Spectral Airglow Temperature Imager Research Articles

The Influence of Sudden Stratospheric Warming on the Development of Ionospheric Storms: The Alma-Ata Ground-Based Ionosonde Observations

This paper examines the response of the ionosphere to the impact of two moderate geomagnetic storms observed on January 17 and 26–27, 2013, under conditions of strong sudden stratospheric warming. The study uses data from ground-based ionosonde measurements at the Alma-Ata ionospheric station (43.25 N, 76.92 E) combined with optical observation data (The Spectral Airglow Temperature Imager (SATI)). Ionosonde data showed that the geomagnetic storms under consideration do not generate ionospheric storms but demonstrate some unusual types of diurnal foF2 variations with large (up to 60%) deviations in foF2 from median values observed during the night/morning periods on 13–15 and 20–23 January, which do not have any relation to solar or geomagnetic activity. Wave-like disturbances in foF2, h’F, and daily averaged foF2 values with a quasi-period of 5–8 days and peak-to-peak amplitude from about 1 MHz to 2 MHz (from 20% to 40%) and ~40 km are observed during the period 9–28 January, after registration of the occurrence of the major SSW event on 6–7 January. The observed variations in the OH emission rate are found to be quite similar to those observed in the ionospheric parameters that assume a community of processes in the stratosphere/mesosphere/ionosphere system. The study shows that the F region of the ionosphere is influenced by processes in the lower ionosphere, in this case by processes associated with sudden stratospheric warming SSW-2013, which led to modification of the structure of the ionosphere and compensation of processes associated with the development of the ionospheric storms.

Gravity wave activity in the middle atmosphere from SATI airglow observations at northern mid-latitude: Seasonal variation and comparison with tidal and planetary wave-like activity

The study investigates the gravity waves activity detected in the mesosphere/lower thermosphere (MLT) region (80–120 km) using airglow observations performed by the Spectral Airglow Temperature Imager (SATI) at the Sierra Nevada Observatory (SNO) (37.06∘N, 3.38∘W). In this analysis column emission rates of the OH Meinel (6–2) and O2 Atmospheric (0–1) bands, as well as rotational temperatures derived from these emission rates are employed for the period of 1998–2015. The long time series allows the determination of gravity waves climatology at this site. The gravity wave activity content exhibits an annual variability with a maximum during winter and a faint increase in summer. It was found that gravity waves with periods of less than 3h are more prevalent than those with periods of 3–6h throughout the year, for both column emission rates and rotational temperatures. The gravity wave activity with periods of less than 3h is larger in summer, while gravity waves with period from 3 to 6 h have maximum activity around autumn-winter. The analysis showed that the gravity waves activity surpassed that of the semidiurnal tides, although was still smaller than the planetary wave activity, especially in summer when the planetary waves appear to dominate the dynamics of the MLT region. In general, wave activity is the main source of variability in both OH and O2 airglow emissions with the planetary wave activity being the main driver of the O2 emission variability. However, the rotational temperatures are more affected by seasonal variations, especially the OH rotational temperatures, accounting for more than the 40% of the overall observed variability.

Semidiurnal tidal activity of the middle atmosphere at mid-latitudes derived from O2 atmospheric and OH(6-2) airglow SATI observations

In this paper, we investigate the tidal activity in the mesosphere and lower thermosphere region at 370N using OH Meinel and O2 atmospheric airglow observations from 1998 to 2015. The observations were taken with a Spectral Airglow Temperature Imager (SATI) installed at Sierra Nevada Observatory (SNO) (37.060N, 3.380W) at 2900 m height. From these observations a seasonal dependence of the amplitudes of the semidiurnal tide is inferred. The maximum tidal amplitude occurs in winter and the minimum in summer. The vertically averaged rotational temperatures and vertically integrated volume emission rate (rotational temperatures and intensities here in after), from the O2 atmospheric band measurements and the rotational temperature derived from OH Meinel band measurements reach the maximum amplitude about 1–4 h after midnight during almost all the year except in August–September where the maximum is found 2–4 h earlier. The amplitude of the tide in the OH intensity reaches the minimum near midnight in midwinter, then it is progressively delayed until 4:00 LT in August–September, and from there on it moves again forward towards midnight.The mean Krassovsky numbers for OH and O2 emissions are 5.9±1.8 and 5.6±1.0, respectively, with negative Krassovsky phases for almost all the year, indicating an upward energy transport. The mean vertical wavelengths for the vertical tidal propagation derived from OH and O2 emissions are 35±20 km and 33±18 km, respectively. The vertical wavelengths together with the phase shift in the temperature derived from both airglow emissions indicate that these airglow emission layers are separated by 7±3 km, on average.

