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Solar Cycle and Long‐Term Trends in the Observed Peak of the Meteor Altitude Distributions by Meteor Radars
The mesosphere/lower thermosphere (MLT, 80–100 km) region is an important boundary between Earth's atmosphere below and space above and may act as a sensitive indicator for anthropogenic climate change. Existing observational and modeling studies have shown the middle atmosphere and the MLT is cooling and contracting because of increasing greenhouse gas emissions. However, trend analyses are highly sensitive to the time periods covered, their length, and the measurement type and methodology used. We present for the first time the linear and 11‐year solar cycle responses in the meteor ablation altitude distributions observed by 12 meteor radars at different locations. Decreasing altitudes were seen at all latitudes (linear trends varying from −10.97 to −817.95 m dec−1), and a positive correlation with solar activity was seen for most locations. The divergence of responses at high latitudes indicates an important and complex interplay between atmospheric changes and dynamics at varying time scales. Plain Language Summary High up in our atmosphere lies the mesosphere/lower thermosphere region (80–100 km); an important transition zone between the atmosphere below and space above. Existing studies indicate that this region is changing (cooling and contracting) in response to increasing greenhouse gas emissions, quite unlike the net warming we see near the surface. However these trend studies are often highly sensitive to choice and length of time period covered, and the methodology and type of measurements used. Here we present for the first time a self‐consistent methodology applied to 12 different meteor radar station datasets located at a diverse range of latitudes. We looked at changes in the mean peak altitude of individual meteoroid detections, and found decreasing peak altitudes at all locations examined (linear trends varying from −10.97 to −817.95 m decade−1) consistent with a global cooling and contracting of the upper atmosphere. We also examined the response to the 11‐year solar cycle and found a positive correlation with solar activity (i.e., increased meteoroid peak altitudes during solar maximum, and vice versa) for low and mid‐latitude locations. However we found an anti‐correlation at high latitudes suggestive of an important and complex interplay between atmospheric changes and dynamics at varying time scales. Key Points Use of geographically diverse meteor radar peak detection altitudes to assess long‐term and 11‐year solar cycle (SC) trends in mesopause region The altitude of observed peak meteor height has decreased over time at all locations, regardless of latitude and data set Positive correlation at low‐ and mid‐latitude locations with the 11‐year SC, but more complex response at high‐latitudes
Journal Article
I see falling stars
\"Young children are naturally curious about the world around them. I See Falling Stars offers answers to their most compelling questions about meteors. Age-appropriate explanations and appealing photos encourage readers to continue their quest for knowledge. Additional text features and search tools, including a glossary and an index, help students locate information and learn new words.\"-- Provided by publisher.
Book
Magnetic Aspect Sensitivity of Nonspecular Meteor Trail Echoes
The ablation of micrometeoroids entering Earth's atmosphere leaves behind a hot, dense column of plasma between 80 and 120 km altitude. Sharp density gradients can drive the plasma unstable, leading to turbulence and waves at the same altitude, which are often observed as coherent radar echoes. These echoes persist for 10s of milliseconds up to several minutes and are known as nonspecular trails. The turbulence from these trails is highly aspect sensitive and typically only observed within a few degrees of perpendicular to the magnetic field. In this letter, we present a new approach to measure the magnetic aspect sensitivity of nonspecular meteor trail echoes using the AMISR‐14 radar system. Using multiple beams, we simultaneously observe each trail at several different angles and directly observe aspect angle effects. Using this approach, we find that at 445 MHz, the observed power decays at 4.58 ± 0.46 dB/degree.
Journal Article
Meteor showers
An illustrated introduction to meteor showers that explains the differences between a meteor and shooting star, how meteors travel through the Earth's atmosphere, and related topics.
