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Winds at the mesosphere and lower thermosphere have been measured by partial reflection radars and specular meteor radars for almost two decades (2004-2022) over Germany and Norway (i.e., middle and high latitudes, respectively). Continuous wind measurements during the mentioned period are important to understand their long-term behavior. The zonal mean wind climatology displays an eastward wind during the winter months and a westward summer jet below ~85km at middle latitudes (~90km at high latitudes). Above the mentioned height, an eastward wind jet is observed. In the meridional wind component, the southward summer wind displays amplitudes between 4 and 5 times less intense than the westward jet. We studied the intensity of the summer wind components, the long-term variability and the possible connection to external forcing (i.e. El Niño-Southern Oscillation, and quasi-biennial oscillation, solar activity and geomagnetic activity). Analyzing the summer winds for low and high geomagnetic activity classified with the Ap index, there is a significant difference between both cases suggesting disturbances in the wind due to high geomagnetic activity. The long-term study shows significant trends at middle latitudes in the monthly summer values of the westward summer jet. As a consequence of the increase in the westward wind, a decrease in the southward component is observed at the same latitudes. While at high latitudes the eastward jet shows a decreasing velocity during July.

This study uses ground-based recordings of low-frequency, inaudible acoustic waves (infrasound) to probe the wind and temperature fluctuations associated with internal gravity waves breaking in the middle atmosphere. Building on the approach introduced by Chunchuzov et al., the recorded waveforms are used to retrieve the effective sound speed fluctuations in an inhomogeneous atmospheric layer of infrasound backscattering. The retrieval procedure was applied to infrasound from controlled blasts related to the disposal of military explosives in Hukkakero, Finland and recorded at the IS37 station in Norway over a four-year period from 2014 to 2017. Our findings indicate that infrasound scattering occurs in the lower mesosphere between 50 and 75 km in altitude in a region where gravity waves interact due to strong nonlinear effects and form thin layers with strong wind shears. The retrieved effective sound speed fluctuations were then analysed in terms of the vertical wave number spectra. The analysis revealed that the spectra follow a kz–3 power law that corresponds to the "universal" saturated spectrum of atmospheric gravity waves within kz ∈ [2.1·10–3; 2.7·10–2] cycles/m. Based on this wavenumber range, we estimate the outer and inner vertical scale of atmospheric inhomogeneities that infrasound is sensitive to as Linner= 33 – 37 m, Louter = 382 – 625 m. Furthermore, the spectra of the retrieved effective sound speed fluctuations were compared to theoretical linear and nonlinear gravity wave saturation theories as well as to independent wind measurements made by the Saura MF radar near the Andøya Space Center in Norway. The comparison showed a good agreement in terms of the amplitude and slopes of the vertical wavenumber spectra in both cases. The overall agreement allows us to suggest that the Saura radar and infrasound-based effective sound speed profiles represent the low- and high-wavenumber regimes of the same "universal" gravity wave spectrum. These results illustrate that the use of infrasound makes it possible to probe fine-scale motions that are not well captured by other techniques. The latter suggests that infrasound observations can be used as a complementary technique to probe internal gravity waves in the middle- and upper atmosphere.

We present a scaling analysis for the stratified turbulent and small-scale turbulent regimes of atmospheric flow with emphasis on the mesosphere. We distinguish rotating-stratified macroturbulence turbulence (SMT), stratified turbulence (ST), and small-scale isotropic Kolmogorov turbulence (KT), and we specify the length and time scales and the characteristic velocities for these regimes. It is shown that the buoyancy scale (Lb) and the Ozmidov scale (Lo) are the main parameters that describe the transition from SMT to KT. We employ the buoyancy Reynolds number and horizontal Froude number to characterize ST and KT in the mesosphere. This theory is applied to simulation results from a high-resolution general circulation model with a Smagorinsky-type turbulent diffusion scheme for the subgrid-scale parameterization. The model allows us to derive the turbulent root-mean-square (rms) velocity in the KT regime. It is found that the turbulent RMS velocity has a single maximum in summer and a double maximum in winter months. The secondary maximum in the winter MLT we associate with a secondary gravity wave–breaking phenomenon. The turbulent rms velocity results from the model agree well with full correlation analyses based on MF-radar measurements. A new scaling for the mesoscale horizontal velocity based on the idea of direct energy cascade in mesoscales is proposed. The latter findings for mesoscale and small-scale characteristic velocities support the idea proposed in this research that mesoscale and small-scale dynamics in the mesosphere are governed by SMT, ST, and KT in the statistical average. Significance Statement Mesoscale dynamics in the middle atmosphere, which consists of atmospheric turbulence and gravity waves, remains a complex problem for atmospheric physics and climate studies. Due to its high nonlinearity, the mesoscale dynamics together with the small-scale turbulence is the primary source of uncertainties and biases in high-altitude general circulation models (GCM) in the middle atmosphere. We use the stratified turbulence theory and the gravity wave–resolving GCM to characterize different scaling regimes and to define various length, time, and velocity scales, that are relevant for the mesoscale and small-scale dynamical regimes. Our results highlight the importance of stratified turbulence in the mesosphere and lower-thermosphere region.

