Newcomb-Benford Law characterization of solar wind magnetic field and geomagnetic indices

Abstract

The Newcomb-Benford Law (NBL) prescribes the probability distribution of the first digit of variables which explore a broad range under conditions including aggregation. Long-term space weather relevant observations and indices necessarily incorporate changes in the contributing number and types of observing instrumentation over time and we find that this can be detected solely by comparison with the NBL. It detects when upstream solar wind magnetic field OMNI HRO Interplanetary Magnetic Field incorporated new data from WIND and ACE after 1995. NBL comparison can detect underlying changes in geomagnetic indices AE (activity dependent background subtraction) and SME (different station types) that select individual stations showing the largest deflection, but not where station data are averaged, as in the SMR index. As composite indices becomes more widespread across the geosciences, the NBL may provide a generic data flag to indicate changes in the constituent raw data, calibration or sampling method.