Plasmaspheric Wave Research Articles

The Study on Modeling of Global Plasmaspheric Hiss Amplitude Based on Deep Learning Algorithm

AbstractPlasmaspheric hiss waves make great significance on the loss of electrons in the Earth's radiation belts. The prediction and reconstruction for global evolution plasmaspheric hiss are critical to investigate the dynamic process of radiation belt. In this study, the realistic variation model of plasmaspheric waves is established based on deep learning technology. Using Light Gradient Boosting Machine and Permutation Importance methods, we first select optimal indices and corresponding historical time series associated with variation of plasmaspheric hiss waves. Then the geomagnetic indices in corresponding time series are considered as input of deep neural network model, and the samples of plasmaspheric hiss waves observed from Van Allen Probe A are utilized for training and validation. The result indicates that the model can roughly reproduce the variation of integrated hiss wave amplitude during geomagnetic storm. Based on the model, we analyze the global evolution of hiss waves during a geomagnetic storm event. In addition, we find that the prediction performance has been greatly improved with the addition of in situ density as an auxiliary input parameter, it provides a new idea of establishing higher accuracy model with auxiliary input of other characteristic parameters.

Plasmaspheric Pi2 Pulsation Enhancement in Response to Plasma Sheet Pi2 Wave Source: Statistical Study Using Van Allen Probes and THEMIS Conjunctions

AbstractTo understand the enhancement of Pi2 pulsations inside the plasmasphere in response to the plasma sheet Pi2 wave source, we conduct a statistical investigation of 208 conjunction events by using simultaneous two‐point measurements with one satellite located in the plasmasphere and the other one located in the plasma sheet. All the events had a Pi2 compressional wave source observed in the plasma sheet as indicated by their association with bursty bulk flows (BBFs), but for about 25% of the events there were no corresponding enhancements in plasmaspheric Pi2 waves. For events with plasmaspheric Pi2 wave enhancements, a cavity or virtual resonance was likely the dominant wave mode, while excitation of field line resonance was also observed. We select two groups of events: strong (weak) group with the plasmaspheric compressional wave enhancements above 75% percentile (below 25% percentile), and conduct a statistical‐significance evaluation of the differences between the two groups. The strong events were observed closer to midnight than the weak events. The plasma sheet wave source that has a larger wave amplification or larger dipolarization associated with BBFs is more likely to excite stronger plasmaspheric wave enhancements. The strong events occurred more often with a pre‐condition of lower Auroral Electrojet (AE)* levels than did weak events. We explain these dependencies as strong events being associated with more favorable conditions that allow the inward‐propagating compressional waves from the plasma sheet wave source to reach the plasmapause and excite the plasmaspheric waves.

Plasmaspheric Hiss: Coherent and Intense

AbstractIntense ~300‐Hz to 1.0‐kHz plasmaspheric hiss was studied using Polar plasma wave data. It is found that the waves are coherent in all local time sectors with the wave coherency occurring in approximately three‐ to five‐wave cycle packets. The plasmaspheric hiss in the dawn and local noon time sector are found to be substorm (AE*) and storm (SYM‐H*) dependent. The local noon sector is also solar wind pressure dependent. It is suggested that coherent chorus monochromatic subelements enter the plasmasphere (as previously suggested by ray tracing models) to explain these plasmaspheric hiss features. The presence of intense, coherent plasmaspheric hiss in the local dusk and local midnight time sectors is surprising and more difficult to explain. For the dusk sector waves, either local in situ plasmaspheric wave generation or propagation from the dayside plasmasphere is possible. There is little evidence to support substorm generation of the midnight sector plasmaspheric hiss found in this study. One possible explanation is propagation from the local noon sector. The combination of high wave intensity and coherency at all local times strengthens the suggestion that the electron slot is formed during substorm intervals instead of during geomagnetic quiet (by incoherent waves). Plasmaspheric hiss is found to propagate at all angles relative to the ambient magnetic field, θkB. Circular, elliptical, and linear polarized plasmaspheric hiss have been detected. No obvious, strong relationship between the wave polarization and θkB was found. This information of hiss properties should be useful in modeling wave‐particle interactions within the plasmasphere.

The dynamics of the plasmasphere: Recent results

The purpose of this paper is to review recent advances in the study of the Earth's plasmasphere. Most of these have been obtained with data from two missions launched in 2000, Cluster and IMAGE. Indeed, those missions have deeply modified our understanding of this region due to their specificity: Cluster is a 4-spacecraft mission and IMAGE a global imaging mission, both types studying the plasmasphere for the first time. We review here some results of recent studies of the global evolution of the plasmasphere under the increase of the geomagnetic activity: plasmaspheric erosion, evolution of the plasmapause, plasmaspheric plumes, modification in the plasmaspheric corotation, refilling of the plasmasphere and evolution towards a smooth plasmasphere during prolonged quiet period. We also review results on plasmaspheric waves, which are formed and propagate at all stages of plasmaspheric evolution.

Advances in Plasmaspheric Wave Research with CLUSTER and IMAGE Observations

This paper highlights significant advances in plasmaspheric wave research with Cluster and Image observations. This leap forward was made possible thanks to the new observational capabilities of these space missions. On one hand, the multipoint view of the four Cluster satellites, a unique capability, has enabled the estimation of wave characteristics impossible to derive from single spacecraft measurements. On the other hand, the Image experiments have enabled to relate large-scale plasmaspheric density structures with wave observations and provide radio soundings of the plasmasphere with unprecedented details. After a brief introduction on Cluster and Image wave instrumentation, a series of sections, each dedicated to a specific type of plasmaspheric wave, put into context the recent advances obtained by these two revolutionary missions.

Coordinated measurements of slot region electron precipitation by plasmaspheric wave bands

It has been hypothesized by Lyons et al. that electrons in the slot region are precipitated by cyclotron resonance interactions with the plasmaspheric whistler mode wave bands. The energy spectra and the variations with L shell of the energy bands of the precipitating electrons have been found by Imhof et al. (1974) to be consistent with cyclotron resonance by waves in the few hundred Hz to few kHz range. Now, for the first time, simultaneous measurements have been made of the precipitating electron spectra, the wave frequency distributions, and the plasma density profiles. The electron measurements were performed from the P78‐1 low‐altitude satellite, whereas the wave and plasma density observations were made with the plasma wave experiment on the ISEE 1 spacecraft. Broad bands are often observed in the electron energy spectra with a well‐defined low‐energy cutoff that decreases in energy with increasing L value in a manner consistent with that calculated for first‐order cyclotron resonance with waves at the high‐frequency cutoff of the band. On the basis of the electron spectra from P78‐1 and the plasma densities obtained from the upper hybrid resonance frequencies measured on ISEE 1, the hiss cutoff frequencies are calculated for an assumed first‐order cyclotron resonance interaction and compared with the wave spectral density profiles measured on ISEE. Overall, the plasma wave and the electron measurements are consistent with each other, supporting the earlier hypothesis for the precipitation mechanisms.