The bottom part of the earth’s ionosphere is the so-called D-region, which is typically less intense than the upper regions. Despite the comparably lower electron number density, the ionization state of the D-region has a significant influence on signal absorption for propagating lower to medium radio frequencies. We present local noon climatologies of electron number density in the middle atmosphere at high latitudes as observed by an active radar experiment. The radar measurements cover nine years from the solar maximum of cycle 24 to the beginning of cycle 25. Reliable electron densities are derived by employing signal processing, applying interferometry methods, and the Faraday International Reference Ionosphere (FIRI) model. For all years a consistent spring-autumn asymmetry of the electron number density pattern as well as a sharp decrease at the beginning of October was found. These findings are consistent with VLF studies showing equivalent signatures for nearby propagation paths. It has been suggested that the meridional circulation associated with downwelling in winter could cause enhanced electron densities through NO transport. However, this mechanism lacks to explain the reduction in electron density in early October.

This study uses low-frequency, inaudible acoustic waves (infrasound) to probe wind and temperature fluctuations associated with breaking gravity waves in the middle atmosphere. Building on an approach introduced by Chunchuzov et al., infrasound recordings are used to retrieve effective sound-speed fluctuations in an inhomogeneous atmospheric layer that causes infrasound backscattering. The infrasound was generated by controlled blasts at Hukkakero, Finland and recorded at the IS37 infrasound station, Norway in the late summers 2014 - 2017. Our findings indicate that the analyzed infrasound scattering occurs at mesospheric altitudes of 50 - 75 km, a region where gravity waves interact under non-linearity, forming thin layers of strong wind shear. The retrieved fluctuations were analyzed in terms of vertical wave number spectra, resulting in approximate kz-3 power law that corresponds to the “universal“ saturated spectrum of atmospheric gravity waves. The kz-3 power law wavenumber range corresponds to vertical atmospheric scales of 33 - 625 m. The fluctuation spectra were compared to theoretical gravity wave saturation theories as well as to independent wind measurements by the Saura medium-frequency radar near Andøya Space Center around 100 km west of IS37, yielding a good agreement in terms of vertical wavenumber spectrum amplitudes and slopes. This suggests that the radar and infrasound-based effective sound-speed profiles represent low- and high-wavenumber regimes of the same “universal“ gravity wave spectrum. The results illustrate that infrasound allows for probing fine-scale dynamics not well captured by other techniques, suggesting that infrasound can provide a complementary technique to probe atmospheric gravity waves.

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.

Sporadic E (Es) is a thin layer of metallic ion plasma that forms in the E region of the Earth’s ionosphere, mostly between 90 and 125 km. It can affect the radio frequencies in the HF range of up to 30 MHz. In the mid-latitudes, the wind shear mechanism causes the formation of the Es layers. In general, solar forcing primarily controls changes in the E layer. On the other hand, the formation of the mid-latitude Es layer is driven by the wind shear associated with lower atmosphere originated wave activities. Since the formation of the Es layer is caused by the lower atmospheric forcing, it can be used as a tracer to estimate the lower atmospheric impact on the upper mesosphere and lower thermosphere (UMLT). Therefore, the study of the long-term changes and trends (if any) in the E and Es layers will throw some light on the effect of the lower atmosphere and solar forcing on the UMLT region.In the present study, we investigate the long-term variation and trends in the E region, using sixty-three years of continuous ionosonde observations over Juliusruh (54.6° N 13.4° E), Europe. Before the trend analysis, predominant long-term variations are estimated using the Lomb-Scargle periodogram analysis. We found that the annual and solar cycle oscillations are strongly present in both foE and foEs. In addition, a weak semi-annual oscillation is also noted in the foE. Furthermore, the model time series data of foE and foEs is created using the period and amplitude of the predominant oscillations. Then, the residual value of foE and foEs is calculated by subtracting the model values from the observation. By using the least square fit analysis, the trend is estimated. Interestingly, weak negative trends in the foE and foEs are found. The plausible causative mechanism for the observed trends will be detailed in the presentation.

