Evidence for an OH(υ) excitation mechanism of CO2 4.3 μm nighttime emission from SABER/TIMED measurements
Evidence for an OH(υ) excitation mechanism of CO2 4.3 μm nighttime emission from SABER/TIMED measurements
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SABER/TIMED 测量中 CO2 4.3 μm 夜间发射的 OH(υ) 激发机制的证据
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发表时间：
2004
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通讯作者：
L. Gordley
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作者：
M. López‐Puertas;M. García‐Comas;B. Funke;R. Picard;J. Winick;P. Wintersteiner;M. Mlynczak;C. Mertens;J. Russell;L. Gordley
[1]2001年12月7日成功发射的TIMED卫星上的SABER仪器测量了从对流层到热层的昼夜CO2 4.3 μm大气排放量，覆盖范围接近全球纬度，信噪比很高。SABER在15 μm附近有三个通道用于测量压温结构，在2.0和1.6 μm附近有两个通道，主要对OH（λ ≤ 9）的泛音辐射敏感，分别为λ = 8-9和λ = 3-5级。本文分析了SABER在7通道上的测量结果，中心在4.3 μm附近，在夜间在安静（无极光）条件下在中间层上部和热层下部拍摄。该区域4.3 μm辐射的测量值远大于局部热力学平衡（LTE）下的预期值，并显示出与OH通道信号的强相关性。Kumer等人[1978]提出，负责4.3 μm发射的CO2（λ 3）能级是通过与N2（1）的振动-振动能量转移从OH（λ 3）激发的，因此激发到CO2（λ 3）。SABER数据（同时测量压力，温度，CO2 4.3 μm发射和OH（CO2）近红外发射）为了解夜间中间层CO2（CO2）的非LTE激发机制提供了前所未有的数据集。我们用CO2的非LTE辐射传输模型研究了SABER 4.3 μm辐射，发现大的辐射可以用OH（OH）到N2（1）到CO2（1）的快速有效的能量传输速率来解释，即在一个OH（OH）分子猝灭后平均激发2.8-3个N2（1）振动量子。考虑了一系列可能增强夜间4.3 μm临边辐射的替代激发机制，发现这些机制并不显著。能量从OH（OH）转移到N2（N2）的机制仍然不确定。OH（OH）的群体不受这种快速转移的掺入的显著影响，因为与O2猝灭相比，OH（OH）的N2猝灭可以忽略不计。
[1] The SABER instrument on board the TIMED satellite, successfully launched on 7 December 2001, measures the CO2 4.3 μm atmospheric emission at day and night, from the troposphere up to the thermosphere, with a near global latitude coverage and with a very high signal-to-noise ratio. SABER has also three channels near 15 μm for the measurements of the pressure-temperature structure and two channels around 2.0 and 1.6 μm, mainly sensitive to the OH(υ ≤ 9) overtone radiation from levels υ = 8–9 and υ = 3–5, respectively. In this paper we analyze the measurements of SABER in channel 7, centered near 4.3 μm, taken at night in the upper mesosphere and lower thermosphere under quiet (nonauroral) conditions. The measurements of the 4.3 μm radiance in this region are much larger than expected under local thermodynamic equilibrium (LTE) and show a strong correlation with the OH channel signal. It was proposed by Kumer et al. [1978] that the CO2(υ3) levels, responsible for the emission at 4.3 μm, were excited from OH(υ) via vibrational-vibrational energy transfer with N2(1) and hence to CO2(υ3). SABER data (measuring simultaneously pressure, temperature, CO2 4.3 μm emission, and OH(υ) near-IR emission) offer an unprecedented data set for understanding the non-LTE excitation mechanisms of CO2(υ3) in the nighttime mesosphere. We have investigated the SABER 4.3 μm radiances with the help of a non-LTE radiative transfer model for CO2 and found that the large radiances can be explained by a fast and efficient energy transfer rate from OH(υ) to N2(1) to CO2(υ3), whereby, on average, 2.8–3 N2(1) vibrational quanta are excited after quenching of one OH(υ) molecule. A series of alternative excitation mechanisms that may enhance the nighttime 4.3 μm limb radiance were considered and found to be insignificant. The mechanism(s) whereby the energy is transferred from OH(υ) to N2(υ) is (are) still uncertain. The populations of OH(υ) are not significantly affected by incorporation of this fast transfer since N2 quenching of OH(υ) is negligible when compared to O2 quenching.