Volume Emission Rate Research Articles

Local-time, seasonal and solar cycle variation of Nitric Oxide radiative emission over Indian longitude sector

• Localtime,seasonal & solar cycle variations of NO emission are studied over Indian longitude. • Maximum volume emission rate(VER), dobule the nighttime mean, is observed at 13 LT. • Peak altitude of NOVER descends downward by 18 km from midnight to noon. • Peak VER & intensity show a winter maximum and a summer minimum. We study the local-time, seasonal and solar cycle variations of Nitric Oxide (NO) infrared radiative emission, as observed by Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the NASA’s Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite, over Indian longitude sector. It covers nineteen (January 2002-December 2020) years of NO radiative emission data in the altitude region of 100–155 km. The NO volume emission rate (VER) shows a strong local-time variation with maximum and minimum, respectively, during local-noon and local-midnight. The peak altitude of NO VER decreases by about 18 km from the midnight to the lowest altitude of 117 km at noon. The mean NO VER also undergoes a significant change between the day and night. The mean daytime NO VER is more than double the night-time counterpart. The seasonal variation of peak NO VER shows a maximum during the month of December and a minimum during March. The peak altitude is maximum during September and minimum during June unlike the peak NO VER. The lowest peak altitude, maximum VER and maximum intensity are observed during winter. The relative change in NO VER between the winter and the summer seasons, peaks around 116 km, increases with altitude above 108 km. The long-term trend of NO VER/intensity shows a clear solar cycle variation with higher values during the higher solar activity periods. The NO intensity exhibits a strong correlation with sunspot number (SSN), F10.7 solar index and Lyman- α during both 23rd and 24th solar cycles, although the peak VER does not coincide with the peak SSN.

On the Relationship of the O(1D) 630.0 nm Dayglow Emission to the F10.7 cm Solar Flux and the Solar Zenith Angle

AbstractThe Wind Imaging Interferometer (WINDII) Empirical Model, which provides the characteristics of the O(1D) 630.0 nm atomic oxygen dayglow emission from the upper atmosphere has been reviewed and updated. It now includes the Integrated Emission Rate, the peak Volume Emission Rate, the Altitude of that peak and the Full Width at Half Maximum as functions of the F10.7 cm Solar Radio Flux and the solar zenith angle (SZA). The model employs 98,617 WINDII observations obtained between the years 1992 and 1996, and the model and observations of the Integrated Emission Rate agree well with one another within 2 standard deviations of 588.7 Rayleigh (R) (106 photons cm−2 sec−1). It is also demonstrated that the impact of latitude, longitude and day of year, independently of their contribution to the SZA, is very small. The WINDII Empirical Model is also shown to agree with results from the TRANSCAR photochemical model. The dayglow is challenging to measure with ground‐based instruments, as the solar scattered light from the daytime sky must be accurately subtracted from the data. Ground‐based measurements of the integrated emission rate have been made by others, with good agreement for observations from Hyderabad during the 2015 summer and winter, but mixed agreement with measurements made over Boston in 2003. The latter results are reviewed and assessed.

Simultaneous Retrievals of Nighttime O(3P) and Total OH Densities From Satellite Observations of Meinel Band Emissions

AbstractRetrieving the total number density [OH], which is used in the chemical balance equations and is the sum of both ground and excited vibrational state populations, is a challenging problem to such a degree there exist no such estimates from recent space observations. We present a novel retrieval approach to simultaneously and self‐consistently derive both [O(3P)] and total [OH] in the nighttime mesosphere and lower thermosphere which operates with the Meinel band volume emission rates and their ratios. Its application to the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) and Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) observations shows a good agreement of the retrieved [O(3P)] taking into account the measurement uncertainties and variation of model inputs used. However, retrieved [OH] show a large discrepancy, mainly above 90 km. SCIAMACHY [OH] is generally in good agreement with WACCM [OH] after accounting for uncertainties, while SABER OH is larger than WACCM [OH] by up to a factor of 2.

