Airglow Images Research Articles

Disconnection and Reconnection in Plasma Bubbles Observed by OI 630 nm Airglow Images From Cariri Observatory

AbstractWe use OI 630 nm airglow images obtained with the All‐sky imager installed at São João do Cariri (7.4°S, 36.5°W) to report the very rare phenomenon of disconnection and reconnection between adjacent plasma bubbles. We report here for the first time observations of the phenomenon at Cariri. These observations show that the phenomenon is independent of the solar flux and occurs between September and December in the Brazilian sector. The phenomenon consists first in separating a part of the bubble followed by its capture by other adjacent bubbles via electrostatic potential fields. Statistically, the phenomenon is of very low occurrence and its probability varies between 1/120 and 1/165 per year, and on certain occasions it is zero.

Airglow Imager, Ionosonde, and HWM Data on 08 July 2018

Airglow Imager, Ionosonde, and HWM Data on 08 July 2018

Imager observation of concentric mesospheric gravity waves over Srinagar, Jammu and Kashmir, India

Using the NARL airglow imager in the Indian subtropical station of Srinagar, Kashmir, India, we report the characteristics of the concentric deformed circular pattern of gravity waves detected at ∼85 km height. OH molecular emission intensities from the height of ∼85 km as observed by the imager in the wide band optical filter of centre wavelength of 840 nm show concentric deformed circular gravity waves drifting northwestward. Using Atmospheric Infrared Sounder (AIRS) image at the centre wavelength of 8.1 µm, deep convective activity around the imager site in the lower atmosphere is recognized as the source mechanism of the observed concentric gravity waves in the mesosphere. The determined phase speed, direction and period of these concentric gravity waves (CGWs) is ∼47 m/s, 150° north of east and ∼10 min (intrinsic period ∼8 min) respectively. At heights of ∼97 km [OI (1S)] and ∼250 km [OI (1D)], these concentric gravity waves are sporadically visible depending on the possible vertical movement of airglow layer height. The dissipated portions of these concentric gravity waves get converted into turbulence at these heights. Using anelastic gravity wave dispersion relation, decreasing horizontal wavelength from the centre of concentric gravity waves is explained. This result is novel in the sense that it disagrees with most of the earlier interpretations of such observations.

A Case Study on the Interaction Between MSTIDs' Fronts, Their Dissipation, and a Curious Case of MSTID's Rotation Over Geomagnetic Low‐Mid Latitude Transition Region

AbstractThis paper reports a rare interaction between two fronts of nighttime medium scale traveling ionospheric disturbances (MSTIDs) and associated phenomena observed over geomagnetic low‐mid latitude transition region on a geomagnetically quiet night (Ap = 5) of 21 May 2020. The event was observed for nearly 8 hours in O(1D) 630.0 nm airglow images captured by an all‐sky imager installed at Hanle (32.7°N, 78.9°E; Mlat. ∼24.1°N), Leh Ladakh, India and supplemented by a digisonde and a global positioning system receiver located within the imager's field of view (FOV). The images revealed a slow‐moving MSTID front being followed by a fast‐moving MSTID front, both traveling southwestward. The third front of the MSTID caught up with the second one, initiating the interaction. As a consequence, a plasma channel was created during the interaction and the MSTIDs' fronts began decaying. Subsequently, they became thin strips and later dissipated within the FOV of the imager. The polarization electric field of the merged region of the two interacting MSTIDs' fronts played a key role in creating the plasma channel. In the later hours of the night, another MSTID with a rotating front was observed, which is a rarely reported phenomenon. The horizontal gradient in the westward wind is a plausible reason for the observed rotation. This study elucidates the complex nature of geomagnetic low‐mid latitude transition region.

