Displays

In the last decade, it was shown that volume emission rates (VMR) for transitions from the levels O₂(b¹Σ⁺_g, v’ = 0 – 2) to the levels O₂(X³Σ^-_g, v’’) can be used as proxies for retrieving the altitude profiles of [O(³P )], [O₃] and [CO₂] in the mesosphere and lower thermosphere (MLT) [1, 2]. Despite the fact that, in single experiments, radiation in the bands 762, 688, and 628 nm corresponding to the abovementioned transitions were observed (e. g., [3]), no systematic measurements of the intensities of these emissions have yet been performed. The main source of excitation of the levels O₂(b¹Σ⁺_g, v’ = 0 – 2) is the energy transfer from the excited O(¹D) atom, along with the resonant absorption of solar radiation in these bands in the mesosphere.

In the framework of the YM2011 model of electronical-vibrational kinetics of the excited products of O₂ and O₃ photolysis, using systematic SABER satellite experimental data on the [O (¹D)] altitude profiles we calculated the altitudinal-latitudinal distributions of the O₂(b¹Σ⁺_g, v’ = 0 – 2) concentrations  and VMR in the corresponding bands, using the 2010 data as an example. It was shown that there is a seasonal dependence of the altitude profiles of the concentrations of excited states O₂(b¹Σ⁺_g, v’ = 0 – 2) obviously related to the seasonal changes of [O(³P)] and [O₃] profiles.

This work was supported by the Russian Foundation for Basic Research  (grant RFBR No. 20-05-00450 A).

1. Yankovsky V. A., Martyshenko K. V., Manuilova R. O., Feofilov A. G. (2016), Oxygen dayglow emissions as proxies for atomic oxygen and ozone in the mesosphere and lower thermosphere, Journal of Molecular Spectroscopy, 327, 209-231, doi:10.1016/j.jms.2016.

2. Yankovsky V. A., Vorobeva E. V., Manuilova R. O. (2019), New techniques for retrieving the [O(3P)], [O3] and [CO2] altitude profiles from dayglow oxygen emissions: Uncertainty analysis by the Monte Carlo method, Advances in Space Research, 64, 1948–1967, https://doi.org/10.1016/j.asr.2019.07.020

3. Torr M. T., Torr D. G. (1985), A Preliminary Spectroscopic Assessment of the Spacelab 1/Shuttle Optical Environment, J. Geophys. Res. A 90, 1683–1690, https://doi.org/10.1029/JA090iA02p01683.

How to cite: Manuilova, R. and Yankovsky, V.: Seasonal-latitudinal distributions of the populations of the states O2(b1, v = 0 - 2) in the daytime mesosphere and lower thermosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-55, https://doi.org/10.5194/egusphere-egu2020-55, 2020.

Simultaneous observations of OH(6,2) and O(¹S) nightglow at the Andes Lidar Observatory (ALO) from September 2011 to April 2018 have been analyzed to investigate an unusual intensity pattern showing an O(¹S) nightglow intensity enhancement concurrent with an OH(6,2) nightglow intensity weakening. About 142 nights have been identified in the time period showing a remarkable biannual occurrence rate with maxima during the equinoxes. A semidiurnal (12-h) tide fitting applied to the 30-min bin size monthly averaged data shows that the largest amplitudes of the semidiurnal tide were observed for the months of April and August-October in the OH(6,2) data and April and September in the O(¹S) data. It was also found that SABER’s atomic oxygen at the O(¹S) peak height is 1.3-2.5 times higher during the nights that displayed the unusual intensity pattern. Simulations using the nonlinear, time-dependent, OH Chemistry Dynamics (OHCD) and Multiple Airglow Chemistry Dynamics (MACD) models have also been used to investigate the effect of a long-period wave on the OH(6,2) and O(¹S) airglow intensities. The simulation results are in good agreement with the observations and replicate the unusual intensity pattern observed in the OH(6,2) and O(¹S) airglow data.

How to cite: Huang, T.-Y., Amaro-Rivera, Y., Vargas, F., and Urbina, J.: The Unusual Intensity Pattern of OH(6,2) and O(1S) Airglow Observed Over the Andes Lidar Observatory, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2150, https://doi.org/10.5194/egusphere-egu2020-2150, 2020.

Water vapor in the atmosphere is an important trace gas, and seriously affects the ground-based astronomical observations due to water vapor attenuation and emission. It is significant to correct the effects of water vapor along the line-of-sight of astronomical target in real time. Here, we discuss a method to retrieve the precipitable water vapor (PWV) from the OH(8-3) band airglow spectrum. The pressure, temperature and water vapor profiles determine the effective absorption cross-section in PWV retrieval, so a simple and effective method of the effective absorption cross-sections using profiles from a standard atmosphere model is discussed. The Monte Carlo simulations are used to estimate the PWV retrieval. Besides, the PWV is calculated using the sky nightglows from UVES and is compared to that from the standard star spectra of UVES observed from 2000 to 2016. The results indicate that The PWV derived from OH(8-3) spectra is in good agreement with that retrieved from UVES standard star equivalent width and the averaged difference between the two is 0.66 mm. The regression result indicates that the slope α=1.06 +/-0.03 and the correlation coefficient is r=0.87. Because the sky emission spectra and the astronomical target are observed at the same time and along the same line-of-sight, the method of PWV retrieved by OH(8-3) band spectra provides a quick and economical means of correcting the effects if water vapor on ground-based astronomical observations locally, in real-time, and along the line-of-sight of astronomical observations.

