Airglow Measurements Research Articles

Science Highlights from the Kjell Henriksen Observatory on Svalbard

The Kjell Henriksen Observatory (KHO) is the world's largest optical observatory for auroral and airglow measurements, operated by the University Centre in Svalbard (UNIS). KHO is a unique site that lies underneath the dayside cusp, a funnel-shaped region where particles from the Sun can directly enter the Earth's upper atmosphere, including the ionosphere. Building on the pioneering observations of its predecessor --- the Auroral Station in Adventdalen, Svalbard --- KHO has played a pivotal role in advancing our understanding of phenomena in the polar atmosphere. The Auroral Station and KHO have amassed climatological measurements over Svalbard for an impressive 40-year period. KHO's diverse instrumentation, combined with other co-located optical and radar infrastructure and in-situ measurements from satellites and sounding rockets, has paved the way for impactful multi-instrument studies. Serving as an accessible testbed for instrument development, new types of instruments have recently been installed, both at KHO and on satellites. Beyond its scientific contributions, KHO has become an integral part of the Longyearbyen community, with students, visitors, and locals participating in tours and educational initiatives. This connection underscores KHO's multi-functional role, not only as a centre for excellent research but also as a vital hub for public outreach and engagement.

On the response of the mesopause region over an Indian Antarctic station Bharati to the geomagnetic storm of 23–24 March 2023

We report, in this work, the changes in the thermal structure of the mesosphere-lower thermosphere (MLT) region over an Indian Antarctic station Bharati (69.4° S, 76.2° E, CGM coordinates 75° S, 97° E) brought about by an intense geomagnetic storm of 23–24 March 2023 (Dst ∼ −155 nT). We use the temperature and OH airglow measurements of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard NASA's Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission satellite to compare the thermal field of the MLT region on these disturbed days with the neighbouring quietest days of 27–28 March. Such comparison reveals both warming and cooling in the MLT region associated with the storm. An extension of this comparative study in the latitude region located poleward of Bharati also shows similar behavior of the MLT region during this geomagnetic storm. Overall, this study reveals the maximum temperature enhancement of ∼39–43 K to occur at around 99 km, a significant warming of ∼4–43 K in 95–105 km, and a decrease of ∼12–16 K in 80–87 km. While the enhancement of temperature in 95–105 km appears to be a consequence of the auroral heating associated with this storm; we are unable to account for the cooling below based on existing theories. Present observation of the development of cooling underneath the region of temperature enhancement during the geomagnetic storm is rare and demands further investigation.

Hydroxyl airglow observations for investigating atmospheric dynamics: results and challenges

Abstract. Measurements of hydroxyl (OH*) airglow intensity are a straightforward and cost-efficient method which allows the derivation of information about the climate and dynamics of the upper mesosphere/lower thermosphere (UMLT) on different spatiotemporal scales during darkness. Today, instrument components can be bought “off-the-shelf” and developments in detector technology allows operation without cooling, or at least without liquid nitrogen cooling, which is difficult to automate. This makes instruments compact and suitable for automated operation. Here, we briefly summarize why an OH* airglow layer exists, how atmospheric dynamics influence it and how temperature can be derived from OH* airglow measurements. Then, we provide an overview of the scientific results regarding atmospheric dynamics (mainly gravity waves (GWs) but also planetary waves (PWs) and infrasound) achieved with OH* airglow measurements. We focus on long-term ground-based OH* airglow measurements or airglow measurements using a network of ground-based instruments. The paper includes further results from global or near-global satellite-based OH* airglow measurements, which are of special importance for characterizing the OH* airglow layer. Additionally, the results from the very few available airborne case studies using OH* airglow instruments are summarized. Scientific and technical challenges for the next few years are described.

