Mesosphere Research Articles

Diurnal Response of CO2 Radiative Cooling to September 7-9, 2017 Storm

The solar and magnetospheric energy deposition into Earth’s high latitude region modulates the magnetosphere-ionospherethermosphere system during geomagnetic storm periods. One of the impacts of geomagnetic storm is the significant thermosphere temperature increment. This temperature increase is regulated by radiative cooling emissions via CO2 at 15 µm and NO 5.3 µm. We utilized CO2 15 µm radiative emissions observations by SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument onboard NASA’s TIMED (Thermosphere Ionosphere Mesosphere Energetics Dynamics) satellite, to investigate the diurnal response during September 7-9, 2017 storm. The volume emission rate of CO2 emission, in the altitude of 100-140 km, is integrated vertically to estimate cooling flux. The geomagnetic storm induced a significant enhancement in CO2 emission across all latitudes and altitudes considered. While the storm typically has stronger impacts on high latitudes, the response in CO2 emission was notably stronger in mid and low latitude regions both during day and night. The nighttime value is generally lower, with a faster response time, as compared to the day time counterpart. Further a strong hemispheric asymmetry is observed both during day and night. This study highlights a complex interplay of solar and magnetospheric influences on the diurnal variation of Earth's upper atmosphere.

Measurement of the vertical distributions of atmospheric pollutants using an uncrewed aerial vehicle platform in Xi'an, China.

Vertical observations of atmospheric pollutants play crucial roles in a comprehensive understanding of the distribution characteristics and transport of atmospheric pollutants. A hexacopter uncrewed aerial vehicle equipped with miniature monitors was employed to measure the vertical distribution of atmospheric pollutants within a height of 1000 m at a rural site in Xi'an, China, in 2021. The concentrations of carbon monoxide (CO) and particulate matter (PM) showed generally decreasing trends with increasing height. The ozone (O3) concentration showed a general increasing trend with height followed by a gradual decreasing trend. Vertical decrements of PM2.5 and CO from 0 to 1000 m were significantly (p < 0.05) lower on observation days during summer (14.0 ± 8.1 μg m-3 and 8.7 ± 6.6 ppb, respectively), compared with those in winter (78.3 ± 14.1 μg m-3 and 34.8 ± 17.3 ppb, respectively). The horizontal transport of PM and CO mostly occurred in the morning and at night during winter observations at an altitude of 400-500 m. During the winter haze, the PM and CO profile concentrations below 500 m increased substantially with the decrease in the height of the thermal inversion layer. Vertical O3 transportation was observed in the afternoon and evening during summer, and a ∼37.7% (11.6 ppb) increase in ground-level O3 was observed in relation to vertical transport from the upper atmosphere. The results provide insights into the vertical distribution and transport of atmospheric pollutants in rural areas near cities.

Precipitation Scaling in Extreme Rainfall Events and the Implications for Future Indian Monsoon: Analysis of High‐Resolution Global Climate Model Simulations

AbstractThe increase in water holding capacity of the atmosphere with temperature, given by the Clausius‐Clapeyron (CC) relationship, describes the changes in extreme rainfall intensities at warmer atmospheric states. We study the characteristics of extreme rainfall events (EREs) during the Indian summer monsoon season with respect to thermodynamic changes and precipitation‐scaling over the Indian subcontinent and its homogeneous rainfall zones. We utilize outputs from a present‐day climate simulation and a time‐slice future climate change projection experiments of a high‐resolution global climate model. Large changes are seen for very EREs (vEREs) which suggests their sensitivity to warmer temperatures. In future, the altered radiative forcing will heat up the upper atmosphere, stabilize it and offset the effect of increasing humidity on precipitation intensity. Our analysis also suggests that more convective clouds and the interplay of increased moisture content and circulation will result in future changes in EREs.