How to cite: Liu, W., Xu, J., Bian, J., Liu, X., Yuan, W., and Wang, C.: The atmospheric water vapor retrieved by OH(8-3) band airglow from astronomical observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2485, https://doi.org/10.5194/egusphere-egu2020-2485, 2020.

Chemiluminescent OH airglow emission dominates the nighttime radiation of the Earth's atmosphere in the near-infrared wavelength regime. It is an important indicator of the state and variability of the mesopause region at about 90 km. However, the interpretation of the line intensities suffers from uncertainties in the knowledge of the complex roto-vibrational level population distribution, which is far from local thermodynamic equilibrium (LTE). For a better understanding, we investigated these populations in detail mainly based on a high-quality high-resolution mean spectrum from the UVES echelle spectrograph at Cerro Paranal in Chile, which allowed us to measure about 1,000 individual lines including numerous resolved Λ-doublet components between 560 and 1060 nm. As the quality of the currently available sets of OH Einstein-A coefficients is not sufficient for accurate population retrievals, we derived an improved set by a semi-empirical approach, which benefited from the measurement of multiple lines with the same upper level. The resulting populations indicate a clear bimodality for each vibrational level, which is characterised by a cold component indicating the ambient temperature at the OH layer heights and a hot non-LTE component dominating high rotational levels. Our promising two-population fits allowed us to constrain the non-LTE contributions to rotational temperatures based on lines with upper states with low rotational and fixed vibrational quantum number, which are widely used to estimate temperatures in the mesopause region. The bimodality is also clearly indicated by the different population changes depending on the effective altitude of the OH emission layer. Only the cold component significantly decreases with increasing altitude. Our results will be very useful for the challenging modelling of the OH thermalisation process.

How to cite: Noll, S., Winkler, H., Goussev, O., and Proxauf, B.: Properties of OH roto-vibrational level populations in the Earth's mesopause region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3169, https://doi.org/10.5194/egusphere-egu2020-3169, 2020.

Atmospheric dynamics is strongly influenced by waves on different scales. Airflow over mountains can lead to all kinds of atmospheric waves, planetary and gravity waves as well as infrasound. Under certain circumstances these waves can propagate through the atmosphere and lead to a re-distribution of energy.

In the case of gravity waves, a stably stratified atmosphere is a mandatory requirement for their generation and vertical propagation. Additionally, the vertical propagation depends on the horizontal wind field.

In the Alpine and pre-Alpine region, we currently operate five OH-airglow imaging systems, which allow the investigation of orographic gravity waves. Depending on tropo-, strato- and mesospheric wind and temperature, it is checked which wavelengths can propagate into the fields of view of our instruments. This is done for a whole year in order to take into account annual and semi-annual cycles in wind and temperature.

Concerning the generation of gravity waves, we put our focus on our OH-airglow imager (FAIM) deployed at Otlica (45.9°N, 13.9°E), Slovenia. Here, we also have additional measurements of an OH-airglow spectrometer (GRIPS). In case studies, we investigate whether strong wind events (Bora) lead to strong gravity waves activity or enhanced potential energy density.

This work received funding from the Bavarian State Ministry of the Environment and Consumer Protection.

How to cite: Wüst, S., Till, J., Sedlak, R., Hannawald, P., Schmidt, C., Stanič, S., and Bittner, M.: Orographic gravity waves in OH-airglow imaging systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2878, https://doi.org/10.5194/egusphere-egu2020-2878, 2020.

Atmospheric gravity waves transport energy and momentum trough the different atmospheric layers from the troposphere up to the mesosphere and above. On the one hand this transport has influence on atmospheric circulation patterns and drives for example the meridional circulation in the mesosphere. On the other hand the prevailing wind field selectively influences the vertical propagation conditions of gravity waves of different phase speed and horizontal propagation direction.

The OH-airglow layer at ca. 86 km altitude (upper mesosphere / lower thermosphere, UMLT) is well-suited for the investigation of atmospheric dynamics, allowing continuous observations of the night-sky throughout the year. Especially, atmospheric gravity waves are prominent features in the data of airglow imaging systems. Furthermore, this altitude region is known to be a region where wave breaking occurs quite often making it particular interesting for quantifying the amount of energy and momentum released due to gravity waves.

Five years of airglow observations with three FAIM (Fast Airglow Imager) systems in and around the Alpine region are analysed regarding high-frequency gravity waves. Prevailing wind fields and tides from meteor radar wind data and ERA5 data are compared with the propagation direction of these waves and show patterns with high correlation. On seasonal timescales, the gravity waves clearly propagate predominantly to the East in summer and to the West in winter regarding the zonal direction. The meridional direction varies between the different years. On diurnal timescales, we find that atmospheric tides significantly impact the main propagation directions of the gravity waves.

We further present a case study of a stereoscopic reconstruction using two synchronized airglow-imagers with overlapping field-of-views. This allows deriving the wave amplitude and a 3D visualization of gravity wave patterns within the airglow layer.

This work received funding from the Bavarian State Ministry of the Environment and Consumer Protection.

How to cite: Hannawald, P., Wüst, S., Bittner, M., Lilienthal, F., and Jacobi, C.: Influence of atmospheric winds and tides on the propagation direction of mesospheric gravity waves observed in OH airglow in the Alpine region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3609, https://doi.org/10.5194/egusphere-egu2020-3609, 2020.

