Vertical Coupling by Solar Semidiurnal Tides in the Thermosphere From ICON/MIGHTI Measurements

Abstract

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.

Day‐to‐Day Variability of the Semidiurnal Tide in the F‐Region Ionosphere During the January 2021 SSW From COSMIC‐2 and ICON

“…An outstanding science challenge in researching the SSW impact on the upper atmosphere is the lack of suitable global observations that allow one to resolve the tidal winds in the E‐region dynamo on a daily basis, that is, the “tidal weather.” Single satellite tidal wind diagnostics such as from the TIMED Doppler Interferometer on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite (TIDI/TIMED) (Oberheide et al., 2011) or more recently from the Michelson Interferometer for Global High‐resolution Thermospheric Imaging on the Ionospheric Connection Explorer (MIGHTI/ICON) (Forbes et al., 2022) can only resolve tidal variations on a monthly or longer timescale, similar to lunar tidal diagnostics from ICON and GOLD (Lieberman et al., 2022). Consequently, SSW variations, while still present, are considerably smoothed in MIGHTI/ICON tidal diagnostics.…”

“…or more recently from the Michelson Interferometer for Global High-resolution Thermospheric Imaging on the Ionospheric Connection Explorer (MIGHTI/ICON) (Forbes et al, 2022) can only resolve tidal variations on a monthly or longer timescale, similar to lunar tidal diagnostics from ICON and GOLD (Lieberman et al, 2022). Consequently, SSW variations, while still present, are considerably smoothed in MIGHTI/ICON tidal diagnostics.…”

On the importance of neutral composition and temperature measurements in the 100–200 km altitude region

“…These waves are known to have profound effects on the thermospheric composition and temperature between 100 and 200 km and above (e.g., Yamazaki and Richmond, 2013;Jones Jr et al, 2014a;Vadas et al, 2014). Ideally, the composition and temperatures measurements in Table 1 coupled with coincident vector wind measurements would be measured at 6 local solar times per day (3 satellites separated apart by 4 h) at the same resolution, allowing one to resolve the daily semidiurnal tidal spectrum as well, in the altitude regime where many of these tides reach their maximum amplitude (e.g., Forbes et al, 2022). Observing the semidiurnal part of the tidal spectrum would add significant benefit as it is wellknown to be important in coupling lower atmospheric variability to T-I variability in composition and temperature during sudden variability in composition and temperature during sudden stratospheric warmings (e.g., Jones Jr et al, 2020;Oberheide et al, 2020; and many others before and after these).…”

Direct Observational Evidence of Altered Mesosphere Lower Thermosphere Mean Circulation from a Major Sudden Stratospheric Warming

“…Based on the occurrence of occasional gaps, data quality issues, and instrument calibrations, MIGHTI allows for stable extraction of solar tides within 41-day moving windows (Cullens et al, 2020;Forbes et al, 2022). In this work, semidiurnal tidal fits are performed using 41-day moving windows on winds averaged in 6 • latitude, 60 • longitude, and 2-hour UT bins extending from 10 • S to 40 • N using the native ∼2.5 km altitude sampling.…”

“…Their removal leaves gaps near 270 • -330 • longitude in the Southern Hemisphere that are not significantly affecting the latitude regions of primary interest for this study. Forbes et al (2022) provide more details on the tidal diagnostics of the composite data, which closely follows the procedure adopted by Gasperini et al (2021) in the analyses of ICON IVM data and by Gasperini et al (2015Gasperini et al ( , 2017Gasperini et al ( , 2018Gasperini et al ( , 2020 in the analysis of Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) observations. After the exact UFKW1 period is determined using spectral analysis, simultaneous least-squares fits are performed on these 41-day windows to de- rive SW2 and UFKW1 amplitudes and phases.…”