This paper presents a quantitative explanation of storm‐enhanced density (SED). The plasma's root origin lies in the fully sunlit equatorial ionosphere where a penetrating zonal electric field drives plasma upward so fast that it cannot recombine. This plasma spills over into the anomaly and then is driven poleward by a penetrating zonal electric field. However, the poleward field cannot extend into the dayside due to high conductivity and the flow stagnates, causing plasma to build up in a narrow channel along the dusk terminator and flow into the convection pattern. It is remarkable that plasma finds its way into the polar cap from the daytime equator. We believe that this plasma structure is connected to the plasmaspheric tails reported in the literature.

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Abstract. We report here on post-midnight uplifts near the magnetic equator. We present observational evidence from digital ionosondes in Brazil, a digisonde in Peru, and other measurements at the Jicamarca Radio Observatory that show that these uplifts occur fairly regularly in the post-midnight period, raising the ionosphere by tens of kilometers in the most mild events and by over a hundred kilometers in the most severe events. We show that in general the uplifts are not the result of a zonal electric field reversal, and demonstrate instead that the uplifts occur as the ionospheric response to a decreasing westward electric field in conjunction with sufficient recombination and plasma flux. The decreasing westward electric field may be caused by a change in the wind system related to the midnight pressure bulge, which is associated with the midnight temperature maximum. In order to agree with observations from Jicamarca and Palmas, Brazil, it is shown that there must exist sufficient horizontal plasma flux associated with the pressure bulge. In addition, we show that the uplifts may be correlated with a secondary maximum in the spread-F occurrence rate in the post-midnight period. The uplifts are strongly seasonally dependent, presumably according to the seasonal dependence of the midnight pressure bulge, which leads to the necessary small westward field in the post-midnight period during certain seasons. We also discuss the enhancement of the uplifts associated with increased geomagnetic activity, which may be related to disturbance dynamo winds. Finally, we show that it is possible using simple numerical techniques to estimate the horizontal plasma flux and the vertical drift velocity from electron density measurements in the post-midnight period.

Abstract. Daytime equatorial electrojet plasma irregularities were investigated using five distinct radar diagnostics at Jicamarca including range-time-intensity (RTI) mapping, Faraday rotation, radar imaging, oblique scattering, and multiplefrequency scattering using the new AMISR prototype UHF radar. Data suggest the existence of plasma density striations separated by 3-5 km and propagating slowly downward. The striations may be caused by neutral atmospheric turbulence, and a possible scenario for their formation is discussed. The Doppler shifts of type 1 echoes observed at VHF and UHF frequencies are compared and interpreted in light of a model of Farley Buneman waves based on kinetic ions and fluid electrons with thermal effects included. Finally, the up-down and east-west asymmetries evident in the radar observations are described and quantified.

[1] The main purpose of this paper is to analyze observations of the 630.0-nm (red line) and 557.7-nm (green line) zenith airglow intensities measured during the month of October 2002 over Arecibo, Puerto Rico. We begin by describing an improved model for calculating the intensity of the red and green airglow lines that takes into account the role of molecular ions. We show, however, that at least for the data used in this study, it is not necessary to include the effects of molecular ions in our calculations. From observations of the airglow emissions on quiet days, we infer the general characteristics of the red-line intensities, which show a minimum before midnight and a peak after midnight. These results are consistent with a decrease in N m F2 and an increase in h m F2 before midnight, followed by the so-called ''midnight collapse.'' We then focus on the storm day of October 1-2, 2002, during which large-amplitude variations in both the red-and green-line intensities were observed and reproduced by the airglow model. An additional peak of N m F2, together with an h m F2 decrease, was observed before midnight, associated with the passage of a large-scale atmospheric gravity wave. The N m F2 nighttime increase requires plasma flux from the plasmasphere, which we find can be as large as 10 9 cm À2 s À1 . The plasmasphere needs an additional source of plasma in order to provide such a large flux, and we explain this by considering the role of the meridional wind in the plasma exchange process. Strong changes in the shape of the F2 region were observed during the downward and upward motion of the F2 layer during the storm period. We have found simple analytical solutions for the height distributions of the electron density in the F2 region by including the effects of recombination and diffusion. These height distributions are in excellent agreement with the measured profiles. Finally, we discuss mesospheric green-line fluctuations and show that good agreement can be obtained for the storm conditions if small adjustments are made to the eddy diffusion coefficients in the mesosphere, which we associate with the passage of the gravity wave. However, we find that some green-line behavior during quiet-time conditions is difficult to explain.