The Ionospheric CONnections (ICON) mission has been continuously operating during the period from January 2020 to December 2021 providing simultaneous measurements of the thermal plasma properties near 600 km altitude and the neutral atmosphere and ionosphere in the altitude range 100 km to 500 km at low and middle latitudes. During this period of extremely low to moderately low solar activity, the evolving properties of the topside ionospheric density, composition, temperature and drift velocity at the satellite location are described using measurements from the Ion Velocity Meter (IVM). In the early months of 2020, the very low solar activity and relatively high abundance of H + in the total plasma density present a challenge to a robust description of the full local time distribution of the topside ion drifts. However, the quality of measurements of the ionospheric composition and temperature are not impacted by low solar activity conditions and changes in the O + and H + concentrations and their effects on the energy balance in the topside can be investigated as solar activity changes. As the relative abundance of O + increases, the susceptibility of the ion drift determination to the local plasma environment around the spacecraft is reduced and a more robust determination of the ion drift at all local times is possible. From October 2020 onward, the relationships between the topside ionospheric dynamics and the ionospheric density and temperature can be investigated and the relationships between the plasma drifts and the underlying neutral wind drivers can be established.

Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Journal of Geophysical Research - Space Physics. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing the latest version by default [v1]Travelling Ionospheric Disturbances Detected by the Scintillation Observations and Response of The Ionosphere to Electrodynamics (SORTIE) CubeSat at 420 km AltitudeAuthorsIrfanAzeemiDGeoffCrowelyiDWanliWuCora ERandallV. LynnHarveyiDSharon L.SharonM. JoanAlexanderiDKarthikVenkatarmaniRussell AlanStonebackMichaelPerdueMatthewDepewErikStrombergiDChadFishAdamReynoldsAnthonySwensonTedTashiDSee all authors Irfan AzeemiDCorresponding Author• Submitting AuthorASTRA LLC.iDhttps://orcid.org/0000-0002-8928-9837view email addressThe email was not providedcopy email addressGeoff CrowelyiDASTRAiDhttps://orcid.org/0000-0002-2058-7254view email addressThe email was not providedcopy email addressWanli WuASTRA LLCview email addressThe email was not providedcopy email addressCora E RandallUniversity of Colorado Boulderview email addressThe email was not providedcopy email addressV. Lynn HarveyiDUniversity of Colorado BoulderiDhttps://orcid.org/0000-0002-7928-0804view email addressThe email was not providedcopy email addressSharon L. SharonNorthWest Research Associatesview email addressThe email was not providedcopy email addressM. Joan AlexanderiDNorthWest Research Associates, CoRA OfficeiDhttps://orcid.org/0000-0003-2495-3597view email addressThe email was not providedcopy email addressKarthik VenkatarmaniASTRA LLCview email addressThe email was not providedcopy email addressRussell Alan StonebackStoneris LLCview email addressThe email was not providedcopy email addressMichael PerdueUniversity of Texas at Dallasview email addressThe email was not providedcopy email addressMatthew DepewUniversity of Texas at Dallasview email addressThe email was not providedcopy email addressErik StrombergiDASTRA LLC.iDhttps://orcid.org/0000-0001-5187-2261view email addressThe email was not providedcopy email addressChad FishASTRA LLCview email addressThe email was not providedcopy email addressAdam ReynoldsASTRAview email addressThe email was not providedcopy email addressAnthony SwensonASTRA LLCview email addressThe email was not providedcopy email addressTed TashiDASTRA LLCiDhttps://orcid.org/0000-0002-3603-4478view email addressThe email was not providedcopy email address

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.

During the 21 August 2017 eclipse two separate DMSP spacecraft passed through the lunar penumbra at local afternoon (F16) and near local sunset (F17) in the topside ionosphere at an altitude of similar to 850 km. Measurements of the in situ electron temperature by the Langmuir probe on each spacecraft showed regions where the temperature decreased on the order of 500 to 1,000K in the shadow. The patterns of these decreases were sporadic inside the shadow but generally showed the same overall shape in both passes. Comparing these patterns of temperature reductions with the projection of the gradient of the solar EUV radiation in the ionosphere suggests that these complex patterns are a result of the nonuniform distribution of the solar EUV radiation on the Sun at the time of the eclipse. Plain Language Summary As the shadow of the Moon moves across the Earth's upper atmosphere, the decrease in ultraviolet light from the Sun causes a cooling of the electrons in the ionosphere. Measurements during the 21 August 2017 eclipse from the DMSP spacecraft showed a complex and puzzling pattern of this temperature drop. The uneven distribution of the ultraviolet light sources from active regions on the Sun's surface is suggested as a possible explanation.

