A large number (~1000) of coincident auroral far ultraviolet (FUV) and ground-based ionosonde observations are compared. This is the largest study to date of coincident satellite-based FUV and ground-based observations of the auroral E region. FUV radiance values from the NASA Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) Global Ultraviolet Imager (GUVI) and the Defense Meteorological Satellite Program (DMSP) F16 and F18 Special Sensor Ultraviolet Spectrographic Imager (SSUSI) are included in the study. A method is described for deriving auroral ionospheric E region maximum electron density (NmE) and height of maximum electron density (hmE) from N Lyman-Birge-Hopfield (LBH) radiances given in two channels using lookup tables generated with the Boltzmann 3-Constituent (B3C) auroral particle transport and optical emission model. Our rules for scaling (i.e., extracting ionospheric parameters from) ionograms to obtain auroral NmE and hmE are also described. Statistical and visual comparison methods establish statistical consistency and agreement between the two methods for observing auroral NmE, but not auroral hmE. It is expected that auroral non-uniformity will cause the two NmE methods to give inconsistent results, but we have not attempted to quantify this effect in terms of more basic principles, and our results show that the two types of NmE observations are well correlated and statistically symmetrical, meaning that there is no overall bias and no scale-dependent bias.

[1] Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) data were analyzed to study the climatological variations of the F 2 region ionosphere. A 30 day running median was applied to the daily medians of each geomagnetic latitude bin (10 0 ) to remove the short-term variability of the data. This permitted a better description of the long-term daytime climatology across the most recent solar minimum to be obtained. Several significant features appeared in this climatology: 1) low-latitude N m F 2 was dominated by the semi-annual anomaly, the equatorial anomaly and the annual asymmetry (anomaly); 2) Semi-annual and annual anomalies extended into the middle latitudes; 3) this extension into the middle latitudes appears to be dependent on variations of solar radiation over the solar cycle, as the variations did not reach as far poleward in 2008 as they did in 2010; 4) The second equinoctial maximum is not centered on the September equinox, but occurred in October; 5) there is an annual variation at high latitudes in which maximum values of N m F 2 occur in summer -there is no indication of a winter anomaly and, in fact, when hemispheres are compared, maximum N m F 2 at middle latitudes always occurs in the summer hemisphere rather than the winter one; 6) the highest values of h m F 2 at low latitudes occur on the summer side of the magnetic equator throughout the four year period, probably resulting from winds blowing from the summer to the winter; 7) minimum values of h m F 2 at middle latitudes occur in winter, when h m F 2 is typically 30 to 50 km lower than it is in summer; 8) elevated h m F 2 also occurs in summer at high latitudes, with a distinct seasonal and hemispheric asymmetry.

This study investigates the interhemispheric nature of polar cap auroras via ultraviolet imaging, combined with particle data, to determine whether they occur on open or closed field lines. Data from the SSUSI (Special Sensor Ultraviolet Spectrographic Imager) instrument on board the DMSP (Defence Meteorological Satellite Program) spacecraft are examined. The DMSP spacecraft are in 90‐min orbits; hence, images of each hemisphere are separated by 45 min providing a good opportunity for interhemispheric study. 21 polar cap arc (PCA) events are recorded in December 2015 which have particle data from the SSJ/4 particle spectrometer associated with an arc in at least one hemisphere. Nine events are found to contain "arcs" consistent with a closed field line mechanism, that is, arcs associated with an ion signature present in both hemispheres. Six events contained arcs that were consistent with an "open field line" mechanism, that is, they were associated with electron‐only precipitation. Events containing arcs that were not consistent with either of these expectations are also explored, including an example of a "non‐conjugate" theta aurora and an interesting example of auroral morphology similar to a PCA which is associated with a geomagnetic storm. Seasonal effects are also investigated through a statistical analysis of PCAs over 4 months in 2015. It is found that PCAs are visible in the SSUSI data at least 20% of the time and that it is likely some are missed due to the spacecraft field of view and poor sensitivity in the summer hemisphere due to increased solar illumination.

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[1] Nightside detached auroras (NDA) during intense magnetic storms are studied by using FUV image data from Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED)/Global Ultraviolet Imager (GUVI), Imager for Magnetopause-toAurora Global Exploration (IMAGE)/FUV, and particle data from DMSP/SSJ/4 instruments. We found that NDA are caused by proton/ion precipitation only. Thin arcshaped NDA are very likely due to soft (<1 keV) proton/ion precipitation. Thick or patchshaped NDA are caused by energetic ($10 keV) proton/ion precipitation. All the cases indicate that the NDA were observed when Dst was less À130 nT. More specifically, the NDA occurred during recovery or the lowest Dst period for each intense storm. The magnetic latitudes of the NDA are between 45°and 55°(L shell: 2.0-3.0). We found that the latitude location of the NDA is quasi-linearly correlated with Dst. The magnetic local time (MLT) of the NDA ranges from 1930 to 0300. All the facts indicate that the source of the NDA is the trapped protons/ions in the ring current. Precipitation of the trapped protons/ions is caused by an interaction between the perpendicularly heated ring current particles and the cold/dense plasma at the plasmapause.