Atomic Oxygen Green Line Research Articles

It's Not Easy Being Green: Kinetic Modeling of the Emission Spectrum Observed in STEVE's Picket Fence

AbstractRecent studies suggest that, despite its aurora‐like appearance, the picket fence may not be driven by magnetospheric particle precipitation but instead by local electric fields parallel to Earth's magnetic field. Here, we evaluate the parallel electric fields hypothesis by quantitatively comparing picket fence spectra with the emissions generated in a kinetic model driven by local parallel electric fields energizing ambient electrons in a realistic neutral atmosphere. We find that, at a typical picket fence altitude of 110 km, parallel electric fields between 40 and 70 Td (∼80–150 mV/m at 110 km) energize ambient electrons sufficiently so that, when they collide with neutrals, they reproduce the observed ratio of N2 first positive to atomic oxygen green line emissions, without producing first negative emissions. These findings establish a quantitative connection between ionospheric electrodynamics and observable picket fence emissions, offering verifiable targets for future models and experiments.

Lower Atmospheric Sources of Observed Thermosphere Medium Scale Traveling Atmospheric Disturbances Over Alaska During the 2012–2013 Winter Months

AbstractThis paper investigates the lower‐to‐upper atmosphere coupling at high latitudes (>60°N) during the northern winter months of 2012–2013 years, which includes a period of major Sudden “Stratospheric” Warming (SSW). We perform statistical analysis of thermosphere wind disturbances with periods of 30–70 min, known as the medium scale traveling atmospheric disturbances (MSTADs) in atomic oxygen green line (557.7 nm) near ∼120 km and red line (630.0 nm) emissions near ∼250 km observed from Scanning Doppler Imagers (SDIs) over Alaska. The SDI MSTADs observations (60°–75°N) are interpreted in conjunction with the previous daytime medium‐scale traveling ionospheric disturbance (MSTID) observations by SuperDARN midlatitudes (35°–65°N) radars in the F‐region ionosphere and western hemisphere, which confirm findings from the SDI instruments. Increases in MSTAD activity from SDIs show correlations with the increasing meridional planetary wave (PW) amplitudes in the stratosphere derived from MERRA2 winds. Furthermore, a detailed study of the lower atmospheric conditions from MERRA2 winds indicates that the lower atmospheric sources of MSTADs are likely due to the stratospheric generated Gravity Waves (GWs) and not orographic GWs. Favorable stratospheric propagation conditions and polar vortex disturbances resulting from the increased PW activity in the stratospheric region both appear to contribute to increased MSTAD activity in the thermosphere. Additionally, the results show that the MSTID activity from SuperDARN HF radars at mid latitudes during the January 2013 SSW is lower than the MSTAD activity in SDI winds at high latitudes.

Global distribution of atomic oxygen in the mesopause region as derived from SCIAMACHY O(1S) green line measurements

AbstractA new data set of atomic oxygen abundance in the upper mesosphere and lower thermosphere is presented. The data are derived from the nighttime atomic oxygen green line limb emission measurements of the SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography) instrument on the European Environmental Satellite. The temporal coverage is October 2002 until April 2012, and the latitudinal extent is 50°S to 80°N at 10 P.M. local time. This data set is compared to other satellite data sets, in particular to recently published data of SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) and the Mass Spectrometer and Incoherent Scatter model. SCIAMACHY atomic oxygen peak abundances are typically 3–6×1011 mol/cm3 at the atomic oxygen maximum region, depending on latitude and season. These values are similar to previous values based on chemiluminescence measurements of the atomic oxygen three‐body recombination reaction but at least 30% lower than atomic oxygen abundances obtained from SABER.

Limb imaging of the Venus O2 visible nightglow with the Venus Monitoring Camera

AbstractWe investigated the Venus O2 visible nightglow with imagery from the Venus Monitoring Camera on Venus Express. Drawing from data collected between April 2007 and January 2011, we study the global distribution of this emission, discovered in the late 1970s by the Venera 9 and 10 missions. The inferred limb‐viewing intensities are on the order of 150 kR at the lower latitudes and seem to drop somewhat toward the poles. The emission is generally stable, although there are episodes when the intensities rise up to 500 kR. We compare a set of Venus Monitoring Camera observations with coincident measurements of the O2 nightglow at 1.27 µm made with the Visible and Infrared Thermal Imaging Spectrometer, also on Venus Express. From the evidence gathered in this and past works, we suggest a direct correlation between the instantaneous emissions from the two O2 nightglow systems. Possible implications regarding the uncertain origin of the atomic oxygen green line at 557.7 nm are noted.

