Tracing the electron density from the corona to 1 AU
Tracing the electron density from the corona to 1 AU
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DOI：
10.1023/a:1005049730506
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发表时间：
1998-11-01
期刊：
影响因子：
2.8
通讯作者：
Bougeret, JL
中科院分区：
文献类型：
--
作者：
Leblanc, Y;Dulk, GA;Bougeret, JL
利用“风”号宇宙飞船上的射电实验波从13.8 MHz到几kHz的观测数据，导出了从日冕到1 Au的黄道平面上的电子密度分布。我们专注于III型爆发的轨迹相交的航天器，确定存在的爆发相关的朗缪尔波，或由3-D等离子体实验观察到的高能电子。对于这些爆发，我们能够确定发射模式，基波或谐波，在1 Au的电子密度，沿着螺旋发射区的距离，以及所花费的时间，因为他们从低电晕1 Au。对于所有考虑的爆发，在爆发开始时的发射模式是基本的，相比之下，在推导许多以前的模型，谐波emission假定。通过测量爆发的开始时间在每个频率，我们能够推导出电子密度模型所有沿着的爆发的轨迹。我们的密度模型，在将1 Au处的密度归一化为n（e）（215 R-0）= 7.2 cm（-3）之后，（我们测量时太阳活动最小时的平均值），n（e）= 3.3 × 10（5）r（-2）+ 4.1 × 10（6）r（-4）+ 8.0 × 10（7）r（-6）cm（-3），其中r的单位为R-O。对于I Au处的其它密度，我们的结果意味着方程中的系数需要乘以n（e）（1 Au）/7.2。原位测量（归一化为1 Au的相同密度），并发现它与in-现场测量和较差的'无线电模型'的基础上，视源位置或假设的排放模式。我们的研究结果的一个含义是，孤立的III型爆发通常不会在日冕和太阳风的密集区域传播，因为它仍然有时假设。
We derive the electron density distribution in the ecliptic plane, from the corona to 1 AU, using observations from 13.8 MHz to a few kHz by the radio experiment WAVES aboard the spacecraft Wind. We concentrate on type III bursts whose trajectories intersect the spacecraft, as determined by the presence of burst-associated Langmuir waves, or by energetic electrons observed by the 3-D Plasma experiment. For these bursts we are able to determine the mode of emission, fundamental or harmonic, the electron density at 1 AU, the distance of emission regions along the spiral, and the time spent by the beams as they proceed from the low corona to 1 AU. For all of the bursts considered, the emission mode at burst onset was the fundamental; by contrast, in deriving many previous models, harmonic emission was assumed.By measuring the onset time of the burst at each frequency we are able to derive an electron density model all along the trajectory of the burst. Our density model, after normalizing the density at 1 AU to be n(e)(215 R-0) = 7.2 cm(-3) (the average value at the minimum of solar activity when our measurements were made), is n(e) = 3.3 x 10(5) r(-2) + 4.1 x 10(6) r(-4) + 8.0 x 10(7) r(-6) cm(-3),with r in units of R-0. For other densities at I AU our result implies that the coefficients in the equation need to be multiplied by n(e)(1 AU)/7.2.We compare this with existing models and those derived from direct, in-situ measurements (normalized to the same density at 1 AU) and find that it agrees very well with in-situ measurements and poorly with 'radio models' based on apparent source positions or assumptions of the emission mode. One implication of our results is that isolated type III bursts do not usually propagate in dense regions of the corona and solar wind, as it is still sometimes assumed.