We explore the spectral characteristics of the horizontal and vertical wind fluctuations, in the troposphere and lower stratosphere, using the Middle Atmosphere Alomar Radar System (MAARSY) during the years 2017-2020 over Andøya, Norway (69.30°N, 16.04°E). The power spectral density covers a broad frequency range of 3.5 d-1 > f > 1 h-1. The power spectra are categorized in different ranges: two frequency ranges (lower and higher than (13 h)-1), four altitude ranges (lower troposphere, middle troposphere, tropopause region, and lower stratosphere), and four seasons (spring, summer, autumn, and winter). We investigated the power-law S(f) ∝ fβ through a least-squares regression. Our results demonstrate that (i) the spectra of the horizontal winds follow a power-law with slopes of about β = -5/3 (at high-frequency), and β = -2 (at low-frequency), respectively, and the slope steepens vertically around the tropopause and seasonally during the summer, and (ii) the slope β in the vertical wind is shallow β > -1, which flattens with altitude. The momentum flux and vertical wind variance exhibit seasonal and altitudinal variations, both of which minimize in summer and maximize at the lower troposphere. The probable reason for such variation will be discussed in the presentation.

Specular meteor radars (SMRs) and partial reflection radars (PRRs) have been observing mesospheric winds for more than a solar cycle over Germany (~54 °N) and northern Norway (~69 °N). This work investigates the mesospheric mean zonal wind and the zonal mean geostrophic zonal wind from the Microwave Limb Sounder (MLS) over these two regions between 2004 and 2020. Our study focuses on the summer when strong planetary waves are absent and the stratospheric and tropospheric conditions are relatively stable. We establish two definitions of the summer length according to the zonal wind reversals: (1) the mesosphere and lower thermosphere summer length (MLT-SL) using SMR and PRR winds, and (2) the mesosphere summer length (M-SL) using PRR and MLS. Under both definitions, the summer begins around April and ends around mid-September. The largest year to year variability is found in the summer beginning in both definitions, particularly at high-latitudes, possibly due to the influence of the polar vortex. At high-latitudes, the year 2004 has a longer summer length compared to the mean value for MLT-SL, as well as 2012 for both definitions. The M-SL exhibits an increasing trend over the years, while MLT-SL does not have a well-defined trend. We explore a possible influence of solar activity, as well as large-scale atmospheric influences (e.g. quasi-biennial oscillations (QBO), El Niño-southern oscillation (ENSO), major sudden stratospheric warming events). We complement our work with an extended time series of 31 years at mid-latitudes using only PRR winds. In this case, the summer length shows a breakpoint, suggesting a non-uniform trend, and periods similar to those known for ENSO and QBO.

The polar summer mesosphere is the Earth’s coldest region, allowing the formation of mesospheric ice clouds. These ice clouds produce strong polar mesospheric summer echoes (PMSE) that are ...

In April 2018 the PMWE1 sounding rocket campaign was conducted at the Andøya Space Center involving coordinated measurements with rockets and ground instruments to measure parameters relevant for testing of the existing theories of polar mesospheric winter echo (PMWE) formation. The Middle Atmosphere Alomar Radar System (MAARSY) was operated to detect PMWE with multiple beam directions to detect favorable launch conditions. A dedicated experiment configuration with five different beam positions was used to point the radar beam along the planned trajectory of the payload. This special radar experiment allowed to obtain basic information about the spatial structure of the PMWE and its dynamical behavior around the flight of the two rockets. PMWE with signal strengths between 10−17 and 10−15 m−1 have been observed by MAARSY during the whole campaign period, starting with a moderate occurrence at the beginning which decreased towards the end of the campaign. Furthermore real common-volume observations by rocket instruments and radar soundings have been carried out at PMWE altitudes on up-leg and down-leg of the rocket flights. The Saura MF radar was operated during both flights probing the mesosphere with a multiple beam scan experiment to derive horizontal winds and electron density profiles. The obtained PMWE characteristics as signal strength and spectral width of the received radar signals as well as estimated horizontal winds and electron densities are presented with particular emphasis to the launch times of the sounding rockets.

A spring-fall asymmetry is observed in daytime amplitude values of very low frequency (VLF) radio wave signals propagating over the North Atlantic during 2011–2019. We explore the processes behind this asymmetry by comparing against mesospheric mean temperatures and the semidiurnal solar tide (S2) in mesospheric winds. The solar radiation influence on VLF subionospheric propagation was removed from the daytime VLF amplitude values, isolating the fall-effect. Similarly, the symmetric background level was removed from mesospheric mean temperatures undertaking comparable analysis. During fall, all three parameters analyzed experience significant deviation from their background levels. The VLF amplitude variation during spring is explained by the seasonal variation in solar illumination conditions, while the fall-effect can be interpreted as a mean zonal wind reversal associated with both a S2 enhancement, and temperature reductions. Decreases in temperature can produce decreases in collision frequency, reducing VLF signal absorption, driving the observed VLF asymmetry.

