Flaming Auroral Rays - An analysis of high-speed spectral imaging and time-dependent electron-transport modelling of precipitation

Abstract

The current understanding of flaming auroral rays is that they are produced by short bursts of electrons precipitating down into the upper atmosphere. The altitude variation of the ionospheric response to such electron precipitation will be dependent on the energy-time dispersion of the incoming electron-bursts.

The aim of this project has been to investigate the source of flaming auroral rays, and to estimate the altitude-time-variation of brightness from multispectral images from the two Auroral Structure and Kinetics (ASK 1 and ASK 3) optical instruments targeted at the wavelengths of atomic oxygen at 7774 Å and molecular nitrogen at 6730 Å. This data is combined with electron-transport calculations from the AURORA code to estimate the time-energy variation of electron-flux in the ionosphere.

By identifying individual, field aligned rays in the spectral images and extracting the image intensity, observed rays can be compared with simulated rays based on modelling of volume emission-rates with time-dependent electron-transport calculations.

The time-energy dispersion of electron fluxes through the ionosphere have not previously been possible to model, and therefore time-resolved excitation-profiles have previously not been possible to calculate. Now, with the time-dependent electron-transport code, AURORA, developed at UiT, this can be done, making it possible to model the time-variation of both prompt and forbidden auroral emissions.

From the imaging of prompt emissions from atomic oxygen (6730 Å) and molecular nitrogen (7774 Å) of flaming auroral rays it has now proven to be possible to determine the time-energy variation of the electron-precipitation.

The current understanding of flaming auroral rays is that they are produced by short bursts of electrons precipitating down into the upper atmosphere. The altitude variation of the ionospheric response to such electron precipitation will be dependent on the energy-time dispersion of the incoming electron-bursts.

The aim of this project has been to investigate the source of flaming auroral rays, and to estimate the altitude-time-variation of brightness from multispectral images from the two Auroral Structure and Kinetics (ASK 1 and ASK 3) optical instruments targeted at the wavelengths of atomic oxygen at 7774 Å and molecular nitrogen at 6730 Å. This data is combined with electron-transport calculations from the AURORA code to estimate the time-energy variation of electron-flux in the ionosphere.

By identifying individual, field aligned rays in the spectral images and extracting the image intensity, observed rays can be compared with simulated rays based on modelling of volume emission-rates with time-dependent electron-transport calculations.

The time-energy dispersion of electron fluxes through the ionosphere have not previously been possible to model, and therefore time-resolved excitation-profiles have previously not been possible to calculate. Now, with the time-dependent electron-transport code, AURORA, developed at UiT, this can be done, making it possible to model the time-variation of both prompt and forbidden auroral emissions.

From the imaging of prompt emissions from atomic oxygen (6730 Å) and molecular nitrogen (7774 Å) of flaming auroral rays it has now proven to be possible to determine the time-energy variation of the electron-precipitation.