Nightglow Emission Research Articles

OI 630.0 nm Post‐Sunset Emission Enhancement as an Effect of Tidal Activity Over Low‐Latitudes

AbstractThe OI 630.0 nm airglow emission variability provides salient information on the dynamical changes taking place in the upper atmosphere at around 250 km. The emission rates vary with the changes in the ambient electron densities and the neutral constituents that are associated with these emissions. On several occasions, enhancements in these emissions are observed during post‐sunset hours, around 21 local time (LT), as measured from Mt. Abu (24.6°N, 72.7°E, 19°N Mag), a low‐latitude location at Indian longitudes. These enhancements occur following the typical monotonic decrease in emission intensity after sunset. The presence of poleward meridional wind preceded by cessation and reversal of equatorward wind at the post‐sunset hours was shown to be the cause for such observed emission enhancements in an earlier study. In this study, the cause of such reversal in meridional winds during post‐sunset hours has been investigated using the variation in electron densities and meridional winds simulated by the Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (WACCM‐X), which also shows enhancements in electron densities similar to those observed in the post‐sunset OI 630.0 nm nightglow emissions, and simultaneous reversal in meridional winds as well. The amplitudes and phases of different components of tides obtained from WACCM‐X meridional winds reveal a significant contribution of higher‐order tides, especially, quarter‐diurnal tides, to the observed reversal in the meridional winds during post‐sunset hours.

A novel infrared imager for studies of hydroxyl and oxygen nightglow emissions in the mesopause above northern Scandinavia

Abstract. The paper describes technical characteristics and presents the first scientific results of a novel infrared imaging system (imager) for studies of nightglow emissions coming from the hydroxyl (OH) and molecular oxygen (O2) layers in the mesopause region (80–100 km) above northern Scandinavia. The OH imager was put into operation in November 2022 at the Swedish Institute of Space Physics in Kiruna (67.86° N, 20.42° E; 400 m altitude). The OH imager records selected emission lines in the OH(3-1) band near 1500 nm to obtain intensity and temperature maps at around 87 km altitude. In addition, the OH imager registers infrared emissions coming from the O2 IR A-band airglow at 1268.7 nm in order to obtain O2 intensity maps at a slightly higher altitude, around 94 km. This technique allows the tracing of wave disturbances in both horizontal and vertical domains in the mesopause region. Validation and comparison of the OH(3-1) rotational temperature with collocated lidar and Aura Microwave Limb Sounder (MLS) satellite temperatures are performed. The first scientific results obtained from the OH imager for the first winter season (2022–2023) are discussed.

Inversion of "O" _"2" " 1.27 μm" nightglow emissions: A climatological analysis using satellite limb-viewed spectra and harmonic analysis method

Inversion of "O" _"2" " 1.27 μm" nightglow emissions: A climatological analysis using satellite limb-viewed spectra and harmonic analysis method

Nocturnal thermospheric neutral wind and temperature measurement using a Fabry-Perot Interferometer: First results from an equatorial Indian station

Results on first systematic measurements of nocturnal thermospheric neutral winds and temperature using a Fabry-Perot Interferometer (FPI) from Trivandrum (8.5°N, 77°E, 0.5° dip latitude), an Indian station close to the geomagnetic equator, are presented. These measurements were made during the low solar activity period of June 2017 to April 2018. The OI 6300 Å thermospheric nightglow emission has been used as the tracer. Using these measurements, nocturnal variability of monthly mean temperature and wind have been obtained. These mean temperature and wind are compared with the predictions of the neutral atmospheric models, NRL (USA)’s Mass Spectrometer and Incoherent Scatter Radar 2000 (MSISE-00) and Horizontal Wind Model 2014 (HWM14). The FPI temperatures reveal an overall decreasing trend beginning post-sunset till the end of observation for all months. The lowest monthly mean temperature was estimated to be 601°K in the pre-morning hours in March 2018, which is about 45°K less than the corresponding model value. There are overall agreements between the FPI and the MSIS model temperatures. Although, in some months,measurements exhibit large deviations from the model predictions indicating its limitations as applied to the equatorial thermosphere. The mean meridional wind is found to agree with the predictions of HWM14 model remarkably well and also corroborates with the wind retrieved from the collocated ionosonde measurements reported earlier from Trivandrum. Meridional wind during solsticial months clearly exhibits signatures of inter-hemispheric flow. The mean zonal wind, however, deviates significantly from the model predictions on most of the occasions. The mean zonal wind is found to be less compared to that reported elsewhere in the African and Brazillian longitude sectors. It is ascribed to be due to the relatively less pre-reversal enhancement (PRE) and the consequent strong ion-drag over Trivandrum. Further, it appears that PRE is relatively stronger in winter solstice than in the equinoxes in agreement with an earlier investigation carried out from Trivandrum.