Some Results of Photometric Measurements of Ionospheric Artificial Airglow at 557.7 and 630 nm Lines of Atomic Oxygen Caused by High-Frequency Radio Emission of the SURA Facility during Development of Sporadic E Layer

The results of analysis of the experimental data collected on 5 September 2021 on 557.7 and 630 nm artificial airglow of the ionosphere induced by powerful HF radio waves at the SURA facility are presented. For optical measurements, a photometric suite located directly next to the SURA facility was used. Fast variations in the atmospheric emission intensity at 557.7 nm, 630 nm, and 391.4 nm with a three-channel photometer and spatial–temporal variations in the 557.7 nm with a CCD camera were measured. An ionospherically reflected pump wave and the stimulated electromagnetic emission (SEE) were recorded. Background ionospheric conditions were registered with ionosonde. For the first time, an increase in the 557.7 nm emission intensity induced by the SURA facility radiation was found concurrently with a partial blocking ionosphere in the F-region and suppression HF-induced phenomena in the F-region (the 630 nm airglow increase and SEE generation, powerful radio wave anomalous absorption) during the sporadic E-layer (Es) development. Additionally, we managed to obtain images showing moving spots of the SURA-induced 557.7 nm emission increased intensity at the Es layer heights.

Simplified Relations for the Martian Night-Time OH* Suitable for the Interpretation of Observations

Observations of excited hydroxyl (OH*) emissions are broadly used for inferring information about atmospheric dynamics and composition. We present several analytical approximations for characterizing the excited hydroxyl layer in the Martian atmosphere. They include the OH* number density at the maximum and the height of the peak, along with the relations for assessing different impacts on the OH* layer under night-time conditions. These characteristics are determined by the ambient temperature, atomic oxygen concentration, and their vertical gradients. The derived relations can be used for the analysis of airglow measurements and the interpretation of their variations.

Signature of the midnight temperature maximum in thermospheric oxygen airglow emissions: Results from the ship-borne airglow measurements from the Indian region

This paper discusses the results from the aeronomy experiment carried out using a multiwavelength photometer operated onboard Sagar Kanya ship from the Indian region, which covered a latitude region from 14.5 N to 2S (7° to −10° Dip latitudes) along the same longitude region (∼72-75E). It has been found that the thermospheric airglows, especially the OI 630.0 nm emission near to the geographic equator exhibits ‘Midnight Brightness’ on different days of observations. Though the magnitudes were found to be less, the OI 777.4 nm and OI 557.7 nm emissions also exhibited intensity variations on those days, indicating a common causative mechanism for the same. The simulation studies using a quasi-two dimensional ionospheric model, revealed that such an enhancement could be due to the F-region collapse associated with the Midnight Temperature Maximum (MTM) phenomenon.

On the relationship of energetic particle precipitation and mesopause temperature

Abstract. Energetic particle precipitation (EPP) has the potential to change the neutral atmospheric temperature in the mesopause region. However, recent results are inconsistent, leaving the mechanism and the actual effect still unresolved. In this study we have searched for electron precipitation events and investigated a possible correlation between D-region electron density enhancements and simultaneous neutral temperature changes. The rotational temperature of the excited hydroxyl (OH) molecules is retrieved from the infrared spectrum of the OH airglow. The electron density is monitored by the European Incoherent Scatter Scientific Association (EISCAT) Svalbard Radar. We use all available experiments from the International Polar Year (IPY) in 2007–2008 until February 2019. Particle precipitation events are characterized by rapid increases in electron density by a factor of 4 at an altitude range of 80–95 km, which overlaps with the nominal altitude of the infrared OH airglow layer. The OH airglow measurements and the electron density measurements are co-located. Six of the 10 analysed electron precipitation events are associated with a temperature decrease of 10–20 K. Four events were related to a temperature change of less than 10 K. We interpret the results in terms of the change in the chemical composition in the mesosphere. Due to EPP ionization the population of excited OH at the top of the airglow layer may decrease. As a consequence, the airglow peak height changes and the temperatures are probed at lower altitudes. The observed change in temperature thus depends on the behaviour of the vertical temperature profile within the airglow layer. This is in agreement with conclusions of earlier studies but is, for the first time, constructed from electron precipitation measurements as opposed to proxies. The EPP-related temperature change recovers very fast, typically within less than 60 min. We therefore further conclude that this type of EPP event reaching the mesopause region would only have a significant impact on the longer-term heat balance in the mesosphere if the lifetime of the precipitation was much longer than that of an EPP event (30–60 min) found in this study.