Hydroxyl (OH) short-wave infrared emissions arising from OH(4-2, 5-2, 8-5, 9-6) as measured by channel 6 of the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) are used to derive OH concentrations of OH(v=4, 5, 8, and 9) between 80 km and 96 km. Retrieved concentrations are used to simulate integrated radiances at 1.6 um and 2.0 um as measured by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, which are not fully covered by the spectral range of SCIAMACHY. On average, SABER 'unfiltered' data is on the order of 40% (at 1.6 um) and 20% (at 2.0 um) larger than the simulations using SCIAMACHY data. 'Unfiltered' SABER data is a product, which accounts for the shape, width, and transmission of the instrument’s broadband filters, which do not cover the full ro-vibrational bands of the corresponding OH transitions. It is found that the discrepancy between SCIAMACHY and SABER data can be reduced by more than 50%, if the unfiltering process is carried out manually using published SABER interference filter characteristics and latest Einstein coefficients from the HITRAN database. Remaining differences are discussed with regard to model parameter uncertainties and radiometric calibration.

How to cite: Kaufmann, M., Zhu, Y., Chen, Q., Xu, J., Gong, Q., Liu, J., Wei, D., Ern, M., and Riese, M.: A comparison of OH nightglow volume emission rates as measured by SCIAMACHY and SABER, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9916, https://doi.org/10.5194/egusphere-egu2020-9916, 2020.

One of the standard methods to remotely sense the temperature of the mesopause region is based on spectroscopic measurements of near-infrared emissions of vibrationally-rotationally excited hydroxyl molecules, and to calculate  rotational temperatures. For the interpretation of the retrieved temperatures, the aspect of rotational thermalization is of great importance. We present results of a first-principle kinetic model of vibrationally-rotationally excited hydroxyl molecules which accounts for chemical production and loss processes as well as radiative and collision-induced vibrational-rotational transitions. The model allows one to assess deviations of the rotational populations from local thermodynamic equilibrium, and to identify the key parameters which control the rotational thermalization processes. The model simulations reproduce the observed bimodality in temperatures, i.e. a cold temperature component dominating the population of low rotational states, and a hot temperature component dominating higher states. The model results are compared to measurement data from the UVES echelle spectrograph at Cerro Paranal in Chile (Presentation EGU2020-3169) which allows us to confine free model parameters such as the rotational state changes in vibrational quenching process.

How to cite: Notholt, J., Winkler, H., and Noll, S.: Model studies on vibrationally-rotationally excited hydroxyl molecules in the mesopause region , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15350, https://doi.org/10.5194/egusphere-egu2020-15350, 2020.

In the nightglow of the atmosphere in the altitude range of 90-105 km, the Barth’ mechanism is the dominant mechanism of excitation of oxygen emissions [1].

The source of oxygen emissions in this altitude range is the three-body reaction of the association of oxygen atoms. The rate coefficient of this reaction, as well as the collision quenching rate coefficients of the excited oxygen components O(¹S), O₂(b¹Σ⁺_g), O₂(a¹Δ_g) depend on the kinetic temperature of the gas. The method of sensitivity analysis for complex photochemical systems developed in [2] allows one to comprehensively consider the temperature dependence of the processes of excitation and quenching for each excited component. Analytical expressions will be obtained for the sensitivity coefficients of the intensities of these emissions depending on temperature and altitude. The formulas obtained are also suitable for estimation of the effect of temperature on the contribution of the Barth’ mechanism to atmospheric dayglow. This work was supported by the Russian Foundation for Basic Research (grant RFBR No. 20-05-00450 A).

1. Krasnopolsky V. A. (2011), Excitation of the oxygen nightglow on the terrestrial planets, Planetary and Space Science, 59, 754-766, doi: 10.1016/j.pss.2011.02.015.

2. Yankovsky V. A., Martyshenko K. V., Manuilova R. O., Feofilov A. G. (2016), Oxygen dayglow emissions as proxies for atomic oxygen and ozone in the mesosphere and lower thermosphere, Journal of Molecular Spectroscopy, 327, 209-231, doi: 10.1016/j.jms.2016.

How to cite: Yankovsky, V.: The effect of atmospheric temperature on the calculations of the intensity of oxygen emissions in the framework of the Barth mechanism: sensitivity study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-57, https://doi.org/10.5194/egusphere-egu2020-57, 2020.

Abstract.The mesosphere and lower thermosphere are the least studied areas of the earth atmosphere. The reason for this is the lack of monitoring. We have the Fabry-Perot interferometer (FPI) installed in middle latitudes of East Siberia in the geophysical observatory of Institute of Solar-Terrestrial Physics SB RAS (51.8N, 103.1E).  The FPI is a unique instrument and has no analogues in Russia.The FPI with a temporal resolution of about 10–15 minutes observes the natural glow of the night atmosphere of 630.0, 557.7 nm and 843 nm, the characteristic heights of these lines are about 250, 100 and 90 km, respectively. In this study, we use data on the behavior of the zonal, meridional component of wind speed and temperature obtained with 557.7 nm line. We analyze the temperature regime and dynamics of the stratospheric polar vortex according to the data of climatic archive - ERA-interim to get the relationship of SSW and wind regime in MLT.  In this study, we consider winter atmosphere in 2017-2019 over East Siberia, namely the period of sudden stratospheric warming. We compared the evolution of stratospheric warming’s with temporary variations in background wind and temperature and tides in the mesosphere and lower thermosphere. It turned out that the sudden stratospheric warming's made a strong effect in upper layers of the atmosphere. During major stratospheric warming's, the zonal and meridional winds reversed and increase in the semidiurnal and thirdrdiurnal tides. Temperature in MLT dramatic drop followed by an increase during sudden stratospheric warming's. Minor sudden stratospheric warming's had a similar (but much lower in intensity) response in the upper atmosphere.

