The Hunga Tonga Hunga-Ha’apai (HTHH) volcanic eruption on 15 January 2022 injected water vapor and SO2 into the stratosphere. Several months after the eruption, significantly stronger westerlies, and a weaker Brewer-Dobson circulation developed in the stratosphere of the Southern Hemisphere and were accompanied by unprecedented temperature anomalies in the stratosphere and mesosphere. In August 2022 the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instrument observed record-breaking temperature anomalies in the stratosphere and mesosphere that alternate signs with altitude. Ensemble simulations carried out with the Whole Atmosphere Community Climate Model (WACCM6) indicate that the strengthening of the stratospheric westerlies explains the mesospheric temperature changes. The stronger westerlies cause stronger westward gravity wave drag in the mesosphere, accelerating the mesospheric mean meridional circulation. The stronger mesospheric circulation, in turn, plays a dominant role in driving the changes in mesospheric temperatures. This study highlights the impact of large volcanic eruptions on middle atmospheric dynamics and provides insight into their long-term effects in the mesosphere. On the other hand, we could not discern a clear mechanism for the observed changes in stratospheric circulation. In fact, an examination of the WACCM ensemble reveals that not every member reproduces the large changes observed by SABER. We conclude that there is a stochastic component to the stratospheric response to the HTHH eruption.

This work examines the weak stratospheric polar vortex (SPV) event of February 2008 and the strong SPV event of February 2021 to understand the potential influence of SPV strength on midlatitude thermospheric composition and ionospheric plasma density. The weak SPV event shows a reduction in thermospheric O/N2 at all longitudes, changes in the ionospheric total electron content (TEC) that vary with longitude, and an intensification of the semidiurnal tides. The strong SPV event shows O/N2 elevated by up to 25% in the Asian sector and a 25% decrease in semidiurnal tidal amplitude. The TEC response during the strong SPV event is complex, but shows enhanced TEC in the Asian sector where O/N2 is elevated. These are the first observations of anomalies in the thermospheric composition and ionospheric plasma associated with a strong polar vortex event.

The ability of satellite instruments to accurately observe long-term changes in atmospheric temperature depends on many factors including the absolute accuracy of the measurement, the stability of the calibration of the instrument, the stability of the satellite orbit, and the stability of the numerical algorithm that produces the temperature data. We present an example of algorithm instability recently discovered in the temperature dataset from the SABER instrument on the NASA TIMED satellite. The instability resulted in derived temperatures that were substantially colder than anticipated from mid-December 2019 to mid-2022. This algorithm-induced change in temperature over one to two years corresponded to the expected change over several decades from increasing anthropogenic CO2. This paper highlights the importance of algorithm stability in developing Geospace Data Records (GDRs) for Earth’s mesosphere and lower thermosphere. A corrected version (Version 2.08) of the temperatures from SABER is described.

Traveling Ionospheric Disturbances (TIDs) are propagating variations in ionospheric electron densities that affect radio communications and can help with understanding energy transport throughout the coupled magnetosphere-ionosphere-neutral atmosphere system. Large scale TIDs (LSTIDs) have periods T ≈30-180 min, horizontal phase velocities vH≈‍100-‍250 m/s, and horizontal wavelengths H>1000 km and are believed to be generated either by geomagnetic activity or lower atmospheric sources. TIDs create concavities in the ionospheric electron density profile that move horizontally with the TID and cause skip-distance focusing effects for high frequency (HF, 3-30 MHz) radio signals propagating through the ionosphere. The signature of this phenomena is manifest as quasi-periodic variations in contact ranges in HF amateur radio communication reports recorded by automated monitoring systems such as the Weak Signal Propagation Reporting Network (WSPRNet) and the Reverse Beacon Network (RBN). In this study, members of the Ham Radio Science Citizen Investigation (HamSCI) present a climatology of LSTID activity using RBN and WSPRNet observations on the 1.8, 3.5, 7, 14, 21, and 28 MHz amateur radio bands from 2017. Results will be organized as a function observation frequency, longitudinal sector (North America and Europe), season, and geomagnetic activity level. Connections to geospace are explored via SYM-H and Auroral Electrojet indexes, while neutral atmospheric sources are explored using NASA’s Modern-Era Retrospective Analysis for Research and Applications Version 2 (MERRA-2).

