Rapid geomagnetic secular variation during the Swarm era and its impact on global field models

Brown, William; Beggan, Ciaran; Macmillan, Susan. 2017 Rapid geomagnetic secular variation during the Swarm era and its impact on global field models. [Poster] In: TSG-VMSG-BGA Joint Assembly 2017, Liverpool, UK, 4-6 Jan 2017. British Geological Survey. (Unpublished)

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Global geomagnetic field models are designed to represent the sources of Earth’s magnetic field and their variation in space and time. Such models are used to study the dynamics of the core, aid satellite operation and make global digital navigation possible – from smartphones to guided drilling. While current models capture the long-period and large-scale features and variations well, it is often difficult to represent the poorly understood small-scale and rapid behaviour of the field, thus making prediction difficult. The mantle and crust filter and mask small-scale spatial and temporal features and field sources external to the Earth contaminate the observations we have. Geomagnetic jerks represent the most rapid observed variations of the internal field, on the scale of months–years. With the prompt provision of ESA Swarm satellite constellation (<4 days) and auxiliary ground observatory measurements (3 months), it is possible to quickly construct up-to-date models of the geomagnetic field and its variations. We derive such a model based on Swarm era (2013–present) data and investigate the occurrence and spatiotemporal characteristics of recent jerks. Previous reports suggest that global models show regions of high secular acceleration associated with the 2014 jerk and that expressions might be seen at European observatories post-2014. We find limited evidence of a jerk in European observatories but do find globally widespread evidence, our models of this signal are in agreement with independent global geomagnetic field models. We also find evidence of a new jerk in 2015 in auxiliary observatory data. In response to these events we show the impact on early, and potential future, discrepancies between International Geomagnetic Reference Field (IGRF) predictions and observations in the period of 2015-2020 as a result of the unpredictable, non-linear secular variation of jerks. With the 2014 jerk occurring during / immediately after the data collection period for IGRF-12 and the new 2015 jerk occurring within one year of release we highlight the deviation from observations, the comparable performance of both simple and complex predictive models and the importance of utilising the ability to regularly update field models. This is likely to remain the case until the rapid dynamics of the core are better understood.

Item Type: Publication - Conference Item (Poster)
NORA Subject Terms: Earth Sciences
Date made live: 09 Jan 2017 16:35 +0 (UTC)

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