Ground-based observations of the natural hydroxyl (OH) nightglow at altitudes of 85-90 km are used for deriving the rotational temperature of excited OH, which is close to the neutral atmospheric temperature. For filtering of mesoscale perturbations, we use differences between pairs of measured values of OH rotational temperature separated with fixed time intervals in the range of 0.5-2 h. The filtering is applied for studying mesoscale variations of temperature near the mesopause according to the data of spectral OH nightglow measurements at observatories of Zvenigorod (56 degrees N, 37 degrees E.) in the years 2004-2016, Tory (52 degrees N, 103 degrees E) in 2012-2017 and Maymaga (63 degrees N, 130 degrees E) in 2000-2015. Monthly-mean values and variances of temperature disturbances with periods 0.7-8.2 h are determined. Semiempirical and statistical approaches are used to estimate and subtract variances of the instrumental dark current noise and uncorrelated in time fluctuations. Seasonal and interannual variations in standard deviations of correlated in time mesoscale perturbations of the OH rotational temperature at the considered observational sites are studied. They can give information about multiyear changes in the activity of atmospheric acoustic-gravity waves propagating through the OH layer near the mesopause. (c) 2023 COSPAR. Published by Elsevier B.V. All rights reserved.

В работе представлены статистические данные зарегистрированных внутренних гравитационных волн над центральной частью Якутии (северо-восточная часть Сибири) за период 2016–2018 гг. и 2020–2022 гг. Данные получены с помощью двух камер всего неба, настроенных на излучение гидроксила OH. Для каждого случая обнаруженных внутренних гравитационных волн рассчитаны такие параметры как: горизонтальная длина волны, период ВГВ, горизонтальная фазовая скорость, азимут направления распространения, время наблюдения и продолжительность. The paper presents statistical data on registered internal gravitational waves over the central part of Yakutia (northeastern Siberia) for the periods of 2016–2018 and 2020–2022. The data were obtained using two whole-sky cameras tuned to hydroxyl OH radiation. For each case of detected internal gravitational waves, parameters such as horizontal wavelength, wave period, horizontal phase speed, azimuth of propagation direction, observation time, and duration were calculated.

The article compares the interannual variability of the atmosphere at the OH glow height, which can be associated with planetary wave propagation, at stations spaced in latitude. As a characteristic reflecting planetary wave activity we consider standard deviations of the average overnight temperature σpw from its monthly average after taking into account the seasonal variation. Joint mesopause temperature measurements at high latitudes at two optical stations Maimaga (63.04° N, 129.51° E) and Tiksi (71.58° N, 128.77° E) began in 2015. The stations are equipped with identical Shamrock (Andor) high image quality infrared spectrographs for registration of OH (3-1) in the near infrared region (~1.5 μm). The main result of studying the planetary wave activity during the 5-year period of simultaneous observations is that at Tiksi station it slightly (by about 1–2 K) exceeds that at Maimaga station. In average annual activity fluctuations, the presence of quasi-biennial oscillations is traced.

Mesoscale variations of the rotational temperature of excited hydroxyl (OH*) are studied at altitudes 85 – 90 km using the data of spectral measurements of nightglow emission at Russian observatories Zvenigorod (56 ° N, 37°E.) in years 2004 – 2016, Tory (52 ° N, 103°E) in 2012 – 2017 and Maimaga (63° N, 130° E) in 2014 - 2019. The filtering of mesoscale variations was made by calculations of the differences between the measured values of OH* rotational temperature separated with time intervals of dt ~ 0.5 - 2 hr. Comparisons of monthly variances of the temperature differences for various dt allow us to estimate coherent and non-coherent in time components of the mesoscale temperature perturbations. The first component can be associated with mesoscale waves near the mesopause. The non-coherent component may be produced by instrument errors and atmospheric turbulence. The results allow us correcting the observed mesoscale temperature variances at all listed sites for contributions of instrumental and turbulent errors. Seasonal and interannual changes in the coherent component of mesoscale variances of the temperature at the observational sites are studied, which may reflect respective changes in the intensity of mesoscale internal gravity waves in the mesosphere and lower thermosphere region. The analysis of nightglows data was supported by the grant #19-35-90130 of the Russian Foundation for Basic Research. Hydroxyl nightglow data at the Tory site were obtained with the equipment of the Center for Common Use «Angara» http://ckp-rf.ru/ckp/3056/ at the ISTP SB RAS within budgetary funding from the Basic Research Program (Project 0278-2021-0003). Data of the “Geomodel” Resource Center of Saint-Petersburg State University were used.

