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Ionization emissions associated with N 2 + 1N band in halos without visible sprite streamers
Author(s) -
Kuo C. L.,
Williams E.,
Bór J.,
Lin Y. H.,
Lee L. J.,
Huang S. M.,
Chou J. K.,
Chen A. B.,
Su H. T.,
Hsu R. R.,
Sátori G.,
Frey H. U.,
Mende S. B.,
Takahashi Y.,
Lee L. C.
Publication year - 2013
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/jgra.50470
Subject(s) - sprite (computer graphics) , halo , electric field , physics , ionization , atomic physics , astrophysics , electron , photon , optics , galaxy , ion , nuclear physics , quantum mechanics , computer science , computer vision
We report the ionization emission associated with N 2 + 1N band in a halo event without visible sprite streamers. To avoid the lightning contamination to the ionization emission, we find halos whose parent lightning light is blocked by the Earth's limb. Five halos in the 2004–2010 Imager of Sprites and Upper Atmospheric Lightning data set were identified as halos without visible sprite streamers. A halo with maximum N 2 1P brightness had significant ionization emission of N 2 + 1N. The time‐integrated photon intensity of N 2 1P, N 2 2P, and N 2 + 1N emission is 2.2 × 10 5 , 2.1 × 10 4 , and 7.4 × 10 2 photons cm −2 , respectively at a distance of 4130 km. The total number of photons of N 2 1P, N 2 2P, and N 2 + 1N band emissions are 4.6 × 10 23 , 4.3 × 10 22 , and 1.6 × 10 21 photons, respectively. In the halo region, the electron density increased as 1–2 orders of magnitude higher than ambient electron density. From the emission ratio of N 2 + 1N to N 2 2P, the reduced electric field is estimated to be 275–325 Td that is higher than the conventional breakdown electric field. The recorded electric field related to this halo event is produced by a lightning discharge that has a total charge moment change of −1450 C km. Based on the estimated electric field from optical emissions, it is found that the lightning‐induced electric field in the bright halo region is significantly relaxed with a rate faster than that estimated using ambient electron density, in agreement with previous modeling results showing that the electron density enhancement due to the ionization processes leads to a short dielectric relaxation time inside the halo region.