An Empirical Model of the Occurrence Rate of Low Latitude Post‐Sunset Plasma Irregularities Derived From CHAMP and Swarm Magnetic Observations

• Published in: Space weather Vol. 22; no. 6
• Main Authors: Stolle, C., Siddiqui, T. A., Schreiter, L., Das, S. K., Rusch, I., Rother, M., Doornbos, E.
• Format: Journal Article
• Language: English
• Published: 01.06.2024
• ISSN: 1542-7390; 1542-7390
• DOI: 10.1029/2023SW003809

The prediction of post‐sunset equatorial plasma depletions (EPDs), often called ionospheric plasma bubbles, has remained a challenge for decades. In this study, we introduce the Ionospheric Bubble Probability (IBP) model, an empirical model to predict the occurrence probability of EPDs derived from 9 years of CHAMP and 9 years of Swarm magnetic field measurements. The model predicts the occurrence probability of EPDs for a given longitude, day of year, local time and solar activity, for the altitude range of about 350–510 km, and low geographic latitudes of ±45°. IBP has been found to successfully reconstruct the distribution of EPDs as reported in previous studies from independent data. IBP has been further evaluated using 1‐year of untrained data of the Ionospheric Bubble Index (IBI). IBI is a Level 2 product of the Swarm satellite mission used for EPD identification. The relative operating characteristics (ROC) curve shows positive excursion above the no‐skill line with Hanssen and Kuiper's Discriminant (H&KSS) score of 0.52, 0.51, and 0.55 at threshold model output of 0.16 for Swarm A, B, and C satellites. Additionally, the reliability plots show proximity to the diagonal line with a decent Brier Skill Score (BSS) of 0.249, 0.210, and 0.267 for Swarm A, B, and C respectively at 15% climatological occurrence rate. These tests indicate that the model performs significantly better than a no‐skill forecast. The IBP model offers compelling glimpses into the future of EPD forecasting, thus demonstrating its potential to reliably predict EPD occurrences. The IBP model is publicly available. Plain Language Summary Post‐sunset equatorial plasma depletions (EPDs), often called ionospheric plasma bubbles, are a severe threat for reliable radio wave communication. However, their predictability has remained a challenge for the scientific community for decades. In this study, we introduce the Ionospheric Bubble Probability (IBP) model predicting the occurrence probability of post‐sunset EPDs for a given longitude, day of year, local time and solar activity, for the altitude range of about 350–510 km, and low geographic latitudes of ±45°. To this aim we have used 9 years of CHAMP and 9 years of Swarm magnetic field measurements. The IBP model predictions have been found to agree well with climatologies derived from independent data and performs largely better than unskilled forecasts. The IBP model is made publicly available. Key Points The Ionospheric Bubble Probability (IBP) model estimates the occurrence probability of post‐sunset equatorial plasma depletions (EPDs) IBP shows high performance in predicting EPD occurrence for longitude, local time, day of year, solar activity, at altitudes of about 350–510 km The IBP model is publicly made available with documentation