. Abstract. Meteor radars have become widely used instruments for studies of atmospheric dynamics, particularly in the 70 to 110...

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 ms-1) 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 (>10 km) transverse to propagation direction, with a relatively large vertical extent (similar to 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.

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.

In the present communication, characteristics of mean winds and planetary waves in the mesosphere lower thermosphere (MLT) region during sudden stratospheric warming (SSW) events using observations from four meteor wind radars located at high, middle, low and equatorial latitudes are discussed. The response of the respective MLT regions to three SSW events that occurred during 2008–09, 2009–10 and 2011–12 winters are investigated. SSW signatures in the MLT zonal and meridional winds over the high latitude station Andenes ($$69.3^\circ\, \mathrm{N}, 16.0^\circ\, \mathrm{E}$$) are found to have significant differences from event to event. Mean wind reversals in the high latitude MLT are found to be preceding the corresponding signatures at $$60^\circ\, \mathrm{N}$$, 10 hPa by a few days. Zonal and meridional wind reversals extend to the MLT region over the mid latitude location Socorro ($$34.1^\circ\, \mathrm{N}, 106.9^\circ\, \mathrm{W}$$). However, MLT region over the low latitude station Thumba ($$8.5^\circ\, \mathrm{N}, 77^\circ\, \mathrm{E}$$) as well as the equatorial station Kototabang ($$0.2^\circ\, \mathrm{S}, 100.3^\circ\, \mathrm{E}$$) are found to be having a minimal response as far as mean winds are concerned. Apart from mean winds, planetary wave activity in the MLT region over the observational sites are examined, which show a systematic progression of planetary waves from high to equatorial latitudes during major as well as minor SSW events. To elucidate the origin of the observed planetary waves in the MLT region, the stratospheric winds are analyzed. Results suggest that the observed planetary waves have originated in the high-mid latitude middle atmospheric region. The present study provides observational evidence for secondary planetary wave generation in the high-mid latitude middle atmosphere and their equatorial propagation in the MLT as predicted by previous numerical modelling studies. Significance of the present study lies in employing a network of meteor radar observations to investigate the SSW signatures in the MLT region over high, middle, low and equatorial latitudes, simultaneously.

A description of the physics of radar meteors from 1945 to the mid-1970s is presented. Concrete designs of various radars in different countries are presented. Harvard project is the best documented of these early radars, and we will focus on that radar. Application of multi-receiver stations for orbit determination became relatively common, especially with the advent of the IGY in 1957. Canada also built the Springhill Meteor Observatory around the time of the IGY, but of special note was the construction of several meteor radars in the USSR. The contribution of Kashcheyev and his scientific group to the development of radar meteor technologies was emphasized. A discussion of some equipment options of Balakleya geophysical complex in different years was held. Problems of meteor radar technologies in solving problems of astronomy and geophysics are noted. "Meteor winds" became a mainstay of upper atmospheric research into dynamical processes after 1960's. Such research was undertaken at multiple sites all over the "Western" global arena as well as in the USSR. In attention is paid to the history of changes in the methods of obtaining, processing and storage of meteor information. Some aspects of the application of innovative technologies in meteor radar systems were discussed, primarily in the study of winds and atmospheric circulation in the meteor zone. The advent of personal computers, plus the somewhat simultaneous development of digitizers in the early 1970's, was a major breakthrough for many areas of scientific research and Meteor studies. This work is the first part of a planned review of radar meteor physics and related technologies from 1945 to 2020.

Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Journal of Geophysical Research - Atmospheres. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing the latest version by default [v1]Interhemispheric Comparisons of Structure and Variability of the Quasi-2-Day Wave at Middle and High LatitudesAuthors Hiroyuki Iimura iD David C. Fritts iD Ruth S. Lieberman Diego Janches Nicholas John Mitchell Werner Singer Steven J. Franke Wayne K. Hocking iDSee all authors Hiroyuki IimuraiDCorresponding AuthorGATS Inc.iDhttps://orcid.org/0000-0001-9174-8396view email addressThe email was not providedcopy email addressDavid C. FrittsiDGATSiDhttps://orcid.org/0000-0002-6402-105Xview email addressThe email was not providedcopy email addressRuth S. LiebermanNASA Goddardview email addressThe email was not providedcopy email addressDiego JanchesNational Aeronautics and Space Administration (NASA)view email addressThe email was not providedcopy email addressNicholas John MitchellUniversity of Bathview email addressThe email was not providedcopy email addressWerner SingerLeibniz-Institute of Atmospheric Physics (LG)view email addressThe email was not providedcopy email addressSteven J. FrankeUniversity of Illinois at Urbana Champaignview email addressThe email was not providedcopy email addressWayne K. HockingiDUniversity of Western OntarioiDhttps://orcid.org/0000-0003-0111-8804view email addressThe email was not providedcopy email address

