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Sudden stratospheric warmings (SSWs) could act as an important mediator in the vertical coupling of atmospheric regions and dramatic variations in the mesosphere and lower thermosphere (MLT) in response to SSWs have been documented. However, due to rare occurrences, SSWs in the Southern Hemisphere (SH) and their impacts on the MLT dynamics are not well understood. This study presents an analysis of MLT winds at ∼80–98 km altitudes measured by meteor radars located at Tierra del Fuego (53.7°S, 67.7°W), King Edward Point (54.3°S, 36.5°W) and King Sejong Station (62.2°S, 58.8°W) near 60°S latitude during the Antarctic winter. Eastward zonal winds from these stations are observed to decrease significantly near the peak date of the 2019 Antarctic SSW, and both zonal and meridional winds in 2019 exhibit considerable differences to the mean winds averaged over other non‐SSW years. A quasi 6‐day oscillation is observed at all three radar locations, being consistent with the presence of the westward propagating zonal wave‐1 planetary wave. The vertical wavelength of this wave is estimated to be ∼55 km, and the enhancement of the wave amplitude during this SSW is noticeable. Evidence of the interaction between the 6‐day wave and the semidiurnal diurnal tide is provided, which suggests a possible mechanism for SSWs to impact the upper atmosphere. This study reports the large‐scale variations in winds in the MLT region at SH midlatitudes to high latitudes in a key dynamic but largely unexplored latitudinal band in response to the 2019 Antarctic SSW. Plain Language Summary: Sudden stratospheric warmings (SSWs) manifest dynamic disruptions in the polar winter stratosphere, characterized as rapid changes in temperature and wind within a few days. Although SSWs are by definition a stratospheric phenomenon, they have significant impacts throughout the middle and upper atmosphere. Many studies of the SSW impacts on the mesosphere and lower thermosphere (MLT) have been performed, mostly for the Northern Hemisphere (NH). In the Southern Hemisphere (SH), SSW events are rare and thus the Antarctic SSWs are not well known. An unusual SSW occurred in the SH during September 2019, and the work presented here focuses on studying the MLT winds observed by three meteor radars located at Tierra del Fuego (53.7°S, 67.7°W) in Argentina, King Edward Point (54.3°S, 36.5°W) on South Georgia Island, and King Sejong Station (62.2°S, 58.8°W) in King George Island. These observations are over a key dynamic but largely unexplored region around the Drake Passage. This study presents the large‐scale variations in the MLT winds at SH midlatitudes to high latitudes which are believed to be in response to the 2019 Antarctic SSW. Possible mechanisms for SSWs to impact the upper atmosphere are discussed. Key Points: Large wind disturbances are observed at ∼80–98 km altitude ∼60°S by three meteor radars during the 2019 Antarctic stratospheric warmingA quasi 6‐day oscillation is observed at different longitudes indicating the presence of the westward propagating zonal wave‐1 waveThis study provides observational evidence of the nonlinear interaction between the 6‐day planetary wave and the semidiurnal tide [ABSTRACT FROM AUTHOR]

Sporadic potassium (Ks) and sodium (Nas) layers were investigated using more than 1,500 h of simultaneous Na/K LIDAR data at São José dos Campos, Brazil (23.1°S, 45.9°W). These events were observed on more than 88% of the analyzed nights. Although Na and K are both alkali metals, their sporadic layers show different behaviors. The Nas layers were in general 0.7 km wider and occurred ∼2 km higher than Ks layers. Moreover, the Nas layers progression is faster than that of Ks layers not only in the process of reaching their maximum amplitude but also in terms of dissipation. Our study showed that most Ns events (80% of Ks layers and 90% of Nas layers) have a strength factor of upto 5. Moreover, on average, Ks presented a strength factor ∼1.3 times stronger than that of Nas. The relative frequency of occurrence for both Ks and Nas layers exhibits an almost semiannual variation, with maxima in January/October and February/September, respectively. On the other hand, no similar variation was observed in the peak density or in the peak height. The peak density shows an annual variation, with a maximum occurring during winter for Ks events and a semiannual variation with a maxima occurring at the equinoxes for Nas. Different seasonal behaviors were also seen in the peak height of the identified layers, with Ks presenting a semiannual variation with maxima around January/October, while an annual variation occurred in Nas with lower layers occurring around winter. Key Points: This study presents the first simultaneous analysis of averaged K and Na sporadic layer parameters in the Southern HemisphereSeasonal and nocturnal variations in sporadic events were observed in K and Na layersThe differing behaviors of neutral sporadic layers were described as seen in K and Na mesospheric layers [ABSTRACT FROM AUTHOR]

We have demonstrated a remote magnetometer based on sodium atoms in the Earth's mesosphere, at a 106‐km distance from our instrument. A 1.33‐watt laser illuminated the atoms, and the magnetic field was inferred from backscattered light collected by a telescope with a 1.55‐m‐diameter aperture. We theoretically predict a shot noise limited measurement sensitivity of 19nT/Hz. The measured sensitivity was 162nT/Hz due to a smaller returned intensity and smaller resonance strength than expected. The value of magnetic field inferred from our measurement is consistent with several models of the Earth's field shape to within a fraction of a percent. Projected improvements in optics, plus the use of advanced lasers or a large telescope, could result in 1‐nT/Hz sensitivity. Plain Language Summary: The upper end of a spinning top will slowly revolve around a vertical axis, a phenomenon known as precession. The precession frequency of the top is proportional to the strength of the gravitational field in which the top sits. This work uses the precession of atomic spins to analogously measure the strength of a magnetic field. The interaction of light with the atoms is sensitive to this precession and allows existing devices to observe the precessing atoms within an instrument. We have, for the first time, measured the magnetic field 100 km from our instrument using naturally occurring sodium atoms in the Earth's mesosphere. Atomic‐based measurements, such as optical magnetometers, are typically performed in well‐controlled environments. Here we demonstrate the ability to initialize quantum spin states and readout the evolution of the state at a significant standoff distance using a modified laser guidestar. The technique provides unique information about the mesospheric region of the atmosphere that is inaccessible by either aircraft or satellites. The small amount of light collected by our telescope creates a much less sensitive measurement than typical optical magnetometers, but methods are discussed that can improve the performance of this initial setup to reach a sensitivity needed for advancing understanding of geomagnetic field fluctuations such as those due to solar eruptions. This novel measurement technique is also an example of feasibility for other remote quantum measurements in the ambient atmosphere. Key Points: Remotely measured the geomagnetic field at a 90‐km altitude, this is an altitude that was previously difficult to monitorMeasured geomagnetic field was 45,441 nT, comparable to geomagnetic models, with a sensitivity of 162 nT/√HzSeveral improvements to the present measurements are discussed; the sensitivity could be improved to better than 1 nT/√Hz [ABSTRACT FROM AUTHOR]