Polar Mesospheric Winter Echoes (PMWE) have been observed by VHF radars for quite some years. Until now, most of the studies were focussed on either major events, that occurred during solar and geomagnetic severely distorted conditions or statistical parameters like their seasonal and interannual occurrence rates as well as altitude distributions were investigated. However, especially the origin of PMWE and underlying processes are still under debate and further observations aim to contribute to this question. Recent PMWE observations with the MAARSY VHF radar included experiments using multiple beam directions to investigate the spatial structure and evolution of PMWE. Within this study we present results of MAARSY radar observations of PMWE layers complemented by simultaneous measurements by the Saura HF radar, located less than 20km apart. Major products of the Saura radar are horizontal winds and electron density within the D region. These parameters are important for both the formation and visibility of PMWE. The spectral width and localization of VHF and HF radar echoes for the presence of PMWE are analyzed and compared in the context of turbulence. Furthermore, observations during the solar minimum for the season 2019/2020 appear to be a suitable period to deepen the investigation of background conditions, excluding intensive geomagnetic disturbances.

The polar summer mesosphere is the Earth’s coldest region, allowing the formation of mesospheric ice clouds, potentially linked to climate change. These clouds produce strong radar echoes that are used as tracers of mesospheric dynamics. Here we report the first observations of extreme vertical drafts in the mesosphere, characterized by velocities larger than 40 m/s, i.e., more than five standard deviations larger than the observed wind variability. The morphology seems to resemble mesospheric bores, however the scales observed are much larger. Powerful vertical drafts, intermittent in space and time, emerge also in direct numerical simulations of stratified flows, predicting non-Gaussian statistics of vertical velocities. This evidence suggests that mesospheric bores might result from the interplay of gravity waves and turbulent motions. Our extreme event is interpreted as a mesospheric "super-bore", impacting mesospheric mixing and ice-formation, and would potentially impact planning of sub-orbital flights, and the investigation of biological material in the near space.

Two experimental sounding rockets were launched from Andøya Space Center(Norway) devoted to investigate the phenomenon of polar mesospheric winterechoes (PMWE). PMWE are relatively strong radar returns during winter,observed at various frequencies (e.g. ≈ 50 MHz Maarsy or ≈ 224 MHz withEISCAT). Despite possible tracing capabilities for dynamics in the Meso-sphere over a wide annual and altitudinal extend, the formation process isstill 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 ofplasma constituents (electrons, ions, charged aerosols), neutral air and tracegases as well as turbulence. In-situ measurements were complemented byground 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.

The exceptionally solar and geomagnetic quiet winter of 2019–2020 provides a very useful scenario to study polar mesospheric radar echoes. Such a condition limits the impact of ionisation caused by geomagnetic storms and particle precipitation and allows to investigate the role of moderate electron densities as well as neutral dynamics in formation and transport of the structures causing these echoes. For this purpose we used the continuous operation of the sensitive VHF Middle Atmosphere Alomar Radar System (MAARSY) in conjunction with the Saura partial reflection radar throughout the winter as key instruments to monitor the Mesosphere. Eight months of radar measurements are analyzed in respect to occurrence, echo power, spectral widths and their relation to practically common volume measurements of electron densities. VHF polar mesospheric echoes observed during 2019/2020 were generally more faint and occurred less frequent than in previous year. The very low occurrence rates of 6.5% at most for the months November to February as well as the complete absence of echoes below 56 km throughout the season are very remarkable. Highest occurrences of echoes with spectral widths mostly below 3 ms−1 were seen for electron densities of 3 ⋅ 108 m−3, while on average Ne ~ 5.5⋅ 108 m−3 were observed for the presence of VHF echoes, representing a necessary prerequisite to observe such VHF radar echoes. VHF radar echoes occurring at altitudes below 75 km furthermore seem to show preferences to distinct electron number density windows.