Data‐Driven Modeling of Atomic Oxygen Airglow over a Period of Three Solar Cycles

AbstractThe Earth's upper atmosphere is a dynamic environment that is continuously affected by space weather from above and atmospheric processes from below. An effective way to observe this interface region is the monitoring of airglow. Since the 1950s, airglow emissions have been systematically measured by ground‐based photometers in specific wavelength bands during the nighttime. The availability of the calibrated data from over 30 years of photometric airglow measurements at Abastumani in Georgia (41.75° N, 42.82° E), at wavelengths of 557.7 and 630.0 nm, enable us to investigate if a data‐driven model based on advanced machine learning techniques can be successfully employed for modeling airglow intensities. A regression task was performed using the time series of space weather indices and thermosphere‐ionosphere parameters. We have found that the developed data‐driven model has good consistency with the commonly used GLOW airglow model and also captures airglow variations caused by cycles of solar activity and changes of the seasons. This enables us to visualize the green and red airglow variations over a period of three solar cycles with a one‐hour time resolution.

What controls the luminosity of polar cap airglow patches?: Implication from airglow measurements in Eureka, Canada in comparison with SuperDARN convection pattern

Polar cap patches are known as islands of enhanced electron density in the polar cap F region ionosphere. To observe the airglow signature of polar cap patches continuously at a fixed point near the center of the MLAT/MLT coordinate system, we started operating an all-sky imager in Eureka, Canada since 2015, where the magnetic latitude is ~87°. By statistically analyzing the 630-nm airglow images from Eureka, it was identified that the luminosity of patches, which is proportional to the electron density in the F region, increases during specific UT interval from 16 to 22 UT. This outstanding UT variation of patch luminosity can be explained simply by the systematic shift of the terminator in the MLAT/MLT coordinate system due to the offset between the geographic and geomagnetic pole. That is, the spatial relationship between the dense source plasma in the sunlit area and the high-latitude convection system controls the UT variation. We also found that when the IMF By is positive, the number of polar cap patches was twice of that in the negative IMF By. By deriving average convection patterns from the archived SuperDARN map potential data, we confirmed that the configuration of plasma convection is more appropriate for patches to be transported toward the magnetic pole during the positive IMF By condition.

Dynamic Changes of the Ionospheric Artificial Airglow Region Caused by High-Power Radio Waves Based on a Joint Analysis of Night-Sky Snapshots in the 630 nm Line and Total Electron Content Variation Maps

We describe a method for joint analysis of the night-sky snapshots and total electron content (TEC) variation maps and present a dynamic spatiotemporal configuration of the TEC variation intensity in the ionospheric airglow region in the red line of atomic oxygen (λ = 630 nm) stimulated by high-power radio waves from the Sura facility. The measurements were performed on the 29th of August, 2016. Two-dimensional TEC variation maps were plotted according to a network of 30 GNSS stations located within a radius of 700 km from the Sura heater. It is shown that the region of the maximum brightness of the artificial ionospheric airglow spot is spatially localized in the region of the minimum intensity of TEC variations, while the region of the maximum intensity of TEC variations corresponds to the region of the minimum brightness of the artificial airglow spot. Quantitative estimates for a cavity with reduced electron density in the artificial airglow region, which forms after the Sura pump wave is switched on, vary in the range ΔNe/Ne ≈ 4–9%, where Ne is the electron density and ΔNe is its variation in the cavity. The proposed experimental technique eliminates the limitations associated with the need for a navigation satellite to flyby directly over the main lobe of the Sura antenna pattern, which significantly increases the chances of successful simultaneous measurements of TEC variations and artificial ionospheric airglow in the 630 nm line.