Acknowledgements. Analysis of stratosphere condition in this work was supported by the Russian Science Foundation, project No. 19-77-00009. Analysis of methosphere condition in ths work was supported by Rusian Foundation for Basic Research project No. 18-05-00594. The measurements were carried out on the instrument of Center for Common Use «Angara» [http://ckp-rf.ru/ckp/ 3056]. The authors gratefully acknowledge the access to the ECMWF ERA-Interim.

How to cite: Roman, V. and Olga, Z.: Study of temperature, wind speed and tides in the upper atmosphere from optical measurements during the 2017-2019 winter's, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-689, https://doi.org/10.5194/egusphere-egu2020-689, 2020.

Acoustic-gravity waves (AGWs) measuring at big heights may be generated in the troposphere and propagate upwards. A high-resolution three-dimensional numerical model was developed for simulating nonlinear AGWs propagating from the ground to the upper atmosphere. The model algorithms are based on the finite-difference analogues of the main conservation laws. This methodology let us obtaining the physically correct generalized wave solutions of the nonlinear equations. Horizontally moving sinusoidal structures of vertical velocity on the ground are used for the AGW excitation in the model. Numerical simulations were made in an atmospheric region having horizontal dimensions up to several thousand kilometers and the height extention up to 500 km. Vertical distributions of the mean temperature, density, molecular viscosity and thermal conductivity are specified using standard models of the atmosphere.

Simulations were made for different horizontal wavelengths, amplitudes and speeds of the wave sources at the ground. After “switch on” the tropospheric wave source, an initial AGW pulse very quickly (for several minutes) could propagate to heights up to 100 km and above. AGW amplitudes increase with height and waves may break down in the middle and upper atmosphere. Wave instability and dissipation may lead to formations of wave accelerations of the mean flow and to producing wave-induced jet flows in the middle and upper atmosphere. Nonlinear interactions may lead to instabilities of the initial wave and to the creation of smaller-scale perturbations. These perturbations may increase temperature and wind gradients and could enhance the wave energy dissipation.

In this study, the wave sources contain a superposition of two AGW modes with different periods, wavelengths and phase speeds. Longer-period AGW modes served as the background conditions for the shorter-period wave modes. Thus, the larger-scale AGWs can modulate amplitudes of small-scale waves. In particular, interactions of two wave modes could sharp vertical temperature gradients and make easier the wave breaking and generating  turbulence. On the other hand, small-wave wave modes might increase dissipation and modify the larger-scale modes.This study was partially supported by the Russian Basic Research Foundation (# 17-05-00458).

How to cite: Gavrilov, N. M. and Kshevetskii, S. P.: Numerical Modeling of Nonlinear Interactions of Spectral Components of Acoustic-Gravity Waves in the Middle and Upper Atmosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-76, https://doi.org/10.5194/egusphere-egu2020-76, 2020.

Energetic particle precipitation (EPP) is an important source of chemical changes in the polar middle atmosphere during winter. Recently, it has been suggested from modeling study that EPP-induced chemical changes can cause dynamic changes of the atmosphere. In this study we investigate the atmospheric responses to medium-to high energy electron (MEE) precipitations during 2005-2013 by using Specific Dynamics Whole Atmosphere Community Climate Model (SD-WACCM). Results show that MEE precipitations significantly increase the amount of NO_x and HO_x, resulting in mesospheric and stratospheric ozone depletions during polar winter. The ozone depletion due to MEE precipitation induces warming in the polar lower mesosphere. Large ozone loss in the polar middle atmosphere leads to clear dynamic impacts, which causes warming by 3-11 K temperature increase and weakening of the zonal wind in the lower mesosphere. Our study show that the MEE precipitation induces not only the chemical effects such as ozone depletion but also clear dynamic effects in the polar middle atmosphere.

How to cite: Lee, J.-H., Song, I.-S., and Jee, G.: Modeling study on the polar middle atmospheric responses to medium energy electron (MEE) precipitation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2520, https://doi.org/10.5194/egusphere-egu2020-2520, 2020.

Atmospheric large-scale disturbances, for instance planetary waves, play a significant role in atmospheric general circulation, influencing its dynamical and thermal conditions. Solar activity may influence the mean temperature at altitudes above 100 km and alter conditions of wave propagation and reflection in the thermosphere. Using numerical simulations of the general atmospheric circulation during boreal winter, statistically confident evidences are obtained for the first time, demonstrating that changes in the solar activity (SA) in the thermosphere at heights above 100 km can influence propagation and reflection conditions for stationary planetary waves (SPWs) and can modify the middle atmosphere circulation below 100 km. A numerical mechanistic model simulating  atmospheric circulation and SPWs at heights 0 – 300 km is used. To achieve sufficient statistical confidence, 80 pairs of 15-day intervals were extracted from an ensemble of 16 pairs of model runs corresponding to low and high SA. Results averaged over these intervals show that impacts of SA above 100 km change the mean zonal wind and temperature up to 10% at altitudes below 100 km. The statistically confident changes in SPW amplitudes due to SA impacts above 100 km reach up to 50% in the thermosphere and 10 – 15% in the middle atmosphere depending on zonal wavenumber. Changes in wave amplitudes correspond to variations of the EP-flux and may alter dynamical and thermal SPW impacts on the mean wind and temperature. Thus, variable conditions of SPW propagation and reflection at thermospheric altitudes may influence the middle atmosphere circulation, thermal structure and planetary waves at different altitudes.