The MF-Saura radar positioned at polar latitudes is very sensitive to enhanced ionization caused by solar and geomagnetic activity. Differing from the intensities normally detected by partial reflections from the ionospheric D region during quiet conditions, distinct layers can be seen due to intense increase of electron number density at as low as 50 km altitude caused by particle precipitation. Effects of energetic particle precipitation on observations by medium frequency (MF) radars have been rarely reported so far, generally associated with solar proton events, which are rather scarce especially during solar minimum conditions. Here, we focus on events associated with precipitation of particles with lower energy (

Emitted high frequency radio waves may be reflected, scattered or refracted by various phenomenon in the atmosphere. The intensity and propagation of the scattered radio wave depends on the properties of the individual scattering phenomenon and of the ambience. Depending on the radar frequency and the ionization intensity radio waves are partially reflected from altitudes of 50 km and above. These reflections are caused by electron density gradients and do not necessarily occur from the nominal pointing direction of the transmission radiation pattern. In several analyses the nominal beam pointing direction is assumed to be the scattering location, which is often not true. For the localization of radar echoes different techniques are known and typically called Angle of Arrival or Direction of Arrival. For this study we investigate three different methods to estimate the Angle of Arrival (AOA) of radar echoes. The first two methods base upon on interferometry, while the third is often referred as MUSIC and shows high potential for the investigated radar. We show results for synthetic, but realistic data as well as real radar data for the antenna array configuration of the radar.

Radars are used since many decades to perform measurements of the atmosphere. Several parameters like echo power, Doppler shift and with this the motion of air parcels or plasma irregularities as well as the angular spread of scatterers are investigated. Besides these examples the spectral width of radar echoes is often referred as a proxy for turbulence. The interpretation of detected echo widths, however, is typically rather challenging. The general assumption is fairly applicable for a perfect antenna radiation pattern represented as a pencil beam. Though, in reality the transmit radiation pattern will have sidelobes that also illuminate atmospheric portions off the nominal pointing direction. As soon as sufficiently strong scatterers exist at these positions, echoes will also be collected and superimposed with the echoes originating from the nominal direction. Additionally, oblique radar echoes might mistakenly be assigned to higher altitudes, from where no echoes are received and thus impair the measurements. These normally unwanted echoes and its spectral portions need to be removed prior to any spectral analysis related to turbulence.

A first sounding rocket campaign dedicated to investigate the creation mechanism of Polar Mesosphere Winter Echoes (PMWE) was conducted in April 2018 from the north Norwegian Andoya Space Center (69 ∘ N, 16 ∘ E). Two instrumented sounding rockets were launched on 13th and 18th of April under PMWE and non-PMWE conditions, respectively. In this paper we give an overview of the PMWE sounding rocket mission. We describe and discuss some results of combined in situ and ground-based measurements which allow to verify existing PMWE theories. Our measurements ultimately show that: a) polar winter mesosphere is abounded with meteor smoke particles (MSP) and intermittent turbulent layers, b) all PMWE observed during this campaign can be explained by neutral air turbulence, c) turbulence creates small-scale structures in all D-region constituents, including free electrons; d) MSP ultimately influence the radar volume reflectivity by distorting the turbulence spectrum of electrons, e) the influence of MSP and of background electron density is just to increase SNR.

Simultaneous measurements of rocket-borne and ground-based instruments in a common volume were performed from Andoya, Norway (69° N, 16° E) in frame of the recent PMWE-project, devoted to clarify the formation mechanism behind polar mesosphere winter echoes (PMWE). This article focuses on measurements of April, 13th 2018. Despite low solar activity, we observe several radar echoes, giving the launch criterion. Combining precise in-situ ionization gauge and wave propagation measurements with ground-based radar measurements on 53.5 and 3.17 MHz, as well as lidar, we were able to measure key parameters of PMWE formation. Carefully analyzing the atmospheric background (i.e., temperature, viscosity, Brunt-Vaisala frequency, and scale heights of electron and neutral density), deriving turbulence parameters by means of radar and rocket, as well as estimating particle sizes of meteor smoke particles (MSP), we got a deep insight into the physical processes behind the PMWE phenomenon. Measurements clearly show that the coherent structures in refractive index variations (forming PMWE) are accompanied by neutral air turbulence, which is reflected in small-scale structures (down to some meters) of neutral and electron density. We analyze and discuss the temporal development of the radar echos by means of spectral width and wind measurements. We show that the behavior of the structures under investigation together with the atmospheric background is consistent with the interpretation, that PMWE were created by turbulence. Furthermore, it becomes clear that charged Meteor Smoke Particles (MSP) and background electron density can only enhance SNR, while turbulence is a prerequisite for their formation.