At the Institute of Cosmophysical Research and Aeronomy, a meridional network of stations has been created, the purpose of which is to monitor the state of the atmosphere at the height of hydroxyl emission (similar to 87 km). The network covers arctic (Tiksi, 71.5 degrees N, 129 degrees E), subarctic (Maimaga, 63 degrees N, 129.5 degrees E) and middle (Neryungri, 56.39 degrees N, 124.43 degrees E) latitudes. Each station is equipped with a spectrograph with a highly sensitive InGaAs infrared photodiode measuring the OH (3-1) band. This paper presents the characteristics of spectrographs designed to measure the radiation intensity of the OH (3-1) band and determine the temperature from its rotational structure. An original technique for measuring the rotational temperature is described, based on minimizing the deviation of the recorded spectrum from the model by the least square method. Estimates of random and systematic errors showed that at a signal-to-noise ratio more than 20, the temperature measurement error is 2 K. Mutual calibration of the instruments showed that the difference in measurements lies within 2 K. The meridional network of stations is fully automated and controlled remotely via the Internet.

Based on the data of Total Electron Content (TEC) and OH rotational temperature, we analyze temporal and spatial features of the level of short-term variability (within the periods of up to several hours) at the ionosphere and the upper mesosphere. The study is carried out at three points located at mid-latitude, subauroral, and high-latitude regions during for more than 5 years period. The dynamics of variability, both in the ionosphere and at the mesopause, have the similar pattern with a clear seasonal variation. The maximum in the variability is registered in winter, and it exceeds up to 5-6 times the variability level during the summer period. This feature is observed regularly. The revealed dynamics does not correlate with changes the in geomagnetic and solar activities. The variability within considered periods is generally related to activity of Internal Gravity Waves in the upper atmosphere. We suggest that a source of the related seasonal variations in the variability may be the stratospheric high-velocity jet stream that develops in the subauroral regions during winter months. We propose a stratosphere disturbance index based on Era-5 Reanalysis data. The index is shown to have a maximum at subpolar regions and experience the similar regular seasonal variation with a maximum during winter months. We show a clear correlation between the mesosphere/ionosphere variability indices and the stratosphere disturbance index. The obtained results indicate a strong coupling between the short-period variability in the ionosphere, in the upper mesosphere, and in the subauroral stratosphere. The study is supported by the Russian Science Foundation Grant No. 20-77-00070.

Results of the study of the temperature in the mesopause region (∼87 km) based on measurement of OH (3-1) emission at the high latitude station Maimaga (63.04° N, 129.51° E) are presented and compared with the Aura (MLS) measurements of temperature at 0.002 hPa in 2013–2018 when flying over the Maimaga station. The average rotational temperature of OH (3-1) was compared with temperatures measured by Aura (MLS) and the background temperatures calculated from them. The results show more correct comparison of the OH (3-1) temperature with the background temperature calculated from Aura (MLS) data. The comparison confirms the observation of high temperatures in the mesopause in winter 2014/2015. In general, the temperature variations measured by two different methods are qualitatively consistent and answer the seasonal variations. Temperature differences can be explained by many factors, e.g., differences in measuring altitudes and techniques.

Temperature data of the mesopause region, obtained for the period 1999-2016 at the Maimaga station (63.04°N, 129.51°E), were studied. Registration of spectra was carried out with the help of light-sensitive infrared spectrographs SP-50, recording the OH (6-2) band. The standard deviation of temperature σpw from its average monthly value after deduction of seasonal temperature course is accepted as a characteristic of planetary wave activity. There is a quasi two-year cycle of planetary wave activity. A correlation is observed between the activity of planetary waves and the F10.7cm index.

We perform a joint analysis of short-period (up to several hours) variability in parameters of the ionosphere, the mesosphere, and the stratosphere at mid-latitude, subauroral, and high-latitude points for a long time interval. The study is based on the ionospheric total electron content (TEC) measurements and data on the OH rotational temperature at the mesopause height. We reveal similar seasonal variations in the dynamics of the short-term variability level, both in the ionosphere and the mesosphere. Maximum variability is observed during winter months and it exceeds the values in summer period up to 5–6 times. The revealed dynamics has no explicit relation to the levels of geomagnetic and solar activities. We suggest that the instabilities in the high-velocity stratospheric subauroral winter jet stream may be a source of the recorded variability seasonal variations in the ionosphere and the mesosphere. We propose a new index to estimate a short-term variability in the stratosphere. The index is shown to experience similar regular seasonal variations with a maximum during winter months. We show a clear correlation between the mesosphere/ionosphere variability indices values and the stratosphere disturbance index. The correlation is shown to be higher for the mesosphere variability index as compared with that in the ionosphere, and at the high-latitude point located closer to the jet stream. The obtained results indicate a strong interrelation between the short-period variability in the ionosphere, in the upper mesosphere, and in the subauroral stratosphere. The results contribute to elucidating the basic mechanisms for a vertical coupling between different atmospheric layers.

