Stochastic properties of the geomagnetic field across the 210 mm chain

We explore the stochastic fractal qualities of the geomagnetic field from 210 mm ground-based magnetometers during quiet and active magnetospheric conditions. We search through 10 years of these data to find events that qualify. Quiet intervals are defined by Kp ≤ 1 for 1,440 consecutive minutes. Similarly, active intervals require Kp ≥ 4 for 1,440 consecutive minutes. The total for quiet intervals is ~4.3×106 minutes and 2×108 minutes for active data points. With this large number of events compiled we then characterize changes in the nonlinear statistics of the geomagnetic field via measurements of a fractal scaling exponent. A clear difference in statistical behavior during quiet and active intervals is implied through analysis of the scaling exponents; active intervals generally have larger values of scaling exponents. This means that although 210 mm data appears monofractal on shorter timescales, it is more properly described as a multifractional Brownian motion. Long-range statistical behavior of the geomagnetic field at a local observation site can be described as a multifractional Brownian motion, thus suggesting the statistical structure required of mathematical models of magnetospheric activity. We also find that low-latitudes have scaling exponents that are consistently larger than for high-latitudes.