The Scintillation Observations and Response of The Ionosphere to Electrodynamics (SORTIE) mission is a 6U CubeSat that has been making ionospheric measurements at 420 km altitude since February 19, 2020. The SORTIE sensor suite includes an Ion Velocity Meter (IVM), which is used in the present study to detect and characterize Traveling Ionospheric Disturbances (TIDs). On July 11, 2020 the SORTIE orbit passed over near-concentric TIDs that were seen in the Total Electron Content (TEC) data from ground-based Global Positioning System receivers distributed across the COntiguous United States (CONUS). The TID wave characteristics estimated from the IVM data agree well with those determined from the ground-based TEC data. The wave periods derived from the SORTIE data are shorter than the TID periods in the TEC data but are anticipated and explained in terms of the classical Doppler effect. A numerical simulation was performed using the Weather Research and Forecasting (WRF) model that shows excitation of atmospheric gravity waves (AGWs) from a deep convective storm over Texas preceding TID observations by SORTIE. We show that these AGWs were observed at stratospheric heights in close proximity to the convective storm by the Atmospheric Infrared Sounder onboard the NASA Aqua satellite, and in the lowermost mesosphere by the Cloud Imaging and Particle Size instrument onboard the NASA Aeronomy of Ice in the Mesosphere satellite. These storm-generated AGWs, or the associated higher-order AGWs, are the likely sources of the TIDs observed in the ground-based TEC and SORTIE IVM data.

The strongest Southern Hemisphere minor sudden stratospheric warming (SSW) in the last 40 years occurred in September 2019 and resulted in unprecedented weakening of the stratospheric polar vortex. Ionospheric total electron content (TEC) observations are used to provide an overview of statistically significant anomalies in the low-latitude ionosphere during this event. Quasi-semidiurnal perturbations of TEC are observed in response to the SSW, similar to those seen during Northern Hemisphere SSWs. Analysis indicates the existence of quasi-periodic oscillations in TEC in the crests of the equatorial ionization anomaly, with strong 5-6 day and 2-3 day periodicities. Ionospheric anomalies from the combined effects of multiple mechanisms exceed a factor of 2, comparable to the strongest anomalies associated with Northern Hemisphere SSWs. These results also indicate, for the first time, a remarkable longitudinal variation in the character and magnitude of variations that could be related to a modulation of the non-migrating diurnal tide.

The polar vortices play a central role in vertically coupling the Sun-Earth system by facilitating the descent of reactive odd nitrogen (NOx = NO + NO2) produced in the atmosphere by energetic particle precipitation (EPP-NOx). Downward transport of EPP-NOx from the mesosphere-lower thermosphere (MLT) to the stratosphere inside the winter polar vortex is particularly impactful in the wake of prolonged sudden stratospheric warming events. This work is motivated by the fact that state-of-the-art global climate models severely underestimate this EPP-NOx transport in the Arctic. As a step toward understanding the transport pathways by which MLT air enters the top of the polar vortex, we explore the extent to which Lagrangian Coherent Structures (LCS) impact the geographic distribution of NO near the polar winter mesopause in the Whole Atmosphere Community Climate Model eXtended version with Data Assimilation Research Testbed (WACCMX+DART). We present planetary wave-driven enhanced NO descent near the polar winter mesopause during 14 case studies from the Arctic winters of 2005/2006 through 2018/2019. During all cases the model is in reasonable agreement with SABER temperatures and SOFIE and ACE-FTS NO. Results show consistent LCS formation at the top of the polar vortex during minor and major SSWs. LCSs act to confine air with elevated NO to high latitudes as it descends into the top of the polar vortex. Descent of NO tends to be enhanced in traveling planetary wave troughs. These results present a new conceptual model of transport in the polar winter mesosphere whereby regional-scale, long-lived LCSs, coincident with the troughs of planetary waves, act to sequester elevated NOx at high latitudes until the air descends to lower altitudes.