Sprites, blue jets, and elves: Optical evidence of energy transport across the stratopause

Abstract

Sprites, blue jets, blue starters, and elves are recently documented optical evidence of previously unknown forms of upward electrical energy transport across the stratopause. These energetic processes have not been incorporated into most models or descriptions of middle- and upper-atmospheric dynamics, in part because the details of the processes themselves are still poorly understood. The earliest (1995) ground based red spectral observations of neutral molecular nitrogen emissions from sprites indicate a low energy phenomena compared to the neutral and ionized emissions observed in lightning or aurora. However, recent sprite observations of ionized molecular nitrogen emissions indicate the presence of higher energy processes. In 1998, the EXL98 aircraft campaign characterized the blue emissions of sprites, blue jets, and elves. Aircraft measurements include filtered images, at 427.8 nm (N + 2 (1NG)) and 340.7 nm (N 2 (2PG)), as well as NUV/blue spectral observations between 320-460 nm, while ground based time-resolved photometric measurements were also made in this wavelength range. We discuss the filtered and spectral NUV observations in conjunction with earlier red (640-920 nm) spectral and filtered photometer observations. The identification of ionized nitrogen emissions indicates processes with electron energies of at least 18.6 eV to produce these emissions, assuming excitation is directly from the N 2 ground state. This paper provides middle- and upper-atmospheric scientists an introduction to these recently discovered phenomena and the current best estimates of the energetic contributions of these phenomena to the atmosphere above the tropopause.