Equatorial planetary waves in the mesosphere observed by airglow periodic oscillations

Planetary scale waves in the equatorial upper mesosphere were studied by measuring the airglow OI557.7 nm, O₂b(0,1) and OH(6,2) emission intensities and OH rotational temperature at São João do Cariri (7.4°S; 36.5°W). From four years of data, 1998–2001, periodic oscillations of the airglow emissions were analyzed using the Lomb–Scargle spectral analysis. An oscillation of 3–4 days was frequently observed, which might be ultra-fast Kelvin waves. No seasonal dependency of the wave activity was found. On some occasions we found a quasi-5-day oscillation with a phase difference between the emissions, suggesting an upward energy flow. This is interpreted as a normal mode Rossby wave.     

Response of OH,O2 and OI5577 airglow emissions to the mesospheric bore in the equatorial region of Brazil

An all-sky CCD imager capable of measuring wave structure in the airglow OH, O₂ and OI (557.7 nm) emissions was operated in the equatorial region at São João do Cariri (Cariri), Brazil (7°S, 36°W), in collaboration with the Instituto Nacional de Pesquisas Espaciais (INPE). Occurrence of mesospheric bore events was studied using the data from September 2000 to September 2002. Sixty-four bore events were detected during the observation period. Most of the bores showed the complementary effects suggested by Dewan and Picard [E.M. Dewan, R.H. Picard, Mesospheric bores. Journal of Geophysical Research 103, 6295–6305, 1998], except in a few cases where the relative variations were inconsistent with this model.     

Fine structure of the ionospheric plasma bubbles observed by the OI 6300 and 5577 airglow images

Simultaneous measurements of the ionospheric airglow OI 630.0 nm and OI 557.7 nm emissions have been carried out by means of an all-sky CCD imager system at Cachoeira Paulista, since October 1998. During a developed phase of plasma depletion (bubble) in the equatorial anomaly region, both emissions show intensity depletions along the geomagnetic North—South direction, and also bifurcation of the bubbles. It is frequently observed that the OI 557.7 image shows more fine structure of the bubble than the OI 630.0. The amplitude of the intensity depletion was also larger for OI557.7 than OI630.0. This might be due to the difference in life time between the O(¹D) and O(¹S) states, which are responsible for the OI 630.0 and OI 557.7 emissions, respectively. The O(¹D) might be affected by thermal relaxation and diffusion processes before the radiative transition.     

Nightside 135.6 nm emission enhancements of mid/low latitudes during geomagnetic storms as observed by the ionosphere PhotoMeter (IPM) on the Chinese meteorological satellite FY-3D

IPM has detected nightside 135.6 nm emission enhancements over a wide latitude range, from the sub-auroral latitudes to the equatorial regions during geomagnetic storms. Our work, presented in this paper, uses the data of IPM to understand these 135.6 nm emission enhancements during of geomagnetic storms and studies the variations of total electron content (TEC) and the F₂ layer peak electron density (NmF2) in the region of enhanced emissions. Middle and low latitude emission enhancements are presented during several medium storms in 2018. The variations of both the integrated electron content (IEC) derived from the nighttime OI 135.6 nm emission by IPM and TEC from the International GNSS Service (IGS) relative to the daily mean of magnetically quiet days of per each latitude bin (30°≦geographic latitude < 40°, 15°≦geographic latitude < 30°, 0°≦geographic latitude < 15°, ?15°≦geographic latitude < 0°, ?30°≦geographic latitude < -15°, ?40°≦geographic latitude < -30°) are investigated and show that on magnetically storm day, IEC by IPM always increases, while TEC from IGC may increase or decrease. Even if both increase, the increase of IEC is greater than that of TEC. From the comparison of IEC and TEC during magnetic storms, it can be seen that the enhancement of the nighttime 135.6 nm emissions is not entirely due to the ionospheric change. The time of IEC enhancements at each latitude bin is in good agreement, which mainly corresponds to the main phase time of the geomagnetic storm event and lasts until the recovery phase. The available ground-based ionosonde stations provide the values of NmF2 which match the 135.6 nm emissions measured by IPM in space and time. The variations of NmF2 squared can characterize the variations of the OI 135.6 nm emissions caused by O⁺ ions and electrons radiative recombination. The study results show that the OI 135.6 nm emission enhancements caused by O⁺ ions and electrons radiative recombination (where NmF2 squared increases) are obviously a contribution to the measured 135.6 nm emission enhancements by IPM. The contribution accounts for at least one of all contributions to the measured 135.6 nm emission enhancements by IPM. However, where the NmF2 squared provided by ionosonde decrease or change little (where the OI 135.6 nm emissions cause by O⁺ ions and electrons radiative recombination also decrease or change little), the emission enhancements measured by IPM at storm-time appear to come from the contributions of other mechanisms, such as energetic neutral atoms precipitation, or the mutual neutralization emission (O+ + O-→2O + h? (135.6 nm)) which also occupies a certain proportion in 135.6 nm airglow emission at night.     

