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- Title
Ionospheric Vertical Correlation Distance Calculation Based on COSMIC Electron Density Profile Data.
- Authors
Zhang, Simin; Wu, Xiaocheng; Hu, Xiong
- Abstract
Background error covariance is an important part of ionospheric assimilation and contains correlation information of the ionospheric background field and error information of the model background field, determines the influence degree of observations on models, and controls the vertical electron density distribution of assimilation results. For more accurate background error covariance determination along the ionosphere vertical direction, we used Constellation Observing System for Meteorology Ionosphere and Climate occultation electron density profile data for vertical correlation distance calculation considering IRI 2016 model errors. The vertical direction correlations are asymmetrical above and below the reference altitude, and with increasing altitude, the vertical correlation distance growth rate may decline or remain unchanged. There are correlation differences in different solar activity years, varying with local time, geomagnetic latitude, and altitude. The vertical correlation distances in high‐solar activity years are greater than that in low‐solar activity years. The correlation distances difference at different times decreases with latitude, with the largest correlation distances at low latitudes. The nighttime distances vary slightly with latitude, while the sunrise correlation distances vary the most relative to other periods. At the same altitude, the correlation distances in the daytime low‐latitude region are the smallest overall, while the correlation distances between the daytime mid‐latitude region and sunrise time are the largest. The point where vertical correlation distances growth stabilize may be correlated with ionospheric hmF2 and upper transition. The IRI model is the most widely used background model in ionospheric assimilation, and the study results could facilitate more accurate vertical background error covariance for ionospheric assimilation. Plain Language Summary: The ionospheric electron density varies dramatically with solar and geomagnetic activity, with an obvious vertical stratification with altitude. But how does the electron density correlation vary in the vertical direction? Under the same conditions, how large a vertical range of electron density will show a strong correlation? By understanding this issue, we can understand the variation in the vertical orientation of the ionosphere and provides quantitatively support for correlation calculations. Constellation Observing System for Meteorology Ionosphere and Climate observed a large number of vertical electron density profiles, and we combine its observation data with the IRI 2016 model to calculate the ionospheric vertical correlation. We find that the correlations differ at different solar activity years, local time, geomagnetic latitudes, and altitudes. The vertical correlations are asymmetric above and below the reference altitude. For the same altitude, the correlation distance is smallest for the daytime low‐latitude region and largest for the daytime mid‐latitude region and sunrise hours. Altogether, our study not only explores the correlation variation in the ionospheric vertical direction but also provides data support for the background error covariance of data assimilation for the ionosphere. Key Points: Ionospheric vertical correlation distances are calculated using Constellation Observing System for Meteorology Ionosphere and Climate occultation data and the IRI 2016 modelThe upward and downward vertical correlation distances vary with altitude depending on Mlat, local time, altitude, and solar activityThis method could provide more detailed calculations for the determination of the ionospheric background error covariance
- Subjects
ELECTRON distribution; IONOSPHERIC electron density; ELECTRON density; ELECTRON configuration; SOLAR activity; LATITUDE
- Publication
Journal of Geophysical Research. Space Physics, 2023, Vol 128, Issue 7, p1
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2023JA031453