Airglow Measurements Research Articles

Results from the intercalibration of optical low light calibration sources 2011

Abstract. Following the 38th Annual European Meeting on Atmospheric Studies by Optical Methods in Siuntio in Finland, an intercalibration workshop for optical low light calibration sources was held in Sodankylä, Finland. The main purpose of this workshop was to provide a comparable scale for absolute measurements of aurora and airglow. All sources brought to the intercalibration workshop were compared to the Fritz Peak reference source using the Lindau Calibration Photometer built by Wilhelm Barke and Hans Lauche in 1984. The results were compared to several earlier intercalibration workshops. It was found that most sources were fairly stable over time, with errors in the range of 5–25%. To further validate the results, two sources were also intercalibrated at UNIS, Longyearbyen, Svalbard. Preliminary analysis indicates agreement with the intercalibration in Sodankylä within about 15–25%.

Partially light-controlled imager based on liquid crystal plate and image intensifier for aurora and airglow measurement

In order to obtain information both of aurora and airglow in one image by the same detector, a PLCI based on liquid crystal plate LCP and super second-generation image intensifier SSGII is proposed in this research. The detection thresholds of the CCD for aurora and airglow are calculated. For the detectable illumination range of 10(4)-10(-2) lx, the corresponding electron count is 1.57×10(5) - 0.2 for every pixel of CCD. The structure and work principle of the PLCI are described. An LC is introduced in the front of CCD to decrease the intensities of aurora in overexposure areas by means of controlling transmittances pixel by pixel, while an image intensifier is set between the LC and CCD to increase the intensity of the weak airglow. The modulation transfer function MTF of this system is calculated as 0.391 at a Nyquist frequency of 15 lp/mm. The curve of transmittance with regard to gray level for the LC is obtained by calibration experiment. Based on the design principle, the prototype is made and used to take photos of objects under strong light greater than 2×10(5) lx. The clear details of [symbols: see text] presented in the image indicate that the PLCI can greatly improve the imaging quality. The theoretical calculations and experiment results prove that this device can extend the dynamic range and it provides a more effective method for upper atmospheric wind measurement.

Estimating the electron energy distribution during ionospheric modification from spectrographic airglow measurements

The electron energy distribution during an Fregion ionospheric modification experiment at the HAARP facility near Gakona, Alaska, is inferred from spectrographic airglow emission data. Emission lines at 630.0, 557.7, and 844.6 nm are considered along with the absence of detectable emissions at 427.8 nm. Estimating the electron energy distribution function from the airglow data is a problem in classical linear inverse theory. We describe an augmented version of the method of Backus and Gilbert which we use to invert the data. The method optimizes the model resolution, the precision of the mapping between the actual electron energy distribution and its estimate. Here, the method has also been augmented so as to limit the model prediction error. Model estimates of the suprathermal electron energy distribution versus energy and altitude are incorporated in the inverse problem formulation as representer functions. Our methodology indicates a heater‐induced electron energy distribution with a broad peak near 5 eV that decreases approximately exponentially by 30 dB between 5–50 eV.

First observation of upper mesospheric semi annual oscillations using ground based airglow measurements from Indian low latitudes

We summarize two years of Mesosphere Lower Thermosphere Photometer (MLTP) operation of mesospheric OH and O2 emission monitoring. The deduced mesospheric OH and O2 temperatures show large variability. Nightly temperature variations over Gadanki (13.5°N, 79.2°E) are dominated by the short period wave features, while tidal amplitudes are relatively small. Our measurements are the first to report a long period seasonal variation at two upper mesospheric altitudes simultaneously over the Indian sector. Our observations reveal the presence of a dominant semi-annual oscillation (∼6months periodicity) together with a shorter period (∼2.5months periodicity) oscillation in both OH and O2 data.