How to cite: Koval, A., Gavrilov, N., Pogoreltsev, A., and Shevchuk, N.: Influence of thermospheric effects of solar activity on the middle atmosphere circulation and stationary planetary waves, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2045, https://doi.org/10.5194/egusphere-egu2020-2045, 2020.

Multi-year temperature time series from OH-airglow infrared (IR) spectrometers deployed at different sites in Europe as part of the Network for the Detection of Mesospheric Change (NDMC) are used to estimate the gravity wave activity in the upper mesosphere / lower thermosphere (UMLT) region.

The seasonal course of gravity wave activity is found to be strongly dependent on the wave period. While there is almost no clear variability of gravity wave activity for periods lower than about 60 minutes, we find strong evidence for an increasing variation throughout the year for periods longer than ca. 60 min. A dominant semi-annual structure with maxima at the solstices is found up to a periodicity of about 200 minutes, where a gradual transition to an annual cycle with maximum activity during winter and minimum activity during summer is observed.

The energy and momentum carried by gravity waves is dissipated in terms of turbulent wave breaking. Using observations of airglow imagers with high spatial and temporal resolution which were operated at the same time as the abovementioned IR-spectrometers we performed an investigation of turbulent gravity wave dynamics. The estimations of the turbulent eddy diffusion coefficient and the energy dissipation rate from the image series of a turbulent wave front agree quite well with the few available values in literature. A machine learning approach for the systematic extraction of turbulent episodes from the very large data set is presented.

This work received funding from the Bavarian State Ministry of the Environment and Consumer Protection.

How to cite: Sedlak, R., Zuhr, A., Hannawald, P., Schmidt, C., Wüst, S., and Bittner, M.: Intra-annual variations of spectrally resolved gravity wave activity and observations of turbulence in the UMLT region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3283, https://doi.org/10.5194/egusphere-egu2020-3283, 2020.

Some of the earliest observations in the transition region between the Earth's atmosphere and space (roughly at 80-120km) come from so called `noctilucent clouds' (NLC) which are located around 83km altitude and consist of water ice particles. They owe their existence to the very cold summer mesopause region (~130K) at mid and high latitudes. There is a long standing dispute whether NLC are indicators of climate change in the middle atmosphere. We use model simulations of the background atmosphere and of ice particle formation for a time period of 138 years to show that an increase of NLC appearance is expected for recent decades due to increased anthropogenic release of methane being oxidized to water vapor in the middle atmosphere. Since the beginning of industrialization the water vapor concentration at NLC heights has presumably increased by about 40 percent (1 ppmv). The water vapor increase leads to a large enhancement of NLC brightness. Increased cooling by enhanced carbon dioxide alone (assuming no water vapor increase) counter-intuitively would lead to a decrease(!) of NLC brightness. NLC existed presumably since centuries, but the chance to observe them by naked eye was very small before the 20th century, whereas it is likely to see an NLC in the modern era. The eruption of volcano Krakatoa in 1883 has seemingly triggered the first observation of an NLC in 1885. In this presentation we extend our analysis from middle to polar latitudes and expand comparison with observations.

How to cite: Lübken, F.-J. and Baumgarten, G.: On the long term evolution of noctilucent clouds, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2733, https://doi.org/10.5194/egusphere-egu2020-2733, 2020.

Observing noctilucent clouds (NLC) by lidar and camera from ground reveals smallest scale structures of tens of meters and their evolution in the vertical and horizontal direction.
At the altitude of nocltilucent clouds (approx. 83 km) these structures are generated by microphysical processes affecting the ice particles, pure fluid dynamics, or a combination of both. On centennial time scales the NLC are linked to microphysical changes, mostly induced by changes of the available water vapor. On scales of hours to days the clouds are linked to temperature or the large scale flow. On scales of minutes the structures are often wave-like and associated with gravity waves and turbulence. 
For timescales below a few minutes only sparse observations were previously available. To systematically investigate the structure of NLC on such scales we make use of the ALOMAR RMR-lidar, located in Northern Norway at 69°N, that is detecting NLC with sub-second resolution since 2011. We have developed a classification scheme to identify the most important features on timescales of a few seconds. 
Furthermore we use a combination of lidar, radar and camera that allows studying simultaneously the horizontal and vertical scales. We will present new results from lidars and cameras that look at noctilucent clouds above ALOMAR and Kühlungsborn (54°N) with different scattering angles. The observations are used to investigate the mechanisms that generate the extraordinary appearance of NLC when observed by naked eye. 

How to cite: Baumgarten, G., Chau, J., Fiedler, J., Gerding, M., Lübken, F.-J., and Schäfer, B.: Revealing small scale dynamics at the altitude of noctilucent clouds, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10770, https://doi.org/10.5194/egusphere-egu2020-10770, 2020.

Earth’s atmosphere supports a variety of internal wave motion which are responsible for spatio-temporal changes in temperature, winds, density, and chemical constituents. One of the most striking dynamical features of the upper atmosphere (i.e. mesosphere and lower thermosphere [MLT], 50-120 km) are atmospheric tides. In particular, the eastward-propagating nonmigrating diurnal tide with zonal wave number 3 (DE3), originating from tropical deep convection, introduces a large longitudinal and local time variability in temperature, wind and density in the MLT region. The DE3 is thus key to understanding how tropospheric weather influences space weather. However, DE3 short-term tidal variability is not well understood and part of the motivation for constellation missions. Single satellites such as TIMED nevertheless provide a pathway to identify multi-timescale tidal variability from days to years. We utilize 16 years of SABER (an instrument onboard the TIMED satellite) DE3 “tidal deconvolution” diagnostic that provides a unique opportunity to investigate interannual changes in short-term (days to weeks) tidal variability on various planetary wave time scales. The approach is based on information-theoretic techniques using Bayesian statistics, time dependent probability density functions and Kullback-Leibler divergence followed by multiple linear regression analysis. In this presentation, we focus on interannual changes in short-term DE3 variability on a 10-day planetary wave timescale and how it changes as a function of the quasi-biennial oscillation (QBO), El Niño-Southern Oscillation (ENSO) and the solar cycle.

