AbstractTwo ∼2‐week Ultra‐Fast Kelvin Wave (UFKW) events centered on days 158(203) during 2021 are investigated using winds, temperatures, plasma drifts and electron densities (Ne) measured by the Ionospheric CONnections (ICON) mission. Eastward‐propagating longitudinal wave‐1 (s = −1) structures with periods 2.5–4.0d, thought to mainly reflect Ultra‐Fast Kelvin waves (UFKWs), reveal ±45 ms−1 zonal winds (U) at 100 km for both events. Height‐latitude structures of the 3.0(3.5)d‐period UFKWs are obtained for the first time for both temperature (T, 94–120 km) and U (94–280 km) between 12°S and 39°N latitude. Maximum values of 36(29) ms−1 for U and 12(15)K for T occur at 102(106) km altitude and within ±3° latitude. The U‐T peak height displacement remains unexplained. Vertical wavelengths are in the range 36–43 km for both U and T during both events. Concurrent with the E‐region dynamo winds, topside (580 km) F‐region field‐aligned (±20–40 ms−1), meridional (±5–10 ms−1) and vertical (±5–10 ms−1) drift and Ne (±20–40%) 2.5–4.0d s = −1 variations are also measured. These key elements of atmosphere‐ionosphere (A‐I) coupling, contemporaneously measured for the first time, are relevant to testing the internal consistency of A‐I models. The mean wind propagation environment of the UFKWs is also quantified, showing no appreciable effects on the UFKW structures, consistent with modeling and theory.

Abstract First results are presented from the conjugate maneuvers performed by NASA's Ionospheric Connection Explorer (ICON) spacecraft. During each several‐minute maneuver, ICON crosses the magnetic equator, measuring the plasma drift at the ∼600‐km apex of a magnetic field line and the neutral wind profiles (∼90–300 km altitude) along both ends of that field line. The analysis utilizes 149 pairs of maneuvers separated by ∼24 hr but at nearly the same location and local time. Principal component regression reveals that 39 ± 7% and 24 ± 9% of the day‐to‐day variance in the daytime vertical and zonal drift, respectively, is attributable to conjugate neutral winds. The remaining variance is likely driven by external potentials from non‐conjugate winds and geomagnetic activity (median Kp 2−). Zonal winds at 100–113 km and >120 km altitude are the primary drivers of conjugate vertical and zonal drift variance, respectively. These observations can test vertical‐coupling mechanisms in whole‐atmosphere models.

The Interferometer for Neutral-Thermosphere Dynamics Imaging (INDI) is an Earth limb viewing optical sensor employing a Doppler Asymmetric Spatial Heterodyne interferometer to obtain red-line (630 nm) thermospheric winds between altitudes of 200 and 300 km.

Algebraic ray traces of various configurations of spatial heterodyne spectrometers are developed to derive general, approximate, formulas for resolving the power, fringe localization plane, and admissible off-axis angle for each configuration. Michelson, all-reflective, and field-widened configurations are considered separately. The derived formulas for each configuration are tested against exact numerical ray traces using optical design software and in general found to be in good agreement.

With the continued development of global atmospheric models, there is a growing need for nearreal-time measurements of upper atmospheric winds.Simultaneously there is a push for smaller, cost-effective satellites which can be deployed singly or as a constellation to provide better temporal and spatial coverage.To meet these needs, the Interferometer for Neutral-Thermosphere Dynamics Imaging (INDI) instrument has been designed to measure red-line (λ=630.0nm) oxygen emissions in the upper atmosphere with a small footprint that will fit in a 6U cubesat or smallsat.INDI uses a Doppler Asymmetric Spatially Heterodyned (DASH) interferometer to observe the wind-induced Doppler shift of thermospheric airglow emission to determine horizontal wind vectors versus altitude.A larger DASH interferometer is included in each of the sensors of the MIGHTI experiment on the ICON Explorer Mission, which launched in 2019.DASH is derived from Spatial Heterodyned Spectroscopy (SHS) which has been utilized successfully for both space and ground based applications.The INDI instrument is currently TRL 4 with plans to develop flight electronics and perform environmental testing, which will bring it to TRL 6.Initial laboratory tests of the INDI hardware using quasi-monochromatic sources, such as a neon lamp and a HeNe laser, show expected performance.

The design, principles of operation, calibration, and data analysis approaches of the Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) on the NASA Ionospheric Connection (ICON) satellite have been documented prior to the ICON launch. Here we update and expand on the MIGHTI wind data analysis and discuss the on-orbit instrument performance. In particular, we show typical raw data and we describe key processing steps, including the correction of a "signal-intensity dependent phase shift," which is necessitated by unexpected detector behavior. We describe a new zero-wind calibration approach that is preferred over the originally planned approach due to its higher precision. Similar to the original approach, the new approach is independent of any a priori data. A detailed update on the wind uncertainties is provided and compared to the mission requirements, showing that MIGHTI has met the ICON mission requirements. While MIGHTI observations are not required to produce absolute airglow brightness profiles, we describe a relative brightness profile product, which is included in the published data. We briefly review the spatial resolution of the MIGHTI wind data in addition to the data coverage and data gaps that occurred during the nominal mission. Finally, we include comparisons of the MIGHTI wind data with ground-based Fabry-Perot interferometer observations and meteor radar observations, updating previous studies with more recent data, again showing good agreement. The data processing steps covered in this work and all the derived wind data correspond to the MIGHTI data release Version 5 (v05).