Simple digital filtering is used for studying mesoscale variations of the rotational temperature of excited hydroxyl (OH*) at heights 85 – 90 km according to the data of spectral measurements at observatories Zvenigorod (56°N, 37°E.) in years 2004 – 2016, Tory (52°N, 103°E) in 2012 – 2017 and Maymaga (63°N, 130°E) in 2000 - 2015. Monthly-mean values and standard deviations of OH* temperature disturbances with periods 0.7 – 8 hr are determined, which may reflect the intensity of internal gravity waves in the mesopause region. The filtering of mesoscale variations was performed by calculating the differences between the measured values of OH* temperature separated with time intervals of 0.5 - 2 hr. Seasonal and interannual changes in the mesoscale variances of the temperature at the observational sites are studied.

The analysis of changes in temperature of mesopause region based on fluctuation measurements of rotational temperature and intensity of molecular emission of hydroxyl OH (6-2) excited at ∼87 km altitude is presented. Observations were carried out at the Maimaga station (63°N, 129.5°E), at a distance of 120 km to the north from Yakutsk. Measurements were conducted with a digital infrared spectrograph. The temperature was determined from the distribution of the emission intensity in the different branches of the molecular hydroxyl band. Comparison OH(6-2) temperature with the calculated data of NRLMSISE-00 model was defined based on the data received from 1999 to 2015. 2320 midnight temperature values of hydroxyl OH (6-2) suitable for comparison were obtained at the Maimaga station over 16 years of measurements. The NRLMSISE-00 model describes temperature changes at the height of the mesopause region from October to April within the experimental fluctuations with a seasonal temperature variation of ∼ 35 K, deviations from the experimental values are no more than 7 ± 4 K. A correlation analysis was performed to compare the rotational temperature OH (6-2) and the NRLMSISE-00 model calculations. When the number of observations at the station Maimaga more than 180 days (about six months) correlation coefficient R> 0.7. This means that the NRLMSISE-00 model accurately describes the temperature changes of the subauroral mesopause.

Исследованы данные температуры области мезопаузы, полученные за период 2013-2018 гг. на станции Маймага (63.04N, 129.51E) и за период 2015-2018 гг. на станции Тикси (71.58 N, 128.77 E). В зимний период сезона наблюдений 2014-2015 характеристика активности внутренних гравитационных волн (ВГВ) gwимеет более низкие значения, чем в другие сезоны, а средненочная температура, наоборот, превышает аналогичные значения в другие сезоны. Для сопоставления рассматривались спутниковые данные температурных профилей полученные EOS MLS (Aura). После выделения и вычитания вклада гравитационной составляющей из температурных профилей EOS MLS для области над станцией Маймага заметно отличие в зимней стратопаузе сезона 2014-2015. В этот сезон в зимний период, с учетом вычета вклада флуктуаций температуры обусловленных ВГВ, наблюдается отсутствие резких потеплений в районе стратопаузы в отличие от остальных сезонов. Измерение параметров планетарных волн в течение периода 2015-2018 гг. совместных наблюдений на станциях Маймага и Тикси показали, что фазы наблюдаемых на обеих станциях волн совпадают, а амплитуды на станции Тикси несколько (12 К) превышают амплитуды на станции Маймага. The temperature data of the mesopause region obtained for the period 2013-2018 at the station Maimaga (63.04 N, 129.51 E) and for the period 2015-2018 at the station Tiksi (71.58 N, 128.77 E) was investigated. During the winter period of the 20142015 observation season, the characteristic of the internal gravity waves (IGW) activity sgw has lower values than in other seasons, and the average night temperature of the mesopause region, on the contrary, exceeds corresponding values in other seasons. For comparison, satellite data of temperature profiles obtained by EOS MLS (Aura) are given. After isolating and subtracting the contribution of the gravitaty waves from the EOS MLS temperature profiles for the region above the st. Maimaga, the difference in the winter stratopause of the 2014-2015 season is noticeable. In this season in winter there is a lack of sharp warming in the stratopause region, in contrast to other seasons, taking into account the deduction of the contribution of temperature fluctuations due to IGW. Measurement of the parameters of planetary waves during the period 2015-2018 of joint observations at Maimaga and Tiksi stations showed that the phases of the waves observed at both stations coincide, and the amplitudes at Tiksi station are several (1-2 K) higher than the amplitudes at Maimaga station.

The temperature data of the mesopause region obtained for the period 2013-2018 at the station Maimaga (63.04 degrees N, 129.51 degrees E) was investigated. During the winter period of the 2014-2015 observation season, the characteristic of the internal gravity waves (IGW) activity sigma(gw) has lower values than in other seasons, and the average night temperature of the mesopause region, on the contrary, exceeds corresponding values in other seasons. For comparison, satellite data of temperature profiles obtained by EOS MLS (Aura) are given. After isolating and subtracting the contribution of the gravitational component from the EOS MLS temperature profiles for the region above the Maimaga station, the difference in the winter stratopause of the 2014-2015 season is noticeable. During this season, the winter stratopause has lower temperatures than in other seasons, taking into account the deduction of the contribution of temperature fluctuations due to IGW.

