Papers by Toralf Renkwitz
Atmospheric Measurement Techniques, Feb 14, 2017
The Middle Atmosphere Alomar Radar System (MAARSY) with its active phased array antenna is design... more 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 for observations with a 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 us to derive 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.
The lowermost boundary of the ionosphere, namely the D region, is very sensitive to solar and geo... more The lowermost boundary of the ionosphere, namely the D region, is very sensitive to solar and geomagnetic disturbances modulating the state of ionisation. The upper D region is widely controlled by incident solar UV radiation. During solar flares enhanced Lyman-alpha radiation as well as X-ray are emitted, which can easily ionize NO at altitudes of 70 km and below. Specifically, increased X-ray fluxes may rapidly change the ionization in the lower D region, specifically if they reach enegeries of 10 to 100 keV.
Characterization of polar mesospheric VHF radar echoes during solar minimum winter 2019/2020. Part I: Ionisation
Journal of Atmospheric and Solar-Terrestrial Physics, Sep 1, 2021
Abstract The exceptionally solar and geomagnetic quiet winter of 2019–2020 provides a very useful... more Abstract 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.
Frontiers in Astronomy and Space Sciences, May 10, 2022
Multiple propagation modes between different bistatic radar links were measured during the operat... more Multiple propagation modes between different bistatic radar links were measured during the operations of a very high frequency (VHF) 32.55 MHz radar system in northern Norway. The Spread Spectrum Interferometric Multistatic meteor radar Observing Network (SIMONe) Norway system detected meteor trails, direct transmitter to receiver signal propagation, over-the-horizon signal propagation from the SIMONe Germany system, ground and/or sea scatter, and ionospheric scatter on 27 August 2021 between 16:30-20:00 UT. These simultaneous detections were during an active ionospheric period with multiple occurrences of energetic charged particle precipitation. The SIMONe systems used continuous-wave (CW) pseudo-random phase modulated transmit signals and interferometry to make it possible to isolate each of these propagation modes and examine their characteristics. Different multistatic links at three receiver locations were analyzed, providing multistatic measurements of the regions with spatial and temporal resolutions on the order of 1.5 km and 2 s. The analysis techniques are described, with characteristics of the radar signal presented for each propagation mode and multistatic link. This study serves to highlight the capabilities of the SIMONe Norway system to research multiple aspects of ionospheric phenomena, specifically in the lower thermosphere-mesosphere boundary region.
Long-term studies of the summer wind in the mesosphere and lower thermosphere at middle and high latitudes
. Continuous wind measurements using partial reflection radars and specular meteor radars have be... more . Continuous wind measurements using partial reflection radars and specular meteor radars have been carried out for nearly two decades (2004–2022) at middle and high latitudes over Germany (∼54° N) and northern Norway (∼69° N), respectively. They provide crucial data for understanding the long-term behavior of winds in the mesosphere and lower thermosphere. Our investigation mainly focuses on the summer season, characterized by the absence of intense planetary wave activity and relatively stable stratospheric conditions. This work presents the long-term behavior, variability and trends of the maximum velocity of the summer eastward, westward and southward winds. In addition, the geomagnetic influence on the summer zonal and meridional wind is explored at middle and high latitudes. The results show that a westward summer maximum is located around 75 km with velocities of 35–54 m/s, while the eastward wind maximum is observed at ∼97 km with amplitudes of 25–40 m/s. A weaker southward wind peak is found around 86 km ranging from 9–16 m/s. The findings indicate significant trends at middle latitudes in the westward summer maxima with increasing winds over the past decades, while the southward winds show a decreasing trend. On the other hand, only the eastward wind in July has a decreasing trend at high latitudes. Evidence of oscillations around 2–3, 4 and 6 years modulate the maximum velocity of the summer winds. Particularly a periodicity between 10.2–11.3 years found in the westward component is more significant at middle latitudes than at high latitudes, possibly due to solar radiation. Furthermore, stronger geomagnetic activity at high latitudes causes an increase in eastward wind velocity, whereas the opposite effect is observed in zonal jets at middle latitudes. The meridional component appears disturbed during high geomagnetic activity, with a notable decrease in the northward wind strength below approximately 80~km at both latitudes.
This study uses low-frequency, inaudible acoustic waves (infrasound) to probe wind and temperatur... more 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 ran...
Long-term study of the summer wind variability in the mesosphere and lower thermosphere over nearly two decades at middle and high latitudes
Winds at the mesosphere and lower thermosphere have been measured by partial reflection radars an... more 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 geom...
Extreme vertical drafts in the polar summer mesosphere: A mesospheric super bore?
The polar summer mesosphere is the Earth’s coldest region, allowing the formation of mesospheric ... more The polar summer mesosphere is the Earth’s coldest region, allowing the formation of mesospheric ice clouds. These clouds produce strong polar mesospheric summer echoes (PMSE) that are used as trac...
In the present study, using sixty-three and fifty-six years of continuous observations, we invest... more In the present study, using sixty-three and fifty-six years of continuous observations, we investigate the long-term oscillations and residual trends, respectively, in the E-and F-region ionosonde measured parameters over Juliusruh, Europe. Using the Lomb-Scargle periodogram (LSP) long-term variations are estimated before the trend estimation. We found that the amplitude of the annual oscillation is higher than the 11-year solar cycle variation in the critical frequencies of the daytime E (foE) and Es (foEs) layers. A weak semi-annual oscillation is also identified in the foE. In the F-region, except for daytime hmF2, and nighttime foF2, the amplitude of the 11-year solar cycle variation is higher than the annual oscillation. The LSP estimated periods and their corresponding amplitudes are used to construct a model E-and F-region ionospheric parameters that are in good agreement with the observation. The linear trend estimation is derived by applying a least-squares fit analysis to the residuals, subtracting the model from the observation. Except for the daytime foF2, all the other parameters like nighttime foF2, day and nighttime h'F, and hmF2 show a negative trend. Present results suggest that the greenhouse effect is a prime driver for the observed long-term trend in the F-region. Interestingly, weak negative trends in the foE and foEs are found which contradicts an earlier investigation. The present study suggests that the changes in the upper stratospheric ozone and mesosphere wind shear variability could be the main driver for the observed weak negative trends in the foE, and foEs, respectively.