Night light polarization: Modeling and observations of light pollution in the presence of aerosols and background skylight or airglow

We introduce a new polarized radiative transfer model able to compute the polarization measured by a virtual instrument in a given nocturnal environment recreating real world conditions (1-dimensional atmospheric and aerosol profiles, 3-dimensional light sources with complex and widespread geometries, terrain obstructions). Initially developed to address the issue of aurorae and nightglow polarization, the model has potential applications in the context of light pollution, or aerosols and air pollution measurements in night time conditions. We provide the physical assumptions behind the model together with the main points regarding its numerical implementation, together with the inherent constraints and liberties it brings. The model, based on single scattering equations in the atmosphere, is first tested on a few simple configurations to assess the effect of several key parameters in controlled environments. The model outputs are then compared to field measurements obtained in four wavelengths at mid-latitude in a dark valley of the French Alps, 20 km away from the closest city. In this context where the nightglow emissions are supposedly stationary and widespread, a convincing fit between the model predictions and observations is found in three wavelengths. This confrontation of ground-based records with our modeling constitutes a proof of concept for the investigation of our polarized environment in nocturnal conditions, in the presence of localized and/or extended sources. It calls for further investigations. In particular we discuss the future need for inter-calibrating the sources and the polarimeter in order to optimally extract the information contained in such measurements, and how multiple-scattering (not implemented in the present study) could impact our observations and their interpretation.

Studies of atmospheric waves by ground-based observations of OH(3–1) emission and rotational temperature using PRL airglow InfraRed spectrograph (PAIRS)

We present a grating based spectrograph, Physical Research laboratory (PRL) Airglow InfraRed Spectrograph (PAIRS) which provides rotationally resolved OH(3–1) band nightglow emissions in the 1.5–1.6 μm spectral region at a resolution of 0.001 μm @ 1.532 μm that enables estimation of corresponding OH rotational temperatures from Thaltej Campus, Ahmedabad (23.0° N, 72.6° E) in India. The data cadence of PAIRS is 100 s providing an opportunity to study small timescale oscillations present at the OH emission altitude. In a first case study we present a detailed characterization of terdiurnal, large- and small-timescale gravity wave (GW) induced oscillations applying Krassovsky's method to nocturnal variations of the OH(3–1) brightness and its rotational temperatures measured with PAIRS. The amplitudes, phases, Krassovsky parameters, and vertical wavelengths of the terdiurnal tide and GWs are calculated using a least square fitting and wavelet analysis techniques. We also demonstrate capabilities of PAIRS in estimating the characteristics of GWs with periodicities smaller than 30 min, which showed upward wave propagation. The PAIRS derived rotational temperatures for 28 nights of observations for the month of December 2020 show good correspondence with the temperatures obtained from SABER for the passes close to the observational station. PAIRS has been automated for carrying out observations in an unattended mode and data analysis schemes have been developed for the derivation of mesospheric temperatures. Thus, PAIRS provides an opportunity for the detailed investigation of tides and GWs, in general, and short timescale nocturnal MLT dynamics, in particular.

