Zheng Ma

This study investigates the heterogeneous impacts of sudden stratospheric warming (SSW) events on the Arctic tropopause and tropopause inversion layer (TIL) using ERA5 reanalysis data from 1979/1980 to 2022/2023. According to the significance of their TIL and tropopause height responses, all 50 SSW events are classified into five categories: significant major, significant minor, non‐significant major, non‐significant minor, and anomalous minor. 65.4% of major SSWs and 12.5% of minor SSWs have significant impacts on the Arctic tropopause and TIL. Notably, anomalous minor SSWs do not strengthen but weaken the TIL, and do not lower but raise the tropopause height. Building upon the established coupling mechanism between the TIL/tropopause and SSW, we analyze the role of background flow changes: stratospheric planetary wave breaking decelerates background westerlies, causing subsequent planetary waves to break at lower altitudes and amplifying both adiabatic heating that drives tropopause descent and dynamical heating that enhances the TIL. We further provide an explanation for the generation of dynamical heating near the tropopause, which arises from the coexistence of residual mean upwelling anomalies induced by planetary wave divergence anomalies at 7–12 km and residual mean downwelling anomalies induced by planetary wave convergence anomalies above 12 km. The breaking of sufficient upward‐propagating planetary waves in the stratosphere satisfies the key dynamical condition required for significant impacts on the tropopause and TIL. When stratospheric planetary wave convergence anomalies are weaker than the local planetary wave divergence anomalies, the TIL is weakened and the tropopause height rises instead.

Using more than two decades (2002–2024) of neutral wind observations from the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) Doppler Interferometer (TIDI), this study investigates the quasi‐biennial oscillation (QBO)‐related variability of the migrating lunar semidiurnal ( M ₂ ) tide in the mesosphere and lower thermosphere. The M ₂ amplitudes maximize at middle latitudes in both hemispheres, with primary seasonal peaks during December/January and secondary peaks during July/August. Pronounced QBO associated differences are identified in the winter hemispheres. Permutation tests show that M ₂ amplitudes are significantly larger during the easterly QBO phase (QBOe) in the Northern Hemisphere during December/January and during the westerly QBO phase (QBOw) in the Southern Hemisphere during July/August. Multiple linear regression analysis further indicates that the relationships between QBO winds and winter‐hemisphere M ₂ amplitudes remain statistically significant after accounting for the potential influences of solar activity and the El Niño–Southern Oscillation. Further analysis reveals that larger wintertime M ₂ amplitudes are consistently associated with weaker mesospheric eastward zonal winds. This correspondence is consistent with the interpretation that QBO‐related changes in planetary‐wave–mean‐flow interactions alter the mesospheric background winds and thereby influence the vertical propagation conditions of the M ₂ tide. These results provide the first global observational evidence for QBO‐associated modulation of the M ₂ tide and highlight the importance of dynamical coupling among the stratosphere, mesosphere, and thermosphere in controlling lunar atmospheric tides.

This study presents an observational investigation of a quasi–18 hr oscillation in mesosphere and lower thermosphere (MLT) zonal winds over Beijing and Wuhan during the 2016 Arctic minor sudden stratospheric warming (SSW), based on meteor radar measurements. Lomb–Scargle spectral analysis reveals a clear enhancement in the 16–20 hr band immediately following the SSW onset. The quasi–18 hr oscillation coexists with an enhanced diurnal tide (DT) and a variable but continuously identifiable quasi–2–day wave (Q2DW), and reaches a maximum amplitude of 24.6 m/s over Beijing and 21.8 m/s over Wuhan, both at 96 km. The temporal evolution shows that the quasi–18 hr oscillation intensifies nearly simultaneously with the DT, whereas the Q2DW remains active before and after the SSW. Phase–closure analysis indicates significantly enhanced phase organization among the 18, 24, and 60 hr components during the onset stage. In addition, bispectral analysis reveals strengthened quadratic phase coupling between the DT and the Q2DW. These results suggest that the quasi–18 hr oscillation is not a direct response to the SSW. Instead, the SSW primarily enhances the DT, which subsequently interacts nonlinearly with the background Q2DW to generate the quasi–18 hr oscillation. This study provides observational support for a two–step mechanism linking SSW–driven tidal modulation and nonlinear wave–wave interaction in the MLT region.