Observations of OI 557.7 nm nightglow at Kolhapur (17° N), India

Abstract. Ground-based nightglow observations of the atomic oxygen green line at 557.7 nm have been carried out at a low latitude station Kolhapur (17° N), India, during November 2003–April 2004 and December 2004–May 2005. The nocturnal behaviour of OI 557.7 nm intensity and a comparative study with simultaneous OH Meinel band temperature measurements has been presented. OI 557.7 nm intensity and OH temperature variations covary on many occasions. It was found that an 8 h tide characterizes the variation of intensity and temperature on most nights, and especially during the month of January. This is the first report of prolonged measurements of OI 557.7 nm emission from India.

A method for the intensification of atomic oxygen green line emission by internal gravity waves

[1] Low-frequency internal gravity waves, such as may be generated by seismic activity and nonlinearly propagated through the stably stratified atmosphere to the E layer of the ionosphere, are shown to cause intensification of atomic oxygen green line emission when their amplitude is sufficiently large. The nonlinear equations for the internal gravity waves are derived with the interaction of the induced currents with the geomagnetic field taken into account. When the source of the internal gravity waves is sufficiently strong, nonlinear vortex structures are predicted to be formed in the upper stratosphere and lower ionosphere. These nonlinear vortex structures are damped owing to Joule losses. The vortices provide a mechanism for increasing the concentration of atomic oxygen in the E layer and hence the associated intensity of the green light radiation at 557.7 nm. Data are discussed that report the observation of enhanced green light emission prior to earthquakes; this could lead to a forecasting model if the connection with seismic activity can be established.

Considering the polarization of the oxygen thermospheric red line for space weather studies

Space weather thermospheric monitoring requires real‐time and large‐scale measurements. In order to monitor the thermospheric variations due to geomagnetic activity, one relies mostly on the measurements of the intensity of the atomic oxygen green line and on the indirect measurement of the total electron content. These two parameters do not allow retrieving the full characteristics of the thermosphere, and a third proxy is required, for example, in orbitography. We propose to use the polarization of the atomic oxygen red line to fulfill this requirement. The first measurements of the polarization of thermospheric nightglow lines have been performed in the first part of the twentieth century and especially during the last International Geophysical Year. Amongst the oxygen visible lines, only the red one seems to be potentially polarized. However, there exists a disagreement between the different measurements. At the origin of the polarization, there is always a dissymmetric mechanism. It triggers either an emission process, a light scattering, or, in the case of the oxygen red line, a collision mechanism. This paper reviews the different experiments performed in the past and proposes to explore this matter with modern facilities. If successful, this investigation could lead to a systematic reanalysis of the previous red line interferometric measurements.

On the response of the O(1S) dayglow emission rate to the Sun's energy input: An empirical model deduced from WINDII/UARS global measurements

More than 520,000 emission rate profiles of the O(1S) dayglow (557.7 nm, the atomic oxygen green line) were measured by the Wind Imaging Interferometer (WINDII) on the Upper Atmospheric Research Satellite (UARS) during 1991–1997, providing an unprecedented and unique resource for studying the O(1S) emission layer, its related physics and chemistry, and the response of the mesosphere and thermosphere to the solar input. The daytime O(1S) emission is one of the most remarkable and persistent phenomena in the Earth's atmosphere between 80 and 280 km. The emission has two components, peaking at 140–180 km and 94–104 km. WINDII measurements show that both components are sensitively correlated with the Sun in the sense that (1) for a given day, the peak emission rates in both the F‐region and the E‐region increase with increasing cosine of the solar zenith angle, the height of the peak emission rate in the F‐region decreases with increasing peak emission rate but that in the E‐region does not have a clear relationship with the peak emission rate; (2) both the peak emission rate and its height in the F‐region as well in the E‐region increase with increasing solar irradiance, i.e., they follow the solar cycle. For the first time an empirical model of the green line emission rate and height of the peak emission are derived from WINDII global measurements over six years as functions of the solar zenith angle and the solar irradiance using the daily solar F10.7 cm flux as a proxy. This model provides a baseline for the unperturbed daytime green line emission for any time and any location. Owing to the direct effect of the solar zenith angle, the emission rate is symmetrical with respect to local noon; and globally, it is symmetrical with respect to the equator at equinox, and is much larger in the summer hemisphere than in the winter hemisphere at solstice. As a result, for a constant solar irradiance, the emission rate has an annual oscillation at mid and high latitudes, and a semiannual oscillation at the equator. In the solar cycle 22, for an overhead Sun, the max/min ratio of the F10.7 cm flux is about four, and the max/min ratio of the integrated O(1S) emission rate is about three. Some unsolved problems regarding the mechanism of the green line emission are reported.