On how atmospheric temperature affects the intensity of oxygen emissions in the framework of the Barth’s mechanism

The three-body recombination of oxygen atoms O + O + M → O2(el) + M is the dominant process of oxygen excitation in the Earth’s nightglow at altitudes of 85–110 km. The rate coefficient of this reaction, as well as the quantum yields of electronically excited products (O2(el) in the electronic states: 5πg, A3Σu+, A′3Δu, c1Σu+, b1Σg+, a1Δg, X3Σg-) depend on the gas kinetic temperature. In addition to the direct one-stage excitation channel of these levels of the O2 molecule, the Barth’s mechanism considers the two-stage energy transfer channel. In this channel, higher excited levels of the O2 act as precursors for the excitation of the O(1S) atom and the underlying electronic levels of the O2. In this study, we use sensitivity analysis to consider the temperature dependence of the processes of excitation and quenching for each of the excited components. The analytical expressions are obtained for the sensitivity coefficients of the Volume Emission Rates depending on temperature for the green line of atomic oxygen O(1S → 1D), the Herzberg I band O2(A3Σu+→X3Σg-) and O2 Atmospheric band O2(b1Σg+,v'=0→X3Σg-, v''=0). With the help of the sensitivity analysis performed in this work, we (a) confirm that the state O2(5πg), produced by the three-body recombination of atomic oxygen, is a precursor for the formation of O2(b1Σg+), (b) estimate the quantum yield of the O2(b1Σg+) state formed as a result of collisional reaction O2(5πg) with O2, and (c) propose a method for determining a type of precursor for production of O(1S) in the Barth's mechanism.

Statistical Structure of Nighttime O2 Aurora From SABER and Its Dependence on Geomagnetic and Solar Activities in Winter

AbstractO2 aurora is one kind of important molecular aurorae that is not fully understood yet. It is hard to be investigated due to the contamination by nightglow. In this work, we studied O2 aurora based on the observations of O2 emission at 1.27 μm from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument during the nighttime over 18 years. The horizontal structure of O2 auroral zone is given for the first time, and the vertical profile of O2 auroral volume emission rate is obtained after removing O2 nightglow contamination. The O2 auroral intensity and the peak height and peak volume emission rate of the vertical profile averaged over the O2 auroral zone are studied in detail. For Kp Levels 1–5, the O2 auroral peak height varies between 104 and 112 km and is negatively correlated with the auroral intensity and peak volume emission rate. The O2 auroral intensity varies between 0.14 and 5.97 kR, and the peak volume emission rate varies between 0.97 × 102 and 41.01 × 102 photons cm−3 s−1. Furthermore, the dependences of the O2 aurora on geomagnetic and solar activities are analyzed. The O2 auroral intensity and peak volume emission rate exponentially increases with increasing Kp index, whereas the peak height decreases with increasing Kp index. The O2 auroral intensity and peak volume emission rate under solar minimum condition are larger than those under solar maximum condition. The peak height under solar minimum condition is lower than that under solar maximum condition.

Retrieval of daytime mesospheric ozone using OSIRIS observations of O<sub>2</sub> (<i>a</i><sup>1</sup>Δ<sub>g</sub>) emission

Abstract. Improving knowledge of the ozone global distributions in the mesosphere–lower thermosphere (MLT) is a crucial step in understanding the behaviour of the middle atmosphere. However, the concentration of ozone under sunlit conditions in the MLT is often so low that its measurement requires instruments with very high sensitivity. Fortunately, the bright oxygen airglow can serve as a proxy to retrieve the daytime ozone density indirectly, due to the strong connection to ozone photolysis in the Hartley band. The OSIRIS IR imager (hereafter, IRI), one of the instruments on the Odin satellite, routinely measures the oxygen infrared atmospheric band (IRA band) at 1.27 µm. In this paper, we will primarily focus on the detailed description of the steps done for retrieving the calibrated IRA band limb radiance (with <10 % random error), the volume emission rate of O2 (a1Δg) (with <25 % random error) and finally the ozone number density (with <20 % random error). This retrieval technique is applied to a 1-year sample from the IRI dataset. The resulting product is a new ozone dataset with very tight along-track sampling distance (<20 km). The feasibility of the retrieval technique is demonstrated by a comparison of coincident ozone measurements from other instruments aboard the same spacecraft, as well as zonal mean and monthly average comparisons between Odin-OSIRIS (both spectrograph and IRI), Odin-SMR and Envisat-MIPAS. We find that IRI appears to have a positive bias of up to 25 % below 75 km, and up to 50 % in some regions above. We attribute these differences to uncertainty in the IRI calibration as well as uncertainties in the photochemical constants. However, the IRI ozone dataset is consistent with the compared dataset in terms of the overall atmospheric distribution of ozone between 50 and 100 km. If the origin of the bias can be identified before processing the entire dataset, this will be corrected and noted in the dataset description. The retrieval technique described in this paper can be further applied to all the measurements made throughout the 19 year mission, leading to a new, long-term high-resolution ozone dataset in the middle atmosphere.