Hans Pfaall's Breath: Edgar Allan Poe and Antebellum Atmospheres

ABSTRACT: This essay examines the connections between Edgar Allan Poe's "The Unparalleled Adventure of One Hans Pfaall" and the scientific and political discourse of antebellum America, particularly insofar as it centered on atmospheric science. This essay argues that Poe's story should be read within an antebellum comprehension of atmospheric science that used the atmosphere as a metaphor to comment on freedom, revolution, and slavery. I read Hans's journey through the atmosphere as a thought experiment addressing the contemporary scientific challenge of measuring the upper atmosphere, while also engaging with the era's scientific literature, notably the work of the French astronomer Benjamin Valz. Furthermore, the essay examines the story's engagement with racial determinism and its commentary on human liberty. I suggest that Hans's interaction with the atmosphere both figuratively and literally reflects upon contemporaneous ruminations about race and bondage. By placing "Hans Pfaall" amidst the scientific discourse on atmospheric and astronomical sciences and examining its political and intellectual underpinnings, the essay contributes to the understanding of Poe's work within the broader context of nineteenth-century science and its metaphorical use in literature to address questions of human liberty and knowledge.

On the Seasonal Variations of the Ion Precipitation Down to the Upper Atmosphere of Mars

We investigate the seasonal variations of ion precipitation, utilizing observations from the Mars Atmosphere and Volatile Evolution mission spanning from 2014 January 4 to 2023 February 14. Our analysis reveals that a diminishing pattern characterizes the transition from Mars season L s 0°–180° to Mars season L s 180°–360°, manifesting as a reduction in precipitating ion fluxes. Additionally, we discern a significant influence of the crustal magnetic field on the seasonal variations in precipitating ion fluxes. Intriguingly, within regions where the crustal magnetic field exhibits a strong quasi-horizontal orientation, opposite seasonal trends become evident. The underlying physical mechanism driving these seasonal variations in ion precipitation is probably attributed to the mass loading effect that may decelerate the solar wind and influence the magnetic pileup. A detailed investigation is further demanded in the future.

The Study of Characteristics and Imaging of Infrared Radiation of Middle and Upper Atmosphere Background

The Study of Characteristics and Imaging of Infrared Radiation of Middle and Upper Atmosphere Background

A study of very high resolution visible spectra of Titan: Line characterisation in visible CH[formula omitted] bands and the search for C[formula omitted

The atmosphere of Titan is a unique natural laboratory for the study of atmospheric evolution and photochemistry akin to that of the primitive Earth, with a wide array of complex molecules discovered through infrared and sub-mm spectroscopy. Here, we explore high resolution visible spectra of Titan (obtained with VLT-UVES) and retrieve an empirical high resolution list of methane absorption features at high resolution, (R=100.000) between 5250 Å and 6180 Å, for which no linelists are yet available. Furthermore, we search for the predicted, but previously undetected carbon trimer, C3, on the atmosphere of Titan, at its 4051 Å band. Our results are consistent with the presence of C3 at the upper atmosphere of Titan, with a column density of 1013 cm−2. This study of Titan’s atmosphere with high-resolution visible spectroscopy presents a unique opportunity to observe a planetary atmosphere where CH4 is the main visible molecular absorber, from which CH4 optical proprieties can be studied. It also showcases the use of a close planetary target to test new methods for chemical retrieval of minor atmospheric compounds, in preparation for upcoming studies of cold terrestrial exoplanet atmospheres.

The Impacts of Dust Storms With Different Transport Pathways on Aerosol Chemical Compositions and Optical Hygroscopicity of Fine Particles in the Yangtze River Delta

AbstractAerosol physicochemical properties during two dust storms (DS1: March 30–31, and DS2: May 7–8) are measured in 2021 in Nanjing, aiming to investigate the impacts of dust storms on aerosol chemical compositions and optical hygroscopicity in the Yangtze River Delta (YRD). During DS1, the dust air masses are transported in the lower atmosphere and pass through the inlands and sea areas before reaching the YRD region. During DS2, the dust air masses are transported in the upper atmosphere and pass through the inlands only. Both of them are accompanied by an increase in black carbon (BC) mass fraction and a decrease in nitrate mass fraction in fine particles (PM2.5, particles with diameters less than 2.5 μm) near the surface. However, the impacts on the mass fractions of organics or sulfate are adverse between DS1 and DS2. During dust‐influence periods the enlarged mass ratios of sulfate to nitrate (greater than 4) promote the occurrence of deliquescent behavior of ambient aerosols although dust aerosols can significantly suppress aerosol optical hygroscopicity. To improve model simulations of aerosol optical hygroscopicity, it is necessary to use a segment parameterization to describe aerosol light scattering enhancement factor during dust‐influence periods. The closure study of optical hygroscopicity parameters with two different methods reveals the impact of aerosol scattering Ångström exponent on the estimation of optical hygroscopicity parameter. The results highlight that the impact of dust storms on aerosol chemical compositions and optical hygroscopicity are different for DS events with different transport pathways.

