Photometric measurements in the SPRITES '95 & '96 campaigns of nitrogen second positive (399.8 nm) and first negative (427.8 nm) emissions

摘要

We have obtained blue photometric measurements of the N_2 second positive 399.8 nm and the N_2~+ first negative 427.8 nm emission from sprites, elves and lightning, along with supporting video images. The pulse width and intensity results for sprites are consistent with those of Suszcynsky et al. (1998). The red emission from sprites has been independently and unambiguously identified by Hampton et al. (1996) and Mende et al. (1995) as the nitrogen first positive band. The source has been attributed to electron impact excitation from low energy electrons (≈1 eV) in the sprite. The short pulse width of the 427.8 nm and 399.8 nm photometer time traces obtained in this investigation are probably not from the same source that produces the red emission. The results reported here indicate an initial energetic ionizing event sufficient to ionize and excite nitrogen followed by secondary electron processes which give rise to the dominant red emission. The photometer results for elves are consistent with the EMP mechanism suggested by Inan et al. (1996). The photometer traces obtained for lightning indicate emissions consistent with a 'continuing current' as the charge redistributes within the thunderstorm cloud. We find that the ratio of the intensity of the 399.8 nm N_2(2P) emission to that of 427.8 nm N_2~+(1N) emission can be used to discriminate among sprites, elves and lightning.