Continuous ground-based multiwavelength airglow measurements

[1] A new spectrograph instrument, called the Continuous High-resolution Instrument for Multiwavelength Echelle Spectroscopy (CHIMES), has been designed to make simultaneous and spatially overlapping ground-based measurements of the green line and red line airglow emissions (5577 A and 6300 A) continuously, 24 hours-a-day. The spectrograph uses a 50 mm long, 50 μm wide slit, and varies the exposure time at different times of day (daytime, twilight, and nighttime), from 2 s in daytime to 10 min at night. It utilizes an Echelle grating to achieve dispersion of 0.05 A/pixel at 5577 A. Daytime 6300 A and 5577 A airglow from this instrument are extracted by comparing the measured spectra to direct solar spectra and extracting small increases in flux in the Fraunhofer absorption lines at those wavelengths, after compensating for the Ring effect contribution. We present the first ground-based measurements of the daytime 5577 A airglow, as well as example measurements of daytime, twilight, and nighttime airglow signatures.

Simultaneous mesosphere-thermosphere-ionosphere parameter measurements over Gadanki (13.5°N, 79.2°E): First results

[1] We report first simultaneous airglow, lidar, and total electron content measurements in the mesosphere-thermosphere-ionosphere system behavior from Gadanki (13.5°N, 79.2°E). The observed variability in mesospheric temperatures and 630 nm thermospheric emission intensity shows large variations from one night to another with clear upward propagating waves at mesospheric altitudes. The deduced mesospheric temperatures compare well with Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER)–derived temperatures, while the variability agrees well with lidar temperatures (on the night of simultaneous observations). The 630.0 nm thermospheric emission intensity and GPS-total electron content data exhibit occurrence of plasma depletions on the nights of 22–23 October and 22–23 May 2009, while no depletions are noted on the nearby nights of 23–24 October and 21–22 May 2009. These first simultaneous data reveal strong gravity-wave growth at upper mesospheric altitudes on the nights when plasma depletions were noted.

Simultaneous Rayleigh lidar and airglow measurements of middle atmospheric waves over low latitudes in India

We utilize simultaneous Rayleigh lidar and mesospheric OH and O2 airglow measurements to identify the dominant and propagating waves within 40–95km altitude regions over a low latitude station Gadanki (13.8°N, 79.2°E). It is found that waves with 0.4–0.6h periodicity are common throughout the altitude range of 40–95km with significant amplitudes. The ground based temperature measurements with lidar and airglow monitoring are found to compare well with SABER data. With simultaneous Rayleigh lidar (temperature) and mesospheric airglow (emission intensity and temperature) measurements, we estimate the amplitude growth and Krassovsky parameters to characterize the propagation and dissipation of these upward propagating waves.

Simulation of the behavior of excited gaseous components in the atmosphere of the Earth: Hot oxygen

The existence of so-called hot oxygen in the atmosphere is substantiated by optical measurements of airglow at high altitudes. According to these observations, nonthermal oxygen concentration is maximum at an altitude of about 550 km, and its temperature is ∼4000 K. The presence of these atoms in the thermosphere causes changes in the thermodynamic conditions in the upper atmosphere of the Earth. In this work, we calculated the global distributions of hot oxygen concentrations and temperature using the Global Self-Consistent Model of Thermosphere, Ionosphere, and Protonosphere of the Earth (GSM TIP) taking into account the main photochemical and dynamic processes. Calculations were performed for moderate solar and geomagnetic activity and winter conditions of January, 2003. The hot oxygen maximum was located in latitude 60° South and at longitude 300° at 24 UT, and its temperature was ∼1500 K. This increased the general temperature of the atmosphere by 100 K in the daytime and 70 K at night. Changes in the speed of neutral gas reached 36 m/s.

Ionospheric electron content and NmF2 from nighttime OI 135.6 nm intensity

[1] This paper derives the theoretical relationship between vertical integrated intensity of OI 135.6 nm oxygen emission with integrated electron content (IEC) from 150 to 800 km altitude as well as F layer peak electron density (NmF2). Local time, seasonal, and solar cycle dependence of the relationship is investigated, and it is proposed as a conversion factor to retrieve IEC and NmF2 values from airglow measurements. The errors associated with the IEC and NmF2 estimation using the derived conversion factor are demonstrated for different local times and solar activity. The theoretical conversion factor is compared with that calculated using airglow measurements by the Global Ultraviolet Imager onboard the Theremosphere, Ionosphere, Mesosphere Energetics and Dynamics mission and the Global Ionospheric Map total electron content as well as the nadir integrated OI 135.6 nm intensity by the Tiny Ionospheric Photometer and NmF2 determined from the Global Positioning System Occultation Experiment, both onboard FORMOSAT-3/COSMIC.