Errors From Asymmetric Emission Rate in Spaceborne, Limb Sounding Doppler Interferometry: A Correction Algorithm With Application to ICON/MIGHTI.

The Michelson Interferometer for Global High‐resolution Thermospheric Imaging (MIGHTI) on NASA's Ionospheric Connection Explorer (ICON) mission is designed to measure the neutral wind and temperature between 90 and 300 km altitude. Using the Doppler Asymmetric Spatial Heterodyne (DASH) spectroscopy technique, observations from MIGHTI can be used to derive thermospheric winds by measuring Doppler shifts of the atomic oxygen red line (630.0 nm) and green line (557.7 nm). Harding et al. (2017, https://doi.org/10.1007/s11214‐017‐0359‐3) (Harding17) describe the wind retrieval algorithm in detail and point out the large uncertainties that result near the solar terminators and equatorial arcs, regions of large spatial gradients in airglow volume emission rates (VER). The uncertainties originate from the assumption of a constant VER at every given altitude, resulting in errors where the assumption is not valid when limb sounders, such as MIGHTI, observe regions with significant VER gradients. In this work, we introduce a new wind retrieval algorithm (Wu20) with the ability to account for VER that is asymmetric along the line of sight with respect to the tangent point. Using the predicted ICON orbit and simulated global VER variation, the greatest impact of the symmetric airglow assumption to the ICON vector wind product is found within 30° from the terminator when the spacecraft is in the dayside, causing an error of at least 10 m/s. The new algorithm developed in this study reduces the error near the terminator by a factor of 10. Although Wu20 improves the accuracy of the retrievals, it loses precision by 75% compared to Harding17.

The use of the 1.27 µm O<sub>2</sub> absorption band for greenhouse gas monitoring from space and application to MicroCarb

Abstract. Monitoring CO2 from space is essential to characterize the spatiotemporal distribution of this major greenhouse gas and quantify its sources and sinks. The mixing ratio of CO2 to dry air can be derived from the CO2∕O2 column ratio. The O2 column is usually derived from its absorption signature on the solar reflected spectra over the O2 A band (e.g. Orbiting Carbon Observatory-2 (OCO-2), Thermal And Near infrared Sensor for carbon Observation (TANSO)/Greenhouse Gases Observing Satellite (GOSAT), TanSat). As a result of atmospheric scattering, the atmospheric path length varies with the aerosols' load, their vertical distribution, and their optical properties. The spectral distance between the O2 A band (0.76 µm) and the CO2 absorption band (1.6 µm) results in significant uncertainties due to the varying spectral properties of the aerosols over the globe. There is another O2 absorption band at 1.27 µm with weaker lines than in the A band. As the wavelength is much closer to the CO2 and CH4 bands, there is less uncertainty when using it as a proxy of the atmospheric path length to the CO2 and CH4 bands. This O2 band is used by the Total Carbon Column Observing Network (TCCON) implemented for the validation of space-based greenhouse gas (GHG) observations. However, this absorption band is contaminated by the spontaneous emission of the excited molecule O2*, which is produced by the photo-dissociation of O3 molecules in the stratosphere and mesosphere. From a satellite looking nadir, this emission has a similar shape to the absorption signal that is used. In the frame of the CNES (Centre National d'Études Spatiales – the French National Centre for Space Studies) MicroCarb project, scientific studies have been performed in 2016–2018 to explore the problems associated with this O2* airglow contamination and methods to correct it. A theoretical synthetic spectrum of the emission was derived from an approach based on A21 Einstein coefficient information contained in the line-by-line high-resolution transmission molecular absorption (HITRAN) 2016 database. The shape of our synthetic spectrum is validated when compared to O2* airglow spectra observed by the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY)/Envisat in limb viewing. We have designed an inversion scheme of SCIAMACHY limb-viewing spectra, allowing to determine the vertical distribution of the volume emission rate (VER) of the O2* airglow. The VER profiles and corresponding integrated nadir intensities were both compared to a model of the emission based on the Reactive Processes Ruling the Ozone Budget in the Stratosphere (REPROBUS) chemical transport model. The airglow intensities depend mostly on the solar zenith angle (both in model and data), and the model underestimates the observed emission by ∼15 %. This is confirmed with SCIAMACHY nadir-viewing measurements over the oceans: in such conditions, we have disentangled and retrieved the nadir O2* emission in spite of the moderate spectral resolving power (∼860) and found that the nadir SCIAMACHY intensities are mostly dictated by solar zenith angle (SZA) and are larger than the model intensities by a factor of ∼1.13. At a fixed SZA, the model airglow intensities show very little horizontal structure, in spite of ozone variations. It is shown that with the MicroCarb spectral resolution power (25 000) and signal-to-noise ratio (SNR), the contribution of the O2* emission at 1.27 µm to the observed spectral radiance in nadir viewing may be disentangled from the lower atmosphere/ground absorption signature with a great accuracy. Indeed, simulations with 4ARCTIC radiative transfer inversion tool have shown that the CO2 mixing ratio may be retrieved with the accuracy required for quantifying the CO2 natural sources and sinks (pressure-level error ≤1 hPa; XCO2 accuracy better than 0.4 ppmv) with the O2 1.27 µm band only as the air proxy (without the A band). As a result of these studies (at an intermediate phase), it was decided to include this band (B4) in the MicroCarb design, while keeping the O2 A band for reference (B1). Our approach is consistent with the approach of Sun et al. (2018), who also analysed the potential of the O2 1.27 µm band and concluded favourably for GHG monitoring from space. We advocate for the inclusion of this O2 band on other GHG monitoring future space missions, such as GOSAT-3 and EU/European Space Agency (ESA) CO2-M missions, for a better GHG retrieval.

