Newcomb-Benford Law as a generic flag for changes in the derivation of long-term solar terrestrial physics timeseries

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 High Resolution (HRO) Interplanetary Magnetic Field incorporated new data from the WIND and Advanced Composition Explorer (ACE) spacecraft after 1995. NBL comparison can detect underlying changes in the geomagnetic Auroral Electrojet (AE) index (activity dependent background subtraction) and the SuperMAG Electrojet (SME) index (different station types) that select individual stations showing the largest deflection, but not where station data are averaged, as in the SuperMAG Ring Current (SMR) index. As composite indices become more widespread across the geosciences, the NBL may provide a generic, data processing independent flag indicating changes in the constituent raw data, calibration or sampling method.