The Floor in the Solar Wind Magnetic Field Revisited
The Floor in the Solar Wind Magnetic Field Revisited
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DOI：
10.1007/s11207-010-9657-6
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发表时间：
2011-12-01
期刊：
影响因子：
2.8
通讯作者：
Ling, A. G.
中科院分区：
文献类型：
--
作者：
Cliver, E. W.;Ling, A. G.
Svalgaard和Cliver（Astrophys. J. Lett. 661，L203，2007）提出，地球上的太阳风磁场强度[B]在年平均值中有一个“下限”值，即千分之一4.6 nT，在太阳极小期接近但没有达到。他们将地板归因于恒定的基线太阳开放通量。在2008年和2009年，这一最低标准的概念因B的年平均值为千分之一4 nT而受到削弱。在这里，我们提出了一个修订后的看法，无论是水平和概念的地板。两个独立的相关性表明，B有一个地板的千分之一2.8 nT的年平均值。这些是i）太阳极场强度和最近四个11年最小值的B年平均值（B（MIN））之间的关系，以及ii）第14周期的峰值太阳黑子数与前一个最小值的B（MIN）之间的前兆关系。这些相关性表明，在11年的最低值，B包括i）千分之一2.8 nT的地板，和ii）主要是由于太阳极场的组成部分，从千分之一0 nT到千分之一3 nT。太阳极区为随后的太阳黑子极大期提供了“种子”。从B（最小值）中去除千分之一2.8 nT的下限，使1996年和2009年最小值之间的B的百分比下降与太阳极场强度的相应下降相一致。基于分解的太阳风（从1972年到2009年的千分之一欧元）到高速流，日冕物质抛射，和缓慢的太阳风，我们认为，在B地板的来源是缓慢的太阳风。在2009年，地球在70%的时间里处于缓慢的太阳风流动中。我们提出，地板对应于一个基线（非循环或基态）开放的太阳能通量的千分之一8x10（13）Wb，这起源于持续的小尺度（超颗粒和颗粒）场。
Svalgaard and Cliver (Astrophys. J. Lett. 661, L203, 2007) proposed that the solar-wind magnetic-field strength [B] at Earth has a "floor" value of a parts per thousand 4.6 nT in yearly averages, which is approached but not broached at solar minima. They attributed the floor to a constant baseline solar open flux. In both 2008 and 2009, the notion of such a floor was undercut by annual B averages of a parts per thousand 4 nT. Here we present a revised view of both the level and the concept of the floor. Two independent correlations indicate that B has a floor of a parts per thousand 2.8 nT in yearly averages. These are i) a relationship between solar polar-field strength and yearly averages of B for the last four 11-year minima (B (MIN)), and ii) a precursor relationship between peak sunspot number for cycles 14 -aEuro parts per thousand 23 and B (MIN) at their preceding minima. These correlations suggest that at 11-year minima, B consists of i) a floor of a parts per thousand 2.8 nT, and ii) a component primarily due to the solar polar fields that varies from a parts per thousand 0 nT to a parts per thousand 3 nT. The solar polar fields provide the "seed" for the subsequent sunspot maximum. Removing the a parts per thousand 2.8 nT floor from B (MIN) brings the percentage decrease in B between the 1996 and 2009 minima into agreement with the corresponding decrease in solar polar-field strength. Based on a decomposition of the solar wind (from 1972 -aEuro parts per thousand 2009) into high-speed streams, coronal mass ejections, and slow solar wind, we suggest that the source of the floor in B is the slow solar wind. During 2009, Earth was in slow solar-wind flows a parts per thousand 70% of the time. We propose that the floor corresponds to a baseline (non-cyclic or ground state) open solar flux of a parts per thousand 8x10(13) Wb, which originates in persistent small-scale (supergranular and granular) field.