Preliminary observations and simulation of nocturnal variations of airglow temperature and emission rates at Pune (18.5°N), India

Preliminary observations of the nocturnal variations of the OH(6-2) and O2b(0-1) nighttime airglow in the mesosphere and lower thermosphere are investigated in the context of tidal influence for the tropical latitude station Pune (18.5°N, 73.85°E). This is the only tropical Spectral Airglow Temperature Imager (SATI) station where the tidal variations of mesosphere and lower thermosphere (MLT) temperature have been determined from ground based SATI observations. The SATI observations obtained since October 2012 reveal the influence of the migrating semidiurnal tides during solstice at this tropical station. There is variability in amplitude and phase obtained from SATI observations. In this paper, SATI observations on 10 Dec 2012 and 3 March 2013 are compared with Whole Atmosphere Community Climate Model (WACCM) simulations. The amplitude of semidiurnal tides is ~25K/30K on 10 Dec 2012 during solstice for OH/O2 temperature. During equinox SATI data indicates existence of semidiurnal tide also. The airglow observations are compared with simulations from the WACCM. The model underestimates the amplitude of the semi diurnal tide during equinox (1.6K/2.7K at 87km/96km) and solstice (~3.8K/4.8K at 87km/96km) for these days. The reason may be related to dampening of tides in the model due to the effect of strong latitudinal shear in zonal wind. The diurnal variation of airglow emission – which the model simulates well – is related to the vertical advection associated with the tides and downward mixing of atomic oxygen.

Ground-based Observations for the Upper Atmosphere at King Sejong Station, Antarctica

【Since the operation of the King Sejong Station (KSS) started in Antarctic Peninsula in 1989, there have been continuous efforts to perform the observation for the upper atmosphere. The observations during the initial period of the station include Fabry-Perot Interferometer (FPI) and Michelson Interferometer for the mesosphere and thermosphere, which are no longer in operation. In 2002, in collaboration with York University, Canada, the Spectral Airglow Temperature Imager (SATI) was installed to observe the temperature in the mesosphere and lower thermosphere (MLT) region and it has still been producing the mesopause temperature data until present. The observation was extended by installing the meteor radar in 2007 to observe the neutral winds and temperature in the MLT region during the day and night in collaboration with Chungnam National University. We also installed the all sky camera in 2008 to observe the wave structures in the MLT region. All these observations are utilized to study on the physical characteristics of the MLT region and also on the wave phenomena such as the tide and gravity wave in the upper atmosphere over KSS that is well known for the strong gravity wave activity. In this article, brief introductions for the currently operating instruments at KSS will be presented with their applications for the study of the upper atmosphere.】

VHF meteor radar at King Sejong Station, Antarctica

Since 2002, we have been observing the mesosphere and lower thermosphere (MLT) region over King Sejong Station (KSS; 62.22°S, 58.78°W), Antarctica, using various instruments such as the Spectral Airglow Temperature Imager (SATI), All Sky Camera (ASC) and VHF meteor radar. The meteor radar, installed in March 2007, continuously measures neutral winds in the altitude region 70-110 km and neutral temperature near the mesopause 24 h·d-1, regardless of weather conditions. In this study, we present results of an analysis of the neutral wind data for gravity wave activity over the tip of the Antarctic Peninsula, where such activity is known to be very high. Also presented is temperature estimation from measurement of the decay times of meteor trails, which is compared with other temperature measurements from SATI and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere Ionosphere Mesosphere Energy and Dynamics (TIMED) satellite.

