Three-dimensional modeling of minor chemical constituents in the mesosphere/lower thermosphere region

Um die Verteilung chemisch aktiver Spurenstoffe im Höhenbereich der Mesosphäre und unteren Thermosphäre (MLT-Region) zu untersuchen, wurde ein bestehendes 3-dimensionales numerisches chemisches Transportmodell (CTM) weiterentwickelt und mit zwei unterschiedlichen Versionen eines dynamischen Modells gekoppelt. Alle wichtigen physikalischen und chemischen Prozesse wurden im Modell berücksichtigt. Zu diesen zählen die in der MLT-Region ablaufenden chemischen Reaktionen, die Photolyse, die molekulare und turbulente Diffusion sowie advektive Transportprozesse. Die wesentlichen Verbesserungen betreffen u. a. die Implementierung eines neuen Transportcodes gekennzeichnet durch extrem geringe numerische Diffusion und die Ableitung der solaren Lyman-α Strahlung aus der Sonnenfleckenrelativzahl als Proxy und deren Berücksichtigung in der Wasserdampfphotolyserate. Das verbesserte CTM wurde mit dynamischen Modellen gekoppelt, welche klimatologische Mittel (COMMA-IAP) bzw. Zustände zum realen Datum (LIMA) berechnen. Diese gekoppelten Modelle wurden insbesondere auf das Studium des Einflusses der solaren Lyman-α Strahlung auf die Aeronomie der MLT-Region, auf die autokatalytische Wasserdampfproduktion als Quelle hoher Mischungsverhältnisse in der Mesosphäre hoher sommerlicher Breiten, auf die Herausbildung des so genannten tertiären Ozonmaximums in winterlichen mittleren und hohen Breiten, auf die Untersuchung nichtlinearer Effekte in der Chemie der MLT-Region, auf den Einfluss stratosphärischer Erwärmungen auf die Spurenstoffverteilung sowie auf Trends der Spurenstoffe in der Mesosphäre auf Grund der Zunahme von Methan, Lachgas und Kohlenstoffdioxyd seit der vorindustriellen Ära angewendet.An existing time-dependent 3-dimensional numerical chemical transport model (CTM) was improved and coupled with two different versions of a dynamical model. All physical processes believed to be important are simulated, including chemical interactions, photochemical dissociation, eddy and molecular diffusion, and advection. The most essential improvements concern the implementation of a new transport scheme marked by almost zero numerical diffusion and the derivation of the solar Lyman-α flux from the sunspot number as proxy and its consideration in the photolysis rate of water vapor. The CTM was coupled with the dynamical models calculating climatologic means (COMMA-IAP) and computing the dynamical state for real dates (LIMA). These coupled models were applied to study some particular phenomena in the mesosphere-lower thermosphere (MLT-region) such as the influence of the variable Lyman-α radiation on the aeronomy, the autocatalytic water vapor production as a source of large mixing ratios within the middle to upper mesosphere in high summery latitudes during, the so-called tertiary ozone maximum formation, the investigation of nonlinear effects of the chemistry, trends of mesospheric minor constituents due to the increase of methane, nitrous oxide and carbon dioxide since the pre-industrial area

Note on consistency between Kalogerakis–Sharma Mechanism (KSM) and two-step mechanism of atmospheric band emission (762 nm)

For more than 30 years, a two-step mechanism was used to explain observed Atmospheric band emission (762 nm) in mesopause region. A new mechanism, which leads to the formation of electronically excited molecular oxygen that gives this emission, was proposed recently. We show, based on an analytical solution, that the fit-functions for Atmospheric band volume emission in the case of the two-step mechanism and the new Kalogerakis–Sharma Mechanism (KSM) have analogous expression. This derivation solves the problem of consistency between the well-known two-step mechanism and the newly proposed KSM

The revised method for retrieving daytime distributions of atomic oxygen and odd-hydrogens in the mesopause region from satellite observations

Atomic oxygen (O) and atomic hydrogen (H) in the mesopause region are critical species, governing chemistry, airglow, and energy budget. However, they cannot be directly measured by satellite remote sensing techniques and so inference techniques, by airglow observations, are used. In this work, we retrieved daytime O and H distributions at ~ 77 km–100 km from the data of observations by the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument at the TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics) satellite in 2003–2015. The retrieval approach considered the reaction H + O3 → O2 + OH in the ozone balance equation. Moreover, we revised all quenching and spontaneous emission coefficients according to latest published data. We then calculated daytime distributions of OH and HO2 at these altitudes with the use of their conditions of photochemical equilibrium

