AS1.19

Polar mesosphere winter echoes (PMWE) are relatively strong radar returns which are regularly observed by mesosphere/stratosphere/troposphere (MST) radars at high latitudes in winter. A sounding rocket project PMWE aimed at investigation of this phenomenon by means of high resolution in situ measurements of all the relevant parameters inside and around the volume probed by the MAARSY radar. Two sounding rocket campaigns were conducted at the Andøya Space (AS, 69 °N, 16 °E) in April 2018 and October 2021, respectively. Two instrumented sounding rockets were launched during each rocket campaing. Both EISCAT in Tromsø and SAURA radar located near the launch site were running throughout the campaign periods. RMR-lidar successfully measured temperature and wind fields on the day of rocket launches in October 2021. In this paper we give an overview and some details of the measurements conducted during the two rocket campaigns and discuss first results.

How to cite: Strelnikov, B., Staszak, T., Seither, P., Friedrich, M., Rapp, M., Stude, J., Latteck, R., Renkwitz, T., Löhle, S., Hörner, I., Eberhart, M., Fasoulas, S., Gumbel, J., Hedin, J., Lübken, F.-J., Baumgarten, G., Fiedler, J., Strelnikova, I., Belova, E., and Hörschgen-Eggers, M. and the PMWE team: Sounding rocket project PMWE for investigation of polar mesosphere winter echoes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6114, https://doi.org/10.5194/egusphere-egu22-6114, 2022.

During the winter, a strong westerly wind surrounds the cold polar stratosphere, forming the polar vortex. In the northern hemisphere the polar vortex is affected by energetic electron precipitation (EEP) which originates from the magnetosphere and is driven by the solar wind. EEP forms reactive nitrogen and hydrogen oxides, NOx and HOx, which destroy ozone and, thus, affects the radiative and thermal balance in the atmosphere. Several studies have shown that the EEP decreases ozone in the winter polar stratosphere and enhances the polar vortex in the northern hemisphere. This EEP effect on polar vortex is also found to depend on different factors such as the quasi-biennial oscillation (QBO) and sudden stratospheric warmings (SSW). Both the QBO and SSWs are believed to modulate the EEP effect via planetary waves, disturbances originating mainly from the troposphere, but the role of planetary waves in this context has not been studied in detail. In this work we examine the EEP effect on northern polar vortex and its dependence on planetary waves. We use the principal component analysis to examine the intensity and spatial distribution of planetary waves in the northern wintertime stratosphere. We then calculate multi linear regressions to estimate the zonal wind responses to EEP also considering planetary waves. We find that the EEP effect on the northern polar vortex is increased when planetary waves are focused at the equatorward side of the polar vortex, while the overall intensity of planetary waves does not significantly modulate the EEP effect.

How to cite: Salminen, A., Asikainen, T., and Mursula, K.: Planetary waves modulating the effect of energetic electron precipitation on polar vortex, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6994, https://doi.org/10.5194/egusphere-egu22-6994, 2022.

State of ionosphere is significantly affected by the dynamics of lower-laying atmosphere. Mesoscale systems are effective sources of atmospheric disturbances that can reach ionospheric heights and significantly alter atmospheric and ionospheric conditions. Large cyclonal systems are recognized to be an efficient source of acoustic and gravity waves that are able to propagate upward and reach the ionospheric heights. Our previous study detected a significant wave-like activity at ionospheric heights following immediately after the cross of the frontal system above the ionospheric station.

In the present paper the effects of the tropospheric variability of standard meteorological parameters associated with the passage of atmospheric frontal systems above the Průhonice station on the upper atmosphere are statistically studied. Our analysis concerns variations in occurrence, height, and critical frequency of sporadic E layer. 

How to cite: Potužníková, K. and Koucká Knížová, P.: A statistical study of the effects of tropospheric variability on the ionosphere parameters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12650, https://doi.org/10.5194/egusphere-egu22-12650, 2022.

