A theoretical model for ionospheric electric fields at mid-and low-latitudes

A theoretical model for ionospheric electric fields at mid- and low-latitudes is developed. In the geomagnetic dipolar coordinate system, we deduce a partial differential equation of electric potential from the ionospheric dynamo theory. The deduced equation is taken as the fundamental equation for the present model. The principal parameters for the model input, the thermospheric neutral winds, the densities and temperatures of electrons, ions and neutral atoms and molecules, are obtained from the empirical models HWM93, IRI90 and MSISE90, respectively. In terms of the relaxation iteration method, the partial equations for electric potential are solved successfully, and then, the ionospheric electric potential, fields, and currents are derived. Our model can reproduce the main features of the ionospheric electrodynamical processes such as the equatorial electric jet (EEJ), so it will be a useful tool for studying the upper atmosphere and ionosphere.

The sudden increase in ionospheric total electron content caused by the very intense solar flare on July 14, 2000

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.

Low latitude ionospheric effects near longitude 120°E during the great geomagnetic storm of July 2000

A great geomagnetic storm occurred on July 15/16, 2000 with a minimum value of about -300 nT in Dst index. Collecting digisonde data from ionospheric stations at Chungli, Wuhan, Kokubunji and Anyang, the ionospheric responses at the low latitudes near longitude 120(E during this storm are analyzed in this paper. There was a strong negative phase storm at low latitudes on July 16. The G-condition in the ionograms was clearly seen on the early first day after the commencement of geomagnetic storm. Those were considered to be caused by the storm-induced increase in the concentration ratios of neutral molecular O2 or N2 to atom O. On July 17 and some days thereafter, a positive phase storm appeared. In addition, anomalous equatorial ionization anomaly (EIA) inhibitions and developments were observed on July 16 and 17. There were also prominent nighttime enhancements in foF2 during these days, and the diurnal variation of foF2 was less clear than before.

NETWORK OBSERVATION OF IONOSPHERIC DISTURBANCES DURING THE WAGS IN OCTOBER,1985

A three-station network of HF Doppler measurements augmented with a single rapid-run ionosonde is used at Wuhan Ionospheric Observatory, China, to monitor the atmosphericgravity wave disturbances during the WAGS campaign. The records observed in the daytimeon October 18, 1985 (in Incoherent Scatter World Day Run) are investigated. It is found thatthere exist two wave trains of disturbances in the daytime: one is a medium-scale internalgravity wave excited locally and the other is a large-scale guided gravity wave propagatingfrom north to south. Both the horizontal propagation and the height variation of the gravitywave disturbances are studied in detail with a new inversion method. The results indicatethat the inversion method makes the simple HF radio experiment system very useful in thestudy of large scale ionospheric disturbances such as gravity waves.