Dynamical Properties of Peak and Time‐Integrated Geomagnetic Events Inferred From Sample Entropy

Abstract

We provide a comprehensive statistical analysis of the sample entropy of peak and time‐integrated geomagnetic events in 2001–2017, considering different measures of event strength, different geomagnetic indices, and a simplified solar wind‐magnetosphere coupling function P*. Our investigations reveal the existence of significant correlations between the entropies of Dst, ap, and P*, and between such entropies and event strengths, as well as good correlations between peak levels of solar wind‐magnetosphere coupling and ring current ( Dst) and ap entropies, suggesting a potential predictability of significant Dst and ap events on the basis of appropriate functions of P*. Sensibly weaker correlations are found with AE entropy. We further show the presence of several significant entropy correlations between geomagnetic indices, solar wind‐magnetosphere coupling, and trapped or precipitated energetic electron and ion fluxes measured by geostationary and low Earth orbit satellites in the outer radiation belt during the same periods. Entropy correlations between Dst and trapped or precipitated 30‐ to 80‐keV ion fluxes at low L and between AE and trapped 40‐keV electron fluxes at geostationary orbit correspond well with ring current properties and substorm‐induced injections, respectively. Entropy correlations between ap and precipitation rates of energetic ion and electron fluxes demonstrate the sensibility of ap index entropy to both low‐energy (5–30 keV) electron injections and ring current. The stronger entropy correlation between solar wind‐magnetosphere coupling and ap than AE likely stems from the more stochastic behavior of electron injections and fast losses near geostationary orbit.

Identification of Fractal Properties in Geomagnetic Data of Southeast Asian Region during Various Solar Activity Levels

“…This finding reaffirms the long standing theory that disturbed days generally has a higher level of scaling exponent compared to quiet days [12,14,60,61], resulting in a higher level of Hurst exponent. The higher level of Hurst exponent also indicates that the entropy of geomagnetic data strongly decreases during disturbed period [62,63]. It was also found that the results from LKW station were slightly higher than that of DAV station, with different levels of deviation for each class.…”

Immediate and delayed responses of power lines and transformers in the Czech electric power grid to geomagnetic storms

“…In contrast, the range indices AE and AL are measured at higher magnetic latitudes >60°inside the auroral region (Mayaud, 1980;Kamide & Rostoker, 2004), and AE saturates at high geomagnetic activity am > 150 (with am a mid-latitude index similar to ap) because the auroral oval then expands equatorward of the magnetometer stations measuring it (Thomsen, 2004;Lockwood et al, 2019). Therefore, ap is probably more appropriate than AE for quantifying the strength of time-integrated geomagnetic disturbances at middle (sub-auroral) geomagnetic latitudes than AE (Thomsen, 2004;Mourenas et al, 2020).…”

“…While ring current variations during storms can be quantified by Dst and SYM-H indices, the magnetic indices that provide a measure of magnetospheric and ionospheric current variations observed during strong substorms are AE, AL, Kp, or ap (Mayaud, 1980;Kamide & Kokobun, 1996;Thomsen, 2004;Mourenas et al, 2020). The ap index (as its logarithmic equivalent Kp) provides a global measure of the range of magnetic field variations at middle latitudes over 3-h time scales, obtained by averaging measurements from different midlatitude magnetometer stations spread in longitude (Mayaud, 1980;Thomsen, 2004).…”

“…Accordingly, we shall consider in Section 4.3 a third parameter of geomagnetic activity, IntAp, corresponding to the daily maximum level of the integral of 3-hourly ap values over a continuously active period of ap ! 15 nT (Mourenas et al, 2019(Mourenas et al, , 2020. This should allow to categorize disturbed days that include contributions to GICs from both (storm-time) ring current variations and strong substorms, usefully complementing the Int(d(SYM-H)/dt) and IntDst parameters.…”

“…IntAE is the daily maximum level of the integral of AE calculated over the same period of continuously high ap ! 15 nT as IntAp (generally corresponding to AE > 200 nT), to ensure that the corresponding substorm-related magnetic disturbances effectively reach middle latitudes (Mourenas et al, 2019(Mourenas et al, , 2020. IntAE provides a measure of cumulative substorm-related disturbances, corresponding to continuous periods of auroral current variations roughly similar to High-Intensity Long-Duration Continuous AE Activity (HILDCAA) events (Tsurutani et al, 2006).…”