This paper presents a study of diurnal tidal winds observed simultaneously by two meteor radars located on each side of the Equator in the equatorial region. The radars were located in Santa Cruz, Costa Rica (10.3∘ N, 85.6∘ W) (hereafter CR) and São João do Cariri, Brazil (7.4∘ S, 36.5∘ W) (hereafter CA). The distance between the sites is 5800 km. Harmonic analysis has been used to obtain amplitudes and phases (hour of peak amplitude) for diurnal, semidiurnal and terdiurnal tides between 82 and 98 km altitude, but in this work we concentrate on the diurnal component. The period of observation was from April 2005 to January 2006. The results were compared to the Global Scale Waves Model (GSWM-09). Magnitudes of zonal and meridional amplitudes from November to January for CR were quite different from the predictions of the model. Concerning phases, the agreement between model and radar meridional tidal phases at each site was good, and a vertical wavelength of 24 km for the diurnal tide was observed practically every month, although on some occasions determination of the vertical wavelength was difficult, especially for the zonal component, due to nonlinear phase variations with height. For the diurnal zonal amplitude, there were notable differences between the two sites. We attribute this site-to-site difference of the diurnal zonal amplitude to the nonmigrating component of the tide and propose that an anomaly was present in the troposphere in the winter (Northern Hemisphere) of 2005–2006 which produced substantial longitudinal variation.

The structure, variability, and mean‐flow interactions of the quasi‐2‐day wave (Q2DW) in the mesosphere and lower thermosphere during January 2015 were studied employing meteor and medium‐frequency radar winds at eight sites from 23°S to 76°S and Microwave Limb Sounder (MLS) temperature and geopotential height measurements from 30°S to 80°S. The event had a duration of ~20–25 days, dominant periods of ~44–52 hr, temperature amplitudes as large as ~16 K, and zonal and meridional wind amplitudes as high as ~40 and 80 m/s, respectively, at middle and lower latitudes. MLS measurements enabled definition of balance winds that agreed well with radar wind amplitudes and phases at middle latitudes where amplitudes were large and quantification of the various Q2DW modes contributing to the full wave field. The Q2DW event was composed primarily of the westward zonal wavenumber 3 (W3) mode but also had measurable amplitudes in other westward modes W1, W2, and W4; eastward modes E1 and E2; and stationary mode S0. Of the secondary modes, W1, W2, and E2 had the larger amplitudes. Inferred MLS balance winds enabled estimates of the Eliassen‐Palm fluxes for each mode, and cumulative zonal accelerations that were found to be in reasonable agreement with radar estimates from ~35°S to 70°S at the lower altitudes at which radar winds were available.

In a series of 10-day campaigns in Ontario and Quebec, Canada, between 2005 and 2007, ozonesondes were launched twice daily in conjunction with continuous high-resolution wind-profiling radar measurements. Windprofilers can measure rapid changes in the height of the tropopause, and in some cases follow stratospheric intrusions. Observed stratospheric intrusions were studied with the aid of a Lagrangian particle dispersion model and the Canadian operational weather forecast system. Definite stratosphere-troposphere transport (STT) events occurred approximately every 2-3 days during the spring and summer campaigns, whereas during autumn and winter, the frequency was reduced to every 4-5 days. Although most events reached the lower troposphere, only three events appear to have significantly contributed to ozone amounts in the surface boundary layer. Detailed calculations find that STT, while highly variable, is responsible for an average, over the seven campaigns, of 3.1% of boundary layer ozone (1.2 ppb), but 13% (5.4 ppb) in the lower troposphere and 34% (22 ppb) in the middle and upper troposphere, where these layers are defined as 0-1 km, 1-3 km, and 3-S km respectively. Estimates based on counting laminae in ozonesonde profiles, with judicious choices of ozone and relative humidity thresholds, compare moderately well, on average, with these values. The lamina detection algorithm is then applied to a large dataset from four summer ozonesonde campaigns at 18 North American sites between 2006 and 2011. The results show some site-to-site and year-to-year variability, but stratospheric ozone contributions average 4.6% (boundary layer), 15% (lower troposphere) and 26% (middle/upper troposphere). Calculations were also performed based on the TOST global 3D trajectory-mapped ozone data product. Maps of STT in the same three layers of the troposphere suggest that the STT ozone flux is greater over the North American continent than Europe, and much greater in winter and spring than in summer or fall. When averaged over all seasons, magnitudes over North America show similar ratios between levels to the previous calculations, but are overall 3-4 times smaller. This may be because of limitations (trajectory length and vertical resolution) to the current TOST-based calculation.

