Out-of-Cycle Update of the US/UK World Magnetic Model for 2015-2020

In early 2018, the World Magnetic Model 2015-2020 (WMM2015) was predicted to exceed its performance specification error tolerances by the end of 2018 or early 2019. Specifically, the grid variation root-mean-square error was about to exceed the 1 degree specification (MIL-PRF89500A) due to fast fluid flows in the Earth’s outer core, especially in the North polar region. An out-of-cycle update of the WMM2015 was developed and released in early 2019 (WMM2015v2) to address this performance degradation. There was a pre-release in September 2018 and this technical note confirms the information provided in that pre-release. It also provides a description of the new model (section 1), how it was produced (section 2) and its uncertainties (section 3). How to Use this Note: A complete description of the WMM2015 is provided in the WMM2015 Technical Report (Chulliat et al., 2015; WMM2015-TR hereafter (http://nora.nerc.ac.uk/id/eprint/510709/)). This new technical note should be seen as an addendum to the WMM2015-TR. It is organized in the same manner as the WMM2015-TR in order to facilitate the retrieval of information by users. It only includes information that is new for the out-of-cycle update, hereafter referred to as WMM2015v2.