Simultaneous airglow, lidar, and radar measurements of mesospheric gravity waves over Japan

To investigate gravity wave dynamics in the mesosphere and lower thermosphere (MLT) region, we conducted coordinated observations of mesospheric gravity waves over Japan during the Aeronomy and Dynamics Observation campaign. Two all‐sky airglow imagers were used in this campaign to derive a two‐dimensional structure of the gravity waves; these imagers were installed at the middle and upper atmosphere (MU) observatory in Shigaraki (34.9°N, 136.1°E) and at the Dynic Astropark Observatory in Taga (35.2°N, 136.3°E). Simultaneous measurements of the horizontal winds and the temperature in the MLT region were provided by the meteor‐mode observations of the MU radar at Shigaraki and by a sodium temperature lidar at Uji (34.9°N, 135.8°E), respectively. On 2 October 2008, gravity waves having a horizontal wavelength of ∼170 km, wave period of ∼1 h, and propagating northeastward at ∼50 m s−1 were observed in the airglow keograms. Similar wave structures were observed in the time series of the meteor wind and lidar temperature data; the polarity of these waves varied consistently with the airglow intensity variations according to the linear theory of gravity waves. The phase speeds and momentum fluxes of the gravity waves, estimated from the wind and temperature observations, were also in good agreement with those obtained from the airglow measurements. These results demonstrate, both qualitatively and quantitatively, that an identical gravity wave structure was detected in all the airglow intensities, radar winds, and lidar temperature.

Arecibo's thermospheric gravity waves and the case for an ocean source

Wave‐like disturbances in electron density ne have been observed in the thermosphere above Arecibo Observatory, Puerto Rico throughout its 45 year history. However, only recently has it become evident that these waves are continuously present in the Arecibo thermosphere. The wave characteristics are fairly constant between day and night and from season to season. High‐resolution electron density measurements obtained by applying the coded long‐pulse radar technique to photoelectron‐enhanced Langmuir waves are presented. These new observations strongly suggest that the perturbations in electron density are the result of internal acoustic‐gravity waves (AGWs) propagating through the Arecibo thermosphere. The AGWs appear to be broadbanded in wave number space. The downward phase trajectories of Δne/ne between 400 and 120 km combined with the low horizontal phase velocities obtained from airglow measurements support the idea that the AGWs are not ducted but rather are locally produced. In addition, the altitudes at which major peaks in Δne/ne are observed follow theoretical estimates for nonducted waves. The nominal period of the AGWs is ∼60 min at 250 km altitude, but periods of ∼20 min are also evident at lower attitudes. Classic sources of AGWs do not appear to be consistent with the Arecibo observations of a continuous flux of background AGWs. Ray tracing of the AGWs combined with 630.0 nm airglow observations point to a source location in the Atlantic Ocean that is roughly 2100 km east northeast of Arecibo. Internal ocean waves generated in response to the internal tide at the mid‐Atlantic Ridge are the most likely source of Arecibo's thermospheric AGWs.

Simultaneous sodium airglow and lidar measurements over India: A case study

In order to understand the substantial variation of sodium (Na) airglow intensity from one night to another, a case study is performed using simultaneous, campaign‐based measurements of Na airglow and Na lidar during March 2007 from Gadanki (13.5°N, 79.2°E), India, during postmidnight hours. The altitude profiles of mesospheric ozone, temperature, and pressure available for the nearest location during the local postmidnight hours are also obtained from the SABER instrument on board the TIMED satellite and are used in conjunction with the above measurements. The average Na airglow intensity level on 20 March 2007 is found to be less compared to that on the next night despite average Na concentration being larger by at least a factor of three. In order to explain the observation, volume emission rates of Na airglow are calculated for both of the nights using the measured parameters. The enhanced quenching due to the ambient gas is suggested to be responsible for the reduced Na airglow intensity level on 20 March 2007 despite higher Na concentration.