Since 1999 radar continuous observations of polar mesospheric echoes have been conducted on the Norwegian island of Andoya (69.30°N, 16.04°E), with the ALWIN radar (1999–2008) and MAARSY (since 2011). Traditionally these observations have been named after their seasonal occurrence, i.e., Polar Mesosphere Summer Echoes (PMSE) and Polar Mesosphere Winter Echoes (PMWE). PMSE are much stronger than PMWE and are known to be due to contributions of charged-dust (ice) particles and turbulence. On the other hand, most PMWE are mainly due to turbulence. Both echoes depend on electron density and its gradients. The use of MAARSY, more 17 dB sensitive than the ALWIN radar, makes it possible to observe turbulence-dominated echoes, usually below 80 km, all year round with a mean seasonal occurrence frequency of about 14%. Their minimum occurrence rate is 2% in July and August, while there are two maxima, one in March/April (22%) and the second one in October (26%). On average the dust-dominated summer echoes starts on 14 May and ends on 26 August (i.e. 105 days) with an average occurrence in June/July of 95%. These summer echoes occur mainly between 80 and 90 km, and present a maximum daily occurrence around 13:00 LT. On the other hand, the turbulence-dominated winter echoes occur mainly between 55 and 80 km with maximum daily occurrence around 11:30 LT. Besides the seasonal and daily occurrence of these echoes, we present the variability of occurrence frequency rates for the summer layers since 1994. After eliminating the effects of geomagnetic and/or solar activity the occurrence of the summer dust-dominated echoes show a positive trend of about 0.32%/yr over the last twenty seven years which might be related to the observed negative mesospheric temperature trends at polar latitudes.

The Andenes specular meteor radar shows meteor-trail diffusion rates increasing on average by ~ 20 % at times and locations where a lidar observes noctilucent clouds (NLCs). This high-latitude effect has been attributed to the presence of charged NLC but this study shows that such behaviors result predominantly from thermal tides. To make this claim, the current study evaluates data from three stations, at high-, mid-, and low-latitudes, for the years 2012 to 2016, comparing diffusion to show that thermal tides correlate strongly with the presence of NLCs. This data also shows that the connection between meteor-trail diffusion and thermal tide occurs at all altitudes in the mesosphere, while the NLC influence exists only at high-latitudes and at around peak of NLC layer. This paper discusses a number of possible explanations for changes in the regions with NLCs and leans towards the hypothesis that relative abundance of background electron density plays the leading role. A more accurate model of the meteor trail diffusion around NLC particles would help researchers determine mesospheric temperature and neutral density profiles from meteor radars.

The Middle Atmosphere Alomar Radar System (MAARSY) is a monostatic radar with an active phased array antenna designed for studies of phenomena in the mesosphere and lower thermosphere. Its design in particular the flexible beam forming and steering capability makes it to a powerful instrument to perform observations with high angular and temporal resolution. The knowledge of the actual radiation pattern is crucial to configure and analyze experiments carried out with the radar. The simulated radiation pattern is evaluated by the observation of cosmic radio emissions which are compared to a Global Sky temperature Maps model consisting of the most recent, thorough and accurate radio astronomy surveys. Additionally to these passive receive-only experiments active two-way experiments are presented, which corroborate the findings of the passive experiments.

The Middle Atmosphere Alomar Radar System (MAARSY) is a monostatic radar with an active phased array antenna designed for studies of phenomena in the mesosphere and lower thermosphere. Its design, in particular the flexible beam forming and steering capability, makes it a powerful instrument to perform observations with high angular and temporal resolution. For the configuration and analysis of experiments carried out with the radar it is essential to have knowledge of the actual radiation pattern. Therefore, during the time since the radar was put into operation various active and passive experiments have been performed to gain knowledge of the radiation pattern. With these experiments the beam pointing accuracy, the beam width and phase distribution of the antenna array were investigated. Here, the use of a sounding rocket and its payload as a radar target is described which was launched in the proximity of the radar. The analysis of these observations allows the detailed investigation of the two-way radiation pattern for different antenna array sizes and beam pointing positions.

The Leibniz-Institute of Atmospheric Physics in Kühlungsborn, Germany (IAP) installed a new powerful VHF radar on the North-Norwegian island Andøya (69.30° N, 16.04° E) from 2009 to 2011. The new Middle Atmosphere Alomar Radar System (MAARSY) replaces the existing ALWIN radar which has been in continuous operation on Andøya for more than 10 yr. MAARSY is a monostatic radar operated at 53.5 MHz with an active phased array antenna consisting of 433 Yagi antennas each connected to its own transceiver with independent control of frequency, phase and power of the transmitted signal. This arrangement provides a very high flexibility of beam forming and beam steering. It allows classical beam swinging operation as well as experiments with simultaneous multiple beams and the use of modern interferometric applications for improved studies of the Arctic atmosphere from the troposphere up to the lower thermosphere with high spatial-temporal resolution. The installation of the antenna was completed in August 2009. An initial expansion stage of 196 transceiver modules was installed in spring 2010, upgraded to 343 transceiver modules in December 2010 and the installation of the radar was completed in spring 2011. Beside standard observations of tropospheric winds and Polar Mesosphere Summer Echoes, multi-beam experiments using up to 91 beams quasi-simultaneously in the mesosphere have been carried out using the different expansion stages of the system during campaigns in 2010 and 2011. These results provided a first insight into the horizontal variability of Polar Mesosphere Summer and Winter Echoes in an area of about 80 km by 80 km with time resolutions between 3 and 9 min.

