A Geomagnetic Estimate of Heliospheric Modulation Potential over the Last 175 Years

IF 2.7 3区 物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS
Mathew J. Owens, Luke A. Barnard, Raimund Muscheler, Konstantin Herbst, Mike Lockwood, Ilya Usoskin, Eleanna Asvestari
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引用次数: 0

Abstract

Galactic cosmic rays (GCRs) interact with the Earth’s atmosphere to produce energetic neutrons and cosmogenic radionuclides, such as 14C. The atmosphere is partially shielded from the interstellar GCR spectrum by both the geomagnetic and solar magnetic fields. Solar shielding is often expressed as the heliospheric modulation potential \(\phi \), which consolidates information about the strength and structure of the solar magnetic field into a single parameter. For the period 1951 to today, \(\phi \) can be estimated from ground-based neutron monitor data. Prior to 1950, 14C in tree rings can be used to estimate \(\phi \) and hence the solar magnetic field, back centuries or millennia. Bridging the gap in the \(\phi \) record is therefore of vital importance for long-term solar reconstructions. One method is to model \(\phi \) using the sunspot number (SN) record. However, the SN record is only an indirect measure of the Sun’s magnetic field, introducing uncertainty, and the record suffers from calibration issues. Here we present a new reconstruction of \(\phi \) based on geomagnetic data, which spans both the entire duration of the neutron monitor record and stretches back to 1845, providing a significant overlap with the 14C data. We first modify and test the existing model of \(\phi \) based on a number of heliospheric parameters, namely the open solar flux \(F_{S}\), the heliospheric current sheet tilt angle \(\alpha \), and the global heliospheric magnetic polarity \(p\). This modified model is applied to recently updated geomagnetic estimates of \(F_{S}\) and cyclic variations of \(\alpha \) and \(p\). This approach is shown to produce an annual estimate of \(\phi \) in excellent agreement with that obtained from neutron monitors over 1951 – 2023. It also suggests that ionisation chamber estimates of \(\phi \) – which have previously been used to extend the instrumental estimate back from 1951 to 1933 – are not well calibrated. Comparison of the new geomagnetic \(\phi \) with 14C estimates of \(\phi \) suggests that the long-term trend is overestimated in the most recent 14C data, possibly due to hemispheric differences in the Suess effect, related to the release of carbon by the burning of fossil fuels. We suggest that the new geomagnetic estimate of \(\phi \) will provide an improved basis for future calibration of long-term solar activity reconstructions.

Abstract Image

对过去 175 年日光层调制潜力的地磁估算
银河宇宙射线(GCR)与地球大气相互作用,产生高能中子和宇宙放射性核素,如 14C。地磁场和太阳磁场会部分屏蔽大气层中的星际 GCR 光谱。太阳屏蔽通常用日光层调制电势(\phi \)来表示,它将太阳磁场强度和结构的信息整合为一个参数。1951 年至今,可以根据地基中子监测器数据估算出 \(\phi \)。在1950年之前,树年轮中的14C可以用来估算(\phi \),从而估算出几个世纪或几千年前的太阳磁场。因此,填补(\phi)记录的空白对于长期太阳重建至关重要。一种方法是利用太阳黑子数(SN)记录来模拟(\\phi \)。然而,太阳黑子数记录只是太阳磁场的间接测量,会带来不确定性,而且该记录还存在校准问题。在这里,我们提出了一种基于地磁数据的新\(\phi \)重建方法,它既跨越了整个中子监测记录的持续时间,又可以追溯到1845年,与14C数据有很大的重叠。我们首先根据一些日光层参数,即开放的太阳通量(F_{S}\)、日光层电流片倾斜角(\α\)和全球日光层磁极性(p\),修改并测试了现有的(\phi \)模型。这个修改后的模型被应用于最近更新的地磁估计值(F_{S}\)以及(α)和(p)的周期变化。结果表明,这种方法得出的(\phi \)年度估计值与1951-2023年中子监测器得出的估计值非常一致。它还表明,电离室对 \(\phi \)的估计值--以前曾用来将仪器估计值从 1951 年回溯到 1933 年--并没有得到很好的校准。新的地磁(\phi \)与14C估计值(\phi \)的比较表明,在最新的14C数据中,长期趋势被高估了,这可能是由于与化石燃料燃烧释放碳有关的苏斯效应的半球差异造成的。我们建议,新的(\phi \)地磁估计将为今后校准长期太阳活动重建提供一个更好的基础。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Solar Physics
Solar Physics 地学天文-天文与天体物理
CiteScore
5.10
自引率
17.90%
发文量
146
审稿时长
1 months
期刊介绍: Solar Physics was founded in 1967 and is the principal journal for the publication of the results of fundamental research on the Sun. The journal treats all aspects of solar physics, ranging from the internal structure of the Sun and its evolution to the outer corona and solar wind in interplanetary space. Papers on solar-terrestrial physics and on stellar research are also published when their results have a direct bearing on our understanding of the Sun.
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