The present paper studies the sudden increase in total electron content (SITEC) on the ionosphere caused by the very intense solar flare on July 14, 2000. According to the well-known Chapman theory of ionization, we derive the relationship between the temporal variation rate, TEC/t, of the total electron content (TEC) and the flare parameters. It is shown that ?TEC/t is proportional to the effective flare radiation flux, I_f, and inversely proportional to the Chapman function, ch(x), of the zenith angle x. TEC data observed by the GPS networks located in China, Southeast Asia and Australia during the very intense solar flare on July 14, 2000 are used to statis- tically investigate the relation between the observed TEC/t and ch(x). The analyses show that the two quantities are inversely proportional to each other, as the theory predicted. The pre- sent work shows that GPS observation is a powerful tool for studying solar flare effects on the ionosphere, i.e. the sudden ionospheric disturbances (SIDs). Because of its advantages of high precision, large geographical distribution and good temporal resolution, GPS TEC observation may reveal quantitatively the process of ionospheric disturbances caused by solar flares. Therefore, our results are of significance in the space weather research.
This paper investigates the large scale travelling ionospheric disturbances (LSTIDs) using the observation data of an HF Doppler array located in Central China. The data observed in a high solar activity year (year 1989) are analyzed to obtain the main propagation parameters of LSTIDs such as period, horizontal phase velocity and propagating direction. Results are outlined as follows: Most of the LSTIDs propagate southward; others tend to propagate northward, mostly in summer; dispersion of most LSTIDs is matched with that of Lamb pseudomode, while others have the dispersion of long period gravity wave mode. The horizontal phase velocities of these two modes are about 220 and 450 m/s respectively. The analysis shows that LSTIDs are strongly pertinent to solar activity and space magnetic storms; thus the results presented here are significant for the research of ionospheric weather in mid-low latitude region.
