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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 (∼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. Plain Language Summary: Extreme events are ubiquitous in geophysical flows. Examples of these events are tornadoes and rogue waves in the lower atmosphere and oceans, respectively. In the mesosphere, the boundary of Earth's atmosphere and outer space, extreme events can also occur, although this region is poorly observed. Here, we present the first observations of extreme vertical velocities (±50 ms−1) in the mesosphere, that are more than five times their expected standard deviation. These observations are possible by tracking and imaging strong mesospheric radar echoes that occur in the summer at polar latitudes, with a radar used in a radio camera mode. The morphology of our observations resembles previously observed instabilities called bores or wave walls, but with much larger vertical velocities and vertical extents. Key Points: First observations of extreme vertical velocities in the polar summer mesosphereThe observed solitary wave in a varicose mode resembles a mesospheric bore, with large vertical extent and vertical velocitiesSuch extreme events might have been missed or ignored in previous observations of vertical velocities or other mesospheric observations [ABSTRACT FROM AUTHOR]

Mean winds and tides in the northern polar Mesosphere and Lower Thermosphere (MLT) have been studied using meteor radars located at Resolute Bay (75° N, 95° W) and Yellowknife (62.5° N, 114.3° W). The measurements for Resolute Bay span almost 12 years from July 1997 to February 2009 and the Yellowknife data cover 7 years from June 2002 to October 2008. The analysis reveals similar wind flow over both sites with a difference in magnitude. The summer zonal flow is westward at lower heights, eastward at upper heights and the winter zonal flow is eastward at all heights. The winter meridional flow is poleward and sometimes weakly equatorward, while non winter months show equatorward flow, with a strong equatorward jet during mid-summer months. The zonal and meridional winds show strong interannual variation with a dominant annual variation as well as significant latitudinal variation. Year to year variability in both zonal and meridional winds exists, with a possible solar cycle dependence. The diurnal, semidiurnal and terdiurnal tides also show large interannual variability and latitudinal variation. The diurnal amplitudes are dominated by an annual variation. The climatological monthly mean winds are compared with CIRA 86, GEWM and HWM07 and the climatological monthly mean amplitudes and phases of diurnal and semidiurnal tides are compared with GSWM00 predictions. The GEWM shows better agreement with observations than the CIRA 86 and HWM07. The GSWM00 model predictions need to be modified above 90 km. The agreements and disagreements between observations and models are discussed. [ABSTRACT FROM AUTHOR]

Over the last 40 years, radar studies of atmospheric backscatter have shown tantalizing evidence for flat, mirror-like partial reflectors embedded in the air. These have been observed at all heights, but especially in the stratosphere (above ∼10 km) and mesosphere (especially in the region 60-90 km altitude), and at a variety of frequencies, from 2 to at least 50 MHz. These structures appear to have vertical depths of only a few meters or less. They often seem independent of atmospheric turbulence scatter. Various explanations have been advanced to account for these unusual structures, but a strong candidate is the possibility that they are due to diffusion waves generated by reflection and/or critical level interactions of gravity waves or infrasound. In this review, we will examine the evidence for these structures, and expand on the possibility that they are indeed organized structures which develop due to the diffusive characteristics of the medium. [ABSTRACT FROM AUTHOR]