The diurnal-eastward propagating tide with zonal wavenumber 3 (DE3) has gained significant attention due to its ability to preferentially propagate to the ionosphere and thermosphere (IT) from the tropical troposphere, thus effectively coupling these atmospheric regions. In this work, we demonstrate the existence of a pronounced zonal wavenumber 4 (WN4) structure in the low-latitude ionosphere during May 27 - June 5, 2020 using concurrent in-situ total ion number density measurements from the Scintillation Observations and Response of The Ionosphere to Electrodynamics (SORTIE) and the Ionospheric Connection Explorer (ICON) satellites. Temperature observations from the Thermosphere Ionosphere Mesosphere Energetics Dynamics Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) instrument near 105 km and output from the Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension (SD/WACCM-X) demonstrate that this global-scale ionospheric WN4 structure is due to DE3 propagating through the lower thermosphere.

Ground-based Global Navigation Satellite System (GNSS) receivers have become an ubiquitous tool for monitoring the ionosphere. Total Electron Content (TEC) data from globally distributed networks of ground-based GNSS receivers are increasingly being used to characterize the ionosphere and its variability. The deployment of these GNSS receivers is currently limited to landmasses. This means that 7/10 of Earth’s surface, which is covered by the oceans, is left unexplored for persistent ionospheric measurements. In this paper, we describe a new low-power dual-frequency Global Positioning System (GPS) receiver, called Remote Ionospheric Observatory (RIO), which is capable of operating from locations in the air, space, and the oceans as well as on land. Two RIO receivers were deployed and operated from the Tropical Atmosphere Ocean buoys in the Pacific Ocean, and the results are described in this paper. This is the first time that GPS receivers have been operated in open waters for an extended period of time. Data collected between September 1, 2018 and December 31, 2019 are shown. The observed TEC exhibits a clear seasonal dependence characterized by equinoctial maxima in the data at both locations. Both RIO receivers, deployed near the geomagnetic equator, show an 18-35% increase in TEC during moderately disturbed geomagnetic periods. Comparisons with the International Reference Ionosphere model show good agreement. The new capability presented in this paper addresses a critical gap in our ability to monitor the ionosphere from the seventy percent of the Earth’s surface that is covered by water.

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.