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Abstract We analyze fixed local time, longitudinal wavenumber‐3 (WN3) and wavenumber‐4 (WN4) structures in the low‐latitude F‐region ionosphere using ICON‐IVM observations of ion drifts, temperatures, and densities from Jan 2020 to Jun 2022. These ionospheric wave patterns are compared to non‐migrating tides and stationary planetary waves in the Mesosphere and Lower Thermosphere (MLT) zonal winds from ICON‐MIGHTI. We find relative amplitudes of ionospheric WN4 are highly correlated with WN4 in MLT zonal winds (cc = 0.80), and particularly with DE3 (cc = 0.77). WN4 shows the strongest correlation with DE3 near ∼110 km altitude and ∼15° magnetic latitude, where MLT winds are approximately field‐aligned with the ionospheric measurements and E‐region conductivities peak. Phase analysis further supports the E‐region dynamo as the dominant mechanism coupling MLT and ionospheric WN4. In contrast, no such evidence is found for WN3, suggesting alternative coupling mechanisms dominate. The relative amplitudes of ionospheric WN3 show correlations with WN3 in MLT zonal winds but with a weaker coefficient (cc = 0.55, and cc = 0.50 with DE2). Variability in ionospheric WN3 is also significantly influenced by the stationary planetary wave SPW3 (cc = 0.30). To test whether thermospheric composition changes contribute to the generation of ionospheric WN3/4, we correlate O/N2wave amplitudes with ionospheric wave amplitudes. We find a significant correlation between ionospheric and O/N2WN3 (cc = 0.41) but only a weak correlation for WN4 (cc = 0.19) consistent with a greater role for composition‐driven coupling in WN3 than WN4.
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Signatures of Polar Vortex Weakening in the MLTI: A Review
Abstract This paper is a collaborative effort that originated at the International Space Science Institute Workshop on “Physical links between Weather and Climate in Space and the Lower Atmosphere” held 22–26 January 2024. Many scientists attended that workshop and contributed their expertise related to polar vortex impacts on upper atmosphere variability. This paper summarizes well-known and newly reported signatures of polar vortex weakening on mesosphere–lower-thermosphere (MLT) temperature, winds, composition, planetary waves, gravity waves, tides, and ionospheric foF2. A variety of observational and modeling results are shown and are consistent with previously published variations in the dynamical and chemical state of the MLT and ionosphere during weak vortex events. We present Superposed Epoch Analysis (SEA) of upper atmosphere diagnostics and phenomena where day 0 is the onset of major SSWs. We also present SEAs where day 0 is the onset of stratopause warmings followed by elevated stratopause events. Our goal in performing two SEAs is to test the sensitivity of 10 hPa versus 1 hPa winds to predict upper atmosphere variability. Results suggest that zonal winds and the semidiurnal migrating solar tide (SW2) in the MLT are more sensitive to zonal wind reversals at 1 hPa rather than 10 hPa. Alternatively, the non-migrating DW2 tide in the equatorial upper mesosphere is best predicted by planetary wave-1 amplitudes in the winter high-latitude upper stratosphere rather than zonal wind reversals. A notable aspect of both SEAs is extremely large event-to-event variability in all diagnostics. Thus, conclusions drawn based on any one event are less robust than those based on many events.
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- PAR ID:
- 10678425
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Springer Nature
- Date Published:
- Journal Name:
- Surveys in Geophysics
- ISSN:
- 0169-3298
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1007/s10712-025-09899-3
