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- Title
Characterization of the Ionospheric Vertical Error Correlation Lengths Based on Global Ionosonde Observations.
- Authors
Yuan, L.; Kodikara, Timothy; Hoque, M. M.
- Abstract
Data assimilation is one of the most important approaches to monitoring the variations of ionospheric electron densities. The construction of the background error covariance matrix is an important component of ionospheric data assimilations. To construct the background error covariance matrix, the information about the spatial ionospheric correlations is required. We present a statistical analysis on the ionospheric vertical error correlation length (VCL) based on a global network of ionosondes and the Neustrelitz Electron Density Model. We show that the locally derived VCL is well‐defined and the VCL does not show a considerable dependency on the geographical seasons while local time dependencies of the VCL are shown to be present. A novel VCL model is also established based on the ionospheric scale heights. We show that the ionospheric VCL can be characterized by the variance ratio between the ionosphere model and ionospheric measurements. The altitudinal variations of VCLs are controlled by the interactions between the inherent VCLs of the ionosphere model and the measurements. Two experiments are conducted at two different latitudes based on the proposed model. The results show that the proposed model is stable and well‐correlated with the observed VCLs, which implies a potential to be generalized for a global correlation model. The proposed model can be used in the temporal evolution of error covariance matrices in the ionospheric 4D‐Variational (4D‐Var) assimilations, which may overcome the main drawbacks of the static error covariance specifications in the ionospheric 4D‐Var assimilations. Plain Language Summary: In ionospheric data assimilations, one of the most important pieces of information is the background error correlation, which controls the spatial spread of observations. In this study, the vertical error correlation length (VCL) will be evaluated locally based on a statistical analysis using the Neustrelitz Electron Density Model and global ionosonde observation network from Global Ionospheric Radio Observatory. For the first time, this study establishes that ionospheric VCLs can be effectively characterized by two primary parameters: the variance ratio and the correlation between the ionospheric model and the observational data. In addition, the study examines the relationships between climatological VCLs and scale heights within empirical ionospheric models. A novel VCL model is proposed based on the statistical analyses. The proposed correlation length models offer utility in the temporal evolution of error covariance matrices within ionospheric 4D variational assimilations, potentially mitigating one of the primary limitations associated with static error covariance specifications in such assimilation procedures. Key Points: Derives ionospheric vertical correlation lengths (VCLs) from global ionosondesDemonstrates that the variance ratio between model and measurements can characterize the ionospheric error VCLProposes a novel ionospheric VCL model based on modeling the variance ratio and vertical scale heights
- Subjects
IONOSPHERIC electron density; IONOSPHERIC techniques; STATISTICAL correlation; ELECTRON density; COVARIANCE matrices; KALMAN filtering
- Publication
Space Weather: The International Journal of Research & Applications, 2024, Vol 22, Issue 3, p1
- ISSN
1539-4956
- Publication type
Article
- DOI
10.1029/2023SW003743