The Fragile State of Industrial Agriculture: Estimating Crop Yield Reductions in a Global Catastrophic Infrastructure Loss Scenario.

Modern civilization relies on a complex, globally interconnected industrial agriculture system to produce food. Its unprecedented yields hinge on external inputs like machinery, fertilizers, and pesticides, rendering it vulnerable to disruptions in production and international trade. Such a disruption could be caused by large-scale damage to the electrical grid. Solar storms, nuclear detonations in the upper atmosphere, pandemics, or cyber-attacks, could cause this severe damage to electrical infrastructure. To assess the impact of such a global catastrophic infrastructure loss on major food crops (corn, rice, soybean, wheat), we employ a generalized linear model. The predictions show a crop-specific yield reduction between 15% and 37% in phase 1, the year after the catastrophe, assuming rationed use of fertilizers, pesticides, and fuel stocks. In phase 2, when all stocks are depleted, yields decrease by 35%-48%. Soybean is less affected in phase 1, while all crops experience strong declines in phase 2. Europe, North and South America, and parts of India, China, and Indonesia face major yield reductions, potentially up to 75%, while most African countries are less affected. These findings underscore the necessity for preparation by highlighting the vulnerability of the food system.

Discrete Aurora at Mars: Insights Into the Role of Magnetic Reconnection

AbstractDiscrete aurora are sporadic emissions of light originating in Mars upper atmosphere. We report nadir imaging observations from MAVEN's Imaging UltraViolet Spectrograph which identify the conditions which trigger electron precipitation causing these events. Prior studies have shown that discrete aurora events in the strong crustal magnetic field region in the southern hemisphere are the brightest and most repeatable compared to events occurring outside the region. Our new data set offers a more complete and accurate characterization of aurora in this area. The region of strongest crustal fields is composed of two distinct magnetic regions, with magnetic fields in opposite directions; discrete aurora events trigger in one region after dusk and in the other before dawn. Magnetic reconnection in these two adjacent regions with the draped interplanetary field may open the crustal fields in these regions during opposing local times. Particle precipitation can then cause discrete aurora at the observed times and locations.

Planetary Wave Modulation of Gravity Waves Over the Andes in 2016

AbstractThe Andes account for the largest source of orographic gravity waves (GWs) in the middle atmosphere. This results from persistent, strong zonal winds at the surface encountering the north‐south mountain chain, producing strong orographic lift, and resulting GWs. Here, we consider GWs in the stratosphere and mesosphere above the Andes as observed by the Cloud Imaging and Particle Size instrument, the Solar Occultation for Ice Experiment on the AIM satellite, and the Sounding of the Atmosphere using Broadband Emission Radiometry instrument onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. GW variability is considered in the context of the location of the stratospheric wintertime westerly jet and planetary wave (PW) amplitude and phase. The occurrence of GWs in the middle and upper atmosphere depends not only on tropospheric sources, like the Andes, but also on the background winds through which they propagate. Results suggest that the propagation of GWs into the mesosphere is well correlated with winds throughout the middle and upper stratosphere. PWs cause the westerly jet to move over the Andes, resulting in an increase in GW amplitude throughout the middle and upper stratosphere. The evolution and variability of GWs are tied closely to the phase of the PW‐1 and are linked to PW‐2 when the PW amplitudes are sufficiently large. GW amplitude, as observed by all three data sets, increases in the upper stratosphere and lower mesosphere when the trough of the PW‐1 in the stratosphere is over the Andes.

