Calibration of Swarm Plasma Densities Overestimation Using Neural Networks

• Published in: Space weather Vol. 22; no. 8
• Main Authors: Smirnov, Artem, Shprits, Yuri, Lühr, Hermann, Pignalberi, Alessio, Xiong, Chao
• Format: Journal Article
• Language: English
• Published: 01.08.2024
• Subjects: calibration; Langmuir probes; neural networks; plasma density; swarm; topside ionosphere
• ISSN: 1542-7390; 1542-7390
• DOI: 10.1029/2024SW003925

Recent studies have shown that the measurements of Langmuir Probes (LPs) onboard ESA's Swarm mission overestimate ion densities on the nightside by up to 50%. The overestimation is due to the assumption of oxygen‐only plasma for ion density calculations, which is often violated at mid‐latitudes on the nightside. In this study, we present a calibration model that resolves the nighttime overestimation by Swarm LPs. Using observations by Swarm FacePlate (FP) as a reference, we develop a neural network (NN) model that adjusts LP data to the FP measurements. The model incorporates dependence on solar and geomagnetic conditions, parameterized by the P10.7 and Hp30 indices, location, day of the year and local time. Our model reveals a distinct double‐crest pattern in nighttime density overestimation by LPs, centered at ∼30° quasi‐dipole latitude in both hemispheres. This overestimation intensifies during low solar activity and shows strong seasonal dependence. During solstices, the crests are more pronounced in the local winter hemispheres, while during equinoxes the crests are weaker and exhibit hemispheric symmetry. This morphology aligns with the presence of light ions diffusing downward from the plasmasphere. Validating the LP data in conjunctions with Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) observations showed a much stronger agreement after applying the developed correction: for Swarm B, nighttime correlation with COSMIC increased from 0.74 to 0.93. The NN‐calibrated LP data set has numerous applications in ionospheric research, and the developed model can provide useful insights into the ion composition in the topside ionosphere. Plain Language Summary Operating since late 2013, ESA's Swarm mission has provided an extensive data set of plasma densities in the topside ionosphere, frequently used in space weather research. Recent studies have shown that the Langmuir Probes (LPs) onboard the Swarm mission overestimate ion densities during nighttime by up to 50%. This overestimation is due to the presence of light ions not accounted for in the ion density calculations. In this study, we develop a new NN‐based calibration model for Swarm observations, which resolves the nighttime overestimation by the LPs for the first time. Our results reveal a distinct double‐crest pattern on the nightside, centered at ∼30° quasi‐dipole latitude in both hemispheres, which corresponds to decreased effective ion masses and thus causes the overestimation of ion densities. This pattern closely mimics the behavior of light ions diffusing downwards from the plasmasphere. The developed NN‐based calibration improves the quality of the LP observations and allows using them for improving the existing models of the topside ionosphere, among other applications. Furthermore, the developed model provides insights into the ion composition and light ion dynamics in the topside ionosphere. Key Points We present a neural network‐based calibration model that resolves the nighttime overestimation of ion densities by Swarm Langmuir Probes (LPs) This overestimation, peaking at 30°QDLat in both hemispheres, mimics the morphology of light ions diffusing downward from the plasmasphere The corrected LP ion densities are in excellent agreement with COSMIC radio occultation data