Analysis of Auroral Contaminations in Observations of OH Airglow

Kurzfassung

OH airglow in the shortwave infrared is frequently used to derive rotational temperatures for long-term series. At high latitudes, however, auroral emissions can interfere with the OH airglow spectrum and lead to significant temperature underestimations. This study analyzes long-term OH airglow measurements from two high-latitude sites: ALOMAR in Norway (GRIPS 9) and Neumayer III in Antarctica (GRIPS 15). The focus lies on the identification and characterization of auroral contaminations, particularly emissions caused by electronically excited N2 molecules and potential OH aurora seen as short-time fluctuations in radiance. Via the development of specific filter parameters and their combination with geomagnetic indices and local geomagnetic data, 90 (ALOMAR) and 117 (Neumayer III) nights with N+ 2 aurora, as well as 42 and 55 nights with potential OH aurora, were identified. The temporal distribution of events differs between the two sites, likely due to geomagnetic longitude. Similar short-term patterns are observed for both auroral types, supporting the auroral origin of OH fluctuations. A comparison with Kp and Dst indices reveals that N2 events occur mainly during moderate to intense geomagnetic storms, while OH fluctuations tend to appear during weaker events. Single spectra affected by auroral contamination can show temperature underestimations of up to 58 K. However, the impact on the yearly mean temperatures and hence, the long-term series is minor (<0.4 K). Therefore, the observed differences between Neumayer III and other NDMC stations cannot be explained by auroral contamination alone, indicating additional atmospheric influences.