Determination of Impacts of Climate Change on Temperature and Rainfall Variations in Some Southern Iraqi Governorate Using GIS

The concept of temperature change is closely related to climate change. Global warming is one of its most prominent manifestations, and the effects of this will be significant on the climate. It will lead to an increase in the intensity of the air cycle, the encroachment of climatic regions towards the poles, an increase in the frequency of extreme weather phenomena, a change in the distribution of heat and rain in different cities of the world, and a rise in sea levels and the threat of most coastal areas. The research aims to determine the variation in temperature, the amount of rain, and its distribution system in the (Basra, Thi Qar, and Missan) during the period (1998 – 2020), and diagnosis of changes in temperature, rain amount, and their cause, as well as its distribution system by analyzing the trend of change in the annual averages of temperature and annual rainfall amounts for the same study period. The results of spatial analysis using GIS for monthly temperature average data for the same period indicated that the general trend of temperature distribution in all study stations is high, and the peaks during the months (June, July, August, and September), where we notice a large and clear increase, especially in recent years, if compared with rates in previous years. As for the rain data analysis in Iraq, the study found that it was limited to five months (Nov., Dec., Jan., March, April), and October month, which represents the beginning of the rainy season in most monitoring stations, and the month of March, which represents its end, did not record any amount of rain, and this means that the depressions which Iraq exposed to during these two months are unable to produce heavy amounts of the rain because of their shallowness, from the spatial distribution of the amount of rain in the study area that the rainfall rates are reduced to the highest level and its irregular distribution, and therefore reflected in the decrease in water resources in the areas under study. A large amount of daily precipitation in Iraq is due to the recurrence of three atmospheric depressions the (Mediterranean, combined, and Sudanese) depression. These responsible depressions are distinguished by their differences from one region to another, the short duration of their stay and recurrence, the weather conditions that dominate them, and the pressure patterns accompanying them in the upper atmosphere layers. Or some of these depressions reach dryness or are accompanied by non-rainy clouds. This makes Iraq’s rains few, leading to many repercussions on climate, the environment, humans, and various activities.

Modeling Total Electron Content and Critical Frequency at F1 and E Layer Boundary

This work investigates the variation of the total electron content TEC and the critical frequency fo in the boundary zone of the F1 and E layers at the low-latitude in the ionosphere. This study takes place at the Ouagadougou station (12.4°N and 358.5°E), in West Africa during the quiet geomagnetic activity of solar cycle 23. Ionosphere is the upper layer of the Earth's atmosphere ionized mainly by solar X- and UV-rays, extending from around 80km altitude up to 1000km [1] [2]. Ultraviolet light from the sun ionizes the atoms and molecules in the Earth's upper atmosphere [3]. For this study we use the 2016 version of International Reference Ionosphere (IRI) model. The quiet periods of maximum and minimum phase of solar cycle 23 are considered [4] [5]. From this study, it emerges that at the E and F1 layer boundary zone, TEC and fo increase during the day as solar irradiance increases and decrease as solar irradiance decreases.

Amplification of Coupled Hot‐Dry Extremes Over Eastern Monsoon China

AbstractHigh air temperatures and low atmospheric humidity can result in severe disasters such as flash droughts in regions characterized by high humidity (monsoon regions). However, it remains unclear whether responses of hot extremes to warming temperature are amplified on dry days as well as the response of dry extremes on hot days. Here, taking eastern monsoon China (EMC) as a typical monsoon region, we find a faster increase in air temperature on drier summer days, and a faster decrease in atmospheric humidity on hotter days, indicating “hotter days get drier” and “drier days get hotter” (i.e., coupling hotter and drier extremes), especially in southern EMC. The southern EMC is also a hotspot where the coupling hot‐dry extremes has become significantly stronger during the past six decades. The stronger hot‐dry coupling in southern EMC is associated with anomalies in large‐scale circulations, such as reduced total cloud cover, abnormal anticyclones in the upper atmosphere, intense descending motion, and strong moisture divergence over this region. Land‐atmosphere feedback enhance the hot‐dry coupling in southern EMC by increasing land surface dryness (seen as a decrease in the evaporation fraction). The decreasing evaporation fraction is associated with drying surface soil moisture, controlled by decreases in pre‐summer 1‐m soil moisture and summer‐mean precipitation. Given hot extremes are projected to increase and atmospheric humidity is predicted to decrease in the future, it is very likely that increasing hot‐dry days and associated disasters will be witnessed in monsoon regions, which should be mitigated against by adopting adaptive measures.

