The Global Ultraviolet Imager (GUVI) onboard the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite senses far ultraviolet emissions from O and N 2 in the thermosphere. Transformation of far ultraviolet radiances measured on the Earth limb into O, N 2 , and O 2 number densities and temperature quantifies these responses and demonstrates the value of simultaneous altitude and geographic information. Composition and temperature variations are available from 2002 to 2007. This paper documents the extraction of these data products from the limb emission rates. We present the characteristics of the GUVI limb observations, retrievals of thermospheric neutral composition and temperature from the forward model, and the dramatic changes of the thermosphere with the solar cycle and geomagnetic activity. We examine the solar extreme ultraviolet (EUV) irradiance magnitude and trends through comparison with simultaneous Solar Extreme EUV (SEE) measurements on TIMED and find the EUV irradiance inferred from GUVI averaged (2002-2007) 30% lower magnitude than SEE version 11 and varied less with solar activity. The smaller GUVI variability is not consistent with the view that lower solar EUV radiation during the past solar minimum is the cause of historically low thermospheric mass densities. Thermospheric O and N 2 densities are lower than the NRLMSISE-00 model, but O 2 is consistent. We list some lessons learned from the GUVI program along with several unresolved issues.

Based on the experiments we consider, we predict that the s/1 variations of Pseed will be found to be similar to those of PEF•, and largely to explain them. Finally, we find reasons, based on the similarity of the DRSF variations to s/1 patterns of the average scintillation index, for not using, as is commonly done, such scintillation patterns as substitutes for PEF• or Pinst patterns.

Abstract. We analyzed measurements of ion number density made by the retarding potential analyzer aboard the Atmosphere Explorer-E (AE-E) satellite, which was in an approximately circular orbit at an altitude near 300 km in 1977 and later at an altitude near 400 km. Large-scale (>60 km) density measurements in the high-altitude regions show large depletions of bubble-like structures which are confined to narrow local time, longitude, and magnetic latitude ranges, while those in the low-altitude regions show relatively small depletions which are broadly distributed in space. For this reason we considered the altitude regions below 300 km and above 350 km and investigated the global distribution of irregularities using the rms deviation z•V/N over a path length of 18 km as an indicator of overall irregularity intensity. Seasonal variations of irregularity occurrence probability are significant in the Pacific regions, while the occurrence probability is always high in the Atlantic-African regions and is always low in the Indian regions. We find that the high occurrence probability in the Pacific regions is associated with isolated bubble structures, while that near 0 ø longitude is produced by large depletions with bubble structures which are superimposed on a large-scale wave-like background. Considerations of longitude variations due to seeding mechanisms and due to F region winds and drifts are necessary to adequately explain the observations at low and high altitudes. Seeding effects are most obvious near 0 ø longitude, while the most easily observed effect of the F region is the suppression of irregularity growth by interhemispheric neutral winds.

[1] We investigate the longitudinal distribution of the vertical E Â B drift velocity and ion density in the lowlatitude ionosphere using the first Republic of China Satellite (ROCSAT-1) data acquired during 1999 -2004. The ROCSAT-1 observations during daytime demonstrate the presence of the longitudinally periodic patterns of the vertical E Â B drift and plasma density on the topside F region (600 km). The four longitude sectors where the peaks in the plasma density are found are coincident with the peaks in the E Â B drift. This observation may indicate the association of the large-scale longitudinal density structure with the daytime E-region dynamo electric field. The density structure exists before the occurrence of the pre-reversal enhancement (PRE) and therefore the PRE is not directly related to this phenomenon. Citation:

[1] The occurrence statistics of equatorial plasma bubbles (EPBs) obtained from lowinclination orbit satellites are significantly affected by the way the data are sampled and the way that the EPBs are counted. To resolve the discrepancy between the EPB occurrence frequency determined by ground-based observations and in situ sampling of plasma density from spacecraft, we have developed a new EPB detection method that minimizes the dependence of the EPB occurrence rate on the data processing method. The global EPB distribution maps are created by analyzing the measurements of the ion density from the first Republic of China satellite (ROCSAT-1) during March 1999 to June 2004. The EPB occurrence probability obtained using our new EPB detection method is a few times greater than that obtained using the conventional method. Our results are comparable to the ground observations. The good agreement of the global EPB distribution with the global morphology of the evening prereversal enhancement (PRE) of vertical ion velocity supports the notion that the PRE is an important factor on a global scale in the generation of EPBs. However, the generation of EPBs is not guaranteed by the occurrence of an intense PRE. Other mechanisms, in addition to the PRE, should be considered as an explanation for the occurrence of EPBs on the topside.