A comparison of OH nightglow volume emission rates as measured by SCIAMACHY and SABER

Abstract. Hydroxyl (OH) short-wave infrared emissions arising from OH(4-2, 5-2, 8-5, 9-6) as measured by channel 6 of the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) are used to derive concentrations of OH(v=4, 5, 8, and 9) between 80 and 96 km. Retrieved concentrations are used to simulate OH(5-3, 4-2) integrated radiances at 1.6 µm and OH(9-7, 8-6) at 2.0 µm as measured by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, which are not fully covered by the spectral range of SCIAMACHY measurements. On average, SABER “unfiltered” data are on the order of 40 % at 1.6 µm and 20 % at 2.0 µm larger than the simulations using SCIAMACHY data. “Unfiltered” SABER data are a product, which accounts for the shape, width, and transmission of the instrument's broadband filters, which do not cover the full ro-vibrational bands of the corresponding OH transitions. It is found that the discrepancy between SCIAMACHY and SABER data can be reduced by up to 50 %, if the filtering process is carried out manually using published SABER interference filter characteristics and the latest Einstein coefficients from the HITRAN database. Remaining differences are discussed with regard to model parameter uncertainties and radiometric calibration.

Simulation and Analysis on Volume Emission Rate and Limb Radiation Intensity of Airglow at Oxygen A(0, 0) Band

临近空间大气参数如温度、密度、风场等对预报模型精度及航天器运行安全等有较大的影响，而气辉的辐射模拟是大气参数反演的重要过程.本文基于光化学模型计算了氧气A（0，0）波段气辉的体发射率和临边辐射强度.基于氧气A（0，0）波段气辉的光化学反应机制、大气动力学和光化学反应理论，建立产生O₂（b¹Σ_<i>g</i>⁺）的光化学模型.计算气辉体发射率，基于临边探测几何路径进行气辉辐射强度模拟.体发射率计算结果与AURIC模型结果的辐射值及辐射高度均一致.基于计算和模拟结果，对氧气A波段气辉体发射率和辐射强度的影响因素进行了分析.

Comparisons of spectrally resolved nightglow emission locally simulated with space and ground level observations

A mesospheric model of the airglow emission is developed to recover the night variations observed at ground level. The model is based on a 1D vertical photochemical model, including the photodissociation and heating processes. The spectral radiation is calculated at high altitude and propagated through the atmosphere to the ground. We also include short scale vertical dynamic such as turbulences and the molecular diffusion. Simulations reveal realistic emissions when compared with space observations. In addition, we estimate the impact of changes associated with parameterized atmospheric tides. The comparison with observations is performed over high altitude and ground level. We confront the model outputs at high altitude with satellite observations (SABER and GOMOS) and the simulations propagated at ground level are compared to local measurements campaigns performed in France and India. Biases between observed and simulated radiances and volume emission rates are suspected to be due to the impact of gravity waves or the large scale dynamic.