The results of measuring the temperature of the atmosphere at the height of the hydroxyl radiation (OH) during the geomagnetic storm of October 29 - 31, 2003 are presented. Measurements of the rotational temperature of the OH (6-2) band emission were carried out at Maimaga station (63 ° N, 129.5 ° E). In addition, the magnitude of OH volume emission, its layer height, atmospheric temperatures, NO, and atomic oxygen obtained by a SABER radiometer installed on the TIMED satellite were analyzed. Simultaneous growth of OH layer temperature, NO and atomic oxygen amounts accompanied by layer downward are observed. First jump coincided with the maximum of geomagnetic activity on 29 October. The next growth took place on November 4th, when the geomagnetic activity decrease.

The temperature of the mesopause region (87 km) is monitored at the Maimaga station (63.04° N, 129.51° E) using the Shamrock (Andor) spectrograph recording the OH band (3, 1). The temperature data obtained for the seasons from 2013 to 2017 are investigated. Standard temperature deviations σgw corresponding to internal gravity waves are obtained. The seasonal variation of the gravitational component of standard deviations of temperature σgw observed at Maimaga station almost coincides for three observation seasons except for the 2014-2015 season. In this observation season, σgw has lower values in winter than in other seasons. In addition, in the 2014-2015 season, average monthly temperatures exceed similar values in other seasons.

Characteristics of spectrographs intended for measurement of radiation intensity of the OH (3-1) band and determination of the atmosphere temperature at a glow height by its rotational structure are presented. The Shamrock 303i spectrographs supplied by high-sensitive infrared InGaAs photodiode register of Andor Technolog company have been installed at the Maimaga (63 degrees N, 129.5 degrees E) and Tixie (71.5 degrees N, 129 degrees E) stations. The technique of measurement of the rotational temperature, estimation of casual and regular errors is described. The calibration measurements with two spectrographs at Majmaga station have shown that the difference of nightly average values of temperature does not exceed errors of measurement with the device.

Целью исследования является выявление особенностей характеристик и динамики внутренних гравитационных волн (ВГВ) в области мезопаузы высоких широт. Эти волны играют существенную роль в термодинамическом равновесии всей атмосферы, тем самым и в формировании климата. Также благодаря возрастанию амплитуды внутренних гравитационных волн по мере их проникновения на большие высоты становится возможным их обнаружение в верхних слоях атмосферы. В данной статье представлена визуализация ВГВ при помощи двух камер всего неба, регистрирующих эмиссии ночного неба на двух разных высотах мезопаузы (87 км и 97 км). Первая камера регистрирует эмиссии полос молекулы гидроксила в ближней инфракрасной области, которые излучаются на высоте 87 км. Вторая камера регистрирует ВГВ в видимой области спектра по зеленой эмиссии атомарного кислорода (557,7 нм), излучающиеся на высоте 97 км. Обе камеры установлены на высокоширотной оптической станции Маймага (63°N, 129.5°E). Для визуализации и обработки данных камер всего неба был использован временной метод обработки (time differencing (TD)). Для гравитационных волн с периодами больше, чем частота съемки, TD-картина усиливает контраст в областях, где волны движутся, усиливаются или ослабляются. По данным камер на примере одной ночи получены горизонтальные характеристики ВГВ (направление распространения, скорость, период и длина волны). На данном примере у обеих камер с самого начала наблюдения происходит медленное перемещение (v~20-35 м/с) короткопериодных волн (длина волны до 10 км) по направлению с северо-запада на юго-восток. Более отчетливое движение начинается с 15:25 (UT) по зеленой эмиссии и с 15:47 (UT) – по эмиссиям гидроксила (разница высот ~10 км). Затем примерно одновременно у обеих камер (~17:30(UT)) начинается резкое движение более крупных волн (λ ~ 40-60км) с направлением распространения на северо-восток со скоростью от 70 до 160 м/с.Ключевые слова: атмосфера, мезосфера, внутренние гравитационные волны, мезопауза,

Since 2013, the optical station of Maimaga (63° N, 129.5° E) has been continuously recording the OH(3,1) hydroxyl band with a spectrograph operating in the near-infrared region (~1.5 μm). In September 2015, a similar spectrograph was mounted at the polar geophysical observatory located in the Tiksi urban locality (71.6° N, 128.7° E). The present work compares the seasonal variation of the mesopause temperature measured at two different- latitude stations. In addition, preliminary comparisons are made for overnight variations for several nights. The comparison shows that there is a very good correlation between data obtained at the two stations, with a correlation coefficient of 0.83. A comparison with the predictions of the CIRA and MSIS empirical atmospheric models revealed a number of discrepancies.