Large-scale circulation of atomic oxygen in the upper mesosphere and lower thermosphere

The variability of the atomic oxygen green line airglow at 557.7 nm, originating from the O( 1S) level, has a long history of observation. Only recently, global observations of the oxygen airglow, interpreted with the help of global circulation models have provided some understanding. Satellite observations of winds and temperatures clearly demonstrate the dynamical influence of tides on the daily variations. Both annual and semi-annual components of the variation have been identified as occurring over the course of the year. From the large-scale circulation of the atmosphere one expects downwelling in the winter at high latitudes, causing enhanced atomic oxygen and enhanced airglow while the opposite is expected in summer. In the present investigation a search is made for this large-scale signature using data from the WIND Imaging Interferometer on the Upper Atmosphere Research Satellite, model results from the Thermosphere–Ionosphere–Mesosphere-Electrodynamics-Global Circulation Model, and earlier published results. A well-defined semi-annual variation of emission rate is found in the tropics, apparently the result of the semi-annual variation of the diurnal tide. Annual and semi-annual patterns are found at mid-latitudes, in satellite and model data, while ground-based observations detect only an annual variation, with a maximum in the autumn. At still higher latitudes the fall peak persists, but with a deep depletion of atomic oxygen in the springtime; this appears to be the signature of the large-scale circulation.

Planetary science. The nightside of Venus.

On 20 November 1999, Slanger et al. [HN1] (1) pointed the giant, 10-m-diameter, Keck I telescope [HN2] at the night side of Venus, our closest planetary neighbor. Venus [HN3] has been scrutinized for 35 years by ground-based telescopes and an armada of spacecraft [HN4], but it took just 8 min of exposure time for the high-resolution Keck spectra [HN5] to yield an important discovery, namely the first evidence for atomic oxygen airglow (2) at visible wavelengths on the nightside of Venus. The telltale sign of this airglow [HN6] was a diffusive emission from the upper atmosphere in the 557.7-nm atomic oxygen green line. This type of emission is prominent in Earth's aurora [HN7] and diffuse background nighttime airglow, but its appearance in the spectrum of the Venus night sky is surprising for several reasons.

Common-volume measurements of mesospheric winds using radar and optical instruments: 1. Comparison of observations

The Millstone Hill incoherent scatter radar (42.6°N, 71.5°W) and the nearby Durham meteor wind radar (43.1°N, 70.9°W) have been used to study the structure of the winds in the mesosphere and lower thermosphere and to investigate the propagation of tidal components from the mesosphere into the lower thermosphere. In general, good agreement is found between the tidal wind amplitudes and phases determined by the two radars, but occasionally, some discontinuities have been observed in the vertical structure of the tidal components in the 90–110 km region. In order to validate the accuracy of the two techniques and the methodologies used in determining neutral winds, two common-volume experiments were conducted in 1996 and 1997 in which the two radar beams were overlayed at an altitude of 100 km. The horizontal components of the measured radar line-of-sight velocities during day-time periods were then compared at the overlapping altitudes of 95–100 km. Night-time measurements were also made using a Fabry–Perot Interferometer co-located with the radar at Millstone Hill which observed the Doppler shift of the atomic oxygen green line emission in the mesosphere. Good overall agreement is found between the instruments within the statistical uncertainties of the measurement techniques, although some differences have been found that are explained by consideration of the data statistics, the exact overlap of common volume within the different beam sizes, and the presence of altitude gradients and small scale irregularities in the sampled volumes of the atmosphere.

