Stratospheric Sudden Warmings (SSWs) followed by the formation of an elevated stratopause at 70-80 km occurred in four of the five recent Arctic winters (2009)(2010)(2011)(2012)(2013). We use global high-latitude temperature measurements from the Solar Occultation for Ice Experiment (SOFIE) to analyze the gravity wave (GW) activity in the upper stratosphere and mesosphere (30-90 km) during different phases of the SSW events. We characterize GW activity in terms of temperature fluctuations and the growth of GW potential energy with altitude. At both 40 and 60 km, compared to the non-SSW year of 2011, the GW activity in the SSW years of 2009, 2010, 2012, and 2013 was reduced after the warming, during the occurrence of an isothermal atmosphere and an elevated stratopause. In contrast, at 80 km the GW activity was highly variable between the individual stratospheric warming events. A case study of GW activity during the 2013 warming event and coincident SOFIE observations of water vapor (H 2 O) from~40 to 90 km indicate a correlation between increase in wave activity at each altitude and the time of descent of dry air. This study supports previous modeling studies' findings that enhanced GW activity is responsible for the downward transport of trace species from the mesosphere to the stratosphere following an SSW event.

Retrieval of the properties of the middle and upper atmosphere can be performed using several different interferometric and photometric methods. The emission-shape and Doppler shift of both atomic and molecular emissions can be observed from the ground and space to provide temperature and bulk velocity. These instantaneous measurements can be combined over successive times/locations along an orbit track, or successive universal/local times from a ground station to quantify the motion and temperature of the atmosphere needed to identify atmospheric tides. In this report, we explore how different combinations of space-based wind and temperature measurements affect the retrieval of atmospheric tides, a ubiquitous property of planetary atmospheres. We explore several scenarios informed by the use of a tidally forced atmospheric circulation model, an empirically based emissions reference, and a low-earth orbit satellite observation geometry based on the ICON mission design. This capability provides a necessary tool for design of an optimal mission concept for retrieval of atmospheric tides from ICON remote-sensing observations. Here it is used to investigate scenarios of limited data availability and the effects of rapid changes in the total wave spectrum on the retrieval of the correct tidal spectrum. An approach such as that described here could be used in the design of future missions, such as the NASA DYNAMIC mission (National Research Council, Solar and space physics: a science for a technological society, 2013).

We report the first lidar observations of regular occurrence of mid-latitude thermosphereionosphere Na (TINa) layers over Boulder (40.13°N, 105.24°W), Colorado. Detection of tenuous Na layers (∼0.1-1 cm −3 from 150 to 130 km) was enabled by high-sensitivity Na Doppler lidar. TINa layers occur regularly in various months and years, descending from ∼125 km after dusk and from ∼150 km before dawn. The downward-progression phase speeds are ∼3 m/s above 120 km and ∼1 m/s below 115 km, consistent with semidiurnal tidal phase speeds. One or more layers sometimes occur across local midnight. Elevated volume mixing ratios above the turning point (∼105-110 km) of Na density slope suggest in situ production of the dawn/dusk layers via neutralization of converged Na + layers. Vertical drift velocity of TINa + calculated with the Ionospheric Connection Explorer Hough Mode Extension tidal winds shows convergent ion flow phases aligned well with TINa, supporting this formation hypothesis.

We present the first coordinated study using two lidars at two separate locations to characterize a 1 h mesoscale gravity wave event in the mesopause region. The simultaneous observations were made with the Student Training and Atmospheric Research (STAR) Na Doppler lidar at Boulder, CO, and the Utah State University Na Doppler lidar and temperature mapper at Logan, UT, on 27 November 2013. The high precision possessed by the STAR lidar enabled these waves to be detected in vertical wind. The mean wave amplitudes are ~0.44 m/s in vertical wind and ~1% in relative temperature at altitudes of 82–107 km. Those in the zonal and meridional winds are 6.1 and 5.2 m/s averaged from 84 to 99 km. The horizontal and vertical wavelengths inferred from the mapper and lidars are ~219 ± 4 and 16.0 ± 0.3 km, respectively. The intrinsic period is ~1.3 h for the airglow layer, Doppler shifted by a mean wind of ~17 m/s. The wave packet propagates from Logan to Boulder with an azimuth angle of ~135° clockwise from north and an elevation angle of ~ 3° from the horizon. The observed phase difference between the two locations can be explained by the traveling time of the 1 h wave from Logan to Boulder, which is about ~2.4 h. The wave polarization relations are examined through the simultaneous quantifications of the three wind components and temperature. This study has developed a systematic methodology for fully characterizing mesoscale gravity waves, inspecting their intrinsic properties and validating the derivation of horizontal wave structures by applying multiple instruments from coordinated stations.

Wind measurements from the Michelson Interferometer for Global High‐resolution Thermospheric Imaging (MIGHTI) instrument on the Ionospheric CONnections (ICON) mission provide new insights into the semidiurnal tidal spectrum in the thermosphere, covering latitudes 9°S–39°N and altitudes 100–280 km altitude throughout 2020. Latitude vs. day of year (DOY) variability of solar semidiurnal tides SE2, S0, SW1, SW2, SW3, and SW4 at 250 km are presented for the first time, and evaluated relative to similar results at 106 km. Using daytime‐only data, height vs. latitude and height vs. DOY variability of SE2, S0, SW1. SW3, and SW4 amplitudes and phases are depicted for the first time, revealing the effects of a dissipative thermosphere on the vertical evolutions of these tidal structures. SW2 is absent from these depictions due to potential aliasing by zonal mean winds. The above results are considered in light of the Climatological Tidal Model of the Thermosphere (CTMT), which is based on fits to tidal winds and temperatures from the Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics mission between 80 and 120 km during 2002–2008, and extrapolated to an altitude of 400 km based on modeled tidal structures propagating in a dissipative thermosphere, but without in situ sources of excitation due to tide‐tide or tide‐ion drag nonlinear interactions. On the basis of comparisons with the CTMT and other characteristics revealed in the MIGHTI tidal structures, it is concluded that in situ sources exist for S0, SW1, SW2, and SW3 in the thermosphere above about 200 km.