Book
African Meteorites
African Meteorites is a comprehensive exploration of meteorite falls and finds across the arid and hot regions of the African continent, offering profound insights into a significant collection of meteorites, second only to Antarctica. The book is divided into seven chapters, covering the origin and formation of meteorites, statistical analyses of meteorite falls in African countries, classes and mass distribution of meteorite finds, allocation and renaming of North West African (NWA) meteorites, exceptional and rare meteorite falls and finds in Eastern Morocco Sahara, protocols for recognizing, recovering, and preserving meteorites in Sahara, and a review of confirmed and proposed meteorite falls, finds, and impact structures in Egypt, Sudan, and Libya. With detailed and updated references complementing the simple presentation, this book is an invaluable resource for meteoriticists, hunters, museums, astronomers, students, and geology and astronomy enthusiasts, on the origin, characteristics, and collection of meteorites discovered in Africa. Key Themes: Meteorite origin, formation, and classificationMeteorite falls and finds in AfricaUnique features of North West Africa (NWA) meteoritesRare and exceptional meteorite falls and finds in Eastern Morocco SaharaProtocols for recognizing and preserving meteorites in the SaharaMeteorite falls, finds, and impact structures in Egypt, Sudan, and Libya Readership: Meteoriticists, geologists, mineralogists, historians, researchers and general readers.
eBook
A Review of Infrasound and Seismic Observations of Sample Return Capsules since the End of the Apollo Era in Anticipation of the OSIRIS-REx Arrival
Advancements in space exploration and sample return technology present a unique opportunity to leverage sample return capsules (SRCs) towards studying atmospheric entry of meteoroids and asteroids. Specifically engineered for the secure transport of valuable extraterrestrial samples from interplanetary space to Earth, SRCs offer unexpected benefits that reach beyond their intended purpose. As SRCs enter the Earth’s atmosphere at hypervelocity, they are analogous to naturally occurring meteoroids and thus, for all intents and purposes, can be considered artificial meteors. Furthermore, SRCs are capable of generating shockwaves upon reaching the lower transitional flow regime, and thus can be detected by strategically positioned geophysical instrumentation. NASA’s OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) SRC is one of only a handful of artificial objects to re-enter the Earth’s atmosphere from interplanetary space since the end of the Apollo era and it will provide an unprecedented observational opportunity. This review summarizes past infrasound and seismic observational studies of SRC re-entries since the end of the Apollo era and presents their utility towards the better characterization of meteoroid flight through the atmosphere.
Journal Article
Meteor!
A quiet rural community is dramatically changed when a meteor crashes down in the front yard of the Gaw family.
Book
Meteor radar vertical wind observation biases and mathematical debiasing strategies including the 3DVAR+DIV algorithm
Meteor radars have become widely used instruments to study atmospheric dynamics, particularly in the 70 to 110 km altitude region. These systems have been proven to provide reliable and continuous measurements of horizontal winds in the mesosphere and lower thermosphere. Recently, there have been many attempts to utilize specular and/or transverse scatter meteor measurements to estimate vertical winds and vertical wind variability. In this study we investigate potential biases in vertical wind estimation that are intrinsic to the meteor radar observation geometry and scattering mechanism, and we introduce a mathematical debiasing process to mitigate them. This process makes use of a spatiotemporal Laplace filter, which is based on a generalized Tikhonov regularization. Vertical winds obtained from this retrieval algorithm are compared to UA-ICON model data. This comparison reveals good agreement in the statistical moments of the vertical velocity distributions. Furthermore, we present the first observational indications of a forward scatter wind bias. It appears to be caused by the scattering center's apparent motion along the meteor trajectory when the meteoric plasma column is drifted by the wind. The hypothesis is tested by a radiant mapping of two meteor showers. Finally, we introduce a new retrieval algorithm providing a physically and mathematically sound solution to derive vertical winds and wind variability from multistatic meteor radar networks such as the Nordic Meteor Radar Cluster (NORDIC) and the Chilean Observation Network De meteOr Radars (CONDOR). The new retrieval is called 3DVAR+DIV and includes additional diagnostics such as the horizontal divergence and relative vorticity to ensure a physically consistent solution for all 3D winds in spatially resolved domains. Based on this new algorithm we obtained vertical velocities in the range of w = ± 1–2 m s−1 for most of the analyzed data during 2 years of collection, which is consistent with the values reported from general circulation models (GCMs) for this timescale and spatial resolution.
Journal Article