Data assimilation of plasmasphere and upper ionosphere using COSMIC/GPS slant TEC measurements

Abstract

Increasing total electron content (TEC) measurements from the low Earth orbiting satellites to Global Positioning System satellites flourish the exploration of the ionosphere and plasmasphere for decades. This paper indicates a method that 3-D Var is applied to assimilate precise orbit determination antenna TEC measurements of Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites into the background global core plasma model (GCPM). The slant TEC data archived in the COSMIC Data Analysis and Archive Center from 500 km to 20,200 km are used to reconstruct a new electron density model. This model has a temporal resolution of 2 h and spatial resolutions of 2.5°in geomagnetic latitude, 5°in longitude, 50 km in the upper ionosphere, and several hundred kilometers in the plasmasphere. Preliminary results show that the data assimilation modifies the initial GCPM forecast to be better coincident with actual COSMIC measurements in internal quality check. Furthermore, independent validation with upper ionosphere-retrieved electron density and TEC of global ionosphere maps implies a reasonable improvement in the estimation of plasmaspheric electron density after the assimilation.

The Two-Parts Step-by-Step Ionospheric Assimilation Based on Ground-Based/Spaceborne Observations and Its Verification

“…Compared with ionosonde observations, the assimilation results not only were greatly improved than the initial models but also added to the daily variation of the ionosonde data. Based on ISR data, the influence of the assimilation algorithm on the electron density structure affected mainly the improvement in the peak density, while it had a weak effect on the peak height, which is consistent with Fu et al's result [18]. Finally, a comparison with the Abel-retrieved EDP from CDAAC/UCAR demonstrated that the result from the G/S+Cor strategy using the calibrated TEC from occultation data was more consistent than that from the G+Cor strategy.…”

Topside correction of IRI by global modeling of ionospheric scale height using COSMIC radio occultation data

“…GIM provides vertical TEC from the ground to the GPS altitude, and it is regarded as an accuracy reference in many researchers' work to validate model improvement [ Yue et al, ; Wu et al, ]. GIM provides global maps that assume a thin shell ionospheric model at 450 km, by mapping line‐of‐sight TEC measurements to VTEC on the grid using a square root information filter [ Mannucci et al , ].…”

“…Therefore, the electron content of higher altitude should be compensated with other data set in order to prepare VTEC of the same vertical coverage with GIM. To focus on the change of topside profiles (up to 800 km) affected by the correction, here we adopted the assimilated plasmasphere model in our former research to provide the electron content component from 800 km to the GPS altitude [ Wu et al, ]. As a result, we actually compared the accumulation of IRI contents (“IRI”) and plasmasphere contents (“Pla”) to GIM at the same location before and after correction.…”

Application of remote sensing for major land geohazards

“…Thirdly, S3-TEC trend better reflects the semi-annual pattern exhibited by GIM-TEC, whereas C6-TEC variation was relatively flat. The reasons for this occurrence are: (1) SWARM's orbit (approximately 500 km) is at a lower altitude than COSMIC (approximately 800 km), which allows a longer signal path for the dual GPS frequencies, and (2) Since the electron density in the plasmasphere (above 1000 km altitude) is significantly lesser than the contributions in the ionosphere, SWARM's TEC would have likely probed the electron 'richer' part of the ionosphere (Wu et al 2015). This is further reflected by a strong cross-correlation between dailyaveraged GIM-TEC and S3-TEC values with a correlation coefficient of 0.86 against 0.40 for the case of C6-TEC.…”

“…In addition, two-dimensional TEC maps derived from these ground-based observations are also frequently used(Akhoondzadeh and Saradjian 2011;He et al 2014;Jhuang et al 2010;Jing et al 2011;Ke et al 2016;Kon et al 2011). Apart from their convenience and global coverage, ionosphere maps (GIMs), such as those produced using long-term TEC data from the Center for Orbit Determination of Europe (CODE), are regarded as the most precise TEC maps available and typically treated as a high-accuracy reference(Mukhtarov et al 2013;She et al 2017;Wu et al 2015). These ionosphere TEC maps from CODE are generated on an hourly-basis and provide relatively good temporal resolution with hourly intervals.…”