Ionospheric tomography: its limitations and reconstruction methods

[1] A global ionospheric total electron content (TEC) model based on the empirical orthogonal function (EOF) analysis method is constructed using the global ionosphere maps provided by Jet Propulsion Laboratory during the years 1999–2009. The importance of different types of variation to the overall TEC variability as well as the influence of solar radiation and geomagnetic activity toward TEC can be well represented by the characteristics of EOF base functions Ek and associated coefficients Pk. The quick convergence of EOF decomposition makes it possible to use the first four orders of the EOF series to represent 99.04% of the overall variance of the original data set. E1 represents the essential feature of global spatial and diurnal variation of the TEC. E2 contains a hemispherically asymmetric pattern manifesting the summer-to-winter annual variation. E3 and E4 can well reflect the equatorial anomaly phenomenon. P1 contains an obvious solar cycle variation pattern as well as annual and semiannual variation components. P2 mainly includes an annual fluctuation component. P3 has a strong annual variation and a weak seasonal variation pattern. P4 has both evident annual and semiannual oscillation components. The Fourier series as a combination of trigonometric and linear functions are used to represent the solar cycle, annual, and semiannual variation of the coefficients. Therefore the global TEC model is established through incorporating the modeled EOF series. The accuracy and quality of the model have been validated through the model-data comparison, which indicates that the model can reflect the majority of the variations and the feature of temporal-spatial distribution of the global ionospheric TEC.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2011JA017238

A global model: Empirical orthogonal function analysis of total electron content 1999–2009 data

Global median model of the F2-layer peak height based on ionospheric radio-occultation and ground-based Digisonde observations

A campaign was conducted in late September 1991 to obtain experimental measurements for use in ionospheric tomography. Four stations receiving signals from the Navy Navigation Satellite System satellites were set up in a meridional chain in Scandinavia covering some 10° of latitude. Measurements of total electron content were made for six satellite passes over a 2-day period coinciding with an extended run of the CP3f latitudinal scan common program of the European incoherent scatter radar. A new reconstruction technique involving the use of two-dimensional basis vectors has been used to convert the total electron content measurements to images of electron density in a height versus latitude plane. Comparisons of the tomographic images and the independent measurements of electron density from the radar show good general agreement. Broadly similar troughs and enhancements are observed by the two techniques, and a latitudinal gradient in the height of the peak density is reproduced in both data sets.

Tomographic reconstruction of ionospheric electron density with European incoherent scatter radar verification

. The ionospheric F2 peak height hmF2 is an important parameter that is much needed in ionospheric research and practical applications. In this paper, an attempt is made to develop a global model of hmF2. The hmF2 data, used to construct the global model, are converted from the monthly median hourly values of the ionospheric propagation factor M(3000)F2 observed by ionosondes/digisondes distributed globally, based on the strong anti-correlation existed between hmF2 and M(3000)F2. The empirical orthogonal function (EOF) analysis method, combined with harmonic function and regression analysis, is used to construct the model. The technique used in the global modelling involves two layers of EOF analysis of the dataset. The first layer EOF analysis is applied to the hmF2 dataset which decomposed the dataset into a series of orthogonal functions (EOF base functions) Ek and their associated EOF coefficients Pk. The base functions Ek represent the intrinsic characteristic variations of the dataset with the modified dip latitude and local time, the coefficients Pk represents the variations of the dataset with the universal time, season as well as solar cycle activity levels. The second layer EOF analysis is applied to the EOF coefficients Pk obtained in the first layer EOF analysis. The coefficients Ak, obtained in the second layer EOF analysis, are then modelled with the harmonic functions representing the seasonal (annual and semi-annual) and solar cycle variations, with their amplitudes changing with the F10.7 index, a proxy of the solar activity level. Thus, the constructed global model incorporates the geographical location, diurnal, seasonal as well as solar cycle variations of hmF2 through the combination of EOF analysis and the harmonic function expressions of the associated EOF coefficients. Comparisons between the model results and observational data were consistent, indicating that the modelling technique used is very promising when used to construct the global model of hmF2 and it has the potential of being used for the global modelling/mapping of other ionospheric parameters. Statistical analysis on model-data comparison showed that our constructed model of hmF2, based on the EOF expansion method, compares better with the observational data than the model currently used in the International Reference Ionosphere (IRI) model.

/pdf/a-global-model-of-the-ionospheric-f2-peak-height-based-on-57r55w6i6x.pdf

N.I. Dvinskikh

Papers

Expansion of ionospheric characteristics fields in empirical orthogonal functions