Transition Energies and Line Oscillator Strengths of the C 2Π(0)-X 2Π(0–6) Absorption Bands of Nitric Oxide. A Theoretical Study

Theoretical absorption oscillator strengths and wavelengths for rotational transitions of the C 2Π(v′ = 0)-X 2Π(v″) bands with v″ = 0–6 of nitric oxide are reported. The Molecular Quantum Defect Orbital method has been used in the calculations and the known interaction between the C 2Π(v = 0) Rydberg and the B 2Π (v = 7) valence states has been dealt with through an appropriate rovibronic energy matrix. We hope that the reported data may be useful in the analysis of the observed ultraviolet nightglow emission from nitric oxide in the upper atmospheres of Earth, Venus, and Mars.

Latitudinal variations in the nocturnal behaviour of OI 630 nm airglow emissions and their relationship with equatorial electrodynamics

Airglow emissions from the thermosphere act as tracers of the behaviour of the upper atmosphere. OI 630 nm nightglow emissions that originate from an altitude of around 250 km in the thermosphere have been investigated using a large field-of-view ground-based optical spectrograph from Mt. Abu (24.6°N, 72.7°E, 19°N Mag.), a low-latitudinal location in India. The latitudinal movement of the crest of the equatorial ionization anomaly (EIA) in both poleward in the evening and equatorward in the night has been reported using the OI 630 nm nightglow emissions. The EIA crest is found to shift away from the equator after the sunset, which has been shown to be directly related to the strength of the twilighttime equatorial electrodynamics. Later in the night, after 20 LT, a clear movement of the crest back towards the equator, known as the reversal of EIA, has been observed. The speeds of the EIA reversals for forty nights in the years 2014 and 2015 have been obtained and are found to be in the range of 10–55 ms−1. As the global equatorial electric fields (E) are irrotational in nature (∇×E=0), simultaneous variations in the daytime electrojet strength over Jicamarca in the American sector have been compared with the nighttime reversal speeds of the EIA over the Indian sector, which show a remarkable relationship with each other. Thus, it is hereby demonstrated that the reversal in EIA as inferred by the OI 630 nm nightglow emissions in our measurements is due to the westward equatorial electric field. It is hereby proposed that the reversal speed derived from optical nightglow measurements can serve as a proxy for the determination of westward electric field over equator for that longitude sector.

Investigations of equatorial plasma bubbles as observed in the OI 630 nm nightglow emissions over off-equatorial and low-latitudinal locations over Indian longitudes

Equatorial plasma bubbles (EPBs), generated over the dip-equator during the sunset time, get mapped over to the low-latitudes through the geomagnetic field lines and contribute to structures of different scales in the nighttime thermosphere-ionosphere system. In the present study, the EPBs are observed in the OI 630 nm nightglow emissions over Mt. Abu and Kolhapur using a High Throughput Imaging Echelle spectrograph (HiTIES) and All-Sky Imager (ASI), respectively. Similar periodicities obtained in these measurements consistently corroborate the presence of the EPBs at both these locations. The strength of the Pre-Reversal Enhancement (PRE) in the zonal electric field has been investigated using the ionosonde data over Trivandrum, a dip-equatorial location. The strength of PRE decides the latitudinal extent of the EPBs. The eastward movement of the EPBs has been estimated to be in the range of 190–90 ms−1, decreasing in magnitude from post-sunset to midnight. The wave number analysis carried out using the observed OI 630 nm emissions in the zonal direction has resulted in a contrasting behaviour during the presence/absence of the EPBs. Based on the analysis of around 1300 images of data, it is revealed that the scale sizes in the range of 250–300 km are omnipresent, whereas, shorter scale sizes (50–250 km) are present only during the presence of EPBs. It is inferred that these shorter scale size gravity waves played a significant role in the seeding the perturbation of the EPBs.

Parker Solar Probe Imaging of the Night Side of Venus.