The Middle Atmosphere Alomar Radar SYstem (MAARSY) with its active phased array antenna is designed and used for studies of phenomena in the mesosphere and lower atmosphere. The flexible beam forming and steering combined with a large aperture array allows observations with high temporal and angular resolution. For both, the analysis of the radar data and the configuration of experiments, the actual radiation pattern needs to be known. For that purpose various simulations as well as passive and active experiments have been conducted. Here, results of meteor head echo observations are presented, which allow derivation of detailed information of the actual radiation pattern for different beam pointing positions and the current health status of the entire radar. For MAARSY, the described method offers robust beam pointing and width estimations for a minimum of a few days of observations.

15th MST Radar WorkshopSession M6: Middle atmosphere dynamics and structureMay 31 (Wed), NIPR Auditorium

15th MST Radar WorkshopSession M6: Middle atmosphere dynamics and structureMay 31 (Wed), NIPR Auditorium

15th MST Radar WorkshopSession M4: MST Radar scattering, turbulence and small-scale processesMay 30 (Tue), NIPR Auditorium

The Middle Atmosphere Alomar Radar System (MAARSY) on the Norwegian island of Andoya is a 53.5 MHz monostatic radar with an active phased array antenna. The total array consists of 433 3-element linearly polarized Yagi antennas and can be configured to receive with multiple antenna sections (currently up to 16 complex receiving channels). In order to exploit its multiple-receiver capability for improving the space-time ambiguities of atmospheric/ionospheric targets, the phase difference between receiving channels has to be measured with good precision. Such phases are intrinsic to the system and are due to different cable lengths, pointing positions, filters, attenuators, amplifiers, antenna impedances, etc. In this work, we have operated MAARSY in a radio passive mode to observe the strong radio signals of Cassiopeia A and Cygnus A sources and calibrate the receiving system. By using the so-called fringe-stopping method, we have been able to calibrate the 16 complex channels, including the smaller antenna module that can be used, i.e., an Hexagon consisting of 7 Yagi antennas. The measured phases have been obtained with a mean standard deviation of ∼ 5 °. We have tested the validity of such phases using meteor-head echoes with different configurations and pointing directions. Given that the procedure is easy to implement, it should be used in a routine manner either to corroborate the stability of the system or to measure new phases after upgrades or repairs.

In 2009/2010 the Leibniz-Institute of Atmospheric Physics (IAP) installed a new powerful VHF radar on the island Andøya in Northern Norway (69.30° N, 16.04° E). The Middle Atmosphere Alomar Radar System (MAARSY) allows studies with high spatial and temporal resolution in the troposphere/lower stratosphere and in the mesosphere/lower thermosphere of the Arctic atmosphere. The monostatic radar is operated at 53.5 MHz with an active phased array antenna consisting of 433 Yagi antennas. Each individual antenna is connected to its own transceiver with independent phase control and a scalable power output of up to 2 kW, which implies high flexibility of beam forming and beam steering. During the design phase of MAARSY several model studies have been carried out in order to estimate the radiation pattern for various combinations of beam forming and steering. However, parameters like mutual coupling, active impedance and ground parameters have an impact on the radiation pattern, but can hardly be measured. Hence, experiments need to be designed to verify the model results. For this purpose, the radar has occasionally been used in passive mode, monitoring the noise power received from both distinct cosmic noise sources like e.g. Cassiopeia A and Cygnus A, and the diffuse cosmic background noise. The analysis of the collected dataset enables us to verify beam forming and steering attempts. These results document the current status of the radar during its development and provide valuable information for further improvement.