A case study of a ducted gravity wave event over northern Germany using simultaneous airglow imaging and wind-field observations

Abstract. An intriguing and rare gravity wave event was recorded on the night of 25 April 2017 using a multiwavelength all-sky airglow imager over northern Germany. The airglow imaging observations at multiple altitudes in the mesosphere and lower thermosphere region reveal that a prominent upward-propagating wave structure appeared in O(1S) and O2 airglow images. However, the same wave structure was observed to be very faint in OH airglow images, despite OH being usually one of the brightest airglow emissions. In order to investigate this rare phenomenon, the altitude profile of the vertical wavenumber was derived based on colocated meteor radar wind-field and SABER temperature profiles close to the event location. The results indicate the presence of a thermal duct layer in the altitude range of 85–91 km in the southwest region of Kühlungsborn, Germany. Utilizing these instrumental data sets, we present evidence to show how a leaky duct layer partially inhibited the wave progression in the OH airglow emission layer. The coincidental appearance of this duct layer is responsible for the observed faint wave front in the OH airglow images compared O(1S) and O2 airglow images during the course of the night over northern Germany.

Disconnection and reconnection in plasma bubbles observed by OI 630 nm airglow images from Cariri Observatory

Disconnection and reconnection in plasma bubbles observed by OI 630 nm airglow images from Cariri Observatory

Disconnection and reconnection in plasma bubbles observed by OI 630 nm airglow images from Cariri Observatory

Disconnection and reconnection in plasma bubbles observed by OI 630 nm airglow images from Cariri Observatory

Rare observations of sprites and gravity waves supporting D, E, F-regions ionospheric coupling

We report rare simultaneous observations of columniform sprites and associated gravity waves (GWs) using the Transient Luminous Events (TLEs) camera and All-sky imager at Prayagraj (25.5° N, 81.9° E, geomag. lat. ~ 16.5° N), India. On 30 May 2014, a Mesoscale Convective System generated a group of sprites over the north horizon that reached the upper mesosphere. Just before this event, GWs (period ~ 14 min) were seen in OH broadband airglow (emission peak ~ 87 km) imaging that propagated in the direction of the sprite occurrence and dissipated in the background atmosphere thereby generating turbulence. About 9–14 min after the sprite event, another set of GWs (period ~ 11 min) was observed in OH imaging that arrived from the direction of the TLEs. At this site, we also record Very Low Frequency navigational transmitter signal JJI (22.2 kHz) from Japan. The amplitude of the JJI signal showed the presence of GWs with ~ 12.2 min periodicities and ~ 18 min period. The GWs of similar features were observed in the ionospheric Total Electron Content variations recorded at a nearby GPS site. The results presented here are important to understand the physical coupling of the troposphere with the lower and upper ionosphere through GWs.

Joint observation of the concentric gravity wave event on the Tibetan Plateau

A concentric gravity wave event was captured by a photographer in Nagarzê County (90.28°N, 28.33°E) between 02:00 and 04:00 (local time) on May 11, 2019. This concentric gravity wave event was also observed by the Suomi National Polar-orbiting Partnership satellite and the all-sky airglow imager at Yangbajing station (90.5°E, 30.1°N). The temporal and spatial information on gravity waves from the photographs provided a rare opportunity to study the propagation of gravity waves over the Tibetan Plateau. According to wind and temperature data from the MERRA-2 reanalysis (Modern-Era Retrospective analysis for Research and Applications, Version 2) and empirical models (NRLMSISE-00 [Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar Exosphere] and HWM [horizontal wind model]), we inversely derived the propagation trajectory from the observed wave pattern to the source region by using the ray-tracing method. The source of the concentric gravity wave was identified as deep convection in Bangladesh (90.6°E, 25.0°N). The maximum background wind speed in the propagation direction (31.05 m/s) was less than the phase speed of 53 m/s, which is consistent with the wind-filtering theory.

