Daily observations of the development of the ionospheric equatorial anomaly by means of differential Doppler shift method

Abstract

The differential Doppler frequency shifts observed by receiving coherent radio signals at frequencies of 150 and 400 MHz transmitted from the polar orbiting satellites of U.S. Navy Navigation Satellite System have been used to deduce the latitudinal variations of the ionospheric total electron content (TEC) near the ionosphere equatorial anomaly crest region. All latitudinal variations of TEC thus obtained for each passage of an NNSS satellite are used to construct daily contour plots of TEC in a latitude versus local time coordinates. It has been shown that these contour plot of TEC can be used to investigate the behavior of TEC around equatorial anomaly erest region. Some results are presented and discussed. pearence (1500 LT) of the maximum development of Appleton, E. V., The anom•dous equatorial belt in the F2-1ayer, j ' the equatorial anomaly; and the southward move-Atmos. Terr. Phys., 5, 348,1954. merit of the anomaly crest before the maximum de-Carnahan, B., H. A. Luther, and J. O. Wilkes, Applied Numerical Methods, John Wiley, New York, 1969. velopment of the anomaly. On February 11 de Mendonca, F., Ionospheric electron content and vadation• (Ap = 20), the behavior of equatorial anomaly finally measured by Doppler shifts in satellite transmissions, J. Geo. returns to its normal characteristics on geomagnetic phys. Res., 67, 2315,1962. quiet day. de Mendonca, F., Ionospheric electron content measurements in Although quite a number of reports have been regions of low magnetic dip and through the Brazilian magnetic anomaly, Space Res., 5, 687,1965. made on geomagnetic storm effects on the total elec-de Mendonca, F., and O.K. Garriott, Ionospheric electron coatton content at individual TEC stations [e.g., Huan•7 tent calculated by a hybrid Faraday-Doppler technique, j. et al., 1974; Essex et al., 1981'1, these seems no earlier Atmos. Terr. Phys., 24, 317,1962.

Adaptive techniques for extraction of pre-seismic parameters of Total Electron Content (TEC) at anomaly crest station

“…The effect is called an anomaly because when the electron density should have been maximum at the equator, it makes a minimum over the magnetic equator, while causing maxima at latitudes 108 or 208 north and south of the equator, respectively. Further, the width of the anomaly undergoes changes with the solar geomagnetic environment (Huang et al 1987, Fukushima 1989, Walker and Chen 1989, Min-Yun and Chang-Shou 1991, Devi et al 2002, Anderson et al 2006. Modifications seen in TEC records at this zone thus carry a host of imprints of complex factors contributed by seismic processes, solar geomagnetic variations, as well as impacts from the equatorial current system, to name a few.…”

Seasonal variations of the ionospheric total electron content in Asian equatorial anomaly regions

“…Owing to the development of satellites, the estimation of ionospheric seasonal behaviors in total electron content (TEC) has been carried out (see papers listed in the works of Huang et al [1987] and Huang et al [1989]). Huang et al [1987] studied the TEC of the northem anomaly crest by analyzing the differential Doppler data from the U.S. Navy Navigation Satellite System (NNSS) and calibrated by the Faraday rotation data of the Japanese geostationary satellite ETS 2. After 1997, NNSS-ionospheric study almost halts due to unavailability of satellite information.…”

Variations of the ionospheric TEC using simultaneous measurements from the China Crustal Movement Observation Network

“…Since V. Appleton (1946) and Liang (1947) found an equatorial anomaly, based on data of ionospheric critical frequencies, much work about this phenomenon has been done. Compared to the data of foF2, the latitudinal distribution of the ionospheric TEC shows a similar structure to the maximum electron density of the ionosphere (Huang et al, 1987). This means that the equatorial anomaly can also be found using TEC data.…”