SR90, strontium shaped-charge critical ionization velocity experiment

In May 1986 an experiment was performed to test Alfven's critical ionization velocity (CIV) effect in free space, using the first high explosive shaped charge with a conical liner of strontium metal. The release, made at 540 km altitude at dawn twilight, was aimed at 48 deg to B. The background electron density was 1.5 x 10(exp 4) cu cm. A faint field-aligned Sr(+) ion streak with tip velocity of 2.6 km/s was observed from two optical sites. Using two calibration methods, it was calculated that between 4.5 x 10(exp 20) and 2 x 10(exp 21) ions were visible. An ionization time constant of 1920 s was calculated for Sr from the solar UV spectrum and ionization cross section which combined with a computer simulation of the injection predicts 1.7 x 10(exp 21) solar UV ions in the low-velocity part of the ion streak. Thus all the observed ions are from solar UV ionization of the slow (less than critical) velocity portion of the neutral jet. The observed neutral Sr velocity distribution and computer simulations indicate that 2 x 10(exp 21) solar UV ions would have been created from the fast (greater than critical) part of the jet. They would have been more diffuse, and were not observed. Using this fact it was estimated that any CIV ions created were less than 10(exp 21). It was concluded that future Sr CIV free space experiments should be conducted below the UV shadow height and in much larger background plasma density

D region electron density derived from sprites

2 sprite carrots were recorded at 100,000 images per second. Analysis of the observations has been submitted to Geophysical Research Letters for publication (1 Oct 2022

Sprite Spectra at 10,000 fps

Analysis of optical spectra from small scale sprite structures observed from aircraft in 2009 and 201

ARTICLE Plasma irregularities in the D-region ionosphere in association with sprite streamer initiation

Sprites are spectacular optical emissions in the mesosphere induced by transient lightning electric fields above thunderstorms. Although the streamer nature of sprites has been generally accepted, how these filamentary plasmas are initiated remains a subject of active research. Here we present observational and modelling results showing solid evidence of pre-existing plasma irregularities in association with streamer initiation in the D-region ionosphere. The video observations show that before streamer initiation, kilometre-scale spatial structures descend rapidly with the overall diffuse emissions of the sprite halo, but slow down and stop to form the stationary glow in the vicinity of the streamer onset, from where streamers suddenly emerge. The modelling results reproduce the sub-millisecond halo dynamics and demonstrate that the descending halo structures are optical manifestations of the pre-existing plasma irregularities, which might have been produced by thunderstorm or meteor effects on the D-region ionosphere

Imaging Observations of Thermal Emissions from Augustine Volcano Using a Small Astronomical Camera

Long-exposure visible-light images of Augustine Volcano were obtained using a charge-coupled device (CCD) camera during several nights of the 2006 eruption. The camera was located 105 km away, at Homer, Alaska, yet showed persistent bright emissions from the north flank of the volcano corresponding to steam releases, pyroclastic flows, and rockfalls originating near the summit. The apparent brightness of the emissions substantially exceeded that of the background nighttime scene. The bright signatures in the images are shown to probably be thermal emissions detected near the long-wavelength limit (~1 (u or mu)) of the CCD. Modeling of the emissions as a black-body brightness yields an apparent temperature of 400 to 450 degrees C that likely reflects an unresolved combination of emissions from hot ejecta and cooler material

Mechanism of column and carrot sprites derived from optical and radio observations

International audience[1] The lightning current waveforms observed simultaneously with high-speed video records of a column and a carrot sprite event are incorporated in a plasma fluid model to provide quantitative explanation of these two distinct morphological classes of transient luminous events. We calculate the strength of the lightning-induced electric field at sprite altitudes using a time integral of the ionization frequency R t 0 i (E/N)dt. For the studied two events, modeling results indicate that these integral values never exceed 18 in the lower ionosphere, which is the minimum value required for the initiation of streamers from single seed electrons according to the Raether-Meek criterion. It is therefore suggested that the presence of electron inhomogeneities is a necessary condition for the initiation of sprite streamers. It is further demonstrated using streamer modeling that a minimum value of the integral 10 is necessary to initiate upward negative streamers from inhomogeneities, corresponding to a minimum charge moment change of 500 C km under typical nighttime conditions. If the integral values in the entire upper atmosphere are smaller than 10, only column sprites can be produced, dominated by downward positive streamers. Citation: Qin, (2013), Mechanism of column and carrot sprites derived from optical and radio observations , Geophys

Effects of Phosphor Persistence on High-Speed Imaging of Transient Luminous Events

International audienceHigh-speed intensified cameras are commonly used to observe and study the transient luminous events known as sprite halos and sprite streamers occurring in the Earth's upper atmosphere in association with thunderstorm activity. In such observations, the phosphor persistence in the image intensifier, depending on its characteristic decay time, might lead to a significant distortion of the optical signals recorded by those cameras. In this paper, we analyze the observational data obtained using different camera systems to discuss the effects of phosphor persistence on high-speed video observations of sprites, and introduce a deconvolution technique to effectively reduce such effects. The discussed technique could also be used to enhance the high-speed images of other transient optical phenomena in the case when the phosphor persistence has a characteristic decay time that is comparable with the temporal resolution of the cameras required to resolve the phenomena