We present images of Venus from the Wide‐Field Imager for Parker Solar Probe (WISPR) telescope on board the Parker Solar Probe (PSP) spacecraft, obtained during PSP's third and fourth flybys of Venus on 2020 July 11 and 2021 February 20, respectively. Thermal emission from the surface is observed on the night side, representing the shortest wavelength observations of this emission ever, the first detection of the Venusian surface by an optical telescope observing below 0.8 μm. Consistent with previous observations at 1 μm, the cooler highland areas are fainter than the surrounding lowlands. The irradiances measured by WISPR are consistent with model predictions assuming a surface temperature of T = 735 K. In addition to the thermal emission, the WISPR images also show bright nightglow emission at the limb, and we compare the WISPR intensities with previous spectroscopic measurements of the molecular oxygen nightglow lines from Venus Express.

Modeling and causative mechanism of OI 630.0 nm nightglow emission over Cachoeira Paulista (22.7oS, 45oW) – Brazil: Seasonal and temporal variability

The seasonal and temporal variability of the OI 630.0 nm nightglow emissions were observed over Cachoeira Paulista (22.7 o S, 45 o W; dip latitude −35°) in Brazil by multichannel photometer during 2014 and 2015. The temporal variation of the OI 630.0 nm nightglow intensity shows a peak during post-midnight hours ( ∼ 25 h 00 LT) during the summer. During autumn, this peak is shifted towards pre-midnight at ∼ 22 h 00 LT. It is noticed that this peak again shifted towards post-midnight at 26 h30 LT and 25 h30 LT during winter and spring, respectively. The intensity increases by a factor of 2–4 in the summer than that observed in other three seasons. The modelling of the nightglow measurements in 2015 is carried out by calculating the excitation rate, emission rate and intensity of OI 630.0 nm nightglow emission in the upper atmosphere at low latitudes. Our calculation suggests that the dissociative recombination of O 2 + with electrons is the main source for the OI 630.0 nm nightglow emission. We report that the model intensities are in good agreement with the measurements at Cachoeira Paulista for all four seasons and the model reproduces all features of peak intensities very well.

Retrieval of mesospheric sodium from OSIRIS nightglow measurements and comparison to ground-based Lidar measurements

The understanding of the excitation mechanism of the sodium D-line nightglow emission is important for many investigations of atomic sodium in the upper mesosphere region. In 1939, Sidney Chapman proposed a first scheme of the chemical reactions involving sodium and ozone to explain the yellow sodium line doublet in the terrestrial nightglow. Later, it became clear that this mechanism could not explain the observed variability in the Na D-line ratio. Hence, Slanger et al. (2005) suggested a modified Chapman mechanism. However, it is well accepted that there is still a parameter that is not well quantified, i.e., the branching ratio fA that defines how many sodium atoms are produced (via the reaction Na + O3) in the excited Na(P2J) state. Here, we retrieve sodium profiles in the mesosphere region from limb measurements carried out with the OSIRIS instrument on the Odin satellite between 2002 and until recently. These profiles are compared to profiles obtained from ground-based Lidar measurements. Until 2010, the Lidar was located in Fort Collins, Colorado at 40.5° N and 105.0° W and was then moved to Logan, Utah at 41.8° N and 111.2° W. In this study, we found 20 nights with measurements suitable for comparison. By adjusting the branching ratio in the retrieval algorithm until the Lidar Na-profile and the satellite Na-profile agree best and combining the three different approaches for the comparison we propose a value of the branching ratio of: 0.064±0.028.

Planetary‐Scale Wave Impacts on the Venusian Upper Mesosphere and Lower Thermosphere