Rocket observations of the atomic and molecular oxygen emissions in the equatorial region

A Brazilian sounding rocket, SONDA III, with two airglow photometers and two ionospheric electron density probes, was launched successfully from Natal (5.8°S, 35.2°W), Brazil, on December 11, 1985, at 23:30 GMT. The observed height profiles of the atomic oxygen OI 5577Å and molecular oxygen Atmospheric (0,0) band at 7619Å emissions are discussed. This is the first simultaneous measurement of these emissions in the equatorial region. A preliminary analysis shows that the two emissions have peak emission heights located between 95 and 96 km, and their half widths are about 6 km. The O₂A 7619Å emission peak, however, is located slightly lower, less than 1 km, than that of the OI 5577Å emission.     

A Method of Inversing the Peak Density of Atomic Oxygen Vertical Distribution in the MLT Region From the OI (557.7nm) Night Airglow Intensity

In this paper, using the MSISE-90 model as the reference atmosphere, we discuss the feasibility and method of deducing the peak densities of the undisturbed atomic oxygen profiles in the MLT region (the mesosphere and lower thermosphere region) from OI (557.7 nm) night airglow intersities. The peak densities for different seasons, latitudes and longitudes are deduced from OI (557.7nm) airglow intensities through this expression. We analyze the features of inversion relative errors and discuss the influence of the variations in temperature on inversion errors. The results indicate that all inversion errors are less than 5% except for those at high altitudes in the summer hemisphere. And the impact of the variations in temperature on errors is not significant.      

Seasonal variation in the solar diurnal tide and its possible influence on the atmospheric sodium layer

In a paper published 12 years ago, we showed that the height of the atmospheric sodium layer at our location is about 1 km lower in November than at any other time of the year. We also showed that the decrease in height of the sodium layer was accompanied by an increase in the intensity of the OI 557.7 nm and OH(9,4) band airglow emissions. At that time we suggested that this behavior could be the result of large scale convective transport in the MLT region. We have now had the opportunity to compare the diurnal variations of the sodium layer and airglow emissions with the tidal winds measured by meteor radar over the past 5 years. We find that the amplitude of the diurnal tide is much smaller in November than at other times of the year. Since most of the sodium measurements and all of the airglow observations are for night-time conditions only, a change in the amplitude of the 24-h tide could strongly influence the average measured sodium and airglow parameters. It is shown that the observed changes in the tidal winds are qualitatively consistent with the sodium measurements, but the amplitude of the observed height change is much greater than would be expected from the tidal winds.     

135.6nm夜气辉峰值电子密度反演算法及误差

根据夜间135.6nm大气辉光光强与F₂层峰值电子密度N_mF₂平方成正比的物理机制,在前期夜间135.6nm气辉辐射激发模型研究的基础上建立了峰值电子密度的反演算法,把全球经纬度分成若干格点,每个格点的电离层及中性成分信息分别由IRI2000和MSISE90提供,将电离层及中性成分廓线输入夜气辉辐射激发模型,计算每个格点135.6nm气辉的辐射强度,然后将各个格点的135.6nm气辉辐射强度与电离层廓线输入的N_mF₂平方拟合得到气辉强度与N_mF₂的转换因子.利用此方法可获得不同地方时、季节和太阳活动周期的转换因子组成查算表,进而根据实际探测的135.6nm气辉辐射强度反演相应时空的N_mF₂.最后对该算法的反演误差进行了综合分析,为该算法适用的时空特性提供重要理论支撑.      