SATI image processing and mesopause temperature determination

The Spectral Airglow Temperature Imager (SATI) instrument registers airglow coming from an annular mesopause segment. The temperatures of various points of this segment are retrieved by sectors of the registered images containing spectral information. A stage of SATI spectrogram processing connected with deriving spectral information from images and the determination of the rotational temperature of oxygen molecules emitting at the altitude of the mesopause is considered.A “moving sector” approach for sector spectra calculation is proposed. Typical for this approach is the possibility for varying the number of calculated sector spectra from one image and the sector angle. The sector angle may be selected depending on the quality features of the images. Two versions, one based on averaging and a second – based on finding the median of the values of all pixels at equal distance from the image center are developed.The determination of a mean temperature based on a whole image mean spectrum is considered as a potential source of systematic and gross errors. A determination of the mean temperature by averaging sector temperatures is proposed. Applying criteria for evaluating the usability of sector temperatures based on azimuthal distribution of sector errors, emission intensities and backgrounds is possible.The moving sector approach is useful with the possibility for a detailed visual evaluation of the azimuthal distribution of retrieved sector variables – rotational temperature, emission rate, background and error.

Seasonal variations of night mesopause temperature in Beijing observed by SATI4

The data observed by a spectral airglow temperature imager (SATI) at Beijing National Observatory of Space Environment from July 23, 2008 to July 31, 2009 are used to study night mesopause temperature in Beijing. From variations of temperature at 87 and 94 km obtained from OH (6-2) and O2 (0–1) airglow spectra, temperature at night is shown lowest in the summer and highest in the winter. In summer, average temperature at 87 km is 173.9 K, lower than average temperature 180.1 K at 94 km. But in winter, average temperature at 87 km is 201.2 K, higher than average temperature 194.8 K at 94 km. The altitude of mesopause in Beijing is below 87 km in summer and above 94 km in winter. There are about 120–150 days when the mesopause locates below 87 km, which is in agreement with the results of SABER/TIMED. Variations of temperatures at 87 and 94 km are analyzed by harmonic method. Our results show that amplitudes of annual oscillation of temperature at 87 and 94 km are 17.5 and 7.8 K respectively. Amplitudes of semi-annual oscillation at 87 and 94 km are 1.6 and 5.3 K, which are smaller than those of annual oscillation. Although there are differences among different observations because of different locations and different instruments, our results are in general agreement with observation at similar latitude as Beijing.

South Korea's renewed focus on space weather

South Korea's renewed focus on space weather

Comparison of calculation models for determination of the mesopause temperature using SATI images

The Spectral Airglow Temperature Imager is an instrument for ground-based spectroscopic measurements of the night-glow atmosphere emissions. This instrument was developed specially for gravity wave investigation. The measured airglow spectra are matched to synthetic spectra calculated in advance for determination of the temperature in the mesopause region where the radiation maximum of some О 2 emissions is situated. The synthetic spectra are transformed into a format which corresponds to the measured spectra in order to be matched. This transformation is based on the known values of the refractive index and the central wavelength of the interference filter used. A substantial part of the processing algorithms of the SATI images is connected with determination of these two filter parameters. The results of the original and newly-proposed algorithms for filter parameter calculation and their importance for the final results for temperature determination on the basis of the О 2 (864–868 nm) emission measurements are presented. Considerable systematic differences (∼20 K) between temperatures at different points in the mesopause retrieved by the two algorithms are established. The advantage of the proposed algorithm over the original one is illustrated by retrieved rotational temperatures and by lower error values. Furthermore, the irregular errors in the nocturnal variation of the temperature retrieved by the original algorithm are absent when the proposed approach is applied. The error investigation in the calculations and the stability of the individual components of the processing algorithms and the calculation models may be helpful in achieving better results and enhancing the potentialities of the SATI instrument.