A Comparative Analysis of the OI 130.4‐nm Emission Observed by NASA's TIMED Mission Using a Monte Carlo Radiative Transfer Model

AbstractRemote sensing of the OI 130.4‐nm emission is potentially a useful means for routine monitoring of the atomic oxygen abundance in the upper atmosphere, especially for altitudes above 300 km where the OI 135.6‐nm emission becomes too dim to be useful. However, to date, the interpretation of the OI 130.4‐nm emission as a proxy for the O density remains ambiguous in that the relative contribution of the external and internal sources to the production of this emission has not been fully understood. In this study, we perform a comparative analysis of the OI 130.4‐nm dayglow observed by NASA's Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission using a Monte Carlo radiative transfer model to investigate the consistency between models and the TIMED/Global UltraViolet Imager (GUVI) data. The solar 130.4‐nm flux is measured by TIMED/Solar EUV Experiment (SEE). The Global Airglow (GLOW) and the Atmospheric Ultraviolet Radiance Integrated Code (AURIC) models are used to calculate the initial volume emission rates due to photoelectron impact excitation, and the NRLMSISE‐00 model is used to provide the atmospheric density and temperature profiles. Our data‐model comparisons suggest that the model predicted contributions from photoelectron impact excitation need to be scaled by a factor of 0.1–0.5 to achieve good fits with the data. Moreover, the modeled solar contributions need to be scaled up/down to fit the observations at small ( 20 )/large ( 60 ) solar zenith angles, with a factor of 0.5–1.7. These scale factors are larger than the uncertainties in the GUVI and SEE instrument calibrations, which might suggest inaccurate model predictions of the dayside O density and temperature variations with solar zenith angles.

Traveling Ionosphere Disturbance Signatures on Ground‐Based Observations of the O(1D) Nightglow Inferred From 1‐D Modeling

AbstractThis paper reports our simulations of the volume emission rate of the O(1D) redline nightglow perturbed by waves traveling across the thermosphere at around 250 km altitude. Waves perturb the electronic and neutral background densities and temperatures in the region and modify the O(1D) layer intensity as it is captured by ground‐based nightglow instruments. The changes in the integrated volume emission rate are calculated for various vertical wavelengths of the perturbations. We demonstrate that, as the solar activity intensifies, the vertical scales of most likely observable TID waves become larger. For high solar activity, we demonstrate that only waves presenting vertical wavelengths larger than 360 km are likely to be observed. The variation of the range of likely observable vertical wavelengths with the solar cycle offers a plausible explanation for the low occurrence rate of TID in measurements of the redline nightglow during high solar activity periods. We have compared our results with those of Negale et al. (2018; https://doi.org/10.1029/2017JA024876) and Paulino et al (2018; https://doi.org/10.5194/angeo-36-265-2018) to verify that observed vertical wavelengths distribute around 140–210 km, in good correspondence with our predicted threshold wavelength 160 km for very low solar cycle period.

High‐Resolution Optical Observations of Neutral Heating Associated With the Electrodynamics of an Auroral Arc

AbstractWe present results that indicate the existence of two distinct neutral heating processes associated with a discrete auroral arc over Svalbard. Within the order of seconds, the thermospheric temperature profile displays a significant response to the arc on spatial scales smaller than 10 km. It is suggested that both heating signatures are associated with the electrodynamic system responsible for the formation of the arc. Pedersen currents produce a temperature increase of approximately 100 K, observed at altitudes between 80 and 160 kilometres, directly adjacent to the arc structure and on its poleward edge only. In contrast, field‐aligned currents produce a variable temperature increase, of approximately 50 K, which is observed within the arc itself and constrained to a narrow altitude range between 90 and 110 km. By utilizing a range of observations and new analysis methods we are able to measure the atmospheric neutral temperature profile, over auroral altitudes, at unprecedented temporal and spatial scales. The High Throughput Imaging Echelle Spectrograph records high‐resolution emission spectra of the aurora, which are then fitted with synthetic N2 spectra, generated with modeled N2 volume emission rate profiles and a library of trial temperature profiles. The N2 volume emission rate profiles are retrieved from the Southampton ionospheric model using precipitating particle energies and fluxes obtained from Auroral Structure and Kinetics and the EISCAT Svalbard Radar. The application of this technique allows us to produce a time series of neutral temperature profiles and measure the localized heating of the neutral atmosphere resulting from the electrodynamics of the arc.