How to cite: Kumari, K. and Oberheide, J.: QBO, ENSO and Solar Cycle Effects in Short-term Nonmigrating Tidal Variability on Planetary Wave Timescales from SABER - An Information-Theoretic Approach , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11856, https://doi.org/10.5194/egusphere-egu2020-11856, 2020.

Solar thermal (migrating) atmospheric tides play an important role in shaping the day-to-day and seasonal variability of the Mesosphere-Lower-Thermosphere (MLT) region. Due the planetary scale of the migrating tides, observations have, however, remained sparse. This study uses meteor-echo wind measurements from a longitudinal array of SuperDARN HF-radars to isolate the amplitude and phase of the migrating diurnal, semidiurnal, and terdiurnal tide. The array of SuperDARN radars, covering nearly 180 degrees longitude at 60±5 degrees North, provide hourly horizontal wind measurements at approximately 95km altitude. The migrating components of the tides are isolated by fitting wave surfaces in space and time. The results are compared with global synoptic wind analyses from the high-altitude version of the Navy Global Environmental Model (NAVGEM-HA) to validate the method. The tides are also compared against those measured at a single station by the Trondheim (66N, 10E) meteor radar. We will present the method, a comparison between (migrating) tidal components in SuperDARN, NAVGEM-HA and the Trondheim meteor radar between 2014 and 2015, and migrating tide climatologies based on 21 years of SuperDARN data.

How to cite: van Caspel, W. E., Espy, P. J., Hibbins, R. E., and McCormack, J. P.: Observations of migrating tides in the mid-latitude MLT using an array of SuperDARN HF-radars, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11653, https://doi.org/10.5194/egusphere-egu2020-11653, 2020.

The acceleration of the large scale circulation by gravity wave is commonly described via the vertical gradient of the vertical flux of horizontal pseudomomentum, or in short of the momentum flux. The momentum flux vector is given by

 (F_px,F_py) = (1-f²/ω²) ( <u'w'>,<v'w'>)

where < > describes the spatial or temporal mean of at least one wavelength or period of the gravity wave. If one is going actually to calculate momentum flux from an observation or high-resolution model, several difficulties arise. First, one has to know the intrinsic frequency ω of the wave, second one tacitly assumes that only a single wave is causing the wind perturbations u', v' and w', and third one needs to find an appropriate averaging interval. One possibility to solve this is to perform spectral analysis. An alternative was introduced by Geller et al. (2013) which, based on the polarization relations, infers ω directly from the perturbation wind temperature quadratics and is hence referred to as WTQ. In a brief study we will investigate the implication of the single wave assumption for the momentum flux calculated from data sets calculating multiple waves.

How to cite: Preusse, P., Geldenhuys, M., and Ern, M.: Limits of the WTQ method for calculating momentum flux, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13462, https://doi.org/10.5194/egusphere-egu2020-13462, 2020.

Investigation of turbulence in the polar mesopause is essential for a better understanding of dynamical or mixing processes in the region. Polar Mesospheric Summer Echoes (PMSEs), occurring at mesopause altitudes during the summer season, are known to be a result of turbulence-induced fluctuations in the refractive index. The presence of ice particles controls and reduce the free-electron diffusivity in D region plasma, which in turn leads to complex, strong radar echoes at very high frequencies.

Often, Doppler spectral width of radar measurements are associated with the strength of turbulence in the target area and traditionally used to estimate turbulent kinetic energy dissipation rates, a fundamental parameter of the turbulence processes. Besides the cooling of summer mesopause region induced by GW drag, the turbulence produced by GW breaking contributes to the total energy budget due to release of turbulent kinetic energy to heat. We use PMSE spectral width measurements observed by Middle Atmosphere Alomar Radar System (MAARSY) during summer of 2016 to study their summer temporal mean profiles as well as temporal evolution and connection to the atmospheric turbulence at PMSE altitudes - 80 and 90 km. The current theoretical models suggest that the radar reflectivity should correlate to the strength of the turbulence; however, such a relation is mainly observed for the weaker PMSEs. The mean summer behaviour of estimated turbulent kinetic energy dissipation rates shows an increase from lower altitudes up to 90 km. It should be noticed that spectral width measurements contain additional broadening rather than turbulence, so derived energy dissipation rates are “upper values” than expected from pure turbulence. The results are still slightly lower than those known from climatology obtained from rocket soundings, mostly at altitudes close to the maximum occurrence of PMSE, 86-87 km.

We discuss a possible consequence of spectral width measurements under strong PMSEs. In such conditions, the strength of the echo does not correlate with the turbulence intensity, and the observed spectral width is weaker. However, the uniform distribution of spectral width values throughout the echo power is expected from the present theoretical understandings. Based on previous studies, strong PMSEs can also be observed during fossil turbulence. The interpretation of connection the spectral with measurements under fossil turbulence with the turbulence energy dissipation rates and the possibility of using PMSEs for the turbulence studies will be discussed.