The Leibniz-Institute of Atmospheric Physics (IAP) in Kühlungsborn started to install a new MST radar on the North-Norwegian island Andøya (69.30° N, 16.04° E) in 2009. The new Middle Atmosphere Alomar Radar System (MAARSY) replaces the previous ALWIN radar which has been successfully operated for more than 10 years. The MAARSY radar provides increased temporal and spatial resolution combined with a flexible sequential point-to-point steering of the radar beam. To increase the spatiotemporal resolution of the observations a 16-port Butler matrix has been built and implemented to the radar. In conjunction with 64 Yagi antennas of the former ALWIN antenna array the Butler matrix simultaneously provides 16 individual beams. The beam forming capability of the Butler matrix arrangement has been verified observing the galactic cosmic radio noise of the supernova remnant Cassiopeia A. Furthermore, this multi beam configuration has been used in passive experiments to estimate the cosmic noise absorption at 53.5 MHz during events of enhanced solar and geomagnetic activity as indicators for enhanced ionization at altitudes below 90 km. These observations are well correlated with simultaneous observations of corresponding beams of the co-located imaging riometer AIRIS (69.14° N, 16.02° E) at 38.2 MHz. In addition, enhanced cosmic noise absorption goes along with enhanced electron densities at altitudes below about 90 km as observed with the co-located Saura MF radar using differential absorption and differential phase measurements.

The Leibniz-Institute of Atmospheric Physics in Kühlungsborn, Germany (IAP) is installing a new powerful VHF radar on the North-Norwegian island Andøya (69.30° N, 16.04° E) in 2009/2010. The new Middle Atmosphere Alomar Radar System (MAARSY) replaces the existing ALWIN radar which has been operated continuously on Andøya for more than 10 years. The new system is a monostatic radar operated at 53.5 MHz with an active phased array antenna consisting of 433 Yagi antennas. The 3-element Yagi antennas are arranged in an equilateral triangle grid forming a circular aperture of approximately 6300 m2. Each individual antenna is connected to its own transceiver with independent phase control and a scalable output up to 2 kW. This arrangement allows very high flexibility of beam forming and beam steering with a symmetric radar beam of a minimum half power beam width of 3.6°, a maximum directive gain of 33.5 dB and a total transmitted peak power of approximately 800 kW. The IF signals of each 7 transceivers connected to each 7 antennas arranged in a hexagon are combined to 61 receiving channels. Selected channels or combinations of IF signals are sent to a 16-channel data acquisition system with 25 m sampling resolution and 16-bit digitization specified which will be upgraded to 64 channels in the final stage. The high flexibility of the new system allows classical Doppler beam swinging as well as experiments with simultaneously formed multiple beams and the use of modern interferometric applications for improved studies of the Arctic atmosphere from the troposphere up to the lower thermosphere with high spatiotemporal resolution.

The Middle Atmosphere Alomar Radar System (MAARSY) is a radar with a large aperture active phased array antenna designed for studies of atmospheric phenomena in the mesosphere and lower thermosphere. Its design in particular the flexible beam forming and steering capability makes it to a powerful instrument to perform observations with high angular and temporal resolution. The knowledge of the actual radiation pattern and radar parameters is crucial to configure and analyze experiments carried out with the radar. For this purpose the simulated radiation pattern is evaluated by the observation of cosmic radio emissions which are compared to a global sky model. Additionally to these passive receive-only experiments active two-way experiments are presented, which corroborate the findings of the passive experiments.

[1] The Middle Atmosphere Alomar Radar System (MAARSY) on the North-Norwegian island Andoya is a 53.5 MHz monostatic radar with an active phased array antenna consisting of 433 Yagi antennas. The 3-element Yagi antennas are arranged in an equilateral triangle grid forming a circular aperture of approximately 6300 m2. Each individual antenna is connected to its own transceiver with independent phase control and a scalable power output up to 2 kW. This arrangement provides a very high flexibility of beam forming and beam steering with a symmetric radar beam of a minimum beam width of 3.6° allowing classical beam swinging operation as well as experiments with simultaneous multiple beams and the use of interferometric applications for improved studies of the Arctic atmosphere from the troposphere up to the lower thermosphere with high spatio-temporal resolution. The installation of the antenna array was completed in August 2009. The radar control and data acquisition hardware as well as an initial expansion stage of 196 transceiver modules was installed in spring 2010 and upgraded to 343 transceiver modules in November 2010. The final extension to 433 transceiver modules has recently been completed in May 2011. Beside standard observations of tropospheric winds and Polar Mesosphere Summer Echoes, the first multi-beam experiments using up to 97 quasi-simultaneous beams in the mesosphere have been carried out in 2010 and 2011. These results provide a first insight into the horizontal variability of polar mesosphere summer and winter echoes with time resolutions between 3 and 9 minutes. In addition, first meteor head echo observations were conducted during the Geminid meteor shower in December 2010.