Frontiers in Astronomy and Space Sciences
Multiple propagation modes between different bistatic radar links were measured during the operat... more Multiple propagation modes between different bistatic radar links were measured during the operations of a very high frequency (VHF) 32.55 MHz radar system in northern Norway. The Spread Spectrum Interferometric Multistatic meteor radar Observing Network (SIMONe) Norway system detected meteor trails, direct transmitter to receiver signal propagation, over-the-horizon signal propagation from the SIMONe Germany system, ground and/or sea scatter, and ionospheric scatter on 27 August 2021 between 16:30–20:00 UT. These simultaneous detections were during an active ionospheric period with multiple occurrences of energetic charged particle precipitation. The SIMONe systems used continuous-wave (CW) pseudo-random phase modulated transmit signals and interferometry to make it possible to isolate each of these propagation modes and examine their characteristics. Different multistatic links at three receiver locations were analyzed, providing multistatic measurements of the regions with spatia...
The polar summer mesosphere is the Earth's coldest region, allowing the formation of mesospheric ... more 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.
Angle of Arrival study of atmospheric high frequency radar echoes
2019 6th International Conference on Space Science and Communication (IconSpace), 2019
Emitted high frequency radio waves may be reflected, scattered or refracted by various phenomenon... more 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.
A comparison of Polar Mesosphere Summer Echo observations from locations in the Arctic and Antarctica
EGU General Assembly Conference Abstracts, Apr 1, 2017
Turbulence generated small-scale structures as PMWE formation mechanism: Results from a rocket campaign
Journal of Atmospheric and Solar-Terrestrial Physics, 2021
Abstract Simultaneous measurements of rocket-borne and ground-based instruments in a common volum... more Abstract 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.
Journal of Atmospheric and Solar-Terrestrial Physics, 2021
A first sounding rocket campaign dedicated to investigate the creation mechanism of Polar Mesosph... more 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 Andøya 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.
The Middle Atmosphere Alomar Radar System: improved capabilities and recent results
Characterization of polar mesospheric VHF radar echoes during solar minimum winter 2019/2020. Part I: Ionisation
Journal of Atmospheric and Solar-Terrestrial Physics, 2021
Abstract The exceptionally solar and geomagnetic quiet winter of 2019–2020 provides a very useful... more Abstract 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.
Radar Observation of Extreme Vertical Drafts in the Polar Summer Mesosphere
Geophysical Research Letters, 2021
The polar summer mesosphere is the Earth's coldest region, allowing the formation of mesosphe... more 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 used as tracers of mesospheric dynamics. Here, we report the first observations of extreme vertical drafts (50 ) in the mesosphere obtained from PMSE, characterized by velocities more than five standard deviations larger than the observed vertical wind variability. Using aperture synthesis radar imaging, the observed PMSE morphology resembles a solitary wave in a varicose mode, narrow along propagation (3–4 km) and elongated ( km) transverse to propagation direction, with a relatively large vertical extent (13 km). These spatial features are similar to previously observed mesospheric bores, but we observe only one crest with much larger vertical extent and higher vertical velocities.
Turbulence generated small-scale structures as PMWE formation mechanism: Results from a rocket campaign
Journal of Atmospheric and Solar-Terrestrial Physics, Jun 1, 2021
Abstract Simultaneous measurements of rocket-borne and ground-based instruments in a common volum... more Abstract 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.
The Middle Atmosphere Alomar Radar SYstem (MAARSY) with its active phased array antenna is design... more 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. 1 Introduction The Middle Atmosphere Alomar Radar System (MAARSY) was built in 2009/2010 by the Leibniz-Institute of Atmospheric Physics (IAP) on the North Norwegian island Andøya (69.3 • N, 16.04 • E) to allow improved studies of various atmospheric heights at high spatial and temporal resolution. Main target regions are the troposphere/lower stratosphere and the mesosphere. MAARSY's main active phased antenna array consists of 433 yagi antennas (see Figure 1), which are connected to their individual transceiver module allowing independent phase and amplitude control. Such a configuration allows both flexible pulse-to-pulse steering and forming of the radar beam by appropriate selection of amplitude and phase distribution over the array elements. A detailed description of the radar and its properties are given by Latteck et al. (2012), while recent geophysical investigations with MAARSY regarding layered phenomena in the mesosphere have been presented in Latteck and Strelnikova (2015) and Sommer et al. (2016). The knowledge of the current radiation pattern characteristics is important for both the design of experiments, e.g. specific experiment settings, and even more crucial for the analysis of radar data. The most important points to know are the beam pointing accuracy, shape and width of the beam, the antenna gain and the position and intensity of side lobes. For the validation of MAARSY's radiation pattern various passive and active experiments were already conducted. In passive experiments cosmic radio emissions from our galaxy as well as distinct radio sources like radio galaxies, supernova remnants and the diffuse background were observed. Subsequently, the derived intensity maps covering from 10 to 90 • of northern declination were compared to the detailed Global Sky Temperature model by de Oliveira-Costa et al.
Uploads
Papers by Toralf Renkwitz