The ionospheric responses to the solar eclipse of September 23, 1987, in the equatorial anomaly crest region have been investigated by using ionospheric vertical sounding, VLF propagation delay time, and differential Doppler shift data observed at Chungli, which is located near the northern equatorial anomaly crest region. It has been found that temporal variations of the F1 layer and D region are mainly controlled by local solar radiation. Quantitative analysis of the variations of the F1 layer critical frequency, ƒ0F1, shows that electrons are removed from the F1 layer through ionic recombination. However, the temporal variations of ƒ>0F2 and electron density above 200 km show that the variations of the F2 layer around the equatorial anomaly region are controlled not by local solar radiation but by solar radiation at the equator. The fountain effect plays an important role even during the solar eclipse. The VLF propagation time delay is controlled by the variations of average path obscuration. Atmospheric gravity waves produced by the moving bow wave front of the solar eclipse are found with a period around 17‐23 min and wavelength about 293 km.
Daily contour charts of the ionospheric total electron content in latitude versus local time coordinates have been used to study the behavior of the development of the equatorial anomaly around the northern anomaly crest region. The daily development of the equatorial anomaly shows quite large day‐to‐day variabilities not only on magnetically disturbed days but also on quiet days. The daily maximum anomaly crest moves poleward as the magnitude of the total electron content of the daily maximum anomaly crest increases. The increase of the equatorial electrojet strength also results in a poleward movement of the anomaly crest. No significant correlation exists between the anomaly crest and the magnetic Ap index. The monthly mean diurnal development of the equatorial anomaly shows a remarkable seasonal difference, with the anomaly largest in equinoxes and slightly larger in winter than in summer.
A development of a direct vision type high‐frequency Doppler frequency sounder and a setup of HF Doppler frequency sounding array at the northern part of Taiwan Island were presented. By use of all typhoons that occurred in 1982 and 1983, the detectability of the typhoon‐generated acoustic‐gravity waves by use of this HF Doppler frequency sounding array was presented. The results show that the acoustic‐gravity waves generated by a typhoon can be detected by this sounding array; however, the detectability is only 2 out of 12.
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.
During the total solar eclipse period on 24 October 1995, the ionospheric data derived from Faraday rotation, differential Doppler frequency shift, and HF Doppler sounding at Lunping Observatory were used to detect the traveling ionospheric disturbances associated with the solar eclipse of that day. These observed ionospheric disturbances were characterized by quasi periodic wave-like trains lasting for several cycles with wavelengths of around 193 km, periods of around 12-14 min and propagated with a hori zontal velocity of around 296 mis from the direction of the eclipse path to the observation site. By use of a simplified bow wave front model, these traveling ionospheric disturbances are interpreted as the freely propagated atmospheric gravity waves generated by the supersonic movement of the Moon's shadow through the Earth's atmosphere along the eclipse path.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.