Estimating Geomagnetically Induced Currents in High‐Voltage Power Lines for the Territory of Kazakhstan

AbstractExtreme solar events, such as powerful solar flares are accompanied by the release of strong solar disturbances, such as coronal mass ejections (CMEs). The impact of CMEs on the Earth's magnetosphere causes geomagnetic storms, which trigger geomagnetic effects measurable in the ionosphere, upper atmosphere, and on and in the ground. During extreme cases, rapidly changing geomagnetic fields generate intense geomagnetically induced currents (GICs), which can cause dramatic effects on man‐made technological systems, including transmission lines and pipelines. In countries with large territories such as Kazakhstan, long power lines contribute to high values of induced currents during periods of extreme geoeffective solar events. It is of interest to estimate the values of GICs in an extensive network of power lines on the territory of Kazakhstan. However, there are no estimations of induced currents in power lines in Kazakhstan, and most estimation techniques are made difficult because of absence of field measurements of Earth conductivity. This study aims to model geoelectric fields on the surface of the Earth for Kazakhstan and to estimate the values of the GICs in 500 kV power lines. This study also compares between two methods for calculating induced voltages in power lines: one based on linear paths and the other based on curvilinear paths between substations of transmission power lines.

A Comparative Assessment of the Distribution of Joule Heating in Altitude as Estimated in TIE‐GCM and EISCAT Over One Solar Cycle

AbstractDuring geomagnetically active times, Joule (or frictional) heating in the Lower Thermosphere‐Ionosphere is a significant source of thermal energy, greatly affecting density, temperature, composition and circulation. At the same time, Joule heating and the associated Pedersen conductivity are amongst the least known parameters in the upper atmosphere in terms of their quantification and spatial distribution, and their parameterization by geomagnetic parameters shows large discrepancies between estimation methodologies, primarily due to a lack of comprehensive measurements in the region where they maximize. In this work we perform a long‐term statistical comparison of Joule heating as calculated by the NCAR Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM) and as obtained through radar measurements by the European Incoherent Scatter Scientific Association (EISCAT). Statistical estimates of Joule heating and Pedersen conductivity are obtained from a simulation run over the 11 year period spanning from 2009 until 2019 and from radar measurements over the same period, during times of radar measurements. The results are statistically compared in different Magnetic Local Time sectors and Kp level ranges in terms of median values and percentiles of altitude profiles. It is found that Joule heating and Pedersen conductivity are higher on average in TIE‐GCM than in EISCAT for low Kp and are lower than EISCAT for high Kp. It is also found that neutral winds cannot account for the discrepancies between TIE‐GCM and EISCAT. Comparisons point toward the need for a Kp‐dependent parameterization of Joule heating in TIE‐GCM to account for the contribution of small scale effects.

Investigation of Titan’s South Polar HCN Cloud during Southern Fall Using Microphysical Modeling

Ice clouds in Titan’s polar stratosphere are implicated in radiative heating and cooling and in transporting volatile organic compounds from where they form in the upper atmosphere to the surface of the moon. In early southern fall, Cassini detected a large, unexpected cloud at an altitude of 300 km over Titan’s south pole. The cloud, which was found to contain HCN ice, was inconsistent with the most recent measurements of temperature in the same location and suggested that the atmosphere had to be 100 K cooler than expected. However, changes to Cassini’s orbit shortly after the cloud’s appearance precluded further observations, and, consequently, the atmospheric conditions and the details of the formation and evolution of the cloud remain unknown. We address this gap in the observational record by using microphysical cloud modeling to estimate the parameter space consistent with published measurements. Based on the nearest available temperature profile retrievals and other observations, we hypothesize that the cloud forms around 300 km and then descends until it reaches the cold lower stratosphere by late southern fall. The observations can be simulated using a cloud microphysical model by introducing a descending cold layer with temperatures near 100 K. In simulations of this scenario, the precipitation from this cloud rapidly removes over 70% of the HCN vapor from the stratosphere. This result suggests that vapor descending into the polar stratosphere during early fall is mostly removed from the stratosphere before the onset of winter and does not circulate to lower latitudes.