Mesospheric Short‐Period Gravity Waves in the Antarctic Peninsula Observed in All‐Sky Airglow Images and Their Possible Source Locations

AbstractThis study presents an analysis of OH airglow images observed from an all‐sky camera (ASC) at King Sejong Station (KSS), Antarctic for the 2012–2016 period. The two‐dimensional power spectra of short‐period gravity waves (<1 hr) as a function of phase velocities are obtained using the M‐transform method that employs the time sequence of ASC images. The amplitudes of the power spectral densities show that the mesospheric wave activity is the largest during winter (May, June, and July) and is the smallest in fall (February, March, and April). Wind‐blocking diagrams are constructed on the same two‐dimensional domain as in the two‐dimensional spectra using horizontal winds obtained from MERRA‐2 reanalysis at z = 0–80 km and from KSS meteor radar data at z = 80–90 km. Climatologically, the spectral regions of slowly propagating gravity waves (<30 m s−1) are overlaid by the wind‐blocking areas, which suggests the filtering of gravity waves with small phase speeds by winds below the upper stratosphere. Eastward propagating gravity waves in winter and intense south‐eastward waves in spring (October) are found to be unfiltered by the stratospheric winds. It is also found from the spectral analysis that these unfiltered gravity waves can originate from the upper stratosphere or the lower mesosphere, and not from the troposphere, which suggests the possibility of ASC observation of the secondary gravity waves generated near the stratopause.

Influence of the semidiurnal lunar tide in the equatorial plasma bubble zonal drifts over Brazil

Abstract. Using OI6300 airglow images collected over São João do Cariri (7.4∘ S, 36.5∘ W) from 2000 to 2007, the equatorial plasma bubble (EPB) zonal drifts were calculated. A strong day-to-day variability was observed in the EPB zonal drifts, which is directly associated with the very complex dynamics of the nighttime thermosphere–ionosphere system near the Equator. The present work investigated the contribution of the semidiurnal lunar tide M2 for the EPB zonal drifts. The M2 presented an amplitude of 3.1 m s−1 in the EPB zonal drifts, which corresponds to 5.6 % of the average drifts. The results showed that the M2 amplitudes in the EPB zonal drifts were solar cycle and seasonally dependent. The amplitude of the M2 was stronger during the high solar activity, reaching over 10 % of the EPB zonal drift average. Regarding the seasons, during the Southern Hemisphere summer, the M2 amplitude was twice as large (12 %) compared to the equinox ones. The seasonality agrees with other observations of the M2 in the ionospheric parameters such as vertical drifts and electron concentration, for instance. On the other hand, the very large M2 amplitudes found during the high solar activity agree with previous observations of the lunar tide in the ionospheric E region.

Ionospheric Plasma Vertical Drift and Zonal Wind Variations Cause Unusual Evolution of EPBs During a Geomagnetically Quiet Night

AbstractPrevious studies show equatorial plasma bubbles (EPBs) mainly occur after sunset and usually drift from west to east. In this work, two EPBs occurred after midnight and lasted to sunrise, and were observed by multi‐instruments (two all‐sky imagers (ASIs), global positioning system, Swarm satellite, and a digisonde) during a geomagnetically quiet night of December 18–19, 2018. Our observations also show that plasma depletion structure (PDS) also occurred at that night. EPBs occurred in the region of PDS and showed a special evolution process during the night. Those PDS gradually disappeared with time, but strip‐like EPBs remained clearly in airglow images. Near sunrise, new PDS appeared to merge with those EPBs to form large PDS. Meanwhile, EPBs showed different zonal drifts within a very narrow longitudinal zone (∼2°). One EPB remained stationary while the other showed a small eastward drift. These results are different from post‐sunset EPBs in previous studies. During the lifetime of those ionospheric plasma irregularities, upward and downward motion of the peak height and virtual height of the ionospheric F region was observed by a digisonde, which indicates that the evolution of EPBs should be related to the vertical drift of ionospheric plasma. Besides, based Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM) simulations, we suggest the different zonal drifts of those EPBs might related to plasma zonal drifts caused by zonal winds.

