Dynamics of the lower thermosphere consistent with satellite observations of 5577 Å airglow: II. Atomic oxygen, local turbulence, and global circulation results

1984 ◽  
Vol 62 (4) ◽  
pp. 382-395 ◽  
Author(s):  
R. D. Elphinstone ◽  
J. S. Murphree ◽  
L. L. Cogger
Keyword(s):  
Oxygen Concentration ◽  
Atomic Oxygen ◽  
Lower Thermosphere ◽  
Eddy Diffusion ◽  
Temporal Variations ◽  
Meridional Flow ◽  
Equatorial Region ◽  
Small Scale ◽  
Global Dynamics ◽  
Atomic Oxygen Concentration

Satellite airglow observations in conjunction with a model for the photochemical and dynamical processes in the altitude range 80 to 120 km have been used to obtain the global and temporal variations of atomic oxygen concentration, eddy diffusion, and circulation. The concentration of atomic oxygen shows midlatitude peaks near equinox, and minima about one month after solstice. Average values at midlatitudes are about 1.3 times those at the equator. Small scale turbulence decreases away from the equatorial region in the postequinox period, while near solstice the turbulence is stronger and more uniform with latitude. At equinox, poleward meridional winds of 5–10 m/s are accompanied by upward winds at the equator and downward winds at midlatitudes. There is a slow transition from the dynamics occurring at equinox to those at solstice. At solstice, vertical wind velocities near 110 km of about 10–15 cm/s are upward in the summer and downward in the winter. About one month after solstice, the strength of global dynamics (both turbulence and circulation) reaches a maximum and the global atomic oxygen concentration is lowest. At this time a summer-to-winter flow occurs at high altitudes (> 110 km) accompanied by a return meridional flow below about 105 km.

scholarly journals Comparison of Global Datasets of Sodium Densities in the Mesosphere and Lower Thermosphere from GOMOS, SCIAMACHY and OSIRIS Measurements and WACCM Model Simulations from 2008 to 2012

2017 ◽  
Author(s):  
Martin P. Langowski ◽  
Christian von Savigny ◽  
John P. Burrows ◽  
Didier Fussen ◽  
Erin C. M. Dawkins ◽  
...  
Keyword(s):  
Seasonal Cycle ◽  
Lower Thermosphere ◽  
Temporal Variations ◽  
Equatorial Region ◽  
Local Times ◽  
Vertical Column ◽  
Model Simulations ◽  
Mesosphere And Lower Thermosphere ◽  
Summer Minimum ◽  
Global Datasets

Abstract. During the last decade, multiple limb sounding satellites have measured the global sodium (Na) number densities in the mesosphere and lower thermosphere (MLT).Datasets are now available from GOMOS, SCIAMACHY (both on Envisat) and OSIRIS/Odin. Furthermore, global model simulations of the Na layer in the MLT simulated with WACCM-Na are available. In this paper, we compare these global datasets. Globally, there is an agreement in the observed and simulated monthly average of Na vertical column densities that were compared with each other. They show a clear seasonal cycle with a summer minimum most pronounced at the poles. They also show signs of a semi-annual oscillation in the equatorial region. The vertical column densities vary between 0.5 × 109 cm−2 to 7 × 109 cm−2 near the poles and between 3 × 109 cm−2 to 4 × 109 cm−2 at the equator. The phase of the seasonal cycle and semi-annual oscillation shows small differences between the different instruments. The full width at half maximum of the profiles is 10 to 16 km for most latitudes, but significantly smaller in the polar summer. The centroid altitudes of the measured sodium profiles range from 89 to 95 km, while the model shows on average 2 to 4 km lower centroid altitudes. This coincides with a 3 km lower mesopause altitude in the WACCM simulations compared to measurements, which may be the reason for the low centroid altitudes. Despite this global 2 to 4 km shift, the model captures latitudinal and temporal variations. The variation of the WACCM dataset during the year at different latitudes is similar to the one of the measurements. Furthermore, the differences between the measured profiles with different instruments and therefore different local times are also present in the model simulated profiles. This capturing of latitutinal and temporal variations is also found for the vertical column densities and profile widths.

scholarly journals The role of atomic oxygen concentration in the ionization balance of the lower ionosphere during solar proton events