AbstractThis work examines the planetary wave‐induced variability within the upper mesosphere/lower thermosphere of Venus by utilizing the Venus Thermospheric General Circulation Model (VTGCM). Rossby and Kelvin wave perturbations are driven by variations in the geopotential height of the VTGCM lower boundary (∼70 km). A suite of simulations was conducted to examine the impact of the individual and combined waves propagating from two different lower boundary conditions (uniform and varying). The Kelvin wave is the more dominant wave which produces the most variability. The combination of the Kelvin and Rossby waves provides a maximum temperature amplitude of 13 K at 92 km and maximum zonal wind amplitude of 23 m/s at 102 km. The combined waves overall are able to propagate up to 125 km. Most of the variation within the temperature, winds, and composition occurs between 70 and 110 km. The varying lower boundary increases the magnitude of the wave deposition and atmospheric responses, but weakly changes the propagation altitude. The thermal variation due to the planetary waves does not reproduce most observed variations. The simulated O2 IR nightglow emission is sensitive to the waves with respect to intensity and local time, but lacks latitudinal variation. The integrated intensity ranges from 1.2 MR to 1.65 MR and the local time ranges from 0.33 local time to 23.6 local time. Overall, planetary waves do affect the atmospheric structure, but there are still large observed variations that planetary waves alone cannot explain (i.e., thermal structure).

First Direct Observational Evidence for Secondary Gravity Waves Generated by Mountain Waves Over the Andes

AbstractA mountain wave with a significant brightness temperature amplitude and ~500 km horizontal wavelength was observed over the Andes on 24–25 July 2017 in Atmospheric Infrared Sounder (AIRS)/Aqua satellite data. In the Modern‐Era Retrospective Analysis for Research and Applications, version 2 (MERRA‐2), reanalysis data, the intense eastward wind flowed over the Andes. Visible/Infrared Imaging Radiometer Suite (VIIRS)/Suomi‐NPP (National Polar‐orbiting Partnership) did not detect the mountain waves; however, it observed concentric ring‐like waves in the nightglow emissions at ~87 km with ~100 km wavelengths on the same night over and leeward of the Southern Andes. A ray tracing analysis showed that the mountain waves propagated to the east of the Andes, where concentric ring‐like waves appeared above a region of mountain wave breaking. Therefore, the concentric ring‐like waves were likely secondary waves generated by momentum deposition that accompanied mountain wave breaking. These results provide the first direct evidence for secondary gravity waves generated by momentum deposition.

Early Morning Equatorial Ionization Anomaly From GOLD Observations

AbstractDuring geomagnetically quiet and solar minimum conditions, spatial variations of the early morning thermosphere‐ionosphere (TI) system are expected to be mainly governed by wave dynamics. To study the postmidnight dynamical coupling, we investigated the early morning equatorial ionization anomaly (EIA) using Global‐scale Observations of the Limb and Disk (GOLD) measurements of OI‐135.6 nm nightglow emission and global navigation satellite system (GNSS)‐based total electron content (TEC) maps. The EIA structures in the OI‐135.6 nm emission over the American landmass resemble, spatially and temporally, those observed in the GNSS‐TEC maps. The early morning EIA (EM‐EIA) crests are well separated in latitude and mostly located over the middle of South America during October–November. In February–April the crests are less separated in latitude and predominantly located over the west coast sector of South America. Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension (WACCMX) simulations with constant solar minimum and quiet‐geomagnetic conditions show that EM‐EIA can occur globally and shows properties similar to longitudinal Wave 4 pattern. Thus, we propose that EM‐EIA is driven by dynamical changes associated with the lower atmospheric waves.

Photochemical modeling of molecular and atomic oxygen based on multiple nightglow emissions measured in situ during the Energy Transfer in the Oxygen Nightglow rocket campaign

Abstract. Electronically excited states of molecular and atomic oxygen (six O2 and two O) were implemented in the proposed Multiple Airglow Chemistry (MAC) model as minor species coupled with each other as well as with the ground states of O2 and O to represent the photochemistry in the upper mesosphere and lower thermosphere (MLT) region. The MAC model combines chemical processes of well-known photochemical models related to identified O2 and O species and some additional processes. Concentrations of excited O2 and O species were retrieved using the MAC model on the basis of the multiple nightglow emissions measured in situ during the Energy Transfer in the Oxygen Nightglow (ETON) rocket campaign. The proposed retrieval procedure to obtain the concentrations of these minor species in the MLT region is implemented by avoiding a priori data sets. Unknown and poorly constrained reaction rates were tuned, and the reaction rates of the well-known models were updated with the MAC model by comparing in situ and evaluated emission profiles as well as in situ and retrieved O concentration profiles. As a result, precursors of O2 and O species responsible for the transitions considered in the MAC model are identified and validated.