Westward Drift of Ionospheric Plasma Irregularities over a Low to Mid-latitude Transition Region in Indian Sector

We report the observation of plasma depletions/plumes in the F region ionosphere over a low to middle latitude transition region in the Indian sector. The observation of these plasma depletions is based on the data obtained in May 2019 through the all-sky airglow CCD imager installed in the campus of University of Kashmir, Srinagar (34.12 °N, 74.83 °E, magnetic latitude 25.91 °N). The depletions on the two consecutive nights of 05 and 06 May 2019 are aligned along the North-South (N-S) direction and drift westward. Several depletion bands along with some enhancement bands are seen in the 630-nm airglow images throughout the two nights. The observed structures show certain characteristics similar to Medium Scale Traveling Ionospheric Disturbances (MSTIDs) but these airglow features are not completely periodic. Further, in the observed depletion bands some East-West asymmetries are observed along with the structured tree-like branches of the airglow depletions. Some depletion bands even bifurcate leading to the inference that the structures are signatures of plasma irregularities rather than the usual MSTIDs observed in low-mid latitude transition region. The westward drift of the depletions especially during geomagnetic quiet times over this region makes this study significant since it offers a possible evidence that shows extension of spread F irregularities from the mid latitude region to the low-mid latitude transition region. In this paper, we point out some possible mechanisms related to the occurrence of plasma depletions at this region and their westward movement during geomagnetic quiet times.

Northward propagation of medium scale traveling ionospheric disturbances over Srinagar, J and K India

We report some interesting medium scale travelling ionospheric disturbances (MSTIDs) observed during the night of September 20, 2020 through an all sky CCD imager installed in Kashmir University (KU), Srinagar, India (34.08° N geographic latitude, 74.79° E and 25.91° N geomagnetic latitude). Three different MSTID events including a post-sunset MSTID, a mid-night MSTID and a pre-dawn MSTID are recorded in the airglow images during this night. The post-sunset and pre-dawn MSTIDs are seen to propagate northward while the MSTID observed near midnight time propagates towards west. As the MSTIDs during the night times over the northern hemisphere generally propagate southwestward, the northward propagation of nighttime MSTIDs over Srinagar makes this result an interesting one. More importantly, three different MSTIDs are observed at different times during the single night whose directions of propagation are not same either. We provide the detailed characteristics and evolution processes of these MSTIDs in this paper. The unusual northward motion of the MSTIDs over the Srinagar region is also addressed. The upward propagation of atmospheric gravity waves during this night is believed to be the responsible candidates for such unusual propagation direction of nighttime MSTIDs over the northern hemisphere.

Rotation, bifurcation and merging of medium-scale traveling ionospheric disturbances over a low-mid latitude transition region

This paper reports the observation of propagating wave structures in OI 630.0 nm airglow images captured by a CCD imager at Kashmir University (KU), Srinagar, India (34.1 °N, 74.8 °E, and 25.9 °N magnetic latitude). These structures were detected on the night of August 17th, 2017, with an average horizontal wavelength around 330 km and average phase velocities around 92 m/s traveling in southwest (SW) direction. The SW moving wave patterns had north-west (NW) to south-east (SE) aligned phase fronts that lasted for ∼150 min and had a time period of about 1 h. Based on observed parameters such as wavelength, time span, and propagating speed, these structures are categorized as nighttime medium-scale traveling ionospheric disturbances (MSTIDs). The observed southwestward movement, phase speed, horizontal wavelength and period of these nighttime MSTIDs are consistent with the existing literature. The appearance of gravity waves in the lower atmosphere during this night means that gravity waves from below, in combination with the Perkins' instability, might be responsible candidates for generation of these MSTIDs. Near midnight the MSTID bands are seen to rotate, bifurcate and some even merging with other bands giving rise to some unique Y-shaped MSTID structures-the first such results observed from this location. These structures align along North-South direction and move westward unlike the MSTID bands before midnight which move towards southwest. In addition, we also report the shrinking phenomena of the post midnight MSTID dark bands.

