominated magnetosphere. Despite such variations during each solar rotation, however, the total amount of open flux produced during each solar rotation varies typically by less than ~30% on either side of the overall average for that epoch. The averages over individual data epochs vary over the solar cycle from ~600 GWb per solar rotation at solar maximum to ~400 GWb at solar minimum. In addition we show that the IMF sector with positive clock angle is favoured for reconnection when the jovian spin axis clock angle is also positive, and vice versa, although this effect represents a first order correction to the voltage, which is primarily modulated by IMF strength and direction.