Observations of non-migrating tides and ionospheric perturbations of O(D) airglow by ISUAL instrument

In this paper, we present the spatial variations of O(¹D) airglow observed by the ISUAL (Imager of Sprites and Upper Atmospheric Lightning) instrument on board the FORMOSAT-2 satellite. With a CCD camera and a 630 nm filter, ISUAL can measure global atmospheric emissions lying between the heights of 80 and 300 km. In days of 3–6 September 2008 and 25–27 February 2009, ISUAL has measured the emissions of O(¹D) airglow with results showing strong longitudinal peak-3 and peak-4 structures. The Lomb-Scargle analyses for these two cases show periods of longitudes of 120° and 90° supporting the DE2 and DE3 non-migrating tides. The 630 nm emissions are enhanced in equatorial regions and are lying along the equator. Over Africa its intensity can sometimes increase up to 80% relative to other longitudes. The perturbation is so strong that non-migrating tides are erased. A case of bimodal distribution with strong emissions at latitudes in equator and mid-latitude in geographic coordinates was observed.     

Thermospheric F-region travelling disturbances detected at low latitude by an OI 630 nm digital imager system

Gravity wave effects in the nocturnal thermospheric F-region domain are seldom detected in the intertropical region by optical (airglow) techniques, especially during geomagnetically quiet times, in part because the low inclination of the magnetic field, as opposed to the case of the mid-latitude region, does not favor significant vertical excursions of ionospheric plasma in response to meridional winds. Such difficulty in detecting gravity wave signatures in the F-region by means of optical techniques tends to increase in the absence of geomagnetic storms because of the lack of strong forcing mechanisms necessary to generate high intensity gravity waves. The purpose of this work is to show that during the quiet day of 9 August 1999, the Terminator may have been a source region of wave-like disturbances in the nocturnal F-region at the low-latitude station Cachoeira Paulista (22°41'S; 45°00W, dip 30°). A digital all-sky OI 630nm imager system located at that station has shown propagating wave-like spatial structures in the airglow intensity near the Terminator. This observation supports a previous study on the evidence of the presence of gravity waves during the post-sunset period at the same location by means of a scanning photometer system (1997, Sobral, J. Atmos. Terr. Phys. 59, 1611–1623). The absence of range-type spread-F as monitored by a local digisonde and the absence of radio wave scintillation as monitored by a local GPS receiver, excludes the hypothesis that the wave-like airglow structures are associated with the occurrence of the ionospheric plasma bubbles. Downwards motion of the iso-density real height contours at 22.0 ms⁻¹ and 33.1 ms⁻¹ are observed. The wave detection by the imager system is reported and discussed here.     

Imaging spectroscopy of the Venus 1.27-μm O2 airglow with ground-based telescopes

Several ground-based observations of the Venus 1.27-μm O₂ airglow were carried out from 2002 to 2005. Spectral image cubes were taken with the Okayama Astrophysical Observatory/infrared imaging spectrometer (superOASIS), the Gunma Astronomical Observatory/Cassegrain Near-Infrared Camera and NASA’s Infrared Telescope Facility/cryogenic echelle spectrograph (CSHELL). The brightest airglow features were found at around the anti-solar point, which is in agreement with previous studies. We derived the rotational temperature distributions on the nightside hemisphere from observed airglow spectra. The temperature shows a weak positive correlation with the airglow intensity. The result indicates the bright region is heated chemically and/or dynamically, and supports the existing scenario for the Venus O₂ airglow. That is, the airglow is excited by the descending oxygen transported from the dayside.     

Evidence of change after 2001 in the seasonal behaviour of the mesopause region from airglow data at El Leoncito

Airglow intensities and rotational temperatures of the OH(6-2) and O₂b(0-1) bands acquired at El Leoncito (32°S, 69°W) provide good annual coverage in 1998–2002, 2006, and 2007, with between 192 and 311 nights of observation per year. These data can therefore be used to derive the seasonal variations during each of these seven years, in airglow brightness and temperatures at altitudes of 87 and 95 km. From 1998 to 2001, seasonal variations are similar enough so that they can be well represented by a mean climatology, for each parameter. On the other hand, these climatologies do not agree with what is usually observed at other sites, maybe due to the particular orographic conditions at El Leoncito. With respect to the last three fully documented years (2002, 2006, and 2007), the similarity from year to year deteriorates, and there are greater differences in the seasonal behaviour, more or less in all the parameters. The differences include, e.g., maxima occurring earlier or later than “normal”, by one or two months. All this may suggest the build-up of a new regime of intraseasonal variability, with a possible relationship to corresponding changes in wave activity.     

