The effects of long-term changes in the Earth's magnetic field on the atmosphere: understanding the past; predicting the future

“地球磁场长期变化对大气的影响：了解过去；这个项目研究地球内部磁场的变化对大气和气候的影响。近年来，地球磁场的变化相对较快。在过去十年中，北极磁极的位置一直在以有记录以来最快的速度移动，速度为每年40-60公里。此外，自1840年以来，磁场强度一直以每世纪5-7%的速度稳步下降，这导致人们猜测我们可能正在走向磁场逆转。一些研究发现了地球磁场变化与气候参数之间的相关性。然而，这种联系的负责机制仍然难以捉摸。该项目将研究地球磁场影响气候的一种可能途径，即由上层大气（~100-500公里）开始的向下传播的变化。这是一个以前从未被研究过的新想法。地球磁场的变化直接影响电离层和磁层，前者是上层大气中的带电部分，后者是地球周围保护我们免受太阳风影响的气泡。我们将使用耦合磁层-电离层-热层（CMIT）模式进行模拟，研究并量化自1600年以来地球磁场的历史变化对耦合高层大气和磁层系统的影响。所发现的响应将与观测到的高层大气的长期趋势和地磁活动指数进行比较，地磁活动指数测量电离层和磁层电流系统对地球主磁场的扰动。我们还将通过外推未来50-200年的当前磁场变化来探索一些潜在的未来情景。然后，我们研究在高层大气中发现的效应对中低层大气的影响程度。我们将使用全大气群落气候模式（WACCM）来完成这项工作，这是一个从地表延伸到高层大气的数值模式，与CMIT模式有部分重叠。在其顶部，WACCM将被迫与项目第一部分中发现的高层大气响应。我们将确定这些强迫的向下传播是否会引起下面大气的显著变化。对流层的任何显著响应都将与已观测到的磁场变化与气候参数之间的相关性进行比较。通过研究过去四个世纪磁场变化对气候的影响，该项目有助于更好地量化大气变率的自然来源。这需要正确地归因于观测到的气候趋势，并更精确地评估人为对气候的影响。两者对于制定缓解战略和准确预测未来气候至关重要。该项目还首次深入了解了磁场变化的影响，这是我们未来可以预期的。特别是磁场反转几乎肯定会对上层大气和地球空间环境以及这个环境所承载的技术系统产生戏剧性的后果。然而，对气候的影响很难预测，因为我们目前还不知道地球磁场会以何种方式和在多大程度上影响气候。这个计划将是我们进一步了解地球磁场和气候之间关系的第一步。

"The effects of long-term changes in the Earth's magnetic field on the atmosphere: understanding the past; predicting the future"This project investigates the effects of changes in the Earth's internal magnetic field on the atmosphere and climate. The Earth's magnetic field has been changing relatively rapidly in recent times. During the last decade, the position of the north magnetic pole has been moving at its fastest rate recorded so far, at 40-60 km/year. In addition, the magnetic field strength has been steadily decreasing at a rate of 5-7% per century since 1840, which has led to speculations that we may be heading for a magnetic field reversal. Some studies have found correlations between changes in the Earth's magnetic field and climate parameters. However, the responsible mechanism for this link has remained elusive. This project will investigate one possible pathway by which the Earth's magnetic field could affect climate, namely the downward propagation of changes initiated in the upper atmosphere (~100-500 km). This is a novel idea that has not been investigated before.Changes in the Earth's magnetic field directly influence the ionosphere, the charged portion of the upper atmosphere, and the magnetosphere, the bubble around the Earth that shields us from the solar wind. We will examine and quantify the effects of historical changes in the Earth's magnetic field that have occurred since 1600 on the coupled upper atmosphere and magnetosphere system, using simulations with the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model. The responses found will be compared to observed long-term trends in the upper atmosphere and indices of geomagnetic activity, which measure perturbations to the Earth's main magnetic field as a result of ionospheric and magnetospheric current systems. We will also explore some potential future scenarios by extrapolating current magnetic field changes into the next 50-200 years.We then investigate to what extent the effects found in the upper atmosphere influence the middle and lower atmosphere. We will do this using the Whole Atmosphere Community Climate Model (WACCM), a numerical model that extends from the surface to the upper atmosphere, partly overlapping with the CMIT model. At its top, WACCM will be forced with the upper atmospheric responses found in the first part of the project. We will determine whether downward propagation of these forcings causes a significant change in the atmosphere below. Any significant response in the troposphere will be compared to the correlations between magnetic field changes and climate parameters that have been observed.By studying the effects of magnetic field changes on the climate over the past four centuries, this project contributes to a better quantification of natural sources of atmospheric variability. This is needed to attribute observed climate trends correctly and assess man-made effects on climate more precisely. Both are essential for developing mitigation strategies and for making accurate predictions of future climate. The project also offers a first insight into the effects of magnetic field changes that we can expect in the future. Especially a magnetic field reversal would almost certainly have dramatic consequences for the upper atmosphere and geospace environment, and the technological systems this environment hosts. However, the effects on climate are very hard to predict, as we currently do not know in what ways and to what extent the Earth's magnetic field can affect climate. The proposed project will be a first step in improving our understanding of the link between the Earth's magnetic field and climate.