Analysis of Global TEC Annual and Semi‐Annual Variations by using IGS Data

Abstract

With the Fourier analysis method, the daytime ionosphere total electron concentration (TEC) is investigated by using global GPS data series from IGS in a high solar activity year (2000). The result shows that the annual variations of daytime TEC are strong in the middle latitudes for the northern and southern hemispheres, and weak in the low latitudes and equatorial region. The amplitudes of semi-annual variations are much larger in the 'far-pole' region (far away from the northern or southern magnetic pole, i.e. northeastern Asia and South American) than those in the 'near-pole' region (North America and Australia). Further studies also show that daytime TEC is maximized at equinox days in most regions, and maximized in winter in the northern 'near-pole' region. In South America and most of Australia, daytime TEC reaches its max value in summer.The atomic/molecular ratio [O/N2] in the neutral atmosphere calculated by the MSIS90 model is also analyzed with the Fourier method. The results indicate that the annual amplitudes of the [O/N2] ratio are large in the northern and southern middle and high latitudes, and the winter anomalies are noticeable very much. According to Rishbeth's opinion, we suggest that the [O/N2] may have important contribution to the TEC annual variations, as well as to the winter anomaly which prevails in the 'near-pole' region. As for the daytime TEC semi-annual variations, we should comprehensively consider the contribution of [O/N2] and the electron production rate associated with the solar zenith angle.

Analysis of the winter and semiannual ionospheric anomalies in 1999–2009 based on GPS global International GNSS Service maps

“…This result verifies that the winter anomaly is strongly related to the change of composition which is closely related to the winter anomaly of (O/N 2 ) in this region [Yu et al, 2006], being the lighter neutral constituents, which are formed in the summer hemisphere convected to the winter hemisphere.…”

A New Global Total Electron Content Empirical Model

“…In fact, other anomalies are present in the ionosphere around the world, such as the NWA anomaly [48]. TEC winter anomalies occurred in the Arctic, North America, and Nordic regions of the Northern Hemisphere [49]. In addition, the ionospheric TEC showed asymmetry between the northern and southern hemispheres [50,51]; in the South and North Poles, the variation characteristics of the ionospheric TEC during polar day or night vary considerably from those of the ionospheric TEC in the middle and low latitudes.…”

A Solution for Real-Time Ionospheric Delay Using an Adaptive Kalman Filter Based on Estimating the Variance Component

“…A new pseudo-measurement is obtained by combining the predicted value in (6) and the observation in (14). Then the new observations are given by (15) and (16):…”

“…However, due to the complexity of the ionosphere, a 2 Mathematical Problems in Engineering remaining ionospheric delay error is still inevitable after the time difference is handled [12][13][14]. By considering the timevarying characteristics of ionospheric delay [15][16][17] and the lack of an actual theoretical model and adopting the least squares variance component estimation (LS-VCE) method to adjust the noise level of DID [18,19], we conduct online, adaptive modeling to obtain the estimated and predicted values of DID and analyze the magnitude and variation characteristics of DID.…”