How to cite: Gudadze, N., Stober, G., Luce, H., and Chau, J. L.: Doppler spectral width studies from polar mesospheric summer echoes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21103, https://doi.org/10.5194/egusphere-egu2020-21103, 2020.

Solar 11-year cycle variations of nighttime ozone near the secondary ozone maximum layer are analyzed with Aura Microwave Limb Sounder (MLS) observations since 2004 that covers complete solar cycle 24. Produced primarily from the recombination of molecular oxygen (O₂) with single oxygen (O) transported from the lower thermosphere, the mesospheric nighttime ozone concentration is proportional to single oxygen density [O], of which the latter is modulated by UV solar cycle variations. MLS nighttime ozone and Solar Radiation and Climate Experiment (SORCE) Solar-Stellar Irradiance Comparison Experiment (SOLSTICE) measured UV show a positive correlation in-phase with the solar cycle. The nighttime ozone correlates strongly with temperature but not monotonously positive nor negative. The slope and sign of the correlation depend on location and season. They are positively correlated in general except for the boreal winter high latitudes.  Because the nighttime [O₃] depends strongly on [O] in the upper mesosphere, it is expected the nighttime [O₃] would follow the [O] distributions, producing similar diurnal, seasonal, and solar-cycle variations, as well as latitudinal distributions as observed in Carbon Monoxide (CO) in the upper mesosphere.

How to cite: Lee, J. N. and Wu, D. L.: Solar cycle modulation of nighttime ozone near the mesopause as observed by MLS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11932, https://doi.org/10.5194/egusphere-egu2020-11932, 2020.

Energetic electron precipitation (EEP) ionizes the Earth's atmosphere and leads to production of nitric oxide (NO) from 50 to 150 km altitude. In this study we investigate the direct and indirect NO response to EEP using the Whole Atmosphere Community Climate Model (WACCM). In comparison to observations from SOFIE / AIM (Solar Occultation For Ice Experiment / Aeronomy of Ice in the Mesosphere), we find that EEP production of NO in the D-region is well simulated when both medium energy electron precipitation and negative and cluster ion chemistry is included in the model. However, the main EEP production of NO occurs in the E-region, and there the observed and modeled production differ. This discrepancy impacts also the D-region, and is seasonally dependent with the highest underestimate of D-region NO occuring during winter. The modeled transport across the mesopause during winter is generally weak, but strengthens with increased gravity wave activity. Increased eddy diffusion, increases NO at all altitudes through the polar MLT region

How to cite: Smith-Johnsen, C., Tyssøy, H. N., Marsh, D., and Smith, A.: The role of EEP forcing and background dynamics on the seasonal NO variability in the MLT region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4946, https://doi.org/10.5194/egusphere-egu2020-4946, 2020.

Evidence are pointing to two potential links between solar wind forcing and atmospheric dynamics in polar regions. The chemical link follows from energetic particle precipitation (EPP) ionizing the higher atmosphere, leading to a production of nitrogen and hydrogen oxides (NOx and HOx), which later on participate in ozone destruction. This can lead to changes in the radiative balance of the atmosphere, followed by related changes in winds. The physical link is related to the interplanetary magnetic field (IMF) and its ability to modulate the global electric circuit (GEC), with a hypothesized link between changes in the GEC and polar tropospheric dynamics through cloud generation processes. By use of ERA-5 reanalysis data and OMNI near Earth solar wind magnetic field and plasma parameter data, we investigate these links with a multiple correlation analysis. Internal atmospheric variability is excluded before the analysis. Time period of the data is 1979-2018. Results concerning the chemical link show a significant negative correlation between EPP (geomagnetic activity index Ap used as a proxy) and pressure anomalies in the local winter inside the polar vortex. The anomaly, starting in the stratosphere, extends downwards to the surface in a matter of days. The results indicate a greater response in the north compared to the south. For the physical link, a significant correlation is seen between the IMF horizontal (By) component and lower tropospheric pressure in the south for certain months in local summer. There seems to be no correlation between the two indices, Ap and By, indicating that these mechanisms operate individually without aliasing between the two. These results imply that solar wind variability can potentially impact polar atmospheric dynamics during specific seasons in different ways. This can enhance our understanding on solar related atmospheric effects.

How to cite: Edvartsen, J., Maliniemi, V., and Nesse Tyssøy, H.: Investigating a link between solar wind variability and atmospheric dynamics in polar regions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4993, https://doi.org/10.5194/egusphere-egu2020-4993, 2020.

Mesospheric frontal systems are waves extending to hundreds of kilometers along their phase fronts and appear like a boundary. They are observed in the upper mesospheric airglow imaging observations of OH, sodium and OI greenline nightglow emissions. It is believed that the fronts result from gravity wave dynamics associated with favorable background conditions like thermal ducting. Many of the frontal systems are identified as mesospheric bores when they are accompanied with sudden airglow intensity changes across the frontal boundary. Most of the frontal systems propagate with phase locked undulations following the leading front, while some induce turbulence behind the front. Though the existence of the frontal systems in the mesosphere is known for more than two decades, their role and importance is not understood properly. In this work, we use airglow data from an all-sky imager located at Tromsø to identify the frontal systems, particularly using OH images. Collocated five-beam sodium lidar measurements are used to identify the structuring in sodium densities around time of passage of the frontal systems. The sodium lidar at Tromsø is a versatile system capable of measuring sodium densities, temperatures and winds in the upper mesospshere region. Hence, we obtain the wind and temperature information to study the background conditions during passage of the intense frontal systems. Though, mostly we focus on OH airglow images as they are observed with broad pass band resulting in higher signal strength, we also utilize images from other emissions like OI greenline and sodium whenever they are available and free from auroral features. Interestingly, we find formation of some unusual structuring in the bottomside sodium layer around the passage of the frontal systems. We show different cases during winter months of the years 2013-14 and 2014-15 and investigate the relationship between unusual bottomside structuring in the sodium layer and passage of the frontal systems.

