Recognizing the blue emission in artificial aurora Original Research Article

On 12th November 2001, during an EISCAT UK/GE artificial aurora campaign, the optical group from the University of Oulu performed optical measurements at the EISCAT site in Ramfjordmoen, including the first measurement of blue emissions in artificial aurora at high latitudes. Optical instruments, including a photometer, a real speed TV camera and a digital camera, were monitoring the emissions. The emissions that the photometer was designed to measure were 557.7 nm (OI), 630.0 nm (OI) and 427.8 nm (image). The energy thresholds of these emissions are approximately 2, 4 and 19 eV, respectively. In the natural aurora the blue emission at around 427.8 nm is always dominated by the image 1NG(0, 1) band. However, there are two weak emission bands lying under this strong emission, namely, the N2 VK(4, 15) (threshold energy 6 eV) and N2 2P(1, 5) (threshold 11 eV). These excitation energies are lower than the energy needed to excite image 1NG(0, 1) level and therefore could have a stronger intensity compared with image 1NG(0, 1) in the spectrum of artificial aurora than in natural aurora. The auroral photometer of the University of Oulu has been designed for investigating natural aurora. The photometer was equipped with two channels measuring different wavelength bands around 427.8 nm. These channels were intended to be used to determine rotational temperature from the ratio of the intensities through the channels. However, here we estimate the intensities of the three overlapping emission bands instead.