A Comparison of Einstein A Coefficients for OH Rotational Temperature Measurements Using a Large Astronomical Data Set

The Einstein A coefficients are considered to be a significant source of uncertainty in the measurement of OH rotational temperatures. Using simultaneous ground and spaced-based observations of OH emission, five sets of Einstein A coefficients were examined for their impact upon rotational temperature calculations. The ground-based observations are taken from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) instrument which is a high resolution, r = λ / Δ λ ≥ 20 , 000 , spectrograph operating in the H-band from approximately 1.5 to 1.7 μ m. APOGEE collected over one-hundred-and-fifty-thousand spectra of the night sky over a period from June 2011 to June 2013. The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite has made simultaneous atmospheric measurements with the APOGEE spectrograph. SABER observes the OH volume emission rate (VER) around 1.6 μ m, providing measurements coincident with those of the OH emission in the APOGEE sky spectra. Four of the five sets of Einstein A coefficients tested yielded statistically identical mean rotational temperatures of approximately 195 K for the OH ( 4 − 2 ) transition. The Einstein A coefficients were found to have a significant impact upon the measured OH ( v ′ = 4 ) vibrational populations with some sets of coefficients yielding populations over 50% greater. Simultaneous SABER observations were used to determine which set of Einstein A coefficients best reflected atmospheric temperatures, and four of the five tested coefficients yielded nearly identical results. The difference between OH rotational temperatures and SABER temperatures was on average 1 K.

Radiative cooling due to NO at 5.3 [formula omitted]m emission as observed by TIMED/SABER over Asian sector

The effect of geomagnetic storms on the peak emission of NO Volume Emission Rate (NO VER) at 5.3 μm, in mesosphere and lower thermosphere (MLT) region, is studied over the Asian sector during 26–29 September 2011 (storm 1) and 18–21 February 2014 (storm 2). The data for peak emission of NO VER is obtained from SABER instrument onboard the NASA’s TIMED satellite. The SABER retrieved data along with the neutral densities obtained from NRLMSISE-00 model have been used to study the latitudinal and longitudinal variation of peak NO VER during the storm period. The variations induced in the peak emission of NO VER is understood with the help of fluctuations in neutral species and the resulting changes in chemistry. It has been found that the peak emission of NO VER is strongly influenced by the storm conditions. The peak emission of NO VER at 5.3 μm is found to be maximum at higher latitudes during the storms. However, the magnitude of peak NO VER gradually decreases towards the equator during the storms. The modeled atomic oxygen number density shows depletion at the higher latitudes corresponding to peak altitude of NO VER. There is a negative correlation between the peak emission of NO VER and Dst index during the main phase of the storm. The peak emission of NO VER and modeled atomic oxygen number density shows the positive correlation at the equator region, while negative correlation at the higher latitudes. At higher latitudes modeled atomic oxygen number density shows positive correlation with Dst index, while negative correlation at the equator. The correlation factors obtained between various parameters related to the storm time radiative cooling strongly support the existing understanding of the variation of NO VER during extreme space weather events.

Perturbations of O(1D) VER, Temperature, Winds, Atomic Oxygen, and TEC at High Southern Latitudes

AbstractThe study investigates previously unrecognized wind reversals of the daytime thermosphere in the Southern Hemisphere at latitudes of 50°S–70°S employing observations of O(1D) airglow volume emission rates (VER), temperature, and neutral winds at 170–300‐km height by the Wind Imaging Interferometer. Atomic oxygen densities derived from the Wind Imaging Interferometer O+ (732–733 nm) emission observations were also considered together with contemporaneous observations of total electron content by the TOPEX Poseidon satellite mission. The O(1D) VER for fall equinox (March/April 1994) and summer solstice (January 1995) revealed a peak in the VER over the longitude range of 50°E–150°E, for both seasons and daytime local times. The Doppler temperatures also exhibited a maximum at the same location and times. The co‐located zonal wind field shows a westward trough at 50°E–150°E with wind speeds reaching −450 m/s and an eastward peak at 200°E–300°E. Meridional winds show a “peak and trough” structure over the 50°E–150°E region, with a distinct eastern boundary at ~150°E. During summer solstice the atomic oxygen is depleted at the region of the O(1D) VER enhancement in the presence of westward zonal wind. However, the total electron content observations showed a peak that coincided with the O(1D) VER and temperature enhancements.

