Hough Mode Extensions (HMEs) and Solar Tide Behavior in the Dissipative Thermosphere

Abstract

Solar thermal tides (hereafter "solar tides") arise from the cyclic heating of the atmosphere due to Earth's rotation. The major sources of heating are the absorption of infrared(ultraviolet) solar radiation by H 2 O(O 3 ) in the troposphere(stratosphere), the latent heating of condensation associated with the daily variation in tropical convection, and the absorption of extreme ultraviolet (EUV) radiation in the thermosphere. It is now widely accepted that much of the tidal spectrum excited in the troposphere and stratosphere propagates vertically, grows in amplitude exponentially with height, achieves maximum amplitudes mainly between 100 and 150 km, and exerts significant dynamic and electrodynamic influences on ionosphere-thermosphere ("IT") dynamics, chemistry and electrodynamics above 100 km (Forbes, 2021).A major impediment to the advancement of our understanding and quantitative specification of atmosphere-IT coupling is the lack of adequate wind and temperature observations in the critical 100-250 km height region where the tidal spectrum evolves with height due to molecular dissipation and collisional interaction with the ionosphere. present some first observational insights into semidiurnal tidal propagation between 100 and 250 km based on daytime wind measurements from the Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument on the Ionospheric CONnections (ICONs) mission. However, these are confined to 61d-mean depictions over a restricted latitude range (9°S-39°N) due to the sampling constraints imposed by the ICON orbit.To aid in understanding atmosphere-IT coupling in the context of tidal winds and temperatures measured by MIGHTI, and F-region plasma drifts and densities measured by the Ion Velocity Meter instrument on ICON, a hybrid data-theory approach (see e.g., Cullens et al., 2020;Forbes et al., 2017) has been implemented as part of the ICON mission. The methodology consists of several steps. First, tides are obtained within 45-day running windows, stepped forward one day at a time, by least-squares (LSQ) fitting day and night wind and temperatures measurements from MIGHTI over the ∼95 to 105 km height and 12°S-42°N latitude region. The individual tides are then LSQ fit with two-dimensional (height vs. latitude, hereafter "htvslat") basis functions rooted in tidal

Longitudinal Variations of Mars Thermosphere CO2, Ar, N2, and O Densities From MAVEN: Dependencies on Species Mass, Solar Flux, and Local Time

“…Concerning solar asynchronous tides propagating into the thermosphere, they will encounter different levels of molecular dissipation as a function of solar cycle, which could in principle introduce a dependence of these tides on level of solar activity. Such a dependence is indeed the case in the terrestrial thermosphere (e.g., Forbes & Zhang, 2022;Oberheide et al, 2009) where an inverse relationship between density amplitude and F10.7 exists. However as noted by Fang et al (2021) and Forbes et al (2021) with reference to the MCD, when cast relative to the zonal mean, thermosphere density perturbations in Mars thermosphere due to upward-propagating tides do not reflect any significant differences when compared between solar average (E10.7 = 140 sfu) and solar minimum (E10.7 = 80 sfu) conditions.…”

“…Concerning solar asynchronous tides propagating into the thermosphere, they will encounter different levels of molecular dissipation as a function of solar cycle, which could in principle introduce a dependence of these tides on level of solar activity. Such a dependence is indeed the case in the terrestrial thermosphere (e.g., Forbes & Zhang, 2022; Oberheide et al., 2009) where an inverse relationship between density amplitude and F10.7 exists. However as noted by Fang et al.…”

Wavenumber‐4 Longitudinal Structure in ICON‐MIGHTI Thermospheric Meridional Wind

“…The semi‐diurnal SW2 tide displays similar seasonal variation in both zonal and meridional winds (Figures 9 and 10) at 30°N–40°N. Forbes and Zhang (2022) studied the height versus latitude variation of tides through Hough Mode Extension (HME) created as a part of the ICON mission. The amplitudes of the DE3, DW1 and SW2 in zonal and meridional winds are greater than 60 m/s around 100 km at the equatorial and low latitudes which are comparable to the amplitudes we have obtained in our analysis.…”

Responses of the Mean Thermosphere Circulation, O/N2 Ratio and Ne to Solar and Magnetospheric Forcing From Above and Tidal Forcing From Below

“…In the TIEGCM‐ICON implementation (Maute, 2017; Maute et al., 2023; see also Cullens et al., 2020; Forbes et al., 2017), the model is driven at its 97 km lower boundary by the spectrum of diurnal and semidiurnal tides derived from winds and temperatures measured by the Michelson Interferometer for Global High‐Resolution Thermospheric Imaging (MIGHTI) instrument on ICON. Similar to the methodology underlying the Climatological Tidal Model of the Thermosphere (CTMT, Oberheide et al., 2011), this is accomplished by fitting Hough Mode Extensions (HMEs, Forbes & Zhang, 2022, and references therein) to the MIGHTI tidal fields between 10°S and 40°N latitude and 94–102 km altitude within 45‐day windows slipped forward 1 day at a time. The 45‐day windows are necessitated by the fact that complete longitudinal and local time coverage are required to extract the tidal spectrum, and given the orbital sampling of ICON/MIGHTI, this is only achieved for the above latitude range within ≈45‐day windows.…”