Tidal oscillations of the Arctic upper mesosphere and lower thermosphere in winter

The upper mesosphere and lower thermosphere of the northern polar cap was investigated using Fabry‐Perot interferometer measurements of the horizontal wind velocity in the lower thermosphere, meridian scanning photometer observations of atomic oxygen green line brightness in the lower thermosphere, and Michelson interferometer records of the infrared Meinel OH bands brightness and rotational temperature in the upper mesosphere. Tidal airglow oscillations in the absence of local solar heating were studied using a superposed epoch analysis of observations obtained around three new‐Moon intervals (November 9–22, 1993, December 7–20, 1993, and January 4–17, 1994) in Eureka (80°N). Tidal harmonics were uncovered with an iterated least chi‐squared fit, and their existence in the data tested using a goodness‐of‐fit probability against a null hypothesis of no oscillations. No single dominant tide was found at all times and altitudes of the winter Arctic upper mesosphere and lower thermosphere. The horizontal wind velocity of the lower thermosphere exhibited all the first three harmonics of the tide, with the largest‐amplitude oscillations shown by the diurnal component of the meridional wave speed. The atmospheric layer near the mesopause that contributes to the OH airglow emission experienced terdiurnal oscillations throughout the winter season. Theoretical polarization relations for evanescent tides, considerations of energy density propagation with altitude, and a day‐by‐day analysis of the zonal and meridional wind speed and temperature all indicate that the terdiurnal tide observed on November was an evanescent zonally symmetric tide. Other data indicate propagating tides, migrating tides, or a mixture of both.

The O2 Herzberg I bands in the equatorial nightglow

Abstract Simultaneous measurements of the nightglow profiles of the O 2 Herzberg I bands, the O 2 Atmospheric (0-0) band and the atomic oxygen green line, carried out at Alcântara (2.3 °S; 44.4 °W), are presented and discussed. This is the first measurement of the vertical profile of the Herzberg I band to be carried out at equatorial latitudes. The atomic oxygen concentration derived from the O 2 Atmospheric (0-0) band emission profile is used to test a photochemical scheme to explain the measured O 2 ( A 3 Σ u + − X 3 Σ g − ) nightglow emission based on atomic oxygen recombination. The kinetic analysis is carried out assuming the emission ratio Herzberg I: Herzberg II = 5:1, 10:1 and the extreme case where Herzberg II brightness = 0. For all three cases studied, the quenching rates required to explain the measurements are higher than the values derived from previous airglow measurements.

Evening and morning twilight enhancement of λ5577 Å atomic oxygen line at Allahabad

A photometer for the observation of twilight airglow emissions has been fabricated. Intensity variation in morning and evening twilight of λ5577 A line of atomic oxygen has been recorded at Allahabad for one year duration from 23rd March, 1987 to 22nd March, 1988. The enhancement in the intensity of the line is found to be irregular. Out of 40 clear evenings and 25 clear mornings from 23rd March, 1987 to 15th June, 1987 enhancement is observed in 24 evenings and 15 mornings. However, no enhancement is observed during the period from 15th September, 1987 to 15th October, 1987. It is found that rise and fall of intensity is exponential during twilight period. Considering different mechanism for the excitation of atomic oxygen green line, it is concluded that none of them are able to explain enhancement. More work is needed to be carried out for the better understanding of the problem.

Neutral atmospheric composition between 60 and 220 km: A theoretical model for mid-latitudes

A new theoretical model for mid-latitude mesosphere and lower thermosphere at equinox conditions has been developed by including new values of various characteristic atmospheric parameters. A value of the eddy diffusion coefficient was deduced compatible with others reported in the literature and we discuss its effect upon the concentration of the different constituents. Photodissociation processes were handled with a detailed division of the different regions of the solar spectrum, mainly in the Schumann-Runge bands, allowing an exact computation of the diurnal O( 1D) and O 2( 1Δ g) altitude profiles produced by solar radiation. The model includes CO, CO 2, N 2 and oxygen and hydrogen compounds. Our results compare well with recent experimental altitude profiles of minor compounds at mesospheric levels. The altitude profiles have been tested to reproduce various nightglow features, such as the Infrared Atmospheric System of O 2( 1Δ g) in 1.27 μm and the atomic oxygen green line. The resulting profiles are in line with results obtained using rocket borne instrumentation. In the thermosphere, the profiles agree with other more elaborate models restricted to this region and with mass spectrometer measurements. Diurnal variation of the concentrations is shown and explained in terms of photochemical and transport processes. Carbon compounds have been included to obtain a comprehensive model that can be used subsequently to obtain an interpretation of the effect of minor compounds on the population ofdifierent CO 2 excited levels giving rise to infrared emission at 4.3 and 15 μm.

