Temporal evolutions of $$\text {N}_2^+$$ N 2 + Meinel (1,2) band near $$1.5.\,\upmu \text {m}$$ 1.5 . μ m

• Main Authors: Nishiyama, Takanori, Taguchi, Makoto, Suzuki, Hidehiko, Dalin, Peter, Ogawa, Yasunobu, Brändström, Urban, Sakanoi, Takeshi
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: figshare 2021
• Subjects: Biophysics; Biochemistry; 29999 Physical Sciences not elsewhere classified; FOS Physical sciences; Medicine; Physiology; FOS Biological sciences; Biotechnology; 59999 Environmental Sciences not elsewhere classified; FOS Earth and related environmental sciences; Ecology; Cancer; Inorganic Chemistry; FOS Chemical sciences; Computational Biology; Antarctic; Kiruna; Syowa Station; Antarc*
• Online Access: https://dx.doi.org/10.6084/m9.figshare.c.5286581; https://springernature.figshare.com/collections/Temporal_evolutions_of_________text_N_2_______N___2_________Meinel_1_2_band_near_________1_5_upmu_text_m_______1_5__________m/5286581

Abstract We have carried out ground-based NIRAS (Near-InfraRed Aurora and airglow Spectrograph) observations at Syowa station, Antarctic ( $$69.0^{\circ }\text {S}$$ 69 . 0 ∘ S , $$39.6^{\circ }\text {E}$$ 39 . 6 ∘ E ) and Kiruna ( $$67.8^{\circ }\text {N}$$ 67 . 8 ∘ N , $$20.4^{\circ }\text {E}$$ 20 . 4 ∘ E ), Sweden for continuous measurements of hydroxyl (OH) rotational temperatures and a precise evaluation of auroral contaminations to OH Meinel (3,1) band. A total of 368-nights observations succeeded for 2 winter seasons, and 3 cases in which $$\text {N}_2^+$$ N 2 + Meinel (1,2) band around $$1.5\,\mu \text {m}$$ 1.5 μ m was significant were identified. Focusing on two specific cases, detailed spectral characteristics with high temporal resolutions of 30 s are presented. Intensities of $$\text {N}_2^+$$ N 2 + band were estimated to be 228 kR and 217 kR just at the moment of the aurora breakup and arc intensification during pseudo breakup, respectively. At a wavelength of $$\text {P}_1(2)$$ P 1 ( 2 ) line ( $$\sim 1523 \,\text {nm}$$ ∼ 1523 nm ), $$\text {N}_2^+$$ N 2 + emissions were almost equal to or greater than the OH line intensity. On the other hand, at a wavelength of $$\text {P}_1(4)$$ P 1 ( 4 ) line ( $$\sim 1542 \,\text {nm}$$ ∼ 1542 nm ), the OH line was not seriously contaminated and still dominant to $$\text {N}_2^+$$ N 2 + emissions. Furthermore, we evaluated $$\text {N}_2^+$$ N 2 + (1,2) band effects on OH rotational temperature estimations quantitatively for the first time. Auroral contaminations from $$\text {N}_2^+$$ N 2 + (1,2) band basically lead negative bias in OH rotational temperature estimated by line-pair-ratio method with $$\text {P}_1(2)$$ P 1 ( 2 ) and $$\text {P}_1(4)$$ P 1 ( 4 ) lines in OH (3,1) band. They possibly cause underestimations of OH rotational temperatures up to 40 K. In addition, $$\text {N}_2^+$$ N 2 + (1,2) band contaminations were temporally limited to a moment around the aurora breakup. This is consistent with proceeding studies reporting that enhancements of $$\text {N}_2^+$$ 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 the polar cap and the sub-auroral zone, where strong aurora intensification is less observed. Further spectroscopic investigations at these wavelengths are needed especially for more precise evaluations of $$\text {N}_2^+$$ 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 in the auroral zone.