The two-year prime mission of the NASA Ionospheric Connection Explorer (ICON) is complete. The baseline operational and scientific objectives have been met and exceeded, as detailed in this report. In October of 2019, ICON was launched into an orbit that provides its instruments the capability to deliver near-continuous measurements of the densest plasma in Earth's space environment. Through collection of a key set of in-situ and remote sensing measurements that are, by virtue of a detailed mission design, uniquely synergistic, ICON enables completely new investigations of the mechanisms that control the behavior of the ionosphere-thermosphere system under both geomagnetically quiet and active conditions. In a two-year period that included a deep solar minimum, ICON has elucidated a number of remarkable effects in the ionosphere attributable to energetic inputs from the lower and middle atmosphere, and shown how these are transmitted from the edge of space to the peak of plasma density above. The observatory operated in a period of low activity for 2 years and then for a year with increasing solar activity, observing the changing balance of the impacts of lower and upper atmospheric drivers on the ionosphere.

The Michelson Interferometer for Global High Resolution Thermospheric Imaging (MIGHTI) successfully measured thermospheric winds onboard the NASA ICON mission. We present an unexpected detector deterioration and its on-orbit characterization using calibration lamps.

Vertical shears of horizontal winds play an important role in the dynamics of the 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 between 100–130 km, varying greatly between orbits. This work focuses on these strong shears, and examines their occurrences, horizontal scales and underlying organization. The wind shears can persist for 1000s km horizontally. Over a large data set, no preferred direction for the strong wind shears 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, regardless of the horizontal extent, show a downward progression with local time, following the climatological winds and upward propagating tides.

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.

In the mesosphere and lower-thermosphere, quasi-2-day waves are spectacular planetary-scale oscillations. Almost all relevant observational studies are based on ground-based single-station or single-satellite methods and, therefore, cannot determine the zonal wavenumber unambiguously. We employ a series of multi-station methods on winds measured by four longitudinally separated low-latitude ground-based radars in the current work. These methods help us to determine two dominant zonal wavenumbers at 80–100 km altitude. These results are used to complement satellite measurements. The agreement between datasets is extraordinary, allowing us to extend the characteristics of the waves to higher altitudes using satellite measurements. The current work was published in He et al. (2021, https://doi.org/10.1029/93jd00380), which was extended into a broad altitude range up to the topside F-region in Forbes et al. (2021, https://doi.org/10.1029/2021JA029961).

A quasi-2-day wave (Q2DW) event during January-February, 2020, is investigated in terms of its propagation from 96 to 250 km as a function of latitude (10°S to 30°N), its nonlinear interactions with migrating tides to produce 16 and 9.6-h secondary waves (SWs), and the plasma drift and density perturbations that it produces in the topside F-region (590-607 km) between magnetic latitudes 18°S and 18°N. This is accomplished through analysis of coincident Ionospheric Connections Explorer (ICON) measurements of neutral winds, plasma drifts and ion densities, and wind measurements from four low-latitude (±15°) specular meteor radars (SMRs). The Q2DW westward-propagating components that existed during this period consist of zonal wavenumbers s = 2 and s = 3, that is, Q2DW+2 and Q2DW+3 (e.g., He, Chau et al., 2021, https://doi.org/10.1029/93jd00380). SWs in the ICON measurements are inferred from Q2DW+2 and Q2DW+3 characteristics derived from traditional longitude-UT fits that potentially contain aliasing contributions from SWs ("apparent" Q2DWs), from fits to space-based zonal wavenumbers that each reflect the aggregate signature of either Q2DW+2 or Q2DW+3 and its SWs combined ("effective" Q2DWs), and based on information contained in published numerical simulations. The total Q2DW ionospheric responses consists of F-region field-aligned and meridional drifts of order ±25 ms-1 and ±5-7 ms-1, respectively, and total ion density perturbations of order (±10%-25%). It is shown that the SWs can sometimes make substantial contributions to the Q2DW winds, drifts, and plasma densities.

Earth’s equatorial ionosphere exhibits substantial and unpredictable day-to-day variations in density and morphology. This presents challenges in preparing for adverse impacts on geopositioning systems and radio communications even 24 hours in advance. The variability is now theoretically understood as a manifestation of thermospheric weather, where winds in the upper atmosphere respond strongly to a spectrum of atmospheric waves that propagate into space from the lower and middle atmosphere. First-principles simulations predict related, large changes in the ionosphere, primarily through modification of wind-driven electromotive forces: the wind-driven dynamo. Here we show the first direct evidence of the action of a wind dynamo in space, using the coordinated, space-based observations of winds and plasma motion made by the National Aeronautics and Space Administration Ionospheric Connection Explorer. A clear relationship is found between vertical plasma velocities measured at the magnetic equator near 600 km and the thermospheric winds much farther below. Significant correlations are found between the plasma and wind velocities during several successive precession cycles of the Ionospheric Connection Explorer’s orbit. Prediction of thermospheric winds in the 100–150 km altitude range emerges as the key to improved prediction of Earth’s plasma environment. Observations from the National Aeronautics and Space Administration Ionospheric Connection Explorer confirm the link between thermospheric winds and ionospheric plasma variability.

