A new perspective on the molecular oxygen and hydroxyl airglow emissions

Abstract

The mesospheric molecular oxygen and hydroxyl airglow emissions have traditionally been measured in order to derive minor species abundances or to diagnose dynamical phenomena. We present a new interpretation of these airglow emissions and show them to be fundamental measures of energy deposition from which rates of atmospheric heating are readily derived. The heating rate due to absorption of ultraviolet radiation in the Hartley band of ozone may be derived from simultaneous measurements of the oxygen atmospheric band and infrared atmospheric band volume emission rates independent of knowledge of the ozone density, the solar irradiance, and the ozone absorption cross sections. The heating rates due to key exothermic reactions may be derived directly from appropriate airglow observations independent of the reactant concentrations and the temperature-dependent reaction rates. The accuracy of heating rates derived directly from airglow measurements is also inherently higher than that obtained in standard approaches. We suggest that heating rates derived in this manner be treated as data products and that they be compared with numerical model computations to enhance understanding of atmospheric thermodynamics. An initial comparison of airglow-derived energy deposition rates with deposition rates traditionally computed from numerical models shows agreement to within 20% for the Hartley band of ozone in the lower and upper mesosphere.

Satellite observations of high nighttime ozone at the equatorial mesopause

“…As with the 1.27 mm emission, the 9.6 mm bands depart from local thermodynamic equilibrium (LTE) in the mesosphere and lower thermosphere. The SABER v1.07 ozone 9.6 mm retrieval incorporates a detailed non-LTE model originally developed by Mlynczak andDrayson [1990a, 1990b], updated with collisional rates from Martin-Torres [1999]. Rate coefficients for the quenching of ozone vibrations and molecular oxygen and molecular nitrogen for all temperatures use the formula for temperature dependence deduced from measurements by Doyennette et al [1992] and Menard et al [1992].…”

“…With the additional information of the ozone amount, the oxygen determination is more accurate and the hydrogen can also be determined. This method, which is used to determine these species in SABER as a Level 2 product, has been described by Mlynczak et al [1998] and Mlynczak [1999] and analyzed by Marsh et al [2006].…”

Solar energy deposition rates in the mesosphere derived from airglow measurements: Implications for the ozone model deficit problem

“…As discussed by Mlynczak [1999] We compute the g factors following Mlynczak [1993], noting that the exoatmospheric value of the g factor is now calculated to be 6.192 x 10 -9 s -l, fully 15% larger as a consequence of the 15% larger band strength currently recommended on the HITRAN [Rothman et al, 1998] spectroscopic database. In computing the g factor we also use the contemporary solar spectrum of Kurucz [ 1994].…”

“…To compute the rates of solar energy deposition and heating we typically require knowledge of the distribution of ozone in altitude, latitude, and longitude, the absorption cross sections of ozone at ultraviolet wavelengths, and the ultraviolet solar irradiance. Recently, Mlynczak [1999] presented a technique whereby the rate of energy deposition in the Hartley band of ozone could be determined directly from measurements of the vertical profile of molecular oxygen dayglow emission (O2(alAg) --> O2(X3Zg)) at 1.27 gm, independent of a knowledge of the ozone concentration, the absorption cross sections, and the solar irradiance. The basic idea is that the 02 airglow is generated directly from ozone photolysis.…”

“…From equations (1) and (2) of this simplified model it is straightforward to show that the rate of energy deposition, which through the first law of thermodynamics is directly proportional to the heating rate in kelvins per day, may be derived directly from the airglow independent of a knowledge of the ozone abundance and the photolysis rate and hence independent of the solar irradiance and ozone absorption cross sections. In the full treatment, given by Mlynczak [1999], in which all sources of O2(alAg) are included, it is shown that the energy deposition rate in the Hartley band of ozone can be derived from simultaneous measurements of both the O2(alAg) and the O2(bly•g) airglow, independent of the solar irradiance, the ozone abundance, and the ozone absorption cross sections. In the work presented…”