Atomic hydrogen in the mesopause region derived from SABER: Algorithm theoretical basis, measurement uncertainty, and results

Abstract

Atomic hydrogen (H) is a fundamental component in the photochemistry and energy balance of the terrestrial mesopause region (80-100 km). H is generated primarily by photolysis of water vapor and participates in a highly exothermic reaction with ozone. This reaction is a significant source of heat in the mesopause region and also creates highly vibrationally excited hydroxyl (OH) from which the Meinel band radiative emission features originate. Concentrations (cm À3) and volume mixing ratios of H are derived from observations of infrared emission from the OH (υ = 9 + 8, Δυ = 2) vibration-rotation bands near 2.0 μm made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. The algorithms for deriving day and night H are described herein. Day and night concentrations exhibit excellent agreement between 87 and 95 km. SABER H results also exhibit good agreement with observations from the Solar Mesosphere Explorer made nearly 30 years ago. An apparent inverse dependence on the solar cycle is observed in the SABER H concentrations, with the H increasing as solar activity decreases. This increase is shown to be primarily due to the temperature dependence of various reaction rate coefficients for H photochemistry. The SABER H data, coupled with SABER atomic oxygen, ozone, and temperature, enable tests of mesospheric photochemistry and energetics in atmospheric models, studies of formation of polar mesospheric clouds, and studies of atmospheric evolution via escape of hydrogen. These data and studies are made possible by the wide range of parameters measured simultaneously by the SABER instrument.

Technical note: Evaluation of the simultaneous measurements of mesospheric OH, HO<sub>2</sub>, and O<sub>3</sub> under a photochemical equilibrium assumption – a statistical approach

“…Three-dimensional fields of temperature and winds are taken from the Canadian Middle Atmosphere Model (CMAM) for the year 2000 (de Grandpre et al, 2000;Scinocca et al, 2008). We use the Walcek scheme (Walcek and Aleksic, 1998;Walcek, 2000) for advective transport and the implicit Thomas algorithm as described in Morton and Mayers (1994) for diffusive transport. The vertical eddy diffusion coefficient is based on the results by Lübken (1997).…”

“…It is also noteworthy that similar models are widely used for calculating concentrations of components with a short lifetime (e.g., O( 1 D) and OH) and subsequently evaluating vertical distributions of eddy diffusivity from measurements of trace gas concentration profiles (e.g., see Massie and Hunten, 1981). Kondo et al (1988) Evans and Llewellyn, 1973;Good, 1976;Pendleton et al, 1983;McDade et al, 1985;McDade and Llewellyn, 1988;Evans et al, 1988;Thomas, 1990;Llewellyn et al, 1993;Llewellyn and McDade, 1996;Mlynczak et al, 2007Mlynczak et al, , 2013aMlynczak et al, , b, 2014Smith et al, 2010;Siskind et al, 2008Siskind et al, , 2015. Russell and Lowe (2003) applied PEO to infer the seasonal and global climatology of atomic oxygen using WINDII/UARS.…”

Daytime ozone loss term in the mesopause region

“…For several decades, these assumptions have been used to determine the distributions of atomic oxygen at specific heights of the MLT via satellite and rocket measurements of ozone and airglow emissions (e.g., Pendleton et al, 1983;Evans and Llewellyn, 1973;Evans et al, 1988;Thomas, 1990;Mlynczak et al, 2007Mlynczak et al, , 2013aMlynczak et al, , b, 2014Smith et al, 2010;Siskind et al, 2015). Kulikov et al (2006Kulikov et al ( , 2009 proposed algorithms for the simultaneous retrieval of O, H, HO 2 and H 2 O by joint OH and O 3 satellite measurements by implementing the assumption about the photochemical equilibrium of ozone.…”

“…Kulikov et al (2006Kulikov et al ( , 2009 determines the values of O and H jointly as the result of an algebraic equations system that is solved under the conditions of the joint photochemical equilibrium of O 3 , OH and HO 2 . Nevertheless, in the majority of investigations (e.g., Pendleton et al, 1983;Evans et al, 1988;Mlynczak et al, 2007Mlynczak et al, , 2013aMlynczak et al, , b, 2014Smith et al, 2010;Siskind et al, 2015), the second term in the denominator of Reaction (R1) is omitted (i.e.,…”

Several notes on the OH* layer

“…A large number of observations are directed at dynamic processes, e.g., gravity waves (GWs), planetary waves, and tides (Tarasick and Shepherd, 1992;Taylor et al, 1991Taylor et al, , 1995aTaylor et al, , b, 1997Makhlouf et al, 1995Makhlouf et al, , 1998Offermann et al, 2009, Shepherd et al, 2012, and references therein). Minor chemical constituents in the mesopause, which are scarcely retrieved by other means, e.g., atomic oxygen (Russell et al, 2005;, ozone (Smith et al, 2008(Smith et al, , 2009, and atomic hydrogen (Thomas, 1990;Takahashi et al, 1996;Mlynczak et al, 2014), were measured by the observation of airglow emission. One of the subjects of investigations by airglow measurements is the trend of temperature (e.g., Espy and Stegman, 2002;Offermann et al, 2006Offermann et al, , 2010.…”