SABER temperature observations in the summer polar mesosphere and lower thermosphere: Importance of accounting for the CO₂ν₂ quanta V–V exchange

Abstract

[1] The polar summer thermal structure, with its cold mesopause and steep temperature gradients, both below and above the mesopause, produces the largest non-LTE effects in the CO 2 n 2 mode manifold states. In this paper we focus on validating the non-LTE model applied for operational temperature retrievals from the SABER 15 mm limb radiance observations for these extreme conditions. We demonstrate that accounting for the redistribution of n 2 quanta among various CO 2 isotopes shifts the retrieved summer 2002 polar mesopause altitude upwards by 2 to 4 km. It brings the SABER temperature measurements into a better agreement with those of falling sphere experiments, lidar observations, as well as with climatological data.

Retrieval of temperature and pressure using broadband solar occultation: SOFIE approach and results

“…We also note that, though the absorbing (lower) states of the 4.3 µm band are in local thermodynamic equilibrium throughout the stratosphere and lower to middle mesosphere, the lower energy state populations of several hot-band transitions are impacted by nLTE processes in the cold polar summer mesopause region and nLTE processes are important for many bands in the lower thermosphere. Starting with SOFIE version 1.02, nLTE effects are explicitly modeled using the CO 2 nLTE models developed for SABER (Lopez-Puertas and Taylor, 2001;Mertens et al, 2001;and Kutepov et al, 2006). Note that the lower energy states of concern for the SOFIE 4.3 µm band are upper energy states for transitions of concern in the emission of the SABER 15 µm bands.…”

CO<sub>2</sub>(ν<sub>2</sub>)-O quenching rate coefficient derived from coincidental SABER/TIMED and Fort Collins lidar observations of the mesosphere and lower thermosphere

“…The altitude, above which the LTE approximation is not applicable, depends on the relationship between these processes: in general, if the V-T processes dominate or the radiative processes are balanced (optically thick media), the vibrational levels populations are close to LTE. For the CO 2 (ν 2 ) vibrational levels involved in formation of I 15 µm , the non-LTE effects become significant above ∼ 75-80 km altitude (López-Puertas and Taylor, 2001;Kutepov et al, 2006;. The importance of k VT rate coefficient for the calculation of CO 2 emission in the MLT was first discussed by Crutzen (1970).…”

“…To demonstrate the influence of k VT on the MLT area, we performed a sensitivity study for an average midlatitude summer atmospheric scenario from MSIS-E-90 model (Hedin, 1991) using a standard set of V-V and V-T rate coefficients (Shved et al, 1998;Kutepov et al, 2006) and the k VT , which was first set to 1.5 × 10 −12 cm 3 s −1 and then to 6.0 × 10 −12 cm 3 s −1 . The results are presented in Fig.…”

Comparing temperature of subauroral mesopause over Yakutia with SABER radiometer data for 2002–2014

“…The vertical profile of the kinetic temperature is calculated from CO 2 15 µm emissions under the condition of non-local thermodynamic equilibrium (non-LTE) at these heights. The algorithm for calculating the temperature profile (which takes into account the non-LTE effect), including all collisional and radiative processes, is described in detail in [Kutepov et al, 2006]. The comparison of SABER measurements with other measurements is used to improve the non-LTE model, which results in a change in the calculated temperature profiles.…”

“…It is necessary to evaluate possible differences between them for a long period. We compare OH(6-2) and O 2 (0-1) rotational temperatures measured during 2002-2014 (the Maimaga high-latitude station (63° N; 129.5° E) infrared spectrograph) with mesopause kinetic temperatures at ~87 and ~95 km heights measured with the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard NASA's TIMED (Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics) spacecraft [Mertens et al, 2001]. Many studies on the comparison between SABER temperatures and those measured with ground-based techniques and instruments have been published in recent years [Remsberg et al, 2008;Smith et al, 2010;French, Mulligan, 2010;Gavrilyeva et al, 2011].…”