Travelling ionospheric disturbances (TIDs) and their neutral counterparts known as travelling atmospheric disturbances (TADs) are believed to play a central role in redistributing energy and momentum in the upper atmosphere and communicating inputs to other locations in the fluid. While these two phenomena are believed to be connected, they may not have a one-to-one correspondence as the geomagnetic field influences the TID but has no direct impact on the TAD. The relative amplitudes of the perturbations seen in the ionosphere and atmosphere have been observed but rarely together. This study reports results from a three-day campaign to observe TIDs and TADs simultaneously over a broad latitudinal region over the eastern United States using a combination of GOLD and a distributed network of ground based Global Navigation Satellite System (GNSS) receivers. These results demonstrate that GOLD and the ground-based total electron content (TEC) observations can see the atmospheric and ionospheric portions of a large-scale travelling disturbance. The phase difference in the perturbations to the GOLD airglow brightness, O/N2 and thermospheric disk temperature are consistent with an atmospheric gravity wave moving through this region. The ionospheric signatures move at the same rate as those in the atmosphere, but their amplitudes do not have a simple correspondence to the amplitude of the signal seen in the atmosphere. This campaign demonstrates a proof-of-concept that this combination of observations is able to provide information on TIDs and TADs, including quantifying their impact on the temperature and chemical composition of the upper atmosphere.

Oblique propagation of gravity waves (GWs) refers to latitudinal propagation (or vertical propagation away from their source) from the low latitude troposphere to the polar mesosphere. This propagation is not included in current gravity wave parameterization schemes, but may be an important component of the global dynamical structure. Previous studies have revealed a high correlation between observations of GW Momentum Flux (GWMF) from monsoon convection and Polar Mesospheric Clouds (PMCs) in the northern hemisphere. In this work, we report on data and model analysis of the effects of Stratospheric Sudden Warmings (SSWs) in the northern hemisphere, on the oblique propagation of GWs from the southern hemisphere tropics, that in turn influence PMCs in the southern summer mesosphere. In response to SSWs, vertical propagation of GWs from high-latitude winter hemisphere is at mid latitudes and appears more slanted toward the equator with increasing altitude, following the weaker stratospheric eastward jet. The oblique propagation of GWs from southern monsoon regions tends to start at higher altitudes with a sharper poleward slanted structure towards the summer mesosphere. The correlation between PMCs in summer southern hemisphere and the zonal GWMF from 50°N to 50°S exhibits a high-correlation pattern that connects the winter stratosphere with the summer mesosphere, indicating the influence of inter-hemispheric coupling mechanism. Temperature and wind anomalies suggest that the dynamics in winter hemisphere can influence the equatorial region, which in turn, can influence the oblique propagation of monsoon GWs.

Both ground- and satellite-based airglow imaging have significantly contributed to our understanding of the low-latitude ionosphere, especially of the morphology and dynamics of the equatorial ionization anomaly (EIA). The NASA Global-scale Observations of the Limb and Disk (GOLD) mission focuses on far-ultraviolet airglow images from a geostationary orbit at 47.5°W. This region is of particular interest at low magnetic latitudes because of the high magnetic declination (i.e., about -20°) and proximity of the South Atlantic magnetic anomaly. Nighttime airglow images from GOLD reveal an exciting feature of the EIA. Using observations from 5 October 2018 to 30 June 2020, we characterize a wave-like structure of few thousands of kilometers seen as poleward and equatorward displacements of the nighttime EIA-crests. Initial analyses show that the mesoscale structure is symmetric about the dip equator and appears nearly stationary with time over the night. In quasi-dipole coordinates, maxima poleward displacements of the EIA-crests are seen at about ±12° latitude and around 20° and 60° longitude (i.e., in geographic longitude at the dip equator, about 53°W and 14°W). The wave-like structure presents typical zonal wavelengths of about 6.7x10^3 km and 3.3x10^3 km. The structure’s occurrence and wavelength are highly variable on a day-to-day basis with no apparent dependence on geomagnetic activity. In addition, a cluster or quasi-periodic wave train of equatorial plasma depletions (EPDs) is often detected within the mesoscale structure. We further outline the difference in observing these EPDs from FUV images and in situ measurements during a GOLD and Swarm mission conjunction.

Vertical shears of horizontal winds play an important role in the dynamics of the middle and upper atmosphere. Prior observations have indicated that these shears predominantly occur in the lower thermosphere. MIGHTI observations from the Ionospheric Connection Explorer indicate that strong wind shears are a common feature of the lower thermosphere and vary greatly between orbits. This work focuses on these strong shears, and examines their occurrences, horizontal scales and underlying organization. No preferred wind shear direction is found. The shears that persist for a short horizontal extent are slightly larger in amplitude and more numerous than those that persist across large horizontal scales. The altitude at which the strongest shears occur often shows a downward progression with local time, following the climatological winds. Consistent with prior observations, the strongest shears are often seen just below the wind maximum, which follows the downward phase propagation consistent with upward propagating tides.

We present a method for estimating incident photoelectrons’ energy spectra as a function of altitude by combining global scale far-ultraviolet (FUV) and radio-occultation (RO) measurements. This characterization provides timely insights important for accurate interpretation of ionospheric parameters inferred from the recently launched Ionospheric Connection Explorer (ICON) observations. Quantification of photoelectron impact is enabled by the fact that conjugate photoelectrons (CPEs) directly affect FUV airglow emissions but not RO measurements. We demonstrate the technique for the estimation of photoelectron fluxes and their spectra by combining coincident ICON-FUV and COSMIC2 measurements and show that a significant fraction of ICON-FUV measurements are affected by CPEs during the winter solstice. A comparison of estimated photoelectron fluxes with the SAMI2-PE model is used to gain further insights into the estimation method and reveals consistent values at low latitudes, while the results suggest that the model might be overestimating photoelectron fluxes by $\sim$10\% at mid latitudes.

The first neutral wind measurements of the Winds Cross-Track (WCT) instrument, taken during the recent Dynamo 2 campaign, are presented and discussed. This campaign launched two sounding rockets with identical payloads, each with a WCT on board, on different days in July, 2021 into the lower ionosphere to characterize the strong, daytime meridional currents of the global dynamo system and also the daytime neutral winds in the lower thermosphere. The two rockets reached apogees of ~124 and ~131 km, and the WCT took measurements above ~80 km on both the up- and downleg of both flights. As the rocket traveled through the atmosphere, the neutral gas was rammed into the instrument, where an ionization gauge measured the gas pressure. By modulating the incoming flux with a rotating baffle, the WCT measured the components of the neutral wind vector perpendicular to the trajectory of the rocket as well as the gas temperature. These in-situ wind and temperature profiles will be compared to the wind profiles observed remotely by the ICON satellite, which was in conjunction with the launch of both Dynamo 2 rockets.