Results from the first VHF profiler research radar in Costa Rica, operating at a central radar frequency of 46.6 MHz, are presented. Emphasis has been on studies of scattering layers detected in the altitude range 1–6 km, with the main goal being to identify regions with radar echoes and observe the temporal evolution of the echoes. Data were obtained over the course of a full year using a vertical resolution of better than 100 m. Layers of strong scatter were observed regularly, often with simultaneous broad spectra, which may indicate enhanced turbulence. Similar layers have been observed over equatorial Indonesia, and these have been associated with the planetary boundary layer. The presence of echo layers was more common during the dry-season months (December–April); in fact during March, two layers were observed in the lower troposphere for more than 35% of the time. Stable pattern structures often occurred for extended periods, but at times the layers could also vary drastically in behavior from 1 day to the next. After sunset, strong echo layers could persist for several hours. Some examples of regularly observed layer behavior are given.

Shock waves and the associated phenomena generated by strongly ablating meteoroids with sizes greater than a few millimeters in the lower transitional flow regime of the Earth's atmosphere are the least explored aspect of meteor science. In this paper, we present a comprehensive review of literature covering meteor generated shock wave phenomena, from the aspect of both meteor science and hypersonic gas dynamics. The primary emphasis of this review is placed on the mechanisms and dynamics of the meteor shock waves. We discuss key aspects of both shock generation and propagation, including the great importance of the hydrodynamic shielding that develops around the meteoroid. In addition to this in-depth review, the discussion is extended to an overview of meteoroid fragmentation, followed by airburst type events associated with large, deep penetrating meteoroids. This class of objects has a significant potential to cause extensive material damage and even human casualties on the ground, and as such is of great interest to the planetary defense community. To date, no comprehensive model exists that accurately describes the flow field and shock wave formation of a strongly ablating meteoroid in the non-continuum flow regime. Thus, we briefly present the current state of numerical models that describe the comparatively slower flow of air over non-ablating bodies in the rarefied regime. In respect to the elusive nature of meteor generated shock wave detection, we also discuss relevant aspects and applications of meteor radar and infrasound studies as tools that can be utilized to study meteor shock waves and related phenomena. In particular, infrasound data can provide energy release estimates of meteoroids entering the Earth's atmosphere. We conclude with a summary of unresolved questions in the domain of meteor generated shock waves; topics which should be a focus of future investigations in the field.

With the recent increase in numbers of small and versatile low-power meteor radars, the opportunity exists to benefit from simultaneous application of multiple systems spaced by only a few hundred km and less. Transmissions from one site can be recorded at adjacent receiving sites using various degrees of forward scatter, potentially allowing atmospheric conditions in the mesopause regions between stations to be diagnosed. This can allow a better spatial overview of the atmospheric conditions at any time. Such studies have been carried out using a small version of such so-called multistatic meteor radars, e.g. Chau et al. (Radio Sci 52:811–828, 2017 , https://doi.org/10.1002/2016rs006225 ). These authors were able to also make measurements of vorticity and divergence. However, measurement uncertainties arise which need to be considered in any application of such techniques. Some errors are so severe that they prohibit useful application of the technique in certain locations, particularly for zones at the midpoints of the radars sites. In this paper, software is developed to allow these errors to be determined, and examples of typical errors involved are discussed. The software should be of value to others who wish to optimize their own MMR systems.

The ability of very high frequency (VHF) (~50 MHz) windprofilers to measure backscatter, winds and turbulence in the troposphere and the lower stratosphere gives them a unique perspective not available with many other remote sounding radar techniques. This capability has been utilized to study the environment of 31 tornadoes generated in the provinces of Ontario and Quebec in Canada over an 11‐year period. Tornadoes were mostly of Enhanced Fujita (EF) types EF0 to EF2, with one being EF3. Focus is on events which produced visible damage. Signals detected show characteristics demonstrating new informative—and potentially predictive—capabilities. A large enhancement in backscattered power immediately above the common volume of the radar and the tornadic supercell, reaching to the tropopause and beyond, when coupled with radar measurements of strong turbulence and wind speeds, provides good radar evidence of tornadic activity.

