Effects of mesoscale gravity waves on sporadic E simulated by a one-dimensional dynamic model
image: In the plots (a) and (b), different characteristics of sporadic E layers over Mohe are shown in the simulation when considering and ignoring the mesoscale gravity waves. The panel in the top right corner illustrates the schematic of dynamical core in the newly developed model.
Credit: Beijing Zhongke Journal Publising Co. Ltd.
This study is led by Dr. Xu Zhou and Dr. Xinan Yue (Institute of Geology and Geophysics, Chinese Academy of Sciences, IGGCAS), cooperated with Dr. Zezhong Li (University of Science and Technology of China) and Dr. Libo Liu (IGGCAS).Sporadic E (Es) refers to the thin layers with enhanced ionization at altitudes of ~95–130 km, which can scatter radio propagation and has significant impacts on radio communication and modern navigation. The Es layers are driven by the strong wind shear due to atmospheric tides, known as tidal ion layers. GWs also exist in the heights of Es layers, but their periods are much shorter than atmospheric tides. These short-period fluctuations can perturb the descending phase of the tides, thus are expected to produce effects on the Es layers. “Previous investigations have predicted possible GW impacts on the Es layers by simulation, but we raised concerns about the numerical solving processes”, said by Xu Zhou, “The vertical gradient of plasma density above and below the thin Es layer is extremely large, so we need to design a model with fine grids and deal with dynamical solving carefully to reduce the spurious numerical diffusion”.
Dr. Xu Zhou and Dr. Xinan Yue, together with Dr. Zezhong Li, who is an expert on model development, sought to develop a new model with low numerical dissipation and high resolution to address this problem. Dr. Zezhong Li has rich experience in modelling equatorial plasma bubbles, which also need to consider the numerical diffusion carefully. After a brief discussion in an academic seminar, Dr. Xu Zhou and Dr. Zezhong Li decided to cooperate and promote this research. After performing a series of numerical tests, they adopted seventh upwind scheme to reconstruct the flux at interfaces and implemented the Adams–Bashforth scheme in the predictor step. “The new model has capability to simulate short-term variation of the thin Es layers driven by the rapid change of neutral wind with good conservation and stability,” Dr. Xu Zhou says.
Dr. Libo Liu, the principal investigator of Heilongjiang Mohe National Observatory of Geophysics, suggested our simulation research can focus on the location of Mohe, considering there is a new lidar that can detect the Es layers with high spatiotemporal resolution established recently. “We hope to see the observation-simulation collaborative research can promote our understanding of short-term variation of Es layers in the near future,” Dr. Xu Zhou says.
The simulation results reveal that the GW influences on the Es layer are complex and varied. The effects include generating fluctuating wavelike structures on the Es layer with frequencies close to the GWs, dispersing the Es layers and increasing thickness, and enhancing the ionized density. “The results are interesting. In the observations of Sanya incoherent scatter radar, we also see the similar rapid change of Es layers,” Dr. Xinan Yue says, “we will continue developing the model and improving the capability to deal with the instabilities inside the Es layers.”
The Es layer in the ionosphere has been investigated for decades. With the development of detection and simulation, more fine structures have been revealed and studied. The mesoscale GW effects shown in this study emphasized the importance of numerical consideration in solving dynamical processes and implied that the better subgrid solving of GWs in global atmospheric models also has significance in ionospheric studies.
See the article:
Effects of mesoscale gravity waves on sporadic E simulated by a one-dimensional dynamic model
https://doi.org/10.26464/epp2024038