Mesospheric temperature observations at Resolute (75°N) in the context of solar flux and quasi‐biennial variations

A spectral airglow temperature imager was operated at Resolute (75°N) in northern Canada from 2001 to 2009, providing mesospheric rotational temperatures from the hydroxyl radical OH Meinel (6,2) band airglow from a nominal altitude of 87 km. The year‐to‐year temperature variability, which included a full maximum to minimum of the solar cycle, was investigated and compared with the temperatures at 22.5 km obtained from radiosonde measurements at the same site. For both data sets, an anticorrelation with the quasi‐biennial oscillation (QBO) was found, in the sense that a positive (eastward) zonal wind at the equator corresponded to negative temperature anomalies for both regions, a relationship that had already been recognized for the lower stratosphere. Plots of the monthly mesospheric temperatures versus solar flux, done separately for the two phases of the QBO, showed a high correlation for the westerly phase of the QBO and a low correlation for the easterly phase, as has been recognized for the lower stratosphere. Finally, when the upper mesospheric monthly temperature anomalies were plotted versus those for the lower stratosphere, a high correlation was found for the westerly phase of the QBO and a low correlation for the easterly phase. This is also a new finding for the upper mesosphere and indicates either a coupling between the two regions or simply a common response to the same source: solar flux, the influence of which is modulated by the QBO.

Mesospheric temperature and atomic oxygen response during the January 2009 major stratospheric warming

The study examines the response of the mesosphere/lower thermosphere to the major stratospheric warming (SSW) event from January 2009, as seen in the OH and O2(0,1) atmospheric band airglow observations nominally at 87 and 94 km, respectively, by a SATI (Spectral Airglow Temperature Imager) instrument installed at the Polar Environment Atmospheric Research Laboratory (PEARL) at Eureka (80°N, 86°W) as part of the Canadian Network for the Detection of Atmospheric Change. At the time of the SSW, the airglow emissions and the derived rotational temperatures appear depleted and decreased, followed by an enhancement of the airglow emission rates during the SSW recovery phase, while the temperatures returned to their pre‐event state. An empirical relationship between OH airglow peak altitude determined by SABER (Sounding of the Atmosphere by Broadband Emission Radiometry) and SATI integrated emission rates allowed perturbed OH and O2(0,1) airglow altitudes to be assigned to the SATI observations. From these, the O volume mixing ratio (VMR), corresponding to the observed OH and O2(0,1) airglow emission rates were modeled. Atomic oxygen depletion by a factor of ∼5 was observed during the SSW and lasted for about 5 days. During the SSW recovery phase, the O VMR giving rise to the observed O2(0,1) airglow emission rates increased by a factor of 3.5 from its pre‐SSW level and 17 times from the peak of the SSW. Perturbations in the OH and O2(0,1) airglow layers with periods of 4, 6, 8, and 12 h indicate nonlinear interaction between zonally symmetric semidiurnal tides and planetary waves.

Climatology of planetary wave type oscillations with periods of 2–20 days derived from O<sub>2</sub> atmospheric and OH(6-2) airglow observations at mid-latitude with SATI

Abstract. The presence of planetary wave type oscillations at mid-latitudes in the mesosphere/lower thermosphere region has been investigated using airglow observations. The observations were taken with a Spectral Airglow Temperature Imager (SATI) installed at Sierra Nevada Observatory (37.06° N, 3.38° W) at 2900 m height. Airglow data of the column emission rate of the O2 Atmospheric (0-1) band and of the OH Meinel (6-2) band and deduced rotational temperatures from 1998 to 2007 have been used in this study. From these observations a climatology of planetary wave type oscillations at this location is inferred. It has been found that the planetary wave type oscillations of 5-day period is predominant in our data throughout the year, with activity greater than 50% during March/April and October/November months. The planetary wave type oscillations of 2-day period is predominant during both solstices, being predominant during winter solstice in O2 while a 10-day oscillation appears throughout the year with activity around 20% and with maximum activity during spring and autumn equinoxes. The 16-day oscillation has maximum occurrence during autumn-winter while its activity is almost disappeared during spring-summer. No clear seasonal dependence of the amplitude of the planetary wave type oscillations was observed in the cases considered in this study. The waves simultaneously detected in the rotational temperatures deduced from both OH and O2 emissions usually show an upward energy propagation and are affected by dissipation processes.

