We have carried out ground-based NIRAS (Near-InfraRed Aurora and airglow Spectrograph) observations at Syowa station, Antarctic (69.0°S, 39.6°E) and Kiruna (67.8°N, 20.4°E), Sweden for continuous measurements of hydroxyl (OH) rotational temperatures and a precise evaluation of aurora contaminations to OH Meinel (3,1) band. A total of 368-nights observations succeeded for two winter seasons, and three cases in which N+2 Meinel (1,2) band around 1.5 μm was significant were identified. Focusing on two specific cases, detailed spectral characteristics with high temporal resolutions of 30 seconds are presented. Intensities of N+2 band were estimated to be 228 kR and 217 kR just at the moment of the aurora breakup and arc intensifications during pseudo breakup, respectively. At a wavelength of P1(2) line (∼ 1523 nm), N+2 emissions were almost equal to or greater than the OH line intensity. On the other hand, at a wavelength of P1(4) line (∼ 1542 nm), the OH line was not seriously contaminated and still dominant to N+2 emissions. Furthermore, we evaluated N+2 (1,2) band effects on OH rotational temperature estimations quantitatively for the first time. Aurora contaminations from N+2 (1,2) band basically lead negative bias in OH rotational temperature estimated by line-pair-ratio method with P1(2) and P1(4) lines in OH (3,1) band. They possibly cause underestimations of OH rotational temperatures up to 40 K. In addition, N+2 (1,2) band contaminations were temporally limited to a moment around aurora breakup. This is consistent with proceeding studies reporting that enhancements of N+2 (1,2) band were observed associated with International Brightness Coefficient 2-3 auroras. It is also suggested that the contaminations would be neglected in polar cap and sub-aurora zone, where strong aurora intensifications are less observed. Further spectroscopic investigations at this wavelength are needed especially for more precise evaluations of to N+2 (1,2) band contaminations. For example, simultaneous 2-D imaging observation and spectroscopic measurement with high spectral resolutions for airglow in OH (3,1) band will make great advances in more robust temperature estimations.