Abstract. The main goals of this work are to characterize and investigate the potential wave sources of four mesospheric fronts identified in the hydroxyl near-infrared (OH-NIR) airglow images, obtained with an all-sky airglow imager installed at Comandante Ferraz Antarctic Station (EACF, as per its Portuguese acronym) located on King George Island in the Antarctic Peninsula. We identified and analyzed four mesospheric fronts in 2011 over King George Island. In addition, we investigate the atmospheric background environment between 80 and 100 km altitude and discuss the ducts and propagation conditions for these waves. For that, we used wind data obtained from a meteor radar operated at EACF and temperature data obtained from the TIMED/SABER satellite. The vertical wavenumber squared, m2 , was calculated for each of the four waves. Even though no clearly defined duct (indicated by positive values of m2 sandwiched between layers above and below with m2  < 0) was found in any of the events, favorable propagation conditions for horizontal propagation of the fronts were found in three cases. In the fourth case, the wave front did not find any duct support and it appeared to dissipate near the zenith, transferring energy and momentum to the medium and, consequently, accelerating the wind in the wave propagation direction (near to south) above the OH peak (88–92 km). The likely wave sources for these four cases were investigated by using meteorological satellite images and in two cases we could find that strong instabilities were potential sources, i.e., a cyclonic activity and a large convective cloud cell. In the other two cases it was not possible to associate troposphere sources as potential candidates for the generation of such wave fronts observed in the mesosphere and secondary wave sources were attributed to these cases. Keywords. Atmospheric composition and structure (airglow and aurora) – meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

Upper-level winds are primarily measured by tracking the position of radiosonde balloons as they rise through the atmosphere. Radiosondes are released from a global network at 0000 UTC and 1200 UTC each day, and data are quickly available to the world's weather services, as well as to the public. The network is relatively coarse spatially, and there are normally only two soundings per day. In an endeavour to provide better spatial and temporal upper-level regional wind measurements, the O-QNet (a demonstration very high frequency wind profiler network for Ontario and Quebec) was installed and has been operated by York, Western, and McGill Universities with support from Mardoc Inc., The Weather Network, and Environment and Climate Change Canada. Initial funding was provided by the Canada Foundation for Innovation, the Ontario Innovation Trust, and Mardoc Inc. The present paper reports primarily on comparisons between winds measured by the O-QNet profilers and the winds reported in the North American Regional Reanalysis (NARR). There is good agreement between the two, which provides support for the use of NARR data to investigate longer term variations in upper- level winds associated with climate change for this region.

Studies of meteor trails have until now been limited to relatively simple models, with the trail often being treated as a conducting cylinder, and the head (if considered at all) treated as a ball of ionized gas. In this article, we bring the experience gleaned from other fields to the domain of meteor studies, and adapt this prior knowledge to give a much clearer view of the microscale physics and chemistry involved in meteor-trail formation, with particular emphasis on the first 100 or so milliseconds of the trail formation. We discuss and examine the combined physicochemical effects of meteor-generated and ablationally amplified cylindrical shock waves that appear in the ambient atmosphere immediately surrounding the meteor train, as well as the associated hyperthermal chemistry on the boundaries of the high temperature post-adiabatically expanding meteor train. We demonstrate that the cylindrical shock waves produced by overdense meteors are sufficiently strong to dissociate molecules in the ambient atmosphere when it is heated to temperatures in the vicinity of 6000 K, which substantially alters the considerations of the chemical processes in and around the meteor train. We demonstrate that some ambient O-2, along with O-2 that comes from the shock dissociation of O-3, survives the passage of the cylindrical shock wave, and these constituents react thermally with meteor metal ions, thereby subsequently removing electrons from the overdense meteor train boundary through fast, temperature-independent, dissociative recombination governed by the second Damkohler number. Possible implications for trail diffusion and lifetimes are discussed.

Reynold E. Silber; Wayne K. Hocking; Maria Gritsevich; Elizabeth A. Silber; Mihai L. Niculescu (1) Department of Earth Sciences, The University of Western Ontario, London, Ontario, N6A 3B7, Canada (2) Department of Physics and Astronomy, The University of Western Ontario, London, Ontario, N6A 3K7 Canada (3) Department of Computational Physics, Russian Academy of Sciences, Vavilova 40, 119333 Moscow, Russia (4) Department of Earth, Environmental and Planetary Science, Brown University, Providence, RI, 02912, USA (5) INCAS National Institute for Aerospace Research "ElieCarafoli", Bucharest 061126, Romania

1 Department of Earth Sciences, The University of Western Ontario, London, Ontario, N6A 3B7, Canada (e-mail: reynold.silber@uwo.ca), 2 Department of Earth, Environmental and Planetary Science, Brown University, Providence, RI, USA, 06912 (e-mail: elizabeth_silber@brown.edu), 3 Department of Physics, University of Helsinki, Gustaf Hällströmin katu 2a, P.O. Box 64, FI-00014 Helsinki, Finland (email: maria.gritsevich@helsinki.fi), 4 Institute of Physics and Technology, Ural Federal University, Mira St. 19, 620002 Ekaterinburg, Russia, 5 INCAS National Institute for Aerospace Research "Elie Carafoli", Flow Physics Department, Numerical Simulation Unit, Bucharest 061126, Romania, 6 Department of Physics and Astronomy, University of Western Ontario, London, Ontario, N6A 3K7 Canada