Wave perturbations in the MLT at high northern latitudes in winter, observed by two SATI instruments

To investigate the Mesosphere and Lower Thermosphere (MLT) region, several ground-based instruments called SATI (Spectral Airglow Temperature Imager) were designed and built to measure airglow emission and temperature in the upper mesosphere. One SATI instrument was installed at Resolute Bay (74.7°N, 94.9°W) and has monitored the polar MLT region since November, 2001. In October 2007 another SATI instrument was installed at Eureka (80.0°N, 86.3°W) at the Polar Environment Atmospheric Research Laboratory (PEARL) as part of the Canadian Network for the Detection of Atmospheric Change (CANDAC) project. SATI is a spatial scanning Fabry–Perot spectrometer measuring column emission rates for several rotational lines of OH and O 2 airglow at 87 and 94 km height. The rotational temperatures are inferred from the ratios of these lines. The measurements are divided into 12 sectors with an annular field of view. The phase differences between the sectors yield information on the horizontal atmospheric wave direction and wavelength. Horizontal perturbations of 2–8 h period have correlatively been observed and investigated at both locations. Short-periodic oscillations identified as gravity waves with periods between 2 and 8 h propagate in southward and eastward directions, but in opposite directions in some cases. The wave propagation characteristics are often different at the two locations; the relationship with the lower mean wind is considered.

Ground-based mesospheric temperatures at mid-latitude derived from O 2 and OH airglow SATI data: Comparison with SABER measurements

Rotational temperatures obtained from the O 2 Atmospheric (0–1) nightglow band and from the OH (6–2) band, with a Spectral Airglow Temperature Imager (SATI) instrument at Sierra Nevada Observatory ( 37 . 06 ∘ N , 3 . 38 ∘ W ) are presented. A revision of the temperatures obtained from the Q branch of the (6–2) Meinel band has been undertaken. First, new experimental Einstein coefficients for these lines have been introduced and the temperatures derived from the Q lines (1, 2 and 3) of the (6–2) OH Meinel band have been compared to those deduced from the P lines (2 and 4) of the same band of spectra taken by a spectrograph at Boston University. The new set of SATI data has been used to analyse the seasonal behaviour of the mesospheric and lower thermospheric temperatures. Atmospheric temperatures deduced from SATI and from satellite observations with the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board the TIMED satellite, have also been compared. SABER temperatures at 95 km are slightly warmer (about 2.5 K) than SATI temperatures while at 87 km they are slightly colder (about 5.7 K). Also, similar patterns of seasonal and day to day variations are found in the temperatures retrieved from both instruments at the latitude of 37 ∘ N .

Correlations of mesospheric variability and their relation to the large-scale circulation during polar winter

WINDII data from the Upper Atmosphere Research Satellite show an integrated OH emission rate systematically increasing with decreasing airglow peak altitude. A Spectral Airglow Temperature Imager (SATI) at 74°N shows strong positive correlations between the integrated emission rate and the rotational OH temperature. Taken together, the two correlations are consistent with vertical motions of the mesopause region, over periods from hours to winter to winter. SABER data are consistent with these correlations. The O 2 atmospheric band shows much weaker correlations. The SATI mesospheric temperatures also correlate with Resolute Bay temperatures for the 22.5 km level, a mesosphere–stratosphere relationship.