The seasonal variation of the daytime lower ionosphere over the North Atlantic, monitored using the propagation of Very Low Frequency (VLF) radio waves, shows an asymmetry when comparing the spring and autumn transitions. The signal variability shows a faster rate of change from summer to winter than from winter to summer, for which the responsible mechanism is still unknown. In this study, we perform a climatological (2008–2021) analysis to determine the northern-hemisphere latitudinal dependence of the spring-fall asymmetry. We employ VLF receivers located in Peru (low-latitude), USA (middle-latitude), UK (middle-latitude), Finland (high-latitude), and Norway (high-latitude). At the same time, we employ neutral mesospheric temperature from MLS, nitric oxide (NO) from SOFIE, and gravity wave (GW) kinetic energy derived from mesospheric horizontal winds. We find that at high-latitude the VLF amplitude variability before summer and during winter follows the seasonal variation of the solar zenith angle, but the measurements during fall do not. After removing the VLF background level, a large deviation is observed during fall, which we call the fall-effect. We explore the processes behind this effect by comparing against mean temperature, NO, and GW seasonal variabilities after removing their respective background levels. We found that the three mesospheric parameters display a fall-effect. Performing a similar analysis for middle latitudes shows that the fall-effect is not clearly observed in both ionospheric and mesospheric parameters. In the case of low-latitudes, no fall-effect is observed. We discuss the possible association between the mesospheric temperature and the VLF variability through collision and absorption. We also discuss the possible role of GW on the D-region.

How to cite: Macotela, L., Clilverd, M., Chau, J., Banyś, D., Raulin, J.-P., and Raita, T.: Latitudinal dependence of the fall-effect observed in the D-region and mesosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6400, https://doi.org/10.5194/egusphere-egu22-6400, 2022.

Previous studies disclosed oscillations of ionospheric parameters, in particular, the critical frequency of the F2 layer, f₀F2, with periods longer than 2 days. This allows suggestions that planetary waves (PWs) propagating from the lower atmosphere can influence the ionospheric electron density. However, someatmospheric modeling showed that PWs with observed periods may have difficulties for direct propagation to altitudes above 110 km. Since 2018, regular observations of ionospheric parameters with the DPS-4 ionosonde are been performed at the Peterhof Scientific Station of Saint Petersburg State University (60° N, 30° E). In this study, we analyzed results for spectra of oscillations of ionospheric parameters in the range of periods 0.5 – 40 days according to these measurements. In addition to these spectra we analyzed similar spectra obtained from the MERRA-2 data of meteorological reanalysis for different locations in the lower and middle atmosphere. Lomb-Scargle spectra were obtained for 90-day running intervals. They contain maxima at periods 1 day and 0.5 day, which may correspond to the diurnal and semidiurnal tides. The spectra also have maxima at periods 2 – 40 days, which can be associated with planetary waves (PWs). The analysis shows that big amplitudes of oscillations with periods τ ~ 2 – 40 d are frequently observed in the northern spring and summer months, when westward stratospheric winds prevent PW propagation from the lower to the upper atmosphere. However, the analysis of atmospheric waveguides revealed that PWs can cross the equator above altitudes of 60 km. Therefore, PWs observed in summer ionosphere can, in prinsiple, propagate from the lower wave sources located in the winter hemisphere.Obtained correlation coefficients between variations of the spectral densities at ionospheric and tropospheric heights at different latitudes demonstrate sufficient statistical confidence for PWs with periods of several days. This gives evidences about possible PW coupling between dynamical processes in the lower atmosphere and ionosphere. The spectral analysis was supported by the Russian Science Foundation (grant #20-77-10006) and the analysis of PW coupling was supported by the Ministry of Education of the Russian Federation (agreement 075-15-2021-583). Used ionosonde data were acquired in the “Geomodel” Resource Center of SPbSU.

How to cite: Maksakova, E., Gavrilov, N. M., and Koval, A. V.: Spectra of Tides and Planetary Waves from Ionosonde and MERRA-2 Data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4146, https://doi.org/10.5194/egusphere-egu22-4146, 2022.

The wind field in the mesosphere and lower thermosphere (MLT), at heights between 80 and 100 km, is dominated by the global scale oscillations of the atmospheric tides. The tides are crucial to the dynamics of the middle and upper atmosphere and hence to understanding the coupling between the lower atmosphere and space. The tides are known to show considerable variability on timescales of days to years, with significant variability at interannual timescales.  However, the nature and causes of this variability remain poorly understood. Here, we present measurements made over the interval 2005 to 2020 of the interannual variability of the 12-hour tide as measured at heights of 80 – 100 km by a meteor radar over the British Antarctic Survey base at Rothera (68°S, 68°W). We use a linear regression analysis to investigate correlations between the 12-hour tidal amplitudes and several climate indices, specifically the solar cycle (as measured by F10.7 solar flux), El Niño Southern Oscillation (ENSO), the Quasi-Biennial Oscillation (QBO) at 10 hPa and 30 hPa, the Southern Annular Mode (SAM) and time. Our observations reveal that the 12-hour tide has a large amplitude and a clearly defined seasonal cycle with monthly mean values as large as 35 ms^-1. We observe substantial interannual variability with monthly mean tidal amplitudes at 95 km exhibiting an interdecile range in spring of 17.2 ms^-1, 12.6 ms^-1 in summer, 23.6 ms^-1 in autumn and 9.0 ms^-1 in winter. We find that F10.7, QBO10, QBO30, SAM and time all have significant correlations at the 95% level, whereas we detect very minimal correlation with ENSO. For example, there is a significant negative correlation between F10.7 solar flux and tidal amplitudes in summer, implying an increase in solar flux is related to a decrease in monthly mean tidal amplitudes in the MLT. These results suggest that the amplitude of the polar 12-hour tide is modulated by the solar cycle, QBO and SAM.