How to cite: Narayanan, V. L., Nozawa, S., Mann, I., Oyama, S., Shiokawa, K., Otsuka, Y., and Saito, N.: Mesospheric fronts in airglow images and the variation of the bottomside sodium layer densities measured by a sodium lidar at Tromsø, Norway , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5218, https://doi.org/10.5194/egusphere-egu2020-5218, 2020.

Quantifying the ionization rates due to medium energy electron (MEE) precipitation into the mesosphere has long been an outstanding question. It is the key to understand the total effect of particle precipitation on the atmosphere. The first MEE ionization rate was provided by the Atmospheric Ionization Module Osnabrück (AIMOS) in 2009. It applies electron measurements by the 0^o electron detector on the MEPED instrument on board the NOAA/POES satellites together with geomagnetic indices. Since then several other efforts to estimate the MEE precipitation and associated ionization rates has been made taking account e.g. of cross contamination by low-energy protons; Full Range Energy Electron Spectra (FRES) and ISSI-19. Recently, a parameterization based on the same electron data, scaled by the geomagnetic index Ap, has been included in the solar-driven particle forcing in the recommendation for Coupled Model Intercomparison Project 6 (CMIP6). Another parameterization aiming to resolve substorm activity applies the SML index, AISstorm. Further, three different methods to construct the total bounce loss cone fluxes based on both MEPED detectors has been suggested by the University of Colorado, University of Oulo, and the University of Bergen. In total, the space physics community offers a wide range of mesospheric ionization rates to be used in studies of the subsequent chemical-dynamical impact of the atmosphere, which are all based on the MEPED electron measurement.

Here we present a review of eight different estimates of energetic electron fluxes and the ionization rates during an event in April 2010. The objective of this comparison is to understand the potential uncertainty related to the MEE energy input in order to assess its subsequent impact on the atmosphere. We find that although the different parameterizations agree well in terms of the temporal variability, they differ by orders of magnitude in ionization strength both during geomagnetic quiet and disturbed periods and show some inconsistency in terms of latitudinal coverage.

How to cite: Nesse Tyssøy, H., Sinnhuber, M., Asikainen, T., van de Kamp, M., Pettit, J., Randall, C., Smith-Johnsen, C., Verronen, P. T., Wissing, J. M., and Yakovchuk, O.: Mesospheric ionization rates due to Medium Energy Electron Precipitation – an overview, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10731, https://doi.org/10.5194/egusphere-egu2020-10731, 2020.

Two experimental sounding rockets were launched from Andøya Space Center
(Norway) devoted to investigate the phenomenon of polar mesospheric winter
echoes (PMWE). PMWE are relatively strong radar returns during winter,
observed at various frequencies (e.g. ≈ 50 MHz Maarsy or ≈ 224 MHz with
EISCAT). Despite possible tracing capabilities for dynamics in the Meso-
sphere over a wide annual and altitudinal extend, the formation process is
still not understood. To clarify the formation mechanism and proof theories,
an experimental setup consisting of two rocket payloads were designed. Aim-
ing for measuring neutral air temperature, relative and absolute densities of
plasma constituents (electrons, ions, charged aerosols), neutral air and trace
gases as well as turbulence. In-situ measurements were complemented by
ground based measurements of multiple radars and lidars.
We show results from contemporaneous multi instrumental in-situ measure-
ments and ground based observations based on the first part of the PMWE-
Project and discuss them in the context of most relevant theories.

How to cite: Staszak, T., Strelnikov, B., Latteck, R., Renkwitz, T., Friedrich, M., and Lübken, F.-J.: First results of combined ground- and rocket-based measurements for investigation of polar mesospheric winter echoes (PMWE), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15235, https://doi.org/10.5194/egusphere-egu2020-15235, 2020.

Solar, auroral, and radiation belt electrons enter the atmosphere at polar regions leading to ionization and affecting its chemistry. Climate models usually parametrize this ionization and the related changes in chemistry based on satellite particle measurements. Precise measurements of the particle and energy influx into the upper atmosphere are difficult because they vary substantially in location and time. Widely used particle data are derived from the POES and GOES satellite measurements which provide electron and proton spectra.

We present electron energy and flux measurements from the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) satellite instruments on board the Defense Meteorological Satellite Program (DMSP) satellites. This formation of now four satellites observes the auroral zone in the UV from which electron energies and fluxes are inferred in the range from 2 keV to 20 keV. We use these observed electron energies and fluxes to calculate ionization rates and electron densities in the upper mesosphere and lower thermosphere (≈ 70–200 km). We present an initial comparison of these rates to other models and compare the electron densities to those measured by the EISCAT radar. This comparison shows that with the current standard parametrizations, the SSUSI inferred auroral (90–120 km) electron densities are larger than the ground-based measured ones by a factor of 2–5. It is still under investigation if this difference is due to collocation (in space and time) and EISCAT mode characteristics or caused by incompletely modelling the ionization and recombination in that energy range.

How to cite: Bender, S., Espy, P., and Paxton, L.: Middle atmosphere ionization from auroral particle precipitation as observed by the SSUSI satellite instruments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18489, https://doi.org/10.5194/egusphere-egu2020-18489, 2020.