Gravity wave momentum flux in the upper mesosphere derived from OH airglow imaging measurements

Abstract We report procedures to identify small-scale (20–100 km) atmospheric gravity waves from OH airglow images to estimate momentum fluxes carried by the waves. We also deduce contamination of background continuum emission in OH image, by comparing a simultaneous observation of OH lines measured by the Spectral Airglow Temperature Imager (SATI). We applied the procedures to a one-night dataset obtained at Shigaraki, Japan (34.9°N, 136.1°E) on November 19, 1999. The background wind, which is essential for deriving the intrinsic parameters of gravity waves, was measured by the Middle and Upper Atmosphere (MU) radar. Contamination of background continuum emission with the OH filter was deduced to be 30%. From these procedures, we found that the gravity waves identified in the OH images were mainly propagating southward or southeastward with horizontal wavelengths of 60–90 km and apparent phase speeds of 40–80 m/s. The estimated momentum fluxes on this night was 1–15 m2 s−2, with an average of 4.9 m2 s−2.

O2 Atmospheric band and OH(6–2) airglow and temperature variability over Spain using SATI observations: Planetary-scale oscillations during autumn

Long-term ground-based airglow observations with a spectral airglow temperature imager (SATI) installed at Sierra Nevada Observatory (37.06°N, 3.38°W) at 2900~m height are used to investigate the main features of the quasi planetary waves in the period range of 3–20 days during autumn at this latitude in the mesosphere and lower thermosphere region. The modulations of periods 5 day, (6–7) day, and 10 day have been clearly detected during autumn at this location, being the most prominent waves detected at this location during the autumn. They have a strong persistence during the autumn period and relative amplitudes are generally constant during the period although a slight tendency to increase seems to be detected towards winter.PACS Nos.: 92.60.hw, 92.60.hb, 92.60.hc, 92.60.hh, 92.60.hv

Springtime effects in the mesosphere and ionosphere observed at northern midlatitudes

Nighttime volume emission rates and rotational temperatures, obtained from simultaneous observations of molecular oxygen and hydroxyl airglow at Almaty (43.25°N, 76.92°E) and Sierra-Nevada (37.2°N, 356.7°E), along with ionospheric density derived from foF2 in the vertical sounding ionograms over Almaty are analysed to study the variability and coupling of parameters observed in the upper mesosphere and ionosphere during the period of February – April, 2000. Ionospheric critical frequency measurements and airglow observations by the Mesopause Rotational Temperature Imager (MORTI) at Almaty and the Spectral Airglow Temperature Imager (SATI) at Sierra-Nevada Observatories show an increase in long-period planetary wave (PW) activity from the end of February until the middle of March, 2000. Very good agreement was found in the temporal variations of emission rates and rotational temperatures from March 1–15, 2000 measured at the Almaty and Sierra-Nevada sites. Similar perturbations could also be seen in the ionospheric critical frequency (ΔfoF2) obtained as a difference between current foF2 values and an ionospheric background level. The perturbations observed have been interpreted employing the Met office stratospheric model results. Latitudinal structure of a quasi 5-day wave was identified, for which the first-symmetric-mode amplitude and symmetric behaviour of phase are in good agreement with theoretical prediction. The analysis of the Met office stratospheric data indicate the presence of westward-propagating PW with periods of ∼5 and 10 days during the period of interest. The temporal correlation between planetary scale oscillations observed in the datasets examined (ionospheric, optical and meteorological) suggest dynamical coupling with the stratosphere. A negative disturbance in ΔfoF2 of ∼25% observed 1 day before a sharp increase in the MORTI mesospheric rotational temperature registered on March 10 at Almaty, is also discussed in the context of the possible stratosphere/mesosphere/ionosphere coupling.

Correlation of airglow temperature and emission rate at Resolute Bay (74.68°N), over four winters (2001–2005)

The rotational temperature and emission rate of the OH (6‐2) Meinel band and the O2 (0‐1) Atmospheric band were monitored with a Spectral Airglow Temperature Imager (SATI), located at Resolute Bay (74.68°N, 94.90°W) since November, 2001. A strong correlation between these two quantities is found in data taken over a single day. This is consistent with previous model and observational results of wave motions in airglow and with model calculations presented here. The same correlation is observed over one month, over one winter and even from winter to winter. This means that similar dynamical processes are involved for perturbations with periods of a few hours or for many days or months. This suggests that all scales of dynamical variations during the polar winter arise from vertical motions, and that the effective source concentration of atomic oxygen at some reference level is remarkably constant.