Gravity wave instability structures and turbulence from more than 1.5 years of OH* airglow imager observations in Slovenia

Abstract. We analysed 286 nights of data from the OH* airglow imager FAIM 3 (Fast Airglow IMager) acquired at Otlica Observatory (45.93∘ N, 13.91∘ E), Slovenia, between 26 October 2017 and 6 June 2019. Measurements have been performed with a spatial resolution of 24 m per pixel and a temporal resolution of 2.8 s. A two-dimensional fast Fourier transform is applied to the image data to derive horizontal wavelengths between 48 m and 4.5 km in the upper mesosphere/lower thermosphere (UMLT) region. In contrast to the statistics of larger-scale gravity waves (horizontal wavelength up to ca. 50 km; Hannawald et al., 2019), we find a more isotropic distribution of directions of propagation, pointing to the presence of wave structures created above the stratospheric wind fields. A weak seasonal tendency of a majority of waves propagating eastward during winter may be due to instability features from breaking secondary gravity waves that were created in the stratosphere. We also observe an increased southward propagation during summer, which we interpret as an enhanced contribution of secondary gravity waves created as a consequence of primary wave filtering by the meridional mesospheric circulation. We present multiple observations of turbulence episodes captured by our high-resolution airglow imager and estimated the energy dissipation rate in the UMLT from image sequences in 25 cases. Values range around 0.08 and 9.03 W kg−1 and are on average higher than those in recent literature. The values found here would lead to an approximated localized maximum heating of 0.03–3.02 K per turbulence event. These are in the same range as the daily chemical heating rates for the entire atmosphere reported by Marsh (2011), which apparently stresses the importance of dynamical energy conversion in the UMLT.

Mesospheric gravity wave activity estimated via airglow imagery, multistatic meteor radar, and SABER data taken during the SIMONe–2018 campaign

Abstract. We describe in this study the analysis of small and large horizontal-scale gravity waves from datasets composed of images from multiple mesospheric airglow emissions as well as multistatic specular meteor radar (MSMR) winds collected in early November 2018, during the SIMONe–2018 (Spread-spectrum Interferometric Multi-static meteor radar Observing Network) campaign. These ground-based measurements are supported by temperature and neutral density profiles from TIMED/SABER (Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry) satellite in orbits near Kühlungsborn, northern Germany (54.1∘ N, 11.8∘ E). The scientific goals here include the characterization of gravity waves and their interaction with the mean flow in the mesosphere and lower thermosphere and their relationship to dynamical conditions in the lower and upper atmosphere. We have obtained intrinsic parameters of small- and large-scale gravity waves and characterized their impact in the mesosphere via momentum flux (FM) and momentum flux divergence (FD) estimations. We have verified that a small percentage of the detected wave events is responsible for most of FM measured during the campaign from oscillations seen in the airglow brightness and MSMR winds taken over 45 h during four nights of clear-sky observations. From the analysis of small-scale gravity waves (λh < 725 km) seen in airglow images, we have found FM ranging from 0.04–24.74 m2 s−2 (1.62 ± 2.70 m2 s−2 on average). However, small-scale waves with FM > 3 m2 s−2 (11 % of the events) transport 50 % of the total measured FM. Likewise, wave events of FM > 10 m2 s−2 (2 % of the events) transport 20 % of the total. The examination of large-scale waves (λh > 725 km) seen simultaneously in airglow keograms and MSMR winds revealed amplitudes > 35 %, which translates into FM = 21.2–29.6 m2 s−2. In terms of gravity-wave–mean-flow interactions, these large FM waves could cause decelerations of FD = 22–41 m s−1 d−1 (small-scale waves) and FD = 38–43 m s−1 d−1 (large-scale waves) if breaking or dissipating within short distances in the mesosphere and lower thermosphere region.

Near-Earth space balloon-based multi-band airglow imager optic design.

