An Examination of FORMOSAT-3/COSMIC Ionospheric Electron Density Profile: Data Quality Criteria and Comparisons with the IRI Model

Kuo-Feng Yang,Hsiao-Tsun Ko,Ching-Lun Su,Chien-Ya Wang,Yen-Hsyang Chu

doi:10.3319/tao.2007.10.05.01(f3c)

Abstract

In this article, we analyze the properties of ionospheric electron density profiling retrieved from FORMOSAT-3/COSMIC radio occultation measurements. Two parameters, namely, the gradient and fluctuation of the topside electron density profile, serve as indicators to quantitatively describe the data quality of the retrieved electron density profile. On the basis of 8 month data (June 2006-January 2007), we find that on average 93% of the electron density profiles have upper electron density gradients and electron density fluctuations smaller than -0.02 #/m^3/m and 0.2, respectively, which can be treated as good data for further analysis. The same results are also achieved for the peak height of the electron density. After removing the questionable data, we compare the general behaviors of the electron density between FORMOSAT-3 and the IRI model. It is found that the global distributions of the peak height and the peak electron density for the FORMOSAT-3/COSMIC data are generally consistent with those for the IRI model. However, a significant difference between their scale heights of the topside electron density profiles is found. It suggests that the shape of the topside electron density profile in the IRI model should be revised accordingly such that it more closely resembles the real situation.

Highlights

Radio occultation technique is an old, but very sophisticated, method for the retrieval terrestrial atmosphere parameters (Fjeldbo et al 1971)
The magnitude of the electron density fluctuation in the polar region depicts a remarked seasonal variation, which is much more intense during winter (December for northern hemisphere) than summer (July for northern hemisphere). This feature is very consistent with the observations of the UHF scintillation activity reported by Aarons et al (1981). They found that the maximum occurrence of the scintillation in the high latitude region, which is associated with the ionospheric plasma irregularities generated either by the charged particle precipitation or by plasma instability (Aarons 1982), appears in months of little or no sunlight at F region heights, and much lower scintillation occurrence appears in sunlight months
It suggests that mean deviation (MD) of the electron density profile seems to be able to serve as an indicator of the degree of electron density fluctuations associated with plasma irregularities

Summary

INTRODUCTION

Radio occultation technique is an old, but very sophisticated, method for the retrieval terrestrial atmosphere parameters (Fjeldbo et al 1971). Except for the atmospheric refractive index, under the straight line assumption of the radio ray path, the height variation of the ionospheric electron density can be retrieved from calibrated total electron content (TEC) in accordance with the Abel transformation, which can be estimated from the phase path difference between L1 (= 1.57542 GHz) and L2 (= 1.22760 GHz) frequencies of GPS signals (Schriner et al 1999). We especially focus on the comparisons of the behaviors of peak electron densities and peak height in the F2-region, and the scale height of the topside electron density profiles between COSMIC ionospheric measurements and IRI model results.

THRESHOLDS FOR DATA QUALITY CONTROL

Mean Deviation of Electron Density Fluctuation

COMPARISON BETWEEN COSMIC MEASUREMENT AND THE IRI MODEL

Findings

DISCUSSION AND CONCLUSION