Neutral temperature and atmospheric water vapour retrieval from spectral fitting of auroral and airglow emissions

• Main Authors: J. M. Chadney, D. K. Whiter
• Format: Article
• Language: English
• Published: Copernicus Publications 2018-11-01
• Series: Geoscientific Instrumentation, Methods and Data Systems
• Online Access: https://www.geosci-instrum-method-data-syst.net/7/317/2018/gi-7-317-2018.pdf

<p>We have developed a spectral fitting method to retrieve upper atmospheric parameters at multiple altitudes simultaneously during times of aurora, allowing us to measure neutral temperatures and column densities of water vapour. We use the method to separate airglow OH emissions from auroral <span class="inline-formula">O⁺</span> and <span class="inline-formula">N₂</span> in observations between 725 and 740&thinsp;nm using the High Throughput Imaging Echelle Spectrograph (HiTIES) located on Svalbard. In this paper, we describe our new method and show the results of Monte Carlo simulations using synthetic spectra which demonstrate the validity of the spectral fitting method and provide an indication of uncertainties on the retrieval of each atmospheric parameter. We show that the method allows for the retrieval of OH temperatures with an uncertainty of 6&thinsp;% when contamination by <span class="inline-formula">N₂</span> emission is small. <span class="inline-formula">N₂</span> temperatures can be retrieved with uncertainties down to 3&thinsp;%–5&thinsp;% when <span class="inline-formula">N₂</span> emission intensity is high. We can determine the intensity ratio between the <span class="inline-formula">O⁺</span> doublets at 732 and 733&thinsp;nm (which is a function of temperature) with an uncertainty of 5&thinsp;%.</p>