标题：Temporal evolutions of $$\text {N}_2^ $$ Meinel (1,2) band near $$1.5.\,\upmu \text {m}$$ associated with aurora breakup and their effects on mesopause temperature estimations from OH Meinel (3,1) band
摘要：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.
其他摘要：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.
