Different Behavior of Density Perturbations Between Dayside and Nightside in the Martian Thermosphere and the Ionosphere Associated With Atmospheric Gravity Waves.

To investigate the excitation mechanism of ionospheric perturbations on Mars by the Neutral Gas and Ion Mass Spectrometer (NGIMS) onboard Mars Atmosphere and Volatile EvolutioN (MAVEN), we categorize ionospheric perturbations into three cases: (a) the ion-neutral coupling cases where ion and neutral perturbations are well coupled, (b) the ion-specific cases where ion perturbations move independently from neutrals, and (c) the coronal mass ejection cases associated with solar wind extreme events. A representative number of cases from total profiles are compared with a numerical model to determine the fraction that can be explained by an atmospheric gravity waves (GW). The neutral perturbations on the dayside at 170-190 km altitudes are in excellent agreement with the GW.

In-Flight Performance of the ICON EUV Spectrograph.

We present in-flight performance measurements of the Ionospheric Connection Explorer EUV spectrometer, , a wide field ( ) extreme ultraviolet (EUV) imaging spectrograph designed to observe the lower ionosphere at tangent altitudes between 100 and 500 km. The primary targets of the spectrometer, which has a spectral range of 54-88 nm, are the Oii emission lines at 61.6 nmand 83.

Observations of Atmospheric Tides in the Middle and Upper Atmosphere of Mars From MAVEN and MRO.

Variability in the Martian upper atmosphere is strongly linked to the lower atmosphere and much of it can be attributed to vertical wave propagation. Atmospheric tides in particular are a well-known phenomenon in the Martian atmosphere that play a key role in the transport of energy as they propagate to higher altitudes. Previous theoretical predictions and observations suggest that tides producing wavenumber-2 and wavenumber-3 patterns are strongest in a fixed local time at high altitudes, however, the energy they carry and the region of deposition are not well characterized.

Neutral Composition Information in ICON EUV Dayglow Observations.

Since the earliest space-based observations of Earth's atmosphere, ultraviolet (UV) airglow has proven a useful resource for remote sensing of the ionosphere and thermosphere. The NASA Ionospheric Connection Explorer (ICON) spacecraft, whose mission is to explore the connections between ionosphere and thermosphere utilizes UV airglow in the typical way: an extreme-UV (EUV) spectrometer uses dayglow between 54 and 88 nm to measure the density of O, and a far-UV spectrograph uses the O 135.6 nm doublet and N Lyman-Birge-Hopfield band dayglow to measure the column ratio of O to N in the upper thermosphere.

Evaluation of Atmospheric 3-Day Waves as a Source of Day-to-Day Variation of the Ionospheric Longitudinal Structure.

We report for the first time the day-to-day variation of the longitudinal structure in height of the F layer (hF) in the equatorial ionosphere using multi-satellite observations of electron density profiles by the Constellation Observing System for Meteorology, Ionosphere and Climate-2 (COSMIC-2). These observations reveal a ~3-day modulation of the hF wavenumber-4 structure viewed in a fixed local time frame during January 30-February 14, 2021. Simultaneously, ~3-day planetary wave activity is discerned from zonal wind observations at ~100 km by the Ionospheric Connection Explorer (ICON) Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI).

First results from the retrieved column O/N ratio from the Ionospheric Connection Explorer (ICON): Evidence of the impacts of nonmigrating tides.

In near-Earth space, variations in thermospheric composition have important implications for thermosphere-ionosphere coupling. The ratio of O to N is often measured using far-UV airglow observations. Taking such airglow observations from space, looking below the Earth's limb allows for the total column of O and N in the ionosphere to be determined.

Validation of ICON-MIGHTI Thermospheric Wind Observations: 2. Green-Line Comparisons to Specular Meteor Radars.

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 ( = 0.

Sensitivity study for ICON tidal analysis.

Retrieval of the properties of the middle and upper atmosphere can be performed using several different interferometric and photometric methods. The emission-shape and Doppler shift of both atomic and molecular emissions can be observed from the ground and space to provide temperature and bulk velocity. These instantaneous measurements can be combined over successive times/locations along an orbit track, or successive universal/local times from a ground station to quantify the motion and temperature of the atmosphere needed to identify atmospheric tides.

Retrieval of Lower Thermospheric Temperatures from O A Band Emission: The MIGHTI Experiment on ICON.

The Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) is a satellite experiment scheduled to launch on NASA's Ionospheric Connection Explorer (ICON) in 2017. MIGHTI is designed to measure horizontal neutral winds and neutral temperatures in the terrestrial thermosphere. Temperatures will be inferred by imaging the molecular oxygen Atmospheric band (A band) on the limb in the lower thermosphere.

On the Specification of Upward-Propagating Tides for ICON Science Investigations.

The National Center for Atmospheric Research (NCAR) Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) will provide a physics-based context for the interpretation of ICON measurements. To optimize the realism of the model simulations, ICON wind and temperature measurements near the ~97 km lower boundary of the TIEGCM will be used to specify the upward-propagating tidal spectrum at this altitude. This will be done by fitting a set of basis functions called Hough Mode Extensions (HMEs) to 27-day mean tidal winds and temperatures between 90 and 105 km altitude and between 12°S and 42°N latitude on a day-by-day basis.

Daytime Ionosphere Retrieval Algorithm for the Ionospheric Connection Explorer (ICON).

The NASA Ionospheric Connection Explorer Extreme Ultraviolet spectrograph, ICON EUV, will measure altitude profiles of the daytime extreme-ultraviolet (EUV) OII emission near 83.4 and 61.7 nm that are used to determine density profiles and state parameters of the ionosphere.

The MIGHTI Wind Retrieval Algorithm: Description and Verification.

We present an algorithm to retrieve thermospheric wind profiles from measurements by the Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument on NASA's Ionospheric Connection Explorer (ICON) mission. MIGHTI measures interferometric limb images of the green and red atomic oxygen emissions at 557.7 nm and 630.

Daytime O/N Retrieval Algorithm for the Ionospheric Connection Explorer (ICON).

The NASA Ionospheric Connection Explorer Far-Ultraviolet spectrometer, ICON FUV, will measure altitude profiles of the daytime far-ultraviolet (FUV) OI 135.6 nm and N Lyman-Birge-Hopfield (LBH) band emissions that are used to determine thermospheric density profiles and state parameters related to thermospheric composition; specifically the thermospheric column O/N ratio (symbolized as ΣO/N). This paper describes the algorithm concept that has been adapted and updated from one previously applied with success to limb data from the Global Ultraviolet Imager (GUVI) on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission.

Inferring Nighttime Ionospheric Parameters With the Far Ultraviolet Imager Onboard the Ionospheric Connection Explorer.

The Ionospheric Connection Explorer (ICON) Far Ultraviolet (FUV) imager, ICON FUV, will measure altitude profiles of OI 135.6 nm emissions to infer nighttime ionospheric parameters. Accurate estimation of the ionospheric state requires the development of a comprehensive radiative transfer model from first principles to quantify the effects of physical processes on the production and transport of the 135.

Time-Delay Integration Imaging with ICON's Far-Ultraviolet Imager.

A Time-Delay Integration (TDI) image processing system has been developed to capture ICON's Far Ultraviolet (FUV) Spectrographic Imager data. The TDI system is designed to provide variable-range motion-compensated imaging of Earth's nightside ionospheric limb and sub-limb scenes viewed from Low Earth Orbit in the 135.6 nm emission of oxygen with an integration time of 12 seconds.