Semimonthly oscillation observed in the start times of equatorial plasma bubbles

Abstract. Using airglow data from an all-sky imager deployed at São João do Cariri (7.4∘ S, 36.5∘ W), the start times of equatorial plasma bubbles was studied in order to investigate the day-to-day variability of this phenomenon. Data from a period over 10 years were analyzed from 2000 to 2010. Semimonthly oscillations were clearly observed in the start times of plasma bubbles from OI6300 airglow images during this period of observation, and four case studies (September 2003, September–October 2005, November 2005 and January 2008) were chosen to show in detail this kind of modulation. Since the airglow measurements are not continuous in time, more than one cycle of oscillation in the start times of plasma bubbles cannot be observed from these data. Thus, data from a digisonde at São Luís (2.6∘ S, 44.2∘ W) in November 2005 were used to corroborate the results. Technical/climate issues did not allow one to observe the semimonthly oscillations simultaneously by the two instruments, but from October to November 2005 there was a predominance of this oscillation in the start times of the irregularities over Brazil. Besides, statistical analysis for the data in the whole period of observation has shown that the lunar tide, which has semimonthly variability, is likely the main forcing for the semimonthly oscillation in the start times of equatorial plasma bubbles. The presence of this oscillation can contribute to the day-to-day variability of equatorial plasma bubbles.

Modelled effects of temperature gradients and waves on the hydroxyl rotational distribution in ground-based airglow measurements

Abstract. Spectroscopy of the hydroxyl (OH) airglow has been a commonly used way to remotely sense temperatures in the mesopause region for many decades. This technique relies on the OH rotational state populations to be thermalized through collisions with the surrounding gas into a Boltzmann distribution characterized by the local temperature. However, deviations of the rotational populations from a Boltzmann distribution characterized by a single temperature have been observed and attributed to an incomplete thermalization of the OH from its initial, non-thermodynamic-equilibrium distribution. Here we address an additional cause for the apparent amount of excess population in the higher rotational levels of the OH airglow brought about by integrating these OH emissions through vertical gradients in the atmospheric temperature. We find that up to 40 % of the apparent excess population, currently attributed to incomplete thermalization, can be due to the vertical temperature gradients created by waves. Additionally, we find that the populations of the different upper vibrational levels are affected differently. These effects need to be taken into account in order to assess the true extent of non-thermodynamic-equilibrium effects on the OH rotational populations.

Global nighttime atomic oxygen abundances from GOMOS hydroxyl airglow measurements in the mesopause region

Abstract. This paper presents a new dataset of nighttime atomic oxygen density [O], derived from OH(8–4) ro-vibrational band emissions, using a non-local thermal equilibrium model, with the aim of offering new insight into the atomic oxygen abundances in the mesopause region. The dataset is derived from the level-1 atmospheric background measurements observed by the Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument aboard Envisat, with the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) measurements for the atmospheric background. Raw data are reprocessed into monthly zonal mean values in 10∘ latitude bins with a fixed altitude grid of 3 km. The dataset spans from 70∘ S to 70∘ N in latitude and from 80 to 100 km in altitude, covering a time period from May 2002 to December 2011 at local times from 22:00 to 00:00 LT. The atomic oxygen density peaks at about 95 km and the highest values are in the range of 3–8 × 1011 atoms cm−3, depending on latitude and season. There is a rapid decrease of [O] below the peak. The annual oscillation (AO), semiannual oscillation (SAO) and the solar cycle impact are distinguished from the [O] longtime series variations. This new GOMOS [O] dataset conforms to other published datasets and is consistent with the [O] datasets obtained from the Scanning Imaging Absorption Spectrometer for Atmospheric CHartographY (SCIAMACHY) OH airglow measurements within about ±20 %.

Consistent Nighttime Atomic Oxygen Concentrations From O2A‐band, O(1S) Green‐Line, and OH Airglow Measurements as Performed by SCIAMACHY

AbstractA new atomic oxygen data set was derived from nighttime SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) O2A‐band measurements. It is compared to atomic oxygen obtained from SCIAMACHY O(1S) green‐line and OH(9‐6)‐band measurements. The three data sets are considered independent of radiometry and, to some extent, methodology. A detailed comparison of atomic oxygen retrieved from these three nightglow measurements is reported for the first time. The agreement of absolute values within 15% supports the current understanding of the photochemistry of the three atomic oxygen proxies involved. As an alternative approach, the O2A‐band model recently proposed by Kalogerakis (2019) is used as well. It is striking that the SCIAMACHY data sets using different atomic oxygen proxies and mostly independent methodology agree much better with each other than with SABER data.

