The solar terminator, due to its unique characteristics, is a remarkable source of atmospheric disturbances. Due to its regularity and constancy, dependent solely on geometric factors, it can serve as a test source of disturbances, which can be used to test the response of the medium through which it passes and determine its state. However, our knowledge of the atmospheric phenomena generated by the terminator is far from complete. One clear indication of the terminator’s influence is geomagnetic disturbances manifested in the vertical and eastward components of the magnetic field measured at magnetic observatories. To determine the sources of geomagnetic disturbances from the solar terminator, which can be identified by the strict phase correlation of these disturbances with the moments of terminator passage, ionospheric irregularities arising during terminator passage were studied. Ionospheric irregularities extending along the boundary of the morning solar terminator were detected in total electron content data, based on measurements by GNSS receivers. Assumptions are made about the possible parameters of the ionospheric current structure that creates variations in the magnetic field associated with the passage of the solar terminator.

Geomagnetic activity reflects the complex coupling between the solar wind, magneto-sphere and ionosphere. While the global Kp index serves as a standard proxy for geo-magnetic disturbances, it obscures regional variations linked to local current systems and ionospheric conductivity. This study investigates regional features of geomagnetic activity using the local K index from the Almaty (AAA) observatory and compares its temporal dynamics with Kp for 2007–2025. A combination of statistical, spectral, wavelet, and nonlinear methods was applied, including power spectral density, continuous and cross-wavelet transforms, multifractal detrended fluctuation analysis, and permutation entropy. These approaches capture both linear and nonlinear features of variability and reveal scale-dependent structures in geomagnetic fluctuations. The results show a high correlation (r ≈ 0.84) between K (AAA) and Kp, but with a consistent positive offset of the local index, indicating sensitivity to regional ionospheric processes. Wavelet coherence highlights strong coupling in the 13–27-day band associated with solar rotation. Multifractal spectra reveal broader, more heterogeneous scaling in Kp and narrower, more intermittent dynamics in K during disturbed periods. Local indices, like K (AAA), thus provide essential insight into mid-latitude electrodynamics, complementing global measures in characterizing the nonlinear spatio-temporal complexity of geomagnetic activity.

Geomagnetic activity reflects the complex coupling between the solar wind, magnetosphere and ionosphere. While the global Kp index serves as a standard proxy for geomagnetic disturbances, it obscures regional variations linked to local current systems and ionospheric conductivity. This study investigates regional features of geomagnetic activity using the local K index from the Almaty (AAA) observatory and compares its temporal dynamics with Kp for 2007 - 2025. A combination of statistical, spectral, wavelet, and nonlinear methods was applied, including power spectral density, continuous and cross-wavelet transforms, multifractal detrended fluctuation analysis, and permutation entropy. These approaches capture both linear and nonlinear features of variability and reveal scale-dependent structures in geomagnetic fluctuations. The results show a high correlation (r ≈ 0.84) between K and Kp, but with a consistent positive offset of the local index, indicating sensitivity to regional ionospheric processes. Wavelet coherence highlights strong coupling in the 13–27-day band associated with solar rotation. Multifractal spectra reveal broader, more heterogeneous scaling in Kp and narrower, more intermittent dynamics in K during disturbed periods. Local indices, like K thus provide essential insight into mid-latitude electrodynamics, complementing global measures in characterising the nonlinear spatio-temporal complexity of geomagnetic activity.

Solar activity exhibits a dominant decadal timescale embedded in nonlinear multiscale dynamics. We present a minimal autonomous three-mode hybrid model to investigate whether such a timescale can arise from internal nonlinear energy exchange rather than external periodic forcing or direct inheritance of a prescribed modal period. The model couples a slow internal reservoir, a tachocline-associated transfer mode, and a nonlinear magnetic subsystem described by Duffing and Van der Pol–Duffing dynamics. Magnetic-energy release is implemented through a threshold-triggered reset, while a D-index-based structural energy-exchange index characterizes relative magnetic-energy changes. The system develops a persistent bounded hybrid regime with a dominant period of approximately 10 yr. Initial-condition ensembles and variations in the intrinsic modal periods demonstrate that this timescale does not simply track the prescribed 11 yr tachocline period. Parameter studies identify the release depth and magnetic recovery rate as stronger controls, supporting an accumulation–release mechanism of timescale selection. Release events exhibit organized recurrence and significant tachocline-phase preference, with localized event skipping separating spectral and release timescales. Saltation-based Lyapunov analysis reveals no robust positive largest exponent for the baseline regime over the investigated finite-time horizons. These results demonstrate that nonlinear energy exchange combined with threshold-mediated accumulation and release can autonomously generate a robust decadal collective timescale in a reduced nonlinear system.