Analogs of columnar sprites initiated in low-pressure air and nitrogen

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Results of experimental studies of red-colored plasma diffuse jets are presented. Such jets are initiated by a capacitive discharge in air or nitrogen at pressures of 0.2–3 Torr fed by voltage pulses with an amplitude of 5–7 kV following with a frequency of 21 kHz. They can be considered as a lab analog of a columnar sprite. The jet is formed by successive ionization waves (streamers). A significant effect of the reduced electric field strength E/N on the color (emission spectrum) of a plasma diffuse jet has been established. It is shown that the transition from red to blue as the jet approaches the additional electrodes and the end flange of the discharge tube is due to an increase in E/N in these regions. This, in turn, explains the change in color of sprites as they approach the top of the storm clouds. An assumption about the influence of noctilucent clouds on the formation of the beaded structure of sprites is made. The plasma parameters (electron Te, vibrational Tv, rotational Tr, and translational Ttr temperatures, as well as E/N) in the region of the capacitive discharge and along the plasma diffuse jet were measured by optical emission spectroscopy. The measurements have shown that with the increase in distance from the electrode assembly, E/N decreases from ∼3500 to ∼200 Td, while Te changes from ∼50 to 3 eV. The gas temperature varies slightly from 400 to 360 K. The measurement results are compared with those of natural red sprites.