AtmoCube A1: airglow measurements in the mesosphere and lower thermosphere by spatial heterodyne interferometry

The Institute for Atmospheric and Environmental Research at the University of Wuppertal and the Institute of Energy and Climate Research Stratosphere at Research Center Juelich developed a CubeSat payload for atmospheric research. The payload consists of a small interferometer for the observation of airglow near 762 nm. The line intensities of the oxygen A-band are used to derive temperatures in the mesosphere and lower thermosphere region. The temperature data will be used to analyze dynamical wave structures in the atmosphere. The interferometer technology chosen to measure the ro-vibrational structure of the O2 atmospheric band near 762 nm is a spatial heterodyne interferometer originally proposed by Connes in 1958. It can be designed to deliver extraordinary spectral resolution to resolve individual emission lines. The utilization of a two-dimensional imaging detector allows for recording interferograms at adjacent locations simultaneously. Integrated in a six-unit CubeSat, the instrument is designed for limb sounding of the atmosphere. The agility of a CubeSat will be used to sweep the line-of-sight through specific regions of interest to derive a three-dimensional image of an atmospheric volume using tomographic reconstruction techniques.

Comparison of Retrieval Methods for Neutral Wind Based on Airglow Measurements by a Ground-based Fabry-Perot Interferometer

利用半径法、完整傅里叶级数描述法和非线性回归法分别对安装在河北省境内国家天文台兴隆园区（40.2°N，117.4°E）的Fabry-Perot干涉仪（FPI）获得的地基中高层大气气辉观测数据进行风速反演.反演结果表明，半径法、完整傅里叶级数描述法和非线性回归法均能很好地反演风速，在误差范围内反演结果存在很好的一致性.相对于半径法和完整傅里叶级数描述法，非线性回归方法更完整地利用了观测数据信息，反演结果可信度较高.

Determination of gravity wave parameters in the airglow combining photometer and imager data

Abstract. Mesospheric airglow measurements of two or three layers were used to characterize both vertical and horizontal parameters of gravity waves. The data set was acquired coincidentally from a multi-channel filter (Multi-3) photometer and an all-sky imager located at São João do Cariri (7.4∘ S, 36.5∘ W) in the equatorial region from 2001 to 2007. Using a least-square fitting and wavelet analysis technique, the phase and amplitude of each observed wave were determined, as well as the amplitude growth. Using the dispersion relation of gravity waves, the vertical and horizontal wavelengths were estimated and compared to the horizontal wavelength obtained from the keogram analysis of the images observed by an all-sky imager. The results show that both horizontal and vertical wavelengths, obtained from the dispersion relation and keogram analysis, agree very well for the waves observed on the nights of 14 October and 18 December 2006. The determined parameters showed that the observed wave on the night of 18 December 2006 had a period of ∼43.8±2.19 min, with the horizontal wavelength of 235.66 ± 11.78 km having a downward phase propagation, whereas that of 14 October 2006 propagated with a period of ∼36.00±1.80 min with a horizontal wavelength of ∼195±9.80 km, and with an upward phase propagation. The observation of a wave taken by a photometer and an all-sky imager allowed us to conclude that the same wave could be observed by both instruments, permitting the investigation of the two-dimensional wave parameter. Keywords. Atmospheric composition and structure (airglow and aurora) – electromagnetics (wave propagation) – history of geophysics (atmospheric sciences)

Multi-instrumented observations of the equatorial F-region during June solstice: large-scale wave structures and spread-F

Typical equatorial spread-F events are often said to occur during post-sunset, equinox conditions in most longitude sectors. Recent studies, however, have found an unexpected high occurrence of ionospheric F-region irregularities during June solstice, when conditions are believed to be unfavorable for the development of plasma instabilities responsible for equatorial spread-F (ESF). This study reports new results of a multi-instrumented investigation with the objective to better specify the occurrence of these atypical June solstice ESF in the American sector and better understand the conditions prior to their development. We present the first observations of June solstice ESF events over the Jicamarca Radio Observatory (11.95° S, 76.87° W, ∼ 1° dip latitude) made by a 14-panel version of the Advanced Modular Incoherent Scatter Radar system (AMISR-14). The observations were made between July 11 and August 4, 2016, under low solar flux conditions and in conjunction with dual-frequency GPS, airglow, and digisonde measurements. We found echoes occurring in the pre-, post-, and both pre- and post-midnight sectors. While at least some of these June solstice ESF events could have been attributed to disturbed electric fields, a few events also occurred during geomagnetically quiet conditions. The late appearance (22:00 LT or later) of three of the observed events, during clear-sky nights, provided a unique opportunity to investigate the equatorial bottomside F-region conditions, prior to ESF, using nighttime airglow measurements. We found that the airglow measurements (630 nm) made by a collocated all-sky camera show the occurrence of ionospheric bottomside F-region perturbations prior to the detection of ESF echoes in all three nights. The airglow fluctuations appear as early as 1 hour prior to radar echoes, grow in amplitude, and then coincide with ESF structures observed by AMISR-14 and GPS TEC measurements. They also show some of the features of the so-called large-scale wave structures (LSWS) that have been detected, previously, using other types of observations and have been suggested to be precursors of ESF. The bottomside fluctuations have zonal spacings between 300 and 500 km, are aligned with the magnetic meridian, and extend at least a few degrees in magnetic latitude.