Disentangling Photoelectrons and Penetrating Solar Wind Electrons in the Dayside Martian Upper Atmosphere

AbstractIn situ produced photoelectrons and precipitating solar wind electrons are two distinct hot electron populations in the dayside Martian upper atmosphere. While each population has been known for decades, its relative contribution to the measured hot electron flux has not been adequately characterized up to now. In this study, we implement a two‐stream kinetic model to compute the hot electron flux for a open magnetic field configuration. By comparing model results to realistic data acquired by the Mars Atmosphere and Volatile Evolution mission, we show that the electron fluxes predicted by the pure photoelectron model are enormously underestimated, especially in the direction toward Mars, but the measurements can be adequately reproduced once solar wind electron precipitation is taken into account. Such a precipitation plays a crucial role above 180 km, not only for hot electrons at all energies that move toward Mars but also for electrons above 1,000 eV that move away from Mars due to the backscattering of precipitating electrons. In contrast, the hot electron population is predicted to be mostly composed of photoelectrons below 180 km. The significance of precipitating solar wind electrons is also evaluated, revealing an appreciable impact on the structure of the dayside Martian upper atmosphere at high altitudes, where electron impact ionization is enhanced by a factor of 7 and cold electron heating enhanced by a factor of 4.

The First Y Dwarf Data from JWST Show that Dynamic and Diabatic Processes Regulate Cold Brown Dwarf Atmospheres

The James Webb Space Telescope (JWST) is now observing Y dwarfs, the coldest known brown dwarfs, with effective temperatures T eff ≲ 475 K. The first published observations provide important information: not only is the atmospheric chemistry out of equilibrium, as previously known, but the pressure–temperature profile is not in the standard adiabatic form. The rapid rotation of these Jupiter-size, isolated, brown dwarfs dominates the atmospheric dynamics, and thermal and compositional changes disrupt convection. These processes produce a colder lower atmosphere, and a warmer upper atmosphere, compared to a standard adiabatic profile. Leggett et al. presented empirical models where the pressure–temperature profile was adjusted so that synthetic spectra reproduced the 1 ≲ λ (μm) ≲ 20 spectral energy distributions of brown dwarfs with 260 ≤ T eff (K) ≤ 540. We show that spectra generated by these models fit the first JWST Y dwarf spectrum better than standard-adiabat models. Unexpectedly, there is no 4.3 μm PH3 feature in the JWST spectrum and atmospheres without phosphorus better reproduce the 4 μm flux peak. Our analysis of new JWST photometry indicates that the recently discovered faint secondary of the WISE J033605.05-014350AB system has T eff ≈ 295 K, making it the first dwarf in the significant luminosity gap between the 260 K WISE J085510.83-071442.5, and all other known Y dwarfs. The adiabat-adjusted disequilibrium-chemistry models are recommended for analyses of all brown dwarfs cooler than 600 K, and a grid is publicly available. Photometric color transformations are provided in an appendix.

Statistical Analysis of the Horizontal Phase Velocity Distribution of Atmospheric Gravity Waves and Medium‐Scale Traveling Ionospheric Disturbances in Airglow Images Over Sata (31.0°N, 130.7°E), Japan

AbstractAtmospheric gravity waves (AGWs) and medium‐scale traveling ionospheric disturbances (MSTIDs) in the upper atmosphere affect atmospheric circulation and radio‐wave transmission including satellite positioning and communications, and high‐frequency radio. The 3‐dimensional (3‐D) spectral analysis of airglow images makes it possible to extract wave parameters of AGWs and MSTIDs. Such spectral analysis of long‐term airglow images has not been performed in the southern part of Japan, which is a unique transition latitude from middle to equatorial region. In this study, we calculated the horizontal phase velocity distribution of AGWs in the mesosphere‐lower‐thermosphere (MLT), and MSTIDs in the F‐region ionosphere by applying the 3‐D spectral analysis method to the 557.7 and 630.0‐nm airglow images obtained at Sata (31.0°N, 130.7°E) in Japan over 20 years from 2000 to 2020. The spectra of AGWs in the MLT region in the 557.7‐nm airglow images show that the poleward (northward) power spectral density (PSD) is stronger in summer, suggesting that the tropospheric convection is a possible source of AGWs and the wave ducting propagation occurred. Westward propagation is also observed in winter, suggesting that wind filtering effect by mesospheric jets plays an important role. The PSD of MSTIDs in the 630‐nm airglow images increases during low solar activity periods, suggesting that MSTIDs are produced by ionospheric plasma instability. The westward PSD of MSTIDs is stronger in summer. These results are an important achievement in clarifying the statistical characteristics of AGWs and MSTIDs over Sata, Japan, based on long‐term airglow observations and 3‐D spectral analysis.