2008 ◽  
Vol 26 (1) ◽  
pp. 131-143 ◽  
Author(s):  
A. Osepian ◽  
V. Tereschenko ◽  
P. Dalin ◽  
S. Kirkwood
Keyword(s):  
Electron Density ◽  
Oxygen Concentration ◽  
Atomic Oxygen ◽  
Negative Ions ◽  
Solar Proton ◽  
Negative Ion ◽  
Proton Event ◽  
Density Profiles ◽  
Oxygen Profile ◽  
Atomic Oxygen Concentration

Abstract. The influence of atomic oxygen concentration on the height distribution of the main positive and negative ions and on electron density in the mesosphere is studied for the conditions prevailing during the solar proton event on 17 January 2005. It is shown by numerical modeling that the electron and ion density profiles are strongly dependent on the choice of the atomic oxygen profile. Experimental measurements of the electron density are used as the criterion for choosing the atomic oxygen profile in the mesosphere. With the help of modeling, the atomic oxygen profile in the daytime in the winter mesosphere is found to lead to a model electron density profile best matching the electron density profile obtained experimentally. As a result, with the help of modeling, we find the atomic oxygen profiles at various solar zenith angles in the winter mesosphere which lead to model electron density profiles matching the electron density profiles obtained experimentally. Alteration of the atomic oxygen concentration leads to a redistribution of the abundance of both positive and negative ion constituents, with changes in their total concentrations and transition heights. In consequence this results in changes of the electron density and effective recombination coefficient. For conditions of low concentration of atomic oxygen (during a solar proton event), the formation of cluster ions is the key process determining electron and ion densities at altitudes up to 77 km. The complex negative CO3− ion is formed up to about 74 km and the final NO3− ion, which is stable in relation to the atomic oxygen, is the dominant negative ion up to 74 km. As a result the transition heights between cluster ions and molecular ions and between negative ions and electron density are located at 77 km and 66 km, respectively.

scholarly journals Atomic oxygen retrievals in the MLT region from SCIAMACHY nightglow limb measurements

2014 ◽  
Vol 7 (10) ◽  
pp. 10829-10881
Author(s):  
O. Lednyts'kyy ◽  
C. von Savigny ◽  
K.-U. Eichmann ◽  
M. G. Mlynczak
Keyword(s):  
Time Series ◽  
Oxygen Concentration ◽  
Atomic Oxygen ◽  
Emission Rate ◽  
Band Pass Filter ◽  
Density Profiles ◽  
Solar Cycle Variation ◽  
The Impact ◽  
Atomic Oxygen Concentration ◽  
Mlt Region

Abstract. Vertical profiles of atomic oxygen concentration in the mesosphere and lower thermosphere (MLT) region were retrieved from sun-synchronous SCIAMACHY/Envisat limb observations of the oxygen 557.7 nm green line emission occurring in the terrestrial nightglow. A band pass filter with noise detection was applied to eliminate contributions from other emissions, the impact of noise and auroral activity. Assuming horizontal homogeneity of each atmospheric layer, and absence of absorption and scattering, vertical volume emission rate profiles were retrieved from integrated limb emission rate profiles. The radiative transfer problem was treated with a linear forward model and inverted using regularized total least squares minimization. Atomic oxygen concentration ([O]) profiles were retrieved at altitudes from 85 to 105 km with approximately 4 km vertical resolution for the period from August 2002 to April 2012 at a constant local time (LT) of approximately 22:00. The retrieval of [O] profiles was based on the generally accepted 2-step Barth transfer scheme including consideration of quenching processes and the use of different available sources of temperature and atmospheric density profiles. A sensitivity analysis was performed for the retrieved [O] profiles to estimate the maximum uncertainty, assuming independent contributions of uncertainty components. The retrieved [O] profiles were compared with reference [O] profiles measured by SABER/TIMED and modelled using NRLMSISE-00 and SD-WACCM4. A comparison of the retrieved [O] profiles with the reference [O] profiles enabled the selection of the most appropriate photochemical model accounting for quenching processes and the most appropriate source of temperature and density profiles for further application of our approach to the [O] profile retrieval. The obtained [O] profile time series show characteristic seasonal variations in agreement with atmospheric models and satellite observations based on analysis of OH Meinel band emissions. Furthermore, a pronounced 11 year solar cycle variation can be identified in the atomic oxygen concentration time series, which will be the subject of further studies.

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