Optical studies of the ionospheric irregularities over the brazilian region by nocturnal images of the OI 630 nm emission

This study is an extension of previous statistical studies (Sobral et al., 1990, 1991, 1999) of both the local time and latitude variations of the zonal drift velocities of ionospheric plasma depletions, over the Brazilian low latitude station Cachoeira Paulista — CP (22.54°S, 45.00°W). The past studies were based on OI 630 nm scanning photometer data and the present one is based on digital OI 630 nm airglow images obtained by an all-sky imager system. These data were gathered between October 1998 and October 1999, at CP. The present results show that, in general, the velocities clearly tended to decrease with local time. Such a decrease should be associated with decreasing intensity of the vertical component of the ambient electric field which, in turn can be accounted for by recombination. All zonal drifts obtained for the 18 nights were eastwards. During equinox, the velocities clearly tended to decrease with local time at lower rates as compared with spring and summer. The highest and lowest zonal drift velocities, from all three seasons considered here, were observed to be in the summer ≈180 ms⁻¹ at 21:45 LT, and in the spring ≈25 ms⁻¹ at 03:15 LT, respectively. Ionospheric plasma bubbles were detected out to the maximum extra-tropical geographical latitude of ≈28° S, which was the highest latitude position analyzed in this study.     

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 О₂ 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 О₂ (864–868 nm) emission measurements are presented.     

Quantifying the relationship between the measurement precision and specifications of a UV/visible sensor on a geostationary satellite

To investigate the feasibility of new satellite observations, including air quality (AQ) observations from geostationary (GEO) orbit, it is essential to link the measurement precision (ε) with sensor specifications in advance. The present study attempts to formulate the linkage between ε and specifications of a UV/visible sensor (signal-to-noise ratio (SNR), full width at half maximum (FWHM) of the slit function, and sampling ratio (SR)) on a GEO satellite. A sophisticated radiative transfer model (JACOSPAR) is used to calculate synthetic radiance spectra that would be measured by a UV/visible sensor observing the atmosphere over Tokyo (35.7°N, 139.7°E) from GEO orbit at 120°E longitude. The spectra, modified according to given sensor specifications, are analyzed by the differential optical absorption spectroscopy technique to estimate the ε for slant column densities of O₃ and NO₂. We find clear relationships: for example, the ε of the O₃ slant column density (molecules cm⁻²) and SNR at 330 nm are linked by the equation log(ε) = −1.06 · log(SNR) + 20.71 in the UV region, and the ε of the NO₂ slant column density and SNR at 450 nm are linked by log(ε) = −0.98 · log(SNR) + 18.00, at a FWHM = 0.6 nm (for the Gaussian slit function) and SR = 4. The relationships are mostly independent of other specifications (e.g., horizontal and temporal resolutions), as they affect ε primarily through SNR, providing constraints in determining the optimal SNR (and alternatively FWHM and SR) for similar UV/visible sensors dedicated for AQ studies.     

The O2+ vibrational distribution in the Venusian ionosphere

Calculations are presented of the vibrational distribution of O₂⁺ in the Venusian ionosphere for a model atmosphere based on Pioneer Venus data. At 100 km, quenching precludes the survival of vibrationally excited O₂⁺. At the exobase, near 200 km, more than half are vibrationally excited. The effects of vibrationally excited O₂⁺ on the hot oxygen corona and the airglow are discussed.     

A model of foreground emission in UV using GALEX deep observations

Foreground emission, mainly airglow and zodiacal light, is a significant contributor in an ultraviolet observation especially from low earth orbit. Its careful estimation and removal are tedious yet unavoidable processes in the study of diffuse UV radiation and by extension interstellar dust studies. Our analysis of deep GALEX observations show that airglow is not only a function of Sun angle but also a strong function of Solar activity at the time of observation. We present here an empirical model of airglow emission, derived from GALEX deep observations, as a function of 10.7 cm Solar flux and Sun angle. We obtained the model by training machine learning models on the data using a variant of the regression algorithm that is both resilient toward outlier data and sensitive to the complexities of the provided data. Our model predictions across various observations show no loss in generalization as well as good agreement with the observed values. We find that the total airglow in an observation is the sum of a baseline part (AG_c) that depends on the Solar flux and Sun angle, and a variable part (AG_v) that depends on the Sun angle and the time of observation with respect to local midnight. We also find that the total airglow can vary between 85 – 390 photon units in FUV and 80 – 465 photon units in NUV.     

