Mechanisms leading to NLTE IR emission in the terrestrial thermosphere and their impact on remote sensing of atmospheric parameters

Abstract

Assuming large signal-to-noise ratio and using the rotationally resolved fundamental vibration-rotation band emission from NO near 5.3 µm we propose a scheme for remotely sensing temperature above the altitudes where the 15 µm emission from CO 2 becomes very weak. We also find that the rotationally resolved 5.3 µm emission can be used to remotely sense N( 4 S) atom, O 2 , and O densities in the terrestrial thermosphere -this being the only method for remotely sensing the first two species.

A first‐principles model of spectrally resolved 5.3 μm nitric oxide emission from aurorally dosed nighttime high‐altitude terrestrial thermosphere

“… Duff et al [2003] have since shown that this rate coefficient is given by the expression k(T) = 6.2 × 10 −12 (T/300) cm 3 /(s‐molecule) instead of the nearly temperature independent value 2.8 × 10 −12 exp(185/T) cm 3 /(s‐molecule) given in the literature [ Herron , 1999]. Sharma et al [2002] have in addition reported the vibrational‐rotation distribution of the nascent NO produced by this reaction at room temperature.…”

“…The radiance level as well as the width of the P and R branches of the spectrum is larger than for the quiescent case (Figure 1) indicating a higher rotational temperature. This is because the reaction of N( 4 S) and N( 2 D) atoms with O 2 produce highly rotationally and vibrationally excited NO [ Duff et al , 1994; Sharma et al , 2002] which, after losing the vibrational energy, is still highly rotationally excited. These highly rotationally excited NO molecules have a larger cross section for vibrational excitation upon impacts with O and yield vibrationally excited NO molecules with higher rotational temperature.…”

“…This reaction is exothermic by 3.76 eV, has no activation energy and produces NO in high rotational and vibrational levels. The rate coefficient of this reaction as function of rotational and vibrational quantum numbers of the nascent NO has been presented previously [ Duff et al , 2002; Sharma et al , 2002]. The highly vibrationally and rotationally excited nascent NO molecules from the N( 2 D) + O 2 reaction lead, as shown by the red curve in Figure 2, to a few R‐branch bandheads and emission over a large spectral range–a result of the calculated rotational temperature of the radiatively relaxed NO(v) produced by the N( 2 D) + O 2 reaction varying with the vibrational level v, 8400 K for v = 1 to 4400 K for v = 12.…”