火星日光中N2 Vegard-Kaplan带辐射的模型计算
Model calculation of N2 Vegard-Kaplan band emissions in Martian dayglow
摘要：
建立了一个N2 Vegard-Kaplan（VK）波段（A^3 Sigma_u ^+ -X^1 Sigma_g ^+）辐射模型，用于解释火星快车号上SPICAM紫外光谱仪的观测结果。稳态光电子通量和体积激发率已被计算使用的分析产额谱技术。由于态间级联对于N2的三重态是重要的，因此在考虑直接激发、级联和猝灭效应的统计平衡下计算N2三重态的任何给定水平的布居。在模型中计算了每个三重态的所有振动能级的相对布居。计算了VK、N2的第一正带（B^3Pi_g - A^3Sigma_u^+）、第二正带（C^3Pi_u - B^3Pi_g）和Wu-Benesch（W^3Delta_u - B^3Pi_g）的视线强度和高度积分头顶强度。在火星热层大气环流模型中，需要将N2密度减少3倍，才能使VK（0-6）的计算临边剖面与SPICAM观测结果相一致。计算进行评估的模型参数，即，电子碰撞截面，太阳EUV通量，和模式大气，对发射强度的影响。用SPICAM观测的N_2/CO_2比值作约束，我们建议120 km处的N_2/CO_2比值为1.1-1.4%，140 km处为1.8-3.2%，170 km处为4-7%。在高太阳活动期间，N2 VK波段发射的头顶强度将比低太阳活动期间高约2.5倍。
英文摘要：
A model for N2 Vegard-Kaplan (VK) band (A^3Sigma_u^+ - X^1Sigma_g^+) emissions in Martian dayglow has been developed to explain the recent observations made by the Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars (SPICAM) ultraviolet spectrograph aboard Mars Express. Steady state photoelectron fluxes and volume excitation rates have been calculated using the analytical yield spectra technique. Since interstate cascading is important for triplet states of N2, the population of any given level of N2 triplet states is calculated under statistical equilibrium considering direct excitation, cascading, and quenching effects. Relative population of all vibrational levels of each triplet state is calculated in the model. Line of sight intensities and height-integrated overhead intensities have been calculated for VK, first positive (B^3Pi_g - A^3Sigma_u^+), second positive (C^3Pi_u - B^3Pi_g), and Wu-Benesch (W^3Delta_u - B^3Pi_g) bands of N2. A reduction in the N2 density by a factor of 3 in the Mars thermospheric general circulation model is required to obtain agreement between calculated limb profiles of VK (0-6) and SPICAM observation. Calculations are carried out to asses the impact of model parameters, namely, electron impact cross sections, solar EUV flux, and model atmosphere, on the emission intensities. Constraining the N2/CO2 ratio by SPICAM observations, we suggest the N2/CO2 ratios to be in the range 1.1-1.4% at 120 km, 1.8-3.2% at 140 km, and 4-7% at 170 km. During high solar activity the overhead intensity of N2 VK band emissions would be ~2.5 times higher than that during low solar activity.
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