Chemistry of the Mesosphere II
Presiding: A K Smith, NCAR Atmospheric Chemistry Division; D Marsh, NCAR Atmospheric Chemistry Division
SA34A-01 INVITED 15:30h
Atomic Oxygen Variability in the Mesopause Region
Atomic oxygen plays a major role in much of the chemistry in the mesopause region. Although the chemistry it is involved in is considered to be well understood, there still remain uncertainties about the oxygen budget and its role in heat budget. One of the factors associated with these uncertainties is how dynamics affects oxygen in this region. Observations from WINDII (Wind Imaging Interferometer) and analyses from the extended CMAM (Canadian Middle Atmosphere Model) suggest that large scale waves result in vertical parcel displacements whose distribution has a standard deviation of the order of 2 km in equatorial regions. The CMAM data suggests that this variability has a geographical dependence as a result of interference effects between various tidal components. The effect of this type of cycling depends on the height being considered. From WINDII results it appears that above ~85 km that oxygen remains a conserved tracer so the dynamics is primarily a complicating factor for interpreting observations. Below 85 km this cycling results in enhanced recombination relative to the recombination rate at the mean parcel height.
SA34A-02 15:50h
A comparison of ozone observations from the SABER experiment
The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite observes mesospheric ozone simultaneously with two different techniques. Emission directly from ozone at 9.6 microns is observed as is emission from the singlet delta metastable state of molecular oxygen at 1.27 microns, the latter formed directly by ozone photolysis and hence a direct proxy for the ozone concentration. Both the ozone and singlet oxygen emissions are in non-local thermodynamic equilibrium (non-LTE) in the mesosphere. There is also substantial non-LTE emission from processes not related to ozone to be accounted for in analyzing each emission feature during the retrieval of the ozone concentration. In this paper we present an overview of the two SABER measurement techniques and we compare the ozone derived from each technique, complete with an uncertainty analysis related to the non-LTE parameters required for the retrieval.
SA34A-03 16:05h
Analysis of MIPAS Ozone Measurements in the 20-100 km Altitude Regime
The Michelson Interferometer for Passive Atmosphere Sounding (MIPAS) on board of ESA's ENVISAT measures the global distribution of infrared emissions by atmospheric gases from 4Μm to 15Μm. The upper atmosphere measurement mode spans altitudes from 20-100 km and allows for the retrieval of species from the tropopause region up to the lower thermosphere. For the modelling of the infrared radiances it is essential to include a detailed non-local thermodynamic equilibrium (non-LTE) model in the retrieval scheme. Ozone abundance is derived from the O3(ν 2) and O3(ν 3) fundamental bands at 13 Μm and 10 Μm. The retrieval yields global maps of day- and nighttime ozone volume mixing ratio for July 2002 and June 2003. The primary and secondary ozone maximum as well as a tertiary ozone maximum at the polar night terminator are observed. This data is compared with measurements of the HALOE and GOMOS instruments and with numerical simulations performed with the NCAR ROSE model. In the 5 Μm region, the high spectral resolution of the MIPAS data allows for the separation of ozone radiance from emissions of other gases. Ozone data in this spectral region stems from highly excited vibrational states and gives information about the chemical pumping process and the collisional relaxation scheme of vibrationally excited ozone.
SA34A-04 16:25h
The Singlet Delta Concentrations of Molecular Oxygen in the Mesosphere, a Comparison Between Model and Observation
The OSIRIS instrument on the Odin spacecraft has been in operation for over four years. Odin is in a sun-synchronous dusk-dawn orbit and the in plane measurements made by OSIRIS are used to produce very high spatial resolution two dimensional, angle along the satellite track and altitude, maps of the Oxygen InfraRed Atmospheric band airglow. This paper will compare OSIRIS observations to simulations from the NCAR Whole Atmosphere Community Climate Model (WACCM). WACCM is a fully-coupled chemical dynamical global circulation model that covers all altitudes from the surface to the thermosphere. Since the Oxygen InfraRed Atmospheric band airglow depends on the distribution of odd-oxygen (Ox = O + O3), the comparison provides a test of our understanding of mesospheric chemistry under the rapidly changing chemistry near the day night terminator.
SA34A-05 16:40h
Critical Evaluation of Chemical Reaction Rates and Collision Cross Sections of Importance in the Earth's Upper Atmosphere and the Atmospheres of Other Planets, Moons, and Comets
We recommend establishment of a long-term program of critical evaluation by domain experts of the rates and cross sections of atomic and molecular processes that are needed for understanding and modeling the atmospheres in the solar system. We envision products resembling those from the ongoing JPL/NASA Panel for Data Evaluation and the efforts of the international combustion modeling community funded by US DOE and its European counterpart. Both of these endeavors already provide some important inputs for modeling the atmospheres of the Earth, planets, moons, and comets. However, their applications restrict the choice of which processes to evaluate and the temperature and pressure ranges to cover, thus leaving large gaps that need to be filled. Interestingly, an older evaluation program once filled some of these gaps. Funded by the US DoD in the 1960s-1980s, the DNA Reaction Rate Handbook provided a thorough treatment of numerous types of collisions and reactions that are important in the Earth's lower ionosphere, and the program even provided funding for new laboratory measurements. Other examples could be given, with the on-line resources at NIST being among the best, but most provide a narrower scope or less critical evaluation. What is needed is not a just a list of processes and numbers (i.e., a "database"), but rather serious comparison of the available information and specific statements from independent expert laboratory/theory data providers about what should be believed, what uncertainty to assign, and what is most in need of redetermination. The major topic areas would include the following: 1. Chemical reactions of neutral atoms and molecules in their ground electronic states 2. Ion-molecule reactions 3. Chemistry, relaxation, and radiation of electronically excited atoms and molecules 4. Vibrational and rotational relaxation and radiation 5. Photoabsorption, photodissociation, and photoionization 6. Electron-impact excitation, dissociation, ionization, and recombination 7. Energetic heavy particle excitation and charge exchange