Bottom side profiles for two close stations at the southern crest of the EIA: Differences and comparison with IRI-2012 and NeQuick2 for low and high solar activity

Bottom side electron density profiles for two stations at the southern crest of the Equatorial Ionization Anomaly (EIA), São José dos Campos (23.1°S, 314.5°E, dip latitude 19.8°S; Brazil) and Tucumán (26.9°S, 294.6°E, dip latitude 14.0°S; Argentina), located at similar latitude and separated by only 20° in longitude, have been compared during equinoctial, winter and summer months under low (year 2008, minimum of the solar cycle 23/24) and high solar activity (years 2013–2014, maximum of the solar cycle 24) conditions. An analysis of parameters describing the bottom side part of the electron density profile, namely the peak electron density NmF2, the height hmF2 at which it is reached, the thickness parameter B₀ and the shape parameter B₁, is carried out. Further, a comparison of bottom side profiles and F-layer parameters with the corresponding outputs of IRI-2012 and NeQuick2 models is also reported. The variations of NmF2 at both stations reveal the absence of semi-annual anomaly for low solar activity (LSA), evidencing the anomalous activity of the last solar minimum, while those related to hmF2 show an uplift of the ionosphere for high solar activity (HSA). As expected, the EIA is particularly visible at both stations during equinox for HSA, when its strength is at maximum in the South American sector. Despite the similar latitude of the two stations upon the southern crest of the EIA, the anomaly effect is more pronounced at Tucumán than at São José dos Campos. The differences encountered between these very close stations suggest that in this sector relevant longitudinal-dependent variations could occur, with the longitudinal gradient of the Equatorial Electrojet that plays a key role to explain such differences together with the 5.8° separation in dip latitude between the two ionosondes. Furthermore at Tucumán, the daily peak value of NmF2 around 21:00 LT during equinox for HSA is in temporal coincidence with an impulsive enhancement of hmF2, showing a kind of “elastic rebound” under the action of the EIA. IRI-2012 and NeQuick2 bottom side profiles show significant deviations from ionosonde observations. In particular, both models provide a clear underestimation of the EIA strength at both stations, with more pronounced differences for Tucumán. Large discrepancies are obtained for the parameter hmF2 for HSA during daytime at São José dos Campos, where clear underestimations made by both models are observed. The shape parameter B₀ is quite well described by the IRI-2012 model, with very good agreement in particular during equinox for both stations for both LSA and HSA. On the contrary, the two models show poor agreements with ionosonde data concerning the shape parameter B₁.     

中国山西地区法布里-珀罗干涉仪测风能力及数据质量检验

介绍了中国气象局山西岢岚大气观测站(39°N, 112°E) 法 布里-珀罗干涉仪(FPI) 的基本 构造、测风能力、程序处理流程、数据质量控制方法以及检验情况. 岢 岚观测站FPI可以观测892.0 (OH)nm, 557.7 (OI)nm和630.0 (OI)nm 波 长处气辉谱线的多普勒移动, 分别计算对应87km, 97km和250km高度处 的大气风速和大气温度, 可给出中间层顶区域及热层风的大气潮汐和扰动 情况. 采用水平风模型(HWM)输出结果进行交叉检验, 对FPI测风数据质量进行验证. 结果显示, 岢岚大气观测站FPI仪器的测风数据 在长期趋势上与HWM模式的输出数据一致, 风速变化幅度有季节性差异, 数据质 量控制方法有效, 测风误差在87km高度处为5.7m·s-1, 97km处 为1.3m·s-1, 250km处为4.1m·s-1, 测风数据 通过了可靠性检验.      

In situ results on the variation of neutral atmospheric hydrogen at venus

The concentrations of neutral hydrogen within the atmosphere of Venus are investigated for the period 1979–1980. During this period, the planet made nearly three orbits about the Sun, so that nearly three complete diurnal cycles were observed from the Pioneer Venus Orbiter (PVO). Values of n(H) are derived from in-situ ion and neutral composition measurements from the Orbiter Ion Mass Spectrometer (OIMS) and the Orbiter Neutral Mass Spectrometer (ONMS) using a charge exchange relationship involving O⁺, H⁺, O and CO₂. The dawn bulge in the diurnal distribution of n(H), reported from the first diurnal cycle by Brinton et al., is found to persist with n(H) peaking at levels near 2 - 5 × 10⁷/cm³ at altitudes below 165 km. At peak levels, the bulge exhibits a concentration ratio up to 400/1 relative to dayside values. Large day to day variations of up to a factor of five in n(H) are frequently encountered, and are attributed to perturbations induced by the solar wind interaction. These short term variations, plus a suggestion of some local time variation in the bulk location, make precise assessment of interannual variations in the n(H) difficult. Between the first diurnal cycle in early 1979 and the third in mid 1980, the decline in solar euv flux was of the order of 10% or less. Allowing for uncertainties due to short term variations, no clear evidence is found for an interannual variation in the hydrogen concentrations.