Excitation of oxygen emissions in the night airglow of the terrestrial planets

The excitation, energy transfer and quenching of O 2 (A 3 Σ u +, C 3 Δ u, c 1 Σ u −) and O( 1S) are discussed, taking into account laboratory measurements and observations on the airglow of the Earth, Venus and Mars. The excitation of O( 1S) occurs by the Barth mechanism with O 2(c) as a precursor: the rate coefficient is 2.5 × 10 −12 cm 3 s −1 for υ > 0 and 2.5 × 10 −12 exp( −1100 T ) cm 3 s −1for υ = 0. The O 2(c) can be formed directly by recombination or by O 2(A) and O 2(C) colliding with other molecules; the O 2(c) yield through quenching of these states is about 0.3 in air and about 1.0 in carbon dioxide. The rate coefficients of some processes that control the molecular oxygen bands and the atomic oxygen green line are estimated.

Properties of the mesosphere and lower thermosphere

The variability and systematic variations of the properties of the upper mesosphere and lower thermosphere are probably the least well known aspects of the terrestrial atmosphere. Satellite measurements of this region are very limited and rocket and remote sounding techniques do not provide comprehensive coverage. Progress is being made in theoretical studies of this region, primarily with regard to tidal effects, and some progress is being made in analyzing the relatively sparse experimental data that are available. Turbulence dynamics of the region has been studied by analyzing structure measurements at Kwajalein, wind data from Natal and systematic variations of the turbopause altitude determined from measurements of the diffusive separation of argon. One question that is being raised at this time, and it is appropriate at a time near solar maximum, is the extent of solar activity control of the properties of this region of the atmosphere. The occurrence rates and magnitudes of the turbulent diffusivity in the 70 to 90 km altitude region appear to correlate with solar activity with a time lag, as do also the incidence of aurora and the atomic oxygen green line intensity. Solar cycle dependence has been identified in mean zonal wind speeds in the 65 to 110 km altitude region above Saskatoon and in lower thermosphere temperatures measured at Heiss Island and at St. Santin. Millstone Hill data show that the mean meridional wind changes during a solar cycle. Solar cycle variations have also been detected in the stratosphere and troposphere.

A measurement of the O 2( b1Σg+− X3Σg−) atmospheric band and the OI( 1S) green line in the nightglow

Simultaneous measurements of the nightglow profiles of the O 2( b 1 Σ g +− X 3 Σ g −) A-band, the atomic oxygen green line and the OH (8−3) Meinel band are presented. The altitude profiles are used to determine both the excitation mechanisms for the oxygen emissions and the atomic oxygen altitude distribution. It is shown that the measurements are consistent with a green line excitation through the Barth mechanism and that the molecular oxygen emission is excited through oxygen recombination and the reaction between OH ∗ and atomic oxygen. The derived atomic oxygen concentrations,6.2 × 10 11cm −3 at 98km, are consistent with the Jacchia (1971) model.

High resolution measurements of the widths of narrow auroral arcs in the atomic oxygen green line and N 2+ first negative emissions

The anomalous inequality in the spatial extents of the OI 557.7 nm and N 2 + 391.4 nm emissions in auroral arcs was investigated by means of a ground-based low-light T.V. system. First reported in 1967 by Romick and Belon, this anomalous distribution has been the source of some controversy and also subsequent attempts to observe it have produced conflicting results. It is shown that for a simplified geometrical situation, when sufficient spatial and temporal resolution is used, the anomaly is not seen.

Analysis of Ogo 6 observations of the O I 5577-A tropical nightglow

Atomic oxygen green line data from the horizon scanning photometer on Ogo 6 have been examined. Unfolding the satellite data from the tropical F region yields altitude and latitude variations of the O(1S) emissions. The spatial variations of the tropical F-region electron density are then calculated by assuming dissociative recombination and using a model atmosphere. Where comparisons to ground based data are possible the results are good. Thus, the satellite observations constitute a form of topside sounding of the ionosphere below the F peak and provide synoptic data about this portion of the ionosphere that are otherwise impractical to obtain.