A Comparison of Electron Densities Derived by Tomographic Inversion of the 135.6‐nm Ionospheric Nightglow Emission to Incoherent Scatter Radar Measurements

AbstractThe 135.6‐nm emission of atomic oxygen has become a workhorse for satellite remote sensing of the nighttime ionosphere. Previous work on interpreting the 135.6‐nm emission established the importance of properly modeling the mutual neutralization and radiative recombination contributions to the volume emission rate and emphasized the importance of modeling and interpreting the transfer and transport of the radiation. Recently, we developed and published a new inversion approach called Volume Emission Rate Tomography, which handles the radiation transfer as part of the tomography process. We compare electron density distributions derived using the Volume Emission Rate Tomography technique to interpret the 135.6‐nm measurements made by the Special Sensor Ultraviolet Limb Imager instruments aboard the Defense Meteorological Satellite Program satellites in 2010. These retrievals are validated against electron densities measured during overflights of the Advanced Research Project Agency Long‐range Tracking and Identification Radar incoherent scatter radar. The mean percentage difference between the Special Sensor Ultraviolet Limb Imager‐derived electron densities and those measured by Advanced Research Project Agency Long‐range Tracking and Identification Radar was 14%, when radiative recombination was the only source considered in the inversion process. When the mutual neutralization and radiation transport sources of emission are included in the inversions, the mean percentage decreased to 4%, thereby confirming that these sources are necessary to accurately derive the electron density from the 135.6‐nm emission.

Simulation and observation for volume emission rates emitted from O2(0-1) and O(1S) nightglow in northwest China.

Being susceptible to the change of atmospheric conditions, the volume emission rate (VER) is very suitable to be used as a light source by passive remote sensing for measuring atmospheric wind and temperature. Thus, the VERs emitted from O2(0-1) and O(S1) of the nightglow at 80-120km are studied in this paper. Based on the Naval Research Laboratory Mass Spectrometer Incoherent Scatter (NRLMSISE-00) model data and the ground-based airglow imaging interferometer (GBAII) instrument observation for a local time and place, simulated VER profiles represented by four layers are obtained for the nightglow of O2(0-1) and O(S1). The O2(0-1) nightglow model peak values at 94km on 6 December 2013 and 8 November 2011 are 8111 photons·cm-3·s-1 and 8406 photons·cm-3·s-1, respectively; however, the O(S1) VER peak at a higher altitude of about 96km on 18 December 2011 is only 338 photons·cm-3·s-1. The upper atmospheric VER values have been derived to transfer into the ground-based detected column intensities by our GBAII prototype. The calculated column integrated emission rates (IERs) of O2(0-1) for 0° and 45° zenith angles are 1.48×107 and 1.91×107 photons·cm-2·s-1, respectively; the calculated column IERs of O(S1) are 5.53×105 and 7.03×105 photons·cm-2·s-1, respectively. Correspondingly, the detected column IERs obtained by GBAII are 2.43×107 for O2(0-1) and 6.57×105 photons·cm-2·s-1 for O(S1).

Atmospheric band fitting coefficients derived from a self-consistent rocket-borne experiment

Abstract. Based on self-consistent rocket-borne measurements of temperature, the densities of atomic oxygen and neutral air, and the volume emission of the atmospheric band (762 nm), we examined the one-step and two-step excitation mechanism of O2b1Σg+ for nighttime conditions. Following McDade et al. (1986), we derived the empirical fitting coefficients, which parameterize the atmospheric band emission O2b1Σg+-X3Σg-0,0. This allows us to derive the atomic oxygen concentration from nighttime observations of atmospheric band emission O2b1Σg+-X3Σg-0,0. The derived empirical parameters can also be utilized for atmospheric band modeling. Additionally, we derived the fit function and corresponding coefficients for the combined (one- and two-step) mechanism. The simultaneous common volume measurements of all the parameters involved in the theoretical calculation of the observed O2b1Σg+-X3Σg-0,0 emission, i.e., temperature and density of the background air, atomic oxygen density, and volume emission rate, is the novelty and the advantage of this work.