Challenges and Gaps in Understanding and Monitoring Low-Latitude F-region Plasma Irregularities

The manuscript highlights the role of neutral wind and vertical coupling between the lower and upper atmosphere in the generation and evolution of equatorial plasma depletions (EPDs) and equatorial plasma irregularities (EPIs) during quiescent conditions. These phenomena impact radio wave propagation, leading to signal degradation and loss, which affects communication and navigation systems. Understanding, monitoring, and forecasting EPIs are thus crucial. Forecasting with high accuracy remains challenging and is often limited to predicting EPIs associated with increased solar and geomagnetic activity. Real-time monitoring systems are essential to capture the variability of irregularities and their development, especially since EPDs also occur during quiescent conditions and can extend to mid-latitudes. International collaboration and data sharing are vital for improving monitoring. Ongoing research focuses on better understanding the role of the neutral wind in creating favorable conditions for EPD generation. Whole atmosphere models are currently developed with high enough resolution to self-consistently simulate the wave spectrum in the thermosphere including gravity waves. Gravity waves were shown to be important for the generation of EPD but their role in seeding plasma irregularities is not yet fully understood. The manuscript describes the current physical understanding of evening and post-midnight EPD generation provides an overview of available observations of EPIs and summarizes advances in statistical and numerical model development. It highlights the gaps and needs to advance our understanding of EPD and EPI generation and evolution.