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- Title
The Four‐Dimensional Variational Neustrelitz Electron Density Assimilation Model: NEDAM.
- Authors
Yuan, L.; Hoque, M. M.; Kodikara, Timothy
- Abstract
With the development of the Global Navigation Satellite System (GNSS) and regional augmentation systems, the influence of the ionosphere on GNSS signals is becoming increasingly important. It is also of particular interest to retrieve the electron density distribution from GNSS observations. We have successfully developed a four‐dimensional variational assimilation scheme, the Neustrelitz Electron Density Assimilation Model (NEDAM), and verified NEDAM by a simulation study using a European ground‐based GNSS network. The performance of NEDAM is validated using two ionosondes and COSMIC‐1 radio occultation observations during the September 2017 geomagnetic storm period. The critical frequency of the F2 layer in NEDAM is much more accurate than that of a physics‐based model driven by observed geophysical indices or the Neustrelitz Electron Density Model (NEDM), when compared to data from two ionosondes. During the storm, the root mean square error of the F2‐layer critical frequency with respect to the two ionosondes is improved by 0.54 and 0.42 MHz, respectively. We also compare two co‐located electron density profiles from the COSMIC‐1 mission with NEDAM and NEDM. It is found that NEDAM is able to reconstruct well not only the peak density but also the peak density height, which is missing in the previous research. Plain Language Summary: With the development of ground‐ and space‐based observation techniques of the upper atmosphere, the capability of monitoring the variation of the Earth's ionosphere is increased drastically. However, due to the lack of three‐dimensional observations with a good coverage, reliable and well defined scheme is required for extracting three‐dimensional snapshots of the Earth's ionospheric electron density. This work presents an advanced four‐dimensional variational scheme NEDAM in the region of 60–20,000 km above the Earth's surface. The work also validates the tomography results with multiple ionospheric observations from satellites and ground‐based radar instruments and compares with empirical and physical models. It is usually a challenge for assimilative models to reproduce the ionospheric parameters such as the peak density height accurately during geomagnetic storms. The performance of NEDAM is validated against two ionosondes and COSMIC radio occultation observations during the September 2017 geomagnetic storm period. The critical frequency of F2‐layer in NEDAM is much more accurate than that of NEDM with respect to the two ionosondes in the region of interests. The developed method will be applied in near real‐time to space weather monitoring, GPS positioning and navigation, as well as to improve our understanding of the morphology and dynamics of the ionosphere. Key Points: A 4D‐Var‐based new global ionosphere electron density assimilation model Neustrelitz Electron Density Assimilation Model (NEDAM) is presentedThe background covariance matrix is approximated by a Gaussian‐Markov random field and the observation covariance is improvedThe accuracy of NEDAM is evaluated using simulated Global Navigation Satellite System observations and two ionosondes and COSMIC‐1 data
- Subjects
ELECTRON density; IONOSPHERIC electron density; ELECTRON distribution; GLOBAL Positioning System; STANDARD deviations; CLUTTER (Radar)
- Publication
Space Weather: The International Journal of Research & Applications, 2023, Vol 21, Issue 6, p1
- ISSN
1539-4956
- Publication type
Article
- DOI
10.1029/2022SW003378