Horizontal winds from four low‐latitude (±15°) specular meteor radars (SMRs) and the Michelson Interferometer for Global High‐resolution Thermospheric Imaging (MIGHTI) instrument on the ICON satellite, are combined to investigate quasi‐2‐day waves (Q2DWs) in early 2020. SMRs cover 80–100 km altitude whereas MIGHTI covers 95–300 km. Q2DWs are the largest dynamical feature of the summertime middle atmosphere. At the overlapping altitudes, comparisons between the derived Q2DWs exhibit excellent agreement. The SMR sensor array analyses show that the dominant zonal wavenumbers are s = +2 and + 3, and help resolve ambiguities in MIGHTI results. We present the first Q2DW depiction for s = +2 and s = +3 between 95 and 200 km, and show that their amplitudes are almost invariant between 80 and 100 km. Above 106 km, Q2DW amplitudes and phases present structures that might result from the superposition of Q2DWs and their aliased secondary waves.

The electrodynamic influence of thermospheric winds is an effect thought to dominate the development of the daytime low-latitude ionosphere, through the generation of dynamo currents and associated vertical plasma drifts. Until recently, observations of the thermospheric and ionopsheric state variables have mainly been defined and compared on climatological time scales, due to their collection from separate observatories with disparate measurement capabilities. These datasets are inadequate for investigation of the actual action of thermospheric drivers as they modify the ionospheric state, as the response clearly changes on 24-hour timescales, and shorter when viewed in the a constant-local-time frame of reference. New observatiions of thermospheric winds, uninterrupted over the 90-300 km altitude range, are now provided by the Ionospheric Connection Explorer along with simultaneous plasma velocity and density measurments. These observations are directly comparable to the wind measurements in crossings of the magnetic equator, where the winds are magnetically conjugate to the drift measurements. Investigation of the noon-sector drifts vs wind drivers is presented. We find that the local driver is clearly evident in the noon-time vertical plasma drifts under all conditions.

Earth’s equatorial ionosphere exhibits significant and unpredictable day-to-day variations in density and morphology . This presents difficulties in preparing for adverse impacts on technological systems even 24 hours in advance . This behavior is now theoretically understood as a manifestation of thermospheric weather, where conditions in the upper atmosphere respond strongly to changes in the spectrum of atmospheric waves that propagate into space from the lower and middle atmosphere, modifying the electrodynamic environment that exerts control over the creation of plasma . The NASA Ionospheric Connection Explorer (ICON) makes the first coordinated space-based observations of the wind-driven dynamo and the plasma state to understand the relation of the plasma environment to the thermospheric weather below. Here we show the first direct measurements of the effects of a wind-driven dynamo in space, where a clear relationship is found between the vertical plasma velocities measured at the magnetic equator near 600 km and the thermospheric winds much farther below, with substantial correlations found between the plasma velocity and thermospheric winds during each of several successive precession cycles of the observatory’s orbit. Prediction of thermospheric winds in the 100 – 150 km range emerges as a key to improved prediction of the Earth’s plasma environment.

The MIGHTI instrument was launched October 2019 on the NASA ICON Explorer mission. This presentation will discuss the performance of the MIGHTI wind sensor and techniques used for calibration and monitoring instrument drifts.

We compare coincident thermospheric neutral wind observations made by the Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI) on the Ionospheric Connection Explorer (ICON) spacecraft, and four ground-based specular meteor radars (SMRs). Using the green-line MIGHTI channel, we analyze 1158 coincidences between Dec 2019 and May 2020 in the altitude range from 94 to 104 km where the observations overlap. We find that the two datasets are strongly correlated (r = 0.82) with a small mean difference (4.5 m/s). Although this agreement is good, an analysis of known error sources (e.g., shot noise, calibration errors, and analysis assumptions) can only account for about a quarter of the disagreement variance. The unexplained variance is 27.8% of the total signal variance and could be caused by unknown errors. However, based on an analysis of the spatial and caused by temporal variability of the wind on scales ≲70 min. The observed magnitudes agree well during temporal averaging of the two measurement modalities, we suggest that some of the disagreement is likely the night, but during the day, MIGHTI observes 16%-25% faster winds than the SMRs. This remains unresolved but is similar in certain ways to previous SMR-satellite comparisons.

Lower thermospheric wind shears are a main driver for sporadic-E in the ionosphere. This presentation will review the spatial resolution of MIGHTI E-region neutral wind observations, implications of the wind shear measurements and sample observations.