The Ionospheric Connections Explorer (ICON) payload includes an Ion Velocity Meter (IVM) to provide measurements of the ion drift motions, density, temperature and major ion composition at the satellite altitude near 575 km. The primary measurement goal for the IVM is to provide the meridional ion drift perpendicular to the magnetic meridian with an accuracy of 7.5 ms-1 for all daytime conditions encountered by the spacecraft within 15° of the magnetic equator. The IVM will derive this parameter utilizing two sensors, a retarding potential analyzer (RPA) and an ion drift meter (IDM) that have a robust and successful flight heritage. The IVM described here incorporates improvements in the design and operation to produce the most sensitive device that has been fielded to date. It will specify the ion drift vector, from which the component perpendicular to the magnetic field will be derived. In addition it will specify the total ion density, the ion temperature and the fractional ion composition. These data will be used in conjunction with measurements from the other ICON instruments to uncover the important connections between the dynamics of the neutral atmosphere and the ionosphere through the generation of dynamo currents perpendicular to the magnetic field and collisional forces parallel to the magnetic field. Here the configuration and operation of the IVM instrument are described as well as the procedures by which the ion drift velocity is determined. A description of the subsystem characteristics, which allow a determination of the expected uncertainties in the derived parameters, is also given.

In an effort to improve instrument resource usage and key development metrics, we have developed a field programmable gate array (FPGA) based sampling controller to be used as the core timing controller for the satellite borne sensor systems developed and produced at the University of Texas at Dallas.12 The newly developed sampling controller core produces the required function triggering patterns and addressing patterns by decoding a continuously running counter output to generate function enable and address selection signals. The system architecture, implementation approach, and results of demonstration design synthesis are described. We present a software design tool that facilitates rapid system development and verification, while providing the basis of the system documentation as part of the design flow. The high level of system modularity and parameterization helps to maximize module reuse from one design to the next, and reduce design effort for each particular design. Compared to previous approaches, the new approach is a significant improvement in key programmatic areas of interest including system documentation, overall system simplicity, and design cycle time.

The Ion Velocity Meter (IVM), a part of the CINDI instrument package on board the C/NOFS spacecraft, makes in situ measurements of plasma temperature, composition, density, and velocity. The 16 April 2008 launch of C/NOFS coincided with the deepest solar minimum since the space age began with F10.7 cm radio fluxes in the 60–70 solar flux unit range. Because of the 13° inclination of the orbit the location of the perigee advances through all local times in about 66 days. This allows seasonal sampling of ionospheric temperature, density, and composition as a function of local time, magnetic latitude, and altitude. Measurements taken near the spacecraft's 402 km perigee altitude indicate an unusually cold low‐density ionosphere with nighttime ion temperatures at the magnetic equator reaching as low as 600 K with an [O+]/[H+] ratio of 4 and maximum daytime temperatures of 1300 K. The O+ to H+ transition height is very low and at the highest altitudes measured H+ comprises over 75% of the ionospheric plasma at all local times. We compare average values of the measured parameters with those from the International Reference Ionosphere and with incoherent scatter radar measurements from Jicamarca.

Typically the solar radio emission at 10.7 cm is used to scale the critical euv radiation that is absorbed by the Earth's neutral atmosphere. In the latter half of 2008 this radio emission from the Sun was at the lowest levels seen in the last 50 years and the persistence of these low levels has never been recorded before. Here we show that these uniquely low levels of solar radiation produce similarly unique behavior in the Earth's ionosphere and the upper atmosphere. Most remarkably, the altitude extent of the ionosphere is significantly smaller than our present reference models would predict for these levels of solar activity. The transition height resides near 450 km at night and rises to only 850 km during the daytime. At night, this unusually contracted ionospheric shell around the equator has a temperature of only 600 K and prior to sunrise the ion number densities at the transition height fall below 10 4 cm −3 .

The bulk motion of the neutral gas at altitudes between about 200 and 600 km is an important factor in predicting the onset of plasma instabilities that are known to distort and/or disrupt high frequency radio communications. These neutral winds have historically been quite difficult to measure, especially from a moving spacecraft. A new space science instrument called the ram wind sensor has been developed to measure the component of the neutral gas velocity that lies along the orbit track of a satellite in low Earth orbit. Laboratory tests of an engineering model of the instrument have been carried out using a supersonic neutral argon beam, in order to validate the measurement concept. The results show that the technique is viable for measurements of neutral flow velocities in future satellite missions.