How to cite: Dempsey, S. M., Noble, P. E., Wright, C. J., Moffat-Griffin, T., and Mitchell, N. J.: Interannual variability of the 12-hour tide in the mesosphere and lower thermosphere in 15 years of meteor-radar observations above Rothera (68o S, 68o W), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-776, https://doi.org/10.5194/egusphere-egu22-776, 2022.

The Mesosphere and Lower Thermosphere (MLT), at 80-100 km altitude, is critical in the coupling of the middle and upper atmosphere and determining momentum and energy transfer between these two regions. However, despite its importance, General Circulation Models (GCMs) have only recently been extended to the MLT region and remain poorly constrained.

We use a long term meteor radar dataset from Rothera on the Antarctic Peninsula to test the eXtended Whole Atmosphere Community Climate Model (WACCM-X). This radar has been running continuously since 2005, resulting in a uniquely long, consistent measure of the winds in the MLT that we can use to investigate long term variability. We find that although some characteristic features are represented well in WACCM-X, the model exhibits considerable biases. In particular, the observations show a ~10m/s eastward wind in Antarctic winter whereas the model predicts winds of the same magnitude but opposite direction. We propose that this difference is due to the lack of secondary gravity wave modelling in WACCM-X.

We also find interannual variability in both the observations and the model. In order to understand these differences, we further investigate the role of external climate processes in driving the winds in this region. Using a linear regression method, we quantify how the (observed and modelled) winds in the Antarctic MLT respond to Solar activity, the El Nino Southern Oscillation (ENSO), the Quasi-Biennial Oscillation (QBO) and the Southern Annular Mode (SAM). For some indices we find good agreement between the observations and model results while for others we see important differences.

How to cite: Noble, P., Wright, C., Hindley, N., Mitchell, N., Cullens, C., England, S., Pedatella, N., and Moffat-Griffin, T.: Long term trends in winds in the mesosphere and lower thermosphere over Rothera (67°S, 68°W) from radar observations and WACCM-X, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-772, https://doi.org/10.5194/egusphere-egu22-772, 2022.

The nighttime near-infrared radiation of the Earth's atmosphere is mainly produced in the mesopause region between 80 and 100 km by chemiluminescent emission of the OH radical. The line radiation of various vibrational and rotational states is therefore a valuable indicator of the chemistry and dynamics in the upper atmosphere. The vertical emission distribution can significantly change with time. It is also expected that the time-averaged effective emission height depends on the studied OH line due to differences in the radiative lifetimes, the collision-related transition probabilities, and the initial level population after the production of the radical. Although the knowledge of the OH emission layering is important for the interpretation of passing perturbations, the line-specific details are still uncertain. 

We have studied the effective emission heights of about 300 OH lines based on near-infrared spectroscopic data from the X-shooter spectrograph at the Very Large Telescope at Cerro Paranal in Chile. The line intensities showed very strong variations due to a rising quasi-two day wave during eight nights at the beginning of 2017. With complementary vertically resolved broad-band observations of OH emission from the limb-sounder SABER on the TIMED satellite, we could link the line-dependent wave phases from the fitting of the X-shooter data with emission altitudes. With a period of about 44 h and a vertical wavelength of about 32 km, the observed wave turned out to be an excellent indicator of line-dependent altitude differences, which reached up to 8 km for the investigated lines. In general, the effective emission altitude increases with increasing vibrational and rotational level. Moreover, the derived wave amplitudes imply the presence of a cold thermalised and a hot non-thermalised population for each vibrational level. As the wave amplitudes also showed a strong dependence on local time, significant interactions between the quasi-two-day wave and other perturbations such as tides are likely.

How to cite: Noll, S., Kausch, W., Schmidt, C., Bittner, M., and Kimeswenger, S.: Vertical layering of OH line emission from X-shooter and SABER observations of a passing quasi-2-day wave, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10039, https://doi.org/10.5194/egusphere-egu22-10039, 2022.