Equatorial Spread F structures and associated airglow intensity variations observed over Gadanki

Abstract. Co-ordinated campaigns have been conducted from Gadanki (13.5° N, 79.2° E, dip lat 6.4° N) by operating simultaneously the Indian MST radar in ionospheric coherent backscatter mode and by monitoring thermosphere airglow line emissions (630.0 nm and 777.4 nm) using a narrow band multi-wavelength scanning photometer during January-March for the past five years (2003–2007) and also during April 2006, as a special campaign. Simultaneous radar and optical observations reveal optical signatures corresponding to a variety of equatorial spread F (ESF) structures. The optical signatures corresponding to ESF structures with wave-like bottomside modulations with plasma plumes, confined bottomside flat and wavelike structures, vertically extended plume structure in the absence of bottomside structure apart from the classical plasma depletions and enhancements are obtained during these campaigns. The plasma depletions and enhancements were identified using optical measurements. In addition, estimations of zonal wavelength of the bottomside structures and the inference of shears in the zonal plasma drift in the presence of confined structures, were carried out using bi-directional airglow measurements. Furthermore, it is found that the vertical columnar intensity of OI 630.0 nm airglow exceeded the slanted columnar intensity in the presence of large bottomside structure. The need for the appropriate physical mechanisms for some of the ESF structures and their characterizations with optical observations are discussed.

Identification of active fossil bubbles based on coordinated VHF radar and airglow measurements

Abstract. Plasma irregularity structures associated with an Equatorial Spread-F (ESF) event were recorded by the Indian VHF Radar on 26–27 April 2006 near midnight hours. The plasma structures were found to be isolated without having bottomside structure. They moved predominantly downward and the structures were found to be less turbulent than their post-sunset counterparts. However, the structures were characterized by meter-scale size irregularities. These structures are identified for the first time as plasma depletion structures using simultaneous, collocated measurements of OI 630.0 nm airglow intensity variations. The variation of the base height of ionospheric F layer over dip equator is also presented to buttress the result. Further, these plasma structures are shown to be "active fossil bubbles".

Equatorial enhancement of the nighttime OH mesospheric infrared airglow

Global measurements of the hydroxyl mesospheric airglow over an extended period of time have been made possible by the NASA SABER infrared sensor aboard the TIMED satellite which has been functioning since December of 2001. The orbital mission has continued over a significant portion of a solar cycle. Experimental data from SABER for several years have exhibited equatorial enhancements of the nighttime mesospheric OH (Δv=2) airglow layer consistent with the high average diurnal solar flux. The brightening of the OH airglow typically means more H+O3 is being reacted. At both the spring and autumn seasonal equinoxes when the equatorial solar UV irradiance mean is greatest, the peak volume emission rate (VER) of the nighttime Meinel infrared airglow typically appears to be both significantly brighter plus lower in altitude by several kilometres at low latitudes compared with midlatitude findings.

Comparison of ionospheric measurements made by digisondes with those inferred from ultraviolet airglow

In this work we compare ionospheric measurements made at several ionosonde stations with parameters inferred from airglow measurements made by the Global Ultraviolet Imager (GUVI) instrument aboard the Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED) spacecraft. The purpose of this comparison is twofold. First, our study provides a validation of the technique of using TIMED/GUVI airglow measurements to infer nighttime electron densities in F region of the ionosphere. Second, we use the global characterization of the ionosphere provided by TIMED/GUVI to identify potential biases in individual ionosonde station records. We have found for peak electron densities over the range 4.0–11.0×105cm−3 that the GUVI measurements are consistent with the ionosonde observations. We have also found some station to station and regional variations that warrant further study.

Discrepancy between the nighttime molecular ion composition given by the International Reference Ionosphere model and airglow measurements at low latitudes

