Qiushuo Wang

Understanding and predicting geospace dynamics is critical for safeguarding space infrastructure. For decades, geospace models have ignored the electrical influence of the lower atmosphere below 95 km, presuming low ionization. Since high‐energy particle precipitation reaches these altitudes and triggers intense ionization, this omission may bias our understanding of geospace dynamics. Here we show that the ionospheric D region, a thin chemically active layer at the lower boundary of geospace near 80 km altitude, exerts electrical influences that actively regulate system‐scale dynamics, with consequences extending to 200,000 km away from Earth. Poker Flat Incoherent Scatter Radar observations show that a significant fraction of Hall current flows in the D region during storm‐time precipitation. By analyzing coupled geospace simulations, we found that particle precipitation‐driven, chemistry‐modulated D‐region conductivity instantly reorganizes high‐latitude current closure. In hours, it shifts the magnetotail reconnection site by several Earth radii, and alters thermospheric mass density, thus satellite drag, by . These results establish a novel coupling between atmospheric chemistry and space physics, with implications for satellite orbital prediction.

Accurate determination of the wave propagation direction is essential for understanding wave–particle interactions in space plasmas as well as the source and propagation characteristics of waves. Traditional wave normal angle (WNA) analysis methods rely on the plane‐wave assumption and cannot describe realistic wave fields with a distribution of propagation directions, while existing wave distribution function (WDF) methods are often unstable when applied to spacecraft observations and require manual parameter tuning, limiting their practical applicability on large data sets. In this work, we develop a fully automatic maximum entropy based wave distribution function (AME‐WDF) method that enables stable and accurate inference of WDFs from observed power spectra without manual supervision. The method introduces a modified accuracy metric, an adaptive leap‐frog kernel number update scheme, and an efficient Discrete Region based initial guess generation procedure, which together ensure convergence, robustness, and automation. Tests on artificial data demonstrate excellent reconstruction performance, accurately reproducing wave propagation structures while preserving the total energy with low errors. Application to chorus wave observations from the Van Allen Probes reveals complex multi‐peak and non‐plane‐wave propagation structures that cannot be resolved using traditional WNA analysis methods. By enabling reliable and automatic reconstruction of realistic wave propagation direction distributions beyond the plane‐wave approximation, the AME‐WDF method provides a powerful tool for large‐scale statistical analyses of spacecraft wave observations and enables more accurate characterization of wave source, propagation, and wave–particle interaction processes in planetary space plasmas.

Rising‐tone chorus elements are traditionally known to grow from low frequencies and extend to high frequencies. Using high‐resolution waveform measurements from the Van Allen Probes, we report a novel observation: equatorward‐propagating chorus waves at a few degrees in latitude are observed at high frequencies only. As these rising‐tone chorus waves propagate equatorward and approach the equator, they intensify and extend to lower frequencies. A multi‐year statistical analysis of Van Allen Probe A observations shows a systematic feature: at higher latitudes of source region, the equatorward‐propagating elements progressively appear at higher frequencies, exhibit narrower bandwidths and weaker amplitudes than the chorus wave elements propagating away from the equator. Such a feature challenges the conventional simple understanding that chorus waves grow from low frequencies and extend to high frequencies at the equator. These observations potentially supports the recently proposed nonlinear upstream–downstream generation framework described by the Trap–Release–Amplify (TaRA) model.

We recently reported the finding of elementary rising‐tone emissions embedded within each harmonic of magnetosonic waves, by investigating wave electric field waveforms measured by Van Allen Probes. The present study further uncovers a new set of fine structures of magnetosonic waves, namely, each elementary rising‐tone may consist of a series of mini harmonics spaced around the O ⁺ gyrofrequency. The measured ion distributions suggest that the proton ring distribution provides free energy to excite the waves, whilst the O ⁺ ions suppress the wave growth around multiples of O ⁺ gyrofrequency, resulting in the formation of mini harmonics. Further investigation suggests that the warm plasma dispersion relation, that is, the ion Bernstein mode instabilities, may contribute to the formation of mini harmonics. The mini harmonic structure implies a new mechanism of energy redistribution among ion species in space plasmas, potentially providing a new acceleration mechanism for O ⁺ ions in the magnetosphere.

The ring current is an important component of the Earth’s near-space environment, as its variations are the direct driver of geomagnetic storms that can disrupt power grids, satellite communications, and navigation systems, thereby impacting a wide range of technological and human activities. Oxygen ions (O+) are one of the major components of the ring current and play a significant role in both the enhancement and depletion of the ring current during geomagnetic storms. Although a standard statistical study can provide average global distributions of ring current ions, it can’t offer insight into the short-term dynamic variations of the global distribution. Therefore, we employed the Artificial Neural Network (ANN) technique to construct a global ring current O+ ion model based on the Van Allen Probes observations. Through optimization of the combination of input geomagnetic indices and their respective time history lengths, the model can well reproduce the spatiotemporal variation of the oxygen ion flux distributions and demonstrates remarkable accuracy and minimal errors. Additionally, the model effectively reconstructs the temporal variation of ring current O+ ions for an out-of-sample dataset. Furthermore, the model provides a comprehensive and dynamic representation of global ring current O+ ion distribution. It accurately captures the dynamics of O+ ions during a geomagnetic storm with the oxygen ion fluxes enhancement and decay, and reveals distinct characteristics for different energy levels, such as injection from the plasma sheet, outflow from the ionosphere, and magnetic local time asymmetry.