Mean Zonal Drift Velocities of Plasma Bubbles Estimated from Keograms of Nightglow All-Sky Images from the Brazilian Sector

We present in this work a method for estimation of equatorial plasma bubble (EPB) mean zonal drift velocities using keograms generated from images of the OI 6300.0 nm nightglow emission collected from an equatorial station–Cariri (7.4° S, 36.5° W), and a mid-latitude station–Cachoeira Paulista (22.7° S, 45° W), both in the Brazilian sector. The mean zonal drift velocities were estimated for 239 events recorded from 2000 to 2003 in Cariri, and for 56 events recorded over Cachoeira Paulista from 1998 to 2000. It was found that EPB zonal drift velocities are smaller (≈60 ms−1) for events occurring later in the night compared to those occurring earlier (≈150 ms−1). The decreasing rate of the zonal drift velocity is ≈10 ms−1/h. We have also found that, in general, bubble events appearing first in the west-most region of the keograms are faster than those appearing first in the east-most region. Larger zonal drift velocities occur from 19 to 23 LT in a longitude range from −37° to −33°, which shows that the keogram method can be used to describe vertical gradients in the thermospheric wind, assuming that the EPBs drift eastward with the zonal wind. The method of velocity estimation using keograms compares favorably against the mosaic method developed by Arruda, D.C.S, 2005, but the standard deviation of the residuals for the zonal drift velocities from the two methods is not small (≈15 ms−1).

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.

Variations of the Nightglow 557.7 nm Emission Intensity during Solar Cycle 23

The results of photometric measurements of the intensity of 557.7 nm nightglow emission at a high geographical latitude of 63° N at the Yakutsk meridian (130° E) on days in 1997–2008 with low geomagnetic activity are presented. Statistical analysis shows that the long-term variations in the intensity of the green line of atomic oxygen are consistent with earlier observations at low and midlatitudes. The average intensity of the 557.7 nm emission for February and March had the largest values, ~400 and ~300 rayleighs, respectively, in the years of the maximum of solar cycle 23. This is likely determined by the growth in the concentration of atomic oxygen at the height of the green line emission upon an increase in solar activity according to the MSIS-90 empirical model. It is known that the green-line intensity may significantly vary at nighttime. Analysis of the coefficient of this emission variation shows that there is no close relationship between this parameter and solar activity.

Multiple Airglow Chemistry approach for atomic oxygen retrievals on the basis of in situ nightglow emissions

Electronically excited states of molecular and atomic oxygen (O2 and O) are coupled with each other as well as with the ground states of O2 and O in the Multiple Airglow Chemistry (MAC) model representing the oxygen airglow and the oxygen photochemistry in the upper Mesosphere and Lower Thermosphere region. The MAC model couples seven O2 and three O states and was developed on the basis of insitu measurements from the ETON (Energy Transfer in the Oxygen Nightglow) campaign employed to tune rate values of unknown or poorly constrained processes. The same rate values are applied in the MAC model verified and validated on the basis of the insitu measurements obtained during the WADIS-2 (WAve propagation and DISsipation in the middle atmosphere), the WAVE2000 (WAVes in airglow structures Experiment, 2000) and WAVE2004 campaigns. Data sets measured using devices aboard the WADIS-2 rocket are considered to be self-consistent because the MAC retrievals of a concentration profile of O in the ground state ([O(3P)]) can be based on these data sets only. The measuring sites of the insitu data sets from the WAVE2000 and WAVE2004 campaigns are collocated with those of remotely obtained data sets, and these data sets are combined for the MAC retrievals. O2 precursors responsible for the oxygen green line emission, emissions in the Atmospheric band and the Infrared Atmospheric band are identified and confirmed by calculations with the validated MAC model.