[1] Global observations of electron density profiles from the COSMIC satellites are used to investigate, for the first time, the altitudinal dependence of the ionospheric response to the recurrent geomagnetic activity at different latitudinal regions during the extreme solar minimum period of 2008. Our results show that the 9-day oscillations in N m F2 are out of phase with those in Kp at high latitudes, whereas they are in phase at low-middle latitudes. This is consistent with changes in neutral composition associated with the recurrent geomagnetic activity. Meanwhile, the 9-day perturbations in the h m F2 and the thickness parameter (H T ) exhibit good correspondence with the perturbations in Kp from pole to pole, suggesting that the ionospheric response is global and undergoes periodic expansion/contraction. Further, the ionospheric response to the recurrent geomagnetic activity strongly depends on altitude. The density perturbations are generally in phase with Kp above the F2 peak, while they are out of phase around the F2 peak at high latitudes. These changes in electron density at different altitudes are explained by different physical processes, such as photoionization-chemistry, particle precipitation, and dynamic and diffusion transport. Citation: Tulasi Ram, S.,

[1] The Jicamarca (11.95°S, 76.87°W) digisonde and the Arequipa (16.47°S, 71.49°W) GPS receiver observed the equatorial F region irregularities on the western South America from April 1999 to March 2000. The spread F measured by the digisonde were classified into four types, and the GPS phase fluctuations derived from the temporal variation of total electron content were divided into three levels to represent the irregularity strength. The observation shows that the occurrences of all four types of spread F are higher in the D months (January, February, November, and December) than in the E months (March, April, September, and October). For the GPS phase fluctuations, both seasonal and nighttime variations show that the occurrences of strong level irregularities are higher than moderate level irregularities in the E months, but the situation is reversed in the D months. Moreover, the occurrence sequences of four types of spread F and three levels of GPS phase fluctuations all can be explained by the E Â B drift variations and the generalized Rayleigh-Taylor instability. For the comparisons between the GPS phase fluctuations and the digisonde spread F/plasma bubbles, results show that the GPS phase fluctuations can represent the appearances of the digisonde spread F, and the strong level of GPS phase fluctuations are associated with the occurrence of topside plasma bubbles. These results imply that the greater GPS phase fluctuation is related to the larger altitudinal range distribution of irregularities.

[1] This work is the first attempt to concurrently study the occurrence probabilities of spread F, GPS phase fluctuations, and plasma bubbles near the crest of equatorial ionization anomaly (EIA). The data were observed by an ionosonde, a GPS receiver, and ROCSAT-1 during 2000, the solar maximum year. Results show that the occurrences of the range spread F (RSF) differ from those of the frequency spread F (FSF). For the seasonal variation, the RSF occurrence has the maximum values in March and September, while the FSF occurrence peaks at June. For the nighttime variation, RSF and FSF peak at 2300 and 0300 LT, respectively. Regarding the GPS phase fluctuations, an index Fp is applied to characterize the irregularity strength. The similarity between the 50 < Fp 200 and RSF occurrences demonstrates that the characteristics of F region irregularities forming 50 < Fp 200 are mainly related to RSF. The occurrence of 200 < Fp is almost absent. The rare event is also found in the observation of plasma bubbles by ROCSAT-1. Furthermore, the seasonal variations in GPS phase fluctuations at the EIA crest and the dip equator have similar trends. This indicates that the F region irregularities of RSF and 50 < Fp 200 at the EIA crest are originated from the equatorial ionosphere. On the other hand, the seasonal variation in occurrence probability of FSF at the EIA crest is close to that of spread F at midlatitudes. This suggests that the generation mechanisms of FSF and midlatitude spread F might be same, but the further study is required.

[1] This is the first report of the most comprehensive 630.0 nm airglow limb images taken using Imager of Sprites and Upper Atmospheric Lightnings (ISUAL) onboard FORMOSAT-2. The limb scans reveal two distinct airglow layers: the upper one corresponds to the thermospheric O( 1 D) emission and the lower one corresponds to the OH (9-3) emissions. Sequences of such observations are combined to generate altitude-latitude maps of the emissions, which reveal intensity enhancements of both the layers at certain locations where they often appear to be linked/joined vertically. A detailed analysis of the location and occurrence of the enhancements in the entire observations, together with simulations of the emissions suiting the ISUAL limb geometry are carried out to understand the causes and related processes.