Collaborative Research: Exploiting Geomagnetic Records to Describe Past and Present Ocean Variability

导电海洋在流经地球磁场时会产生电流和相关的磁场。这些电流随着海洋电导率和速度的变化而变化，可以通过陆地和卫星磁力计进行远程探测。因此，有机会从磁力计数据中恢复海洋流动和电导率的可变性。提取的信号非常有用，因为它们代表导电性和导电性传输的深度积分，可以作为测量持续时间内热含量和热传输的代用品--这些量一直很难用其他方法测量。磁力计数据来自数百个陆地磁力观测站(有些每小时的数据可以追溯到一个世纪以前)以及现代卫星磁力测量。这项拟议的工作将从陆地地磁观测站的长期记录中提取过去的海洋可变性，开发预测海洋磁场的正演模型，并最终开发用于陆地和卫星观测的数据同化策略。该项目将审查海洋电动力学的两个基本组成部分，并开发一种新的数据类型，用于监测和了解海洋的可变性和海平面的剧烈变化。这里使用的模型中的电磁场模块将公开提供。将组织讲习班，向学生和初级职业科学家介绍地磁观测站数据的分析及其与海洋学应用的联系。从地磁数据中提取海洋信号具有挑战性，因为信号相对较弱，需要对信号有先验知识。这项建议通过从火奴鲁鲁地磁观测站数据中提取的一个世纪的海洋潮汐变化的初步工作，证明了方法的可行性。这些独立的数据证实了以前在火奴鲁鲁验潮仪数据中发现的潮汐幅度增加的趋势，这被归因于海洋变暖。将对檀香山系列进行彻底分析，以优化海洋潮汐信号的提取。这些方法将被扩展到提取那里的其他可预测的海洋信号，如惯性振荡和年际振荡。类似的方法将应用于其他地方的地磁观测站数据。扩展将包括对来自多个地点以及来自卫星数据和地磁场模型的数据进行典型相关多变量分析。其他任务将包括开发和使用正演模型，以计算给定潮汐和环流海洋模型流的磁场(和电场)。提取的信号代表电导率和电导率传输的深度积分，可用作测量持续时间内热含量和热传输的代用指标--这些量一直很难用其他方法测量。因此，除了解决海洋电动力学的基本组成部分外，拟议的工作还将有助于开发一种新的数据类型，用于监测和了解海洋变异性和海平面变化。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The electrically conducting ocean generates electric currents and associated magnetic fields as it flows through the Earth’s magnetic field. These electric currents vary in time with changes in the ocean’s electrical conductivity and velocity, and can be detected remotely by land and satellite magnetometers. There is therefore an opportunity to recover ocean flow and conductivity variability from magnetometer data. Extracted signals are very useful, as they represent depth integrals of conductivity and conductivity transport, which can stand as proxies for heat content and heat transport over the measurement durations – quantities that have been hard to measure with other methods. Magnetometer data come from hundreds of land magnetic observatories (some with hourly data extending back a century) as well as from modern satellite magnetic surveys. The proposed work will extract past ocean variability from long, land geomagnetic observatory records, develop forward models for predicting the oceanic magnetic fields, and ultimately develop data assimilation strategies for both land and satellite observations. This project will examine both fundamental components of ocean electrodynamics and exploit a new data type for monitoring and understanding ocean variability and steric sea-level changes. The electromagnetic field modules in the model used here will be made publicly available. Workshops will be organized to introduce students and early career scientists to analysis of geomagnetic observatory data and its connection to oceanographic applications.Extracting oceanic signals from magnetic data is challenging because the signals are relatively weak and a priori knowledge of the signal is required. This proposal demonstrates method feasibility with preliminary work on a century of ocean tidal variability extracted from the Honolulu geomagnetic observatory data. These independent data confirm a trend toward increasing tidal amplitudes previously found in Honolulu tide gauge data that has been attributed to ocean warming. The Honolulu series will be thoroughly analyzed to optimize the extraction of ocean tidal signals. The methods will be extended to extract other predictable ocean signals there, such as inertial oscillations and interannual oscillations. Similar methods will be applied to geomagnetic observatory data from other locations. Extensions will include canonical-correlation multivariate analyses of data from multiple locations as well as from satellite data and geomagnetic field models. Additional tasks will involve the development and use of forward models to calculate the magnetic (and electric) fields given tidal and circulation ocean model flow. Extracted signals represent depth integrals of conductivity and conductivity transport, useful as proxies for heat content and heat transport over the measurement durations – quantities that have been hard to measure with other methods. Thus, in addition to addressing fundamental components of ocean electrodynamics the proposed work will be useful in exploiting a new data type for monitoring and understanding ocean variability and steric sea-level changes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.