Reducing the diameter of the cathode hole in a plane anode-hollow cathode geometry to 200 µm has allowed us to generate direct current discharges in argon at atmospheric pressure. Up to pressure times cathode hole diameter (pD) values of approximately 5 Torr cm, and at sub-mA currents, glow discharges (predischarges) are observed with a shape which is determined by the vacuum electric field. In the same pD range, but at higher currents of up to approximately 4 mA, the discharges are of the hollow cathode discharge type. At pD values exceeding 5 Torr cm the predischarges turn into surface discharges along the mica spacer between the electrodes. At currents >4 mA filamentary, pulsed discharges are observed. Qualitative information on the electron energy distribution in the microdischarges has been obtained by studying the VUV emission from ionized argon atoms and the argon excimer radiation at 130 nm. The results of the spectral measurements indicate the presence of a relatively large concentration of electrons with energies >15 eV over the entire pressure range. The fact that the current-voltage characteristic of the microdischarges has a positive slope over much of the current range where excimer radiation is emitted indicates the possibility of forming arrays of these discharges and using them in flat panel excimer lamps.

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The North American Thermosphere Ionosphere Observing Network (NATION), comprising a new network of Fabry-Perot interferometers (FPIs), to be deployed in the Midwest of the United States of America is described. FPIs will initially be deployed to four sites to make coordinated measurements of the neutral winds and temperature in the Earth's thermosphere using measurements of the 630 nm redline emission. The observing strategy of the network will take into account local observing conditions, and common volume measurements from multiple sites will be made in order to estimate local vector wind quantities. The network described is expandable, and as additional FPI sites are installed in North America, or elsewhere, the goal of providing the upper atmospheric research community with a robust dataset of neutral winds and temperatures can be achieved.

Observations of thermospheric neutral winds and temperatures obtained during a geomagnetic storm on 2 October 2013 from a network of six Fabry‐Perot interferometers (FPIs) deployed in the Midwest United States are presented. Coincident with the commencement of the storm, the apparent horizontal wind is observed to surge westward and southward (toward the equator). Simultaneous to this surge in the apparent horizontal winds, an apparent downward wind of approximately 100 m/s lasting for 6 h is observed. The apparent neutral temperature is observed to increase by approximately 400 K over all of the sites. Observations from an all‐sky imaging system operated at the Millstone Hill observatory indicate the presence of a stable auroral red (SAR) arc and diffuse red aurora during this time. We suggest that the large sustained apparent downward winds arise from contamination of the spectral profile of the nominal thermospheric 630.0 nm emission by 630.0 nm emission from a different (nonthermospheric) source. Modeling demonstrates that the effect of an additional population of 630.0 nm photons, with a distinct velocity and temperature distribution, introduces an apparent Doppler shift when the combined emissions from the two sources are analyzed as a single population. Thus, the apparent Doppler shifts should not be interpreted as the bulk motion of the thermosphere, calling into question results from previous FPI studies of midlatitude storm time thermospheric winds. One possible source of contamination could be fast O related to the infusion of low‐energy O+ ions from the magnetosphere. The presence of low‐energy O+ is supported by observations made by the Helium, Oxygen, Proton, and Electron spectrometer instruments on the twin Van Allen Probes spacecraft, which show an influx of low‐energy ions during this period. These results emphasize the importance of distributed networks of instruments in understanding the complex dynamics that occur in the upper atmosphere during disturbed conditions.

A high resolution 36 m Å (FWHM), optically thin emission study of the N 2 c 1 + u (4, 3) and (3, 2) Rydberg bands excited by electron impact at 100 eV has been completed in the extreme ultraviolet (EUV). A model of the perturbed rotational line intensity distribution of the bands shows the effects of electronic state mixing between the c 1 + u Rydberg state and the b 1 + u valence state. By normalizing the model to the published predissociation yield for J = 9 the laboratory spectrum can be used to determine the predissociation yields for each rotational level of v = 3 and 4. Based on a 25% accuracy of the model fit to the measured signal intensities it is found that the predissociation yields of the c , v = 4 rotational levels increase as the percentage of b 1 + u character increases. On the other hand, the predissociation yields of the c , v = 3 rotational levels reach a maximum for 5 < J < 10. The mean predissociation yields for c , v = 3 and 4 levels are a function of temperature and are found to be 0.41 and 0.58, respectively at 300 K. The J -dependent predissociation yields indicate that the emission cross section is a function of temperature. The remainder of the bands forming the v progressions (v = 0-5) from v = 3 and (v = 0-6) from v = 4 were studied at 64 m Å (FWHM) resolution. Using this composite spectrum of the two progressions the electron impact emission cross sections of the N 2 c , v = 3 and 4 levels at 300 K were determined and compared with previous results.