Delineating the effect of upward propagating migrating solar tides with the TIEGCM-ICON

Abstract

Introduction: The vertical coupling of the lower and upper atmosphere via atmospheric solar tides is very variable and affects the thermosphere and ionosphere system. In this study, we use Ionospheric Connection (ICON) explorer data from 220–270 Day Of Year (DOY), 2020 when large changes in the migrating semidiurnal tide (SW2) and the zonal and diurnal mean (ZM) zonal wind occur within 8 days.Method: We use the ICON Level4 product, the thermosphere-ionosphere-electrodynamics general circulation model (TIEGCM) driven by tides fitted to ICON observations via the Hough Mode Extension (HME) method. The effect of the upward propagating tides is isolated by examining the difference between two TIEGCM simulations with and without tidal HME forcing at the model lower boundary.Results: The simulations reveals that the solar SW2 changes its latitudinal structure at 250 after DOY 232 from two peaks at mid latitudes to one broad low latitude peak, while at 110 km the two-peak structure persists. The ZM zonal wind at 250 km undergoes a similar dramatic change. These SW2 changes are associated with the prevalence of antisymmetric HMEs after DOY 232. The migrating diurnal, terdiurnal and quaddiurnal tides at 250 km undergo similar variations as SW2. TW3 is strong in the thermosphere and most likely caused by non-linear tidal interaction between DW1 and SW2 above 130 km. Surprisingly, the solar in situ forcing of TW3 and SW2 in the upper thermosphere is not nearly as important as their upward propagating tidal component. Associated with the strong dynamical changes, the zonal and diurnal mean NmF2 decreases by approximately 15%–20%, which has a major contribution from the O/N2 decrease by roughly 10%. These changes are stronger than general seasonal behavior.Discussion: While studies have reported on the dynamical changes via SW2 in the mesosphere-lower thermosphere (MLT) region during the equinox transition period, this study is, to our knowledge, the first to examine the effects of rapid changes in SW2 on the upper thermosphere and ionosphere. The study highlights the potential of using ICON-TIEGCM for scientific studies.

Evening Solar Terminator Waves in Earth's Thermosphere: Neutral Wind Signatures Observed by ICON‐MIGHTI

“…Liu et al., 2018), whereas the TIEGCM cannot self‐consistently resolve atmospheric processes below its 97 km lower boundary (Qian et al., 2014). Including ICON HMEs into the TIEGCM partially accounts for lower atmospheric effects by including data‐informed diurnal and semidirunal tidal propagation up from the lower atmosphere (Maute et al., 2023), suggesting that global‐scale waves from the lower atmosphere may play a role in STW generation. The presence of STW signatures in models with the lower atmosphere but their absence in those without suggests that the lower atmosphere plays an important role in STW generation.…”

“…The TIEGCM describes thermospheric and ionospheric dynamics, energetics, and chemistry, coupled with ionospheric electrodynamics (Qian et al., 2014; Richmond, 1995). In this study, we used TIEGCM‐ICON, ICON's Level 4 data product (Maute, 2017; Maute et al., 2023; Maute & ICON Team, 2022), which includes two runs of the TIEGCM: a simulation which incorporates data‐driven 42‐day averages of diurnal and semidiurnal tidal forcing at the 97 km lower boundary via the Hough Mode Extension (HME) from MIGHTI horizontal winds and temperatures (Cullens et al., 2020; Forbes et al., 2017), and one without such a tidal specification. The background at the lower boundary is obtained from global averages of horizontal winds (Drob et al., 2008) and neutral temperatures and densities (Picone et al., 2002).…”

“…To determine whether current global models capture the physics necessary to reproduce STW signatures observed by MIGHTI, we compare the observations to simulations from three different models: the Thermosphere-Ionosphere-Electrodynamics General Circulation Model for the Ionospheric Connection Explorer (TIEGCM-ICON) (Maute, 2017), SD-WACCM-X 2.0 (H.-L. Liu et al, 2018;Maute & HAO WACCM team, 2022), and the HIAMCM (Becker, Goncharenko, et al, 2022;Becker & Vadas, 2020, 2022.…”

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

“…The remainder of this paper is focused on characterizing, diagnosing and comparing the DZM thermosphere circulations, O/N 2 ratios, and electron densities (Ne) as a function of height (100-400 km), latitude (90°S-90°N) and day of year (DOY, 1-365) due (a) solely to observation-based tides propagating up from below 100 km altitude, and (b) solely due to solar flux and magnetospheric (hereafter "SM") forcing. This is accomplished using the version of the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) developed for the Ionospheric CONnections (ICON) mission, TIEGCM-ICON (Maute, 2017; see also Maute et al, 2023), which is forced at its lower boundary by the observed tidal spectrum; and an additional simulation with this tidal forcing omitted, supplemented by a third simulation with variable SM forcing replaced by constant SM forcing. The details of how these model results are manipulated to achieve our end goals is described in the next Section.…”

Non‐Migrating Structures in the Northern Midlatitude Thermosphere During December Solstice Using ICON/MIGHTI and FPI Observations

“…The additional DE3 can also generate SPW4 in situ as well as a longitudinally symmetric quatradiurnal tide that is, Q0. Maute et al (2023) analyzed ICON neutral wind observations from the August-September 2020 period following a Hough Model Extension tidal analysis. They showed that SW2 was upwardly propagating from 110 to 250 km in the upper atmosphere, and that the latitudinal and temporal variations of DW1, TW3 and QW4 migrating tides were closely related to that of SW2.…”