As a common tracer in the atmosphere, airglow can be used as an important means to study the interaction between the lower atmosphere, near space, and ionosphere. In the near-Earth space, the high-altitude balloon can realize long time flight, which makes the airglow detection realize both high range resolution and time resolution. In this paper, a balloon-based multi-band airglow imager is designed, which can observe OI (557.7 nm), Na (589.3 nm), OI (630.0 nm), and OH (720-910 nm) with annular field of view (30° inner ring and 80° outer ring), and its resolution is 500 m at 250 km. The multi-band airglow imager designed in this paper is equipped in the payload cabin and raised to above 30 km for flat flying for more than 6 h. The experimental results show that the imager worked normally, and airglow images were photographed and stored; the optical system can stand the harsh environment in the near space. The multi-band airglow imager designed in this paper will take part in other near-space exploration tasks in the future and obtain corresponding results.

First Simultaneous Observation of a Night Time Medium‐Scale Traveling Ionospheric Disturbance From the Ground and a Magnetospheric Satellite

AbstractMedium‐scale traveling ionospheric disturbances (MSTIDs) are a phenomenon widely and frequently observed over the ionosphere from high to low latitudes. Night time MSTIDs are caused generally by the polarization electric field in the ionosphere. However, propagation of this polarization electric field to the magnetosphere has not yet been identified. Here, we report the first observation of the polarization electric field and associated density variations of a night time MSTID in the magnetosphere. The MSTID event was observed by an all‐sky airglow imager at Gakona (geographical latitude: 62.39°N, geographical longitude: 214.78°E, magnetic latitude: 63.20°N), Alaska. The Arase satellite passed over the MSTID in the inner magnetosphere at 0530–0800 UT (2030–2300 LT) on November 3, 2018. This MSTID, observed in 630 nm airglow images, was propagating westward with a horizontal wavelength of ∼165 km, a north–south phase front, and a phase velocity of ∼80 m/s. The Arase satellite footprint on the ionosphere crossed the MSTID in the direction nearly perpendicular to the MSTID phase fronts. The electric field and electron density observed by the Arase satellite showed periodic variation associated with the MSTID structure with amplitudes of ∼2 mV/m and ∼150 cm−3, respectively. The electric field variations projected to the ionosphere are mainly in the east‐west direction and are consistent with the direction of the polarization electric field expected from MSTID growth by E × B drift. This observation indicates that the polarization electric field associated with the MSTID in the ionosphere is projected onto the magnetosphere, causing plasma density fluctuations in the magnetosphere.

A Study of Magnetic Conjugate Property in a Large Density Irregularity Structure Using Hilbert‐Huang Transform

AbstractA large density irregularity structure in latitudinal extent was observed by the sun‐synchronous orbiting FORMOSAT‐5 satellite at 720 km topside ionosphere in the South American sector on November 24, 2018 during a magnetically quiet time. The observed density irregularity structure has a latitudinal extent of ∼30° across the dip equator, and a longitudinal width of ∼6°. Unlike previously studied equatorial plasma bubble structures with the airglow images that indicate hemispheric magnetic conjugate similarity, the gross feature of this large density irregularity structure indicates a north‐south hemispheric asymmetry in density variation. We use the Hilbert‐Huang Transform analysis to study the irregularity structure in different scales of density variations. It is found that the amplitude of density variations in the scale sizes from 22.5 to 450 km all indicate the hemispheric asymmetry. However, the spectral property of density variations in the two hemispheres is almost identical to each other. This implies that the density irregularity structure which originates from the same Rayleigh‐Taylor (RT) instability process has preserved the spectral characteristics inside the magnetic flux tube. Therefore, the cause that fails to preserve the magnetic conjugate property in the density irregularity structure comes from the fact that the background ionospheric density distribution has a north‐south hemispherical asymmetry in the beginning of the RT instability process. This hemispheric asymmetrical density distribution is caused by the seasonal variation of density distributions in the two hemispheres and the prevailing inter‐hemispheric neutral wind during solstices in the South American sector.