The 630‐nm nighttime airglow is radiated by O(1D) atoms, which are produced by the dissociative recombination of O2+ ions. The typical approach used to calculate the red line emission rate at night is based on the assumption that O2+ is mainly produced by the reaction of O+ with molecular oxygen. In the case that the O2+ density is much smaller than the O+ density, [O+] = ne in the F2 region. Good agreement between measured nighttime integrated emission rates and the emission rates calculated by this typical approach, using both electron densities measured by incoherent scatter radars and given by the International Reference Ionosphere (IRI) model, has been shown. However, the O2+ densities given by the IRI model are much higher than the densities produced by the reaction of O+ with O2, and these densities do not correspond to the condition [O+] = ne. In this case, the typical approach cannot be applied and molecular ions must be included in the emission rate calculations. The integrated emission rates calculated including the molecular ion density given by the IRI model have been found to be much higher than the measured 630.0‐nm emission rates. This discrepancy takes place at latitudes below about ±30° in the western longitude sector, mainly for the period from March to November, and the disagreement is higher than 1 order of magnitude at the equator. In addition, we model the F2 region green line O(1S) emission at 557.7 nm resulting from the dissociative recombination of O2+. Using measurements of this volume emission rate made by the Wind Imaging Interferometer (WINDII) satellite, we are able to show that IRI overestimates the O2+ density (and ion fraction) on the bottomside of the F2 region. A revision of the ion composition in the IRI model on the bottomside seems to be needed on the basis of these results. Airglow measurements may be useful in constraining such a revision. A revision could utilize the formulae for the relationship between the molecular ion densities and neutral densities derived here, using the Mass Spectrometer Incoherent Scatter (MSIS) neutral densities and the IRI electron density. These calculations are based on the assumption that O2+ and NO+ are only produced through ion‐molecular reactions. Such a revision would correct the magnitude and altitudinal dependence of the molecular ion fraction in the IRI model.

Using airglow measurements to observe gravity waves in the Martian atmosphere

In this paper, we present the first results of model simulations of the airglow response to gravity waves propagating in the Martian atmosphere. This modeling activity has been done in support of the development of two systems to monitor gravity wave activity in the Martian atmosphere through the measurement of contrast in the images of selected airglow features: a zenith-sky imaging system (MARES-Ground) designed to operate from the ground, and an orbiter-based imaging system (MARES-GWIM). Both systems are also briefly described here as well.

Observational study of the 4‐day wave in the mesosphere preceding the sudden stratospheric warming events during 1995 and 2002

We have examined the Michelson Interferometer (MI) OH airglow measurements at the South Pole Station and the National Center for Environment Prediction (NCEP) temperatures to investigate the dynamical effects of sudden stratospheric warming (SSW) events on the Antarctic mesosphere and stratosphere. Comparisons of stratospheric and mesospheric temperatures at the South Pole during the 1995 and 2002 observing seasons show evidence of mesospheric cooling preceding the SSW events. Spectral analyses of South Pole OH air glow brightness measurements from the 1995 and 2002 observing season and NCEP stratospheric temperatures show amplification of the 4‐day wave planetary wave before the start of the mesospheric cooling trend, the latter preceding the onset of SSW event. A similar behavior of planetary wave is also seen in the stratosphere where the 4‐day wave is seen to grow in amplitude just before the peak of the sudden increase in temperatures.

Observations of elevated power near the Brunt‐Väisälä frequency

High‐frequency peaks close to the Brunt‐Väisälä frequency (N) are observed in the spectra of the nightglow brightness derived from OH Meinel airglow measurements made over the foothills of the Rocky Mountains in Boulder (40°03′N, 105°14′W), Colorado during the summer of 1999. Over a 57‐day period there were 28 nights of sufficient duration and continuity to support reliable spectral analyses. Measurements for these nights yield persistently spectral features near N. The periods of the spectral peaks are in the range ∼5.6–5.8 min, usually appearing as a double‐peaked feature. These periods are compared with values of the Brunt‐Väisälä period (τN) derived from concurrent lidar soundings of the temperature of the upper mesosphere and lower thermosphere over Fort Collins (40°35′N, 105°03′W), Colorado, about 49 km distant from Boulder. Detailed comparisons of the observed periods and the profiles of N suggest that the double‐peaked features in the spectra may arise because the OH M nightglow emissions is double‐peaked, as observed by Evans and Llewellyn (1972) and by Llewellyn et al. (2002). Several theories are explored for the spectral enhancement. The data do not support a definitive answer, but we favor an explanation in terms of orographically excited waves related to the proximity of our airglow observations to the Rocky Mountains. A strong possibility is the parametric excitation described by Klostermeyer (1990). This explanation requires the presence of a large‐amplitude low‐frequency primary wave and is supported by the observed frequent occurrence of strong wave activity in the approximately hour period range.