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Table 4 Forecast error (in nT) over recent 5-year periods for different forecasting strategies

From: A candidate secular variation model for IGRF-12 based on Swarm data and inverse geodynamo modelling

  2005.0–2010.0 2009.0–2014.0
Nocast 398.3 438.4
Linear extrapolation 66.0 57.5
Coupled Earth 76.2 81.4
Steady flow 62.5 59.3
  1. The forecast error is expressed as the root-mean-squared difference between the true geomagnetic field, defined by an update of the CHAOS-4 field model (Olsenet al. 2014) including preliminary Swarm data, and the forecast at the terminal epoch. Nocast assumes that the field does not change. Linear extrapolation assumes a linear variation whose slope is specified by the exact knowledge of the secular variation up to degree 13 at the start of the forecast period (2005.0 or 2009.0), as specified by the update of the CHAOS-4 field model; “Coupled Earth” means that the forecast is based on the integration of the full coupled Earth dynamo model, Steady flow means that the forecast is based on the sole integration of the three-dimensional induction equation (with magnetic diffusion)