Aeronomy of the Venus Upper Atmosphere

We present aeronomical observations collected using remote sensing instruments on board Venus Express, complemented with ground-based observations and numerical modeling. They are mostly based on VIRTIS and SPICAV measurements of airglow obtained in the nadir mode and at the limb above 90 km. They complement our understanding of the behavior of Venus’ upper atmosphere that was largely based on Pioneer Venus observations mostly performed over thirty years earlier. Following a summary of recent spectral data from the EUV to the infrared, we examine how these observations have improved our knowledge of the composition, thermal structure, dynamics and transport of the Venus upper atmosphere. We then synthesize progress in three-dimensional modeling of the upper atmosphere which is largely based on global mapping and observations of time variations of the nitric oxide and O2 nightglow emissions. Processes controlling the escape flux of atoms to space are described. Results based on the VeRA radio propagation experiment are summarized and compared to ionospheric measurements collected during earlier space missions. Finally, we point out some unsolved and open questions generated by these recent datasets and model comparisons.

Mesospheric OH layer altitude at midlatitudes: variability over the Sierra Nevada Observatory in Granada, Spain (37° N, 3° W)

Abstract. The mesospheric OH layer varies on several timescales, primarily driven by variations in atomic oxygen, temperature, density and transport (advection). Vibrationally excited OH airglow intensity, rotational temperature and altitude are closely interrelated and thus accompany each other through these changes. A correct interpretation of the OH layer variability from airglow measurements requires the study of the three variables simultaneously. Ground-based instruments measure excited OH intensities and temperatures with high temporal resolution, but they do not generally observe altitude directly. Information on the layer height is crucial in order to identify the sources of its variability and the causes of discrepancies in measurements and models. We have used SABER space-based 2002–2015 data to infer an empirical function for predicting the altitude of the layer at midlatitudes from ground-based measurements of OH intensity and rotational temperature. In the course of the analysis, we found that the SABER altitude (weighted by the OH volume emission rate) at midlatitudes decreases at a rate of 40 m decade−1, accompanying an increase of 0.7 % decade−1 in OH intensity and a decrease of 0.6 K decade−1 in OH equivalent temperature. SABER OH altitude barely changes with the solar cycle, whereas OH intensity and temperature vary by 7.8 % per 100 s.f.u. and 3.9 K per 100 s.f.u., respectively. For application of the empirical function to Sierra Nevada Observatory SATI data, we have calculated OH intensity and temperature SATI-to-SABER transfer functions, which point to relative instrumental drifts of −1.3 % yr−1 and 0.8 K yr−1, respectively, and a temperature bias of 5.6 K. The SATI predicted altitude using the empirical function shows significant short-term variability caused by overlapping waves, which often produce changes of more than 3–4 km in a few hours, going along with 100 % and 40 K changes in intensity and temperature, respectively. SATI OH layer wave effects are smallest in summer and largest around New Year's Day. Moreover, those waves vary significantly from day to day. Our estimations suggest that peak-to-peak OH nocturnal variability, mainly due to wave variability, changes within 60 days at least 0.8 km for altitude in autumn, 45 % for intensity in early winter and 6 K for temperature in midwinter. Plausible upper limit ranges of those variabilities are 0.3–0.9 km, 40–55 % and 4–7 K, with the exact values depending on the season.