Daytime ozone loss term in the mesopause region

For the retrieval of atomic oxygen via ozone observations in the extended mesopause region under sunlight conditions, two assumptions are used: first, the photochemical equilibrium of ozone and, second, that the ozone losses are dominated by ozone's dissociation from solar UV radiation, silently ignoring the O3 destruction by atomic hydrogen. We verify both by 3-D modeling. We found that ozone approaches photochemical equilibrium at 75–100 km for daytime conditions. Hence, the first assumption is valid. However, the reaction of ozone with atomic hydrogen was found to be an important loss process and should not be omitted in retrieving atomic oxygen

Simultaneous in Situ Measurements of Small-Scale Structures in Neutral, Plasma, and Atomic Oxygen Densities During the WADIS Sounding Rocket Project

In this paper we present an overview of measurements conducted during the WADIS-2 rocket campaign. We investigate the effect of small-scale processes like gravity waves and turbulence on the distribution of atomic oxygen and other species in the mesosphere–lower thermosphere (MLT) region. Our analysis suggests that density fluctuations of atomic oxygen are coupled to fluctuations of other constituents, i.e., plasma and neutrals. Our measurements show that all measured quantities, including winds, densities, and temperatures, reveal signatures of both waves and turbulence. We show observations of gravity wave saturation and breakdown together with simultaneous measurements of generated turbulence. Atomic oxygen inside turbulence layers shows two different spectral behaviors, which might imply a change in its diffusion properties

Greenhouse gas effects on the solar cycle response of water vapour and noctilucent clouds

The responses of water vapour (H2O) and noctilucent clouds (NLCs) to the solar cycle are studied using the Leibniz Institute for Middle Atmosphere (LIMA) model and the Mesospheric Ice Microphysics And tranSport (MIMAS) model. NLCs are sensitive to the solar cycle because their formation depends on background temperature and the H2O concentration. The solar cycle affects the H2O concentration in the upper mesosphere mainly in two ways: directly through the photolysis and, at the time and place of NLC formation, indirectly through temperature changes. We found that H2O concentration correlates positively with the temperature changes due to the solar cycle at altitudes above about 82 km, where NLCs form. The photolysis effect leads to an anti-correlation of H2O concentration and solar Lyman-α radiation, which gets even more pronounced at altitudes below ∼83 km when NLCs are present. We studied the H2O response to Lyman-α variability for the period 1992 to 2018, including the two most recent solar cycles. The amplitude of Lyman-α variation decreased by about 40 % in the period 2005 to 2018 compared to the preceding solar cycle, resulting in a lower H2O response in the late period. We investigated the effect of increasing greenhouse gases (GHGs) on the H2O response throughout the solar cycle by performing model runs with and without increases in carbon dioxide (CO2) and methane (CH4). The increase of methane and carbon dioxide amplifies the response of water vapour to the solar variability. Applying the geometry of satellite observations, we find a missing response when averaging over altitudes of 80 to 85 km, where H2O has a positive response and a negative response (depending on altitude), which largely cancel each other out. One main finding is that, during NLCs, the solar cycle response of H2O strongly depends on altitude

Morphology of the excited hydroxyl in the Martian atmosphere: A model study. Where to search for airglow on Mars?

<p>The data for Remote Sensing article figures.</p&gt

Morphology of the excited hydroxyl in the Martian atmosphere: A model study. Where to search for airglow on Mars?

<p>The data for Remote Sensing article figures.</p&gt

Semi-annual variation of excited hydroxyl emission at mid-latitudes

Ground-based observations show a phase shift in semi-annual variation of excited hydroxyl (OH∗) emissions at mid-latitudes (43∘ N) compared to those at low latitudes. This differs from the annual cycle at high latitudes. We examine this behaviour by utilising an OH∗ airglow model which was incorporated into a 3D chemistry–transport model (CTM). Through this modelling, we study the morphology of the excited hydroxyl emission layer at mid-latitudes (30–50∘ N), and we assess the impact of the main drivers of its semi-annual variation: temperature, atomic oxygen, and air density. We found that this shift in the semi-annual cycle is determined mainly by the superposition of annual variations of temperature and atomic oxygen concentration. Hence, the winter peak for emission is determined exclusively by atomic oxygen concentration, whereas the summer peak is the superposition of all impacts, with temperature taking a leading role