Systematic behavior of semiempirical global ionospheric models in quiet geomagnetic conditions

Abstract

[1] Semiempirical ionospheric models are widely used in many applications. In this work we analyze the global representation of the vertical total electron content (VTEC) derived from the La Plata single-layer GPS ionospheric model (LPIM), the international reference ionosphere (IRI) model, and the Bent model. To perform this analysis, we compare the output from these models with VTEC determinations from the TOPEX/Poseidon (T/P) satellite. The analysis of the differences is performed over a large number of selected quiet geomagnetic days during the year 1997. From these comparisons we can conclude that LPIM gives the best global VTEC representation, even without modeling the ionospheric equatorial anomaly. The mean global difference between the VTEC determined by T/P and computed by LPIM is in the range of 2 and 3 TECU (1 TECU = 10 16 el/m 2 ). IRI and Bent models tend to show larger discrepancies with T/P during the summer solstices in both Northern and Southern Hemispheres.

Plasmaspheric Electron Content Inferred from Residuals between GNSS-Derived and TOPEX/JASON Vertical TEC Data

“…We conclude that systematic biases arise from T/J vTEC and result in a greater T/J vTEC than GNSS-derived vTEC. Although systematic biases in Figure 5a-d are somewhat different for different datasets, the bias magnitudes are consistent with previous investigations [18][19][20][21][22][23]. What is responsible for the different systematic biases of T/J vTEC?…”

“…Jee et al [15] compared GPS vTEC and T/J vTEC for 1998-2009, and reported a positive relative TEC difference (i.e., GPS vTEC > T/J vTEC) in the PEC contribution to the ionosphere, which was largest in the early morning sector (up to 100%). However, many studies have found that T/J vTEC has a positive systematic bias of 2-5 TECu above real ionospheric TEC values when compared to other independent sources (i.e., T/J vTEC > GPS vTEC) [17][18][19][20][21][22][23]. This is paradoxical because GPS satellite altitude (~20,000 km) is higher than that of T/J satellites (~1336 km); thus, GPS vTEC should be larger than T/J vTEC due to it including the plasmasphere contribution above the T/J satellite orbital altitude.…”

“…Chelton et al [17] pointed out that the relative TEC bias indicates a systematic error in the T/J sea state bias (SSB) correction, which is an empirical model with limited accuracy, and SSB assembles corrections for the sum of the electromagnetic (EM) bias, skewness bias and tracker bias. Meza et al [20] performed a comparison of GPS-based la plata ionospheric model (LPIM) with T/J estimates during quiet geomagnetic days in 1997. They concluded that systematic biases for T/J-LPIM were 2.5-3.0 TECu, and larger during equinox than during solstice periods.…”

A method to ingest GPS‐TEC into the NeQuick ionospheric model

“…It can be appreciated that no value exceeds from ±6 TECU, which is considered a quite encouraging result. After Meza et al [2002], we know that empirical ionospheric models driven by climatological parameters are affected by errors larger than the ±6 TECU found in this work. The individual residuals do not show systematic behaviors, they seem to be similar for either solstices or equinoxes and they tend to reach slightly higher values in the afternoon, from about 15 to 19 LT.…”

Wavelet analysis and forecasting of VTEC obtained with GPS observations over European latitudes

“…However, long-and shortterm predictions of the TEC are needed for numerous applications. It is well-known that empirical and semiempirical ionospheric models, such as IRI (Bilitza, 2001), Bent model (Bent and Llewellyn, 1973) or Nequick model (Hochegger et al, 2000), provide a good prediction mostly in the case of quiet conditions or average ionospheric parameters (Meza et al, 2002). Regional or local models (Gulyaeva, 1999;Unnikrishnan et al, 2002) in many cases offer a more precise prediction than global climatologic ones.…”