Using meteor radar observations and reanalysis data, we investigate the variations of the 12.42‐hr oscillations in the mesosphere and lower thermosphere (MLT) region over Yinchuan (YC, 38.8°N, 106.8°E) during four Arctic winters from 2020 to 2024. By comparing the observed oscillation signatures with the evolution of sudden stratospheric warming events, polar vortex weakening (PVW) events, quasi‐biennial oscillation (QBO) phases, and nonlinear wave interactions, we identified distinct mechanisms governing 12.42‐hr oscillation amplification at different altitudes. Below 90 km, the enhancement of the 12.42‐hr oscillation is primarily attributed to nonlinear interactions between the solar semidiurnal tide and quasi‐16‐day waves. Above 90 km, however, the observed enhancements correspond to the lunar semidiurnal tide (LSD) and exhibit a strong dependence on the intensity of PVW events. Although QBO‐related modulation can influence the oscillation, it is not a consistently dominant factor in the upper MLT region, where the oscillation strength more closely follows the variability of PVW events. These findings highlight two distinct physical pathways shaping the 12.42‐hr oscillations in the MLT region: nonlinear wave‐wave coupling below 90 km and polar vortex‐controlled modulation of the LSD above 90 km. This study provides new insights into the dynamical processes governing tidal variability during Arctic winters.

Using Arecibo incoherent scatter radar (ISR) observations from 1971 to 2019, we present a statistical analysis of 224 ionospheric midnight collapse events characterized by rapid decreases in the F‐region peak height near local midnight. Events are classified into geomagnetically disturbed and quiet periods. Both the first and second collapses occur more frequently during storms (97.2% and 22.2%) than during quiet conditions (92.2% and 15.5%). Although the overall distributions of onset time, duration, initial height, and magnitude are broadly similar, distinct storm‐time enhancements emerge. The first collapse initiates at higher altitudes and descends more rapidly during disturbed periods, while the second collapse exhibits stronger storm‐time amplification, with onset heights elevated by 15–50 km and magnitudes enhanced by up to ∼59 km. Decomposition of the ISR line‐of‐sight velocity shows that storm‐time modifications in both the field‐aligned () and perpendicular () ion drifts jointly regulate the vertical ion drift, producing the observed morphological differences between disturbed and quiet conditions. Specifically, storm‐time enhancements of the meridional wind () modulate , while electric‐field‐driven perturbations primarily affect . Tidal analysis further shows that geomagnetic activity amplifies major thermospheric tides, particularly the 12‐hr and 8‐hr components, and wind reconstructions highlight the central role of the 8‐hr tide in driving the storm‐time wind variability. Together, these results demonstrate that geomagnetic storms modify midnight collapse morphology through coupled electrodynamic forcing and tidal modulation of the neutral wind, which jointly control vertical ion transport over Arecibo.

This study investigates the global structure of the lunar semidiurnal (M ₂ ) tide in the mesosphere and low thermosphere region based on the neutral winds obtained from Thermosphere, Ionosphere, Mesosphere Energetics & Dynamics (TIMED)/TIMED Doppler Interferometer (TIDI). A clear signature of the semidiurnal variation with lunar local time (M ₂ tide) is observed in the zonal and meridional winds. The seasonal‐latitudinal distributions of M ₂ amplitude depict peaks in January, July, and December at midlatitudes in both hemispheres. The hemispheric symmetric and asymmetric structures of M ₂ amplitudes are both observed. An asymmetric structure appears near July in the zonal wind and near December in the meridional wind. Hough mode decomposition of the observed M ₂ tide indicates that the latitudinal structure in July is predominantly governed by the (2, 3) and (2, 4) modes in the zonal wind, whereas the (2, 3) mode dominates the meridional wind structure in December. The latitudinal distributions of zonal‐mean zonal wind in the mesosphere are likely responsible for these asymmetric features, with hemispheric differences in zonal jets and the weakening of the northern polar vortex being probable contributing factors.

Based on temperature data from the Mars Climate Sounder onboard Mars Reconnaissance Orbiter, this study investigates quasi‐6.5‐sol waves (Q6.5SWs) in the Southern Hemisphere (SH) of Mars from Mars Year (MY) 30 to MY 36. We report, for the first time, unseasonal enhancements of Q6.5SWs in the mid‐to‐high latitudes of the SH, coinciding with three early dust storm events in MY31, MY34, and MY36. In contrast, Q6.5SW activity in the SH remains generally weak during dust storms in other Martian years. Our analysis suggests that the unseasonal enhancement of Q6.5SWs is primarily driven by significant temperature increases associated with dust storms, while variations in zonal mean zonal wind may also play a secondary role in modulating wave amplitudes.

Spectral structure of gravity waves (GWs) attracted much attention because it is related to wave dissipation mechanism and parameterization effect. Although many works have studied the spectral variation of GWs and attributed this change to factors such as height, season and latitude, impact of observational resolution on wave spectrum was rarely reported. By averaging and downsampling 5‐m resolution radiosonde temperature, we construct two data sets with lower resolutions to investigate the effect of data resolution on vertical wavenumber spectrum of GWs. The constructed average and downsample data sets correspond to two measurement techniques in actual observations. The results indicate that a lower resolution causes a shallower slope of power spectrum density (PSD) due to its filter effect on high wavenumber spectrum close to the saturation spectrum. Nevertheless, there are some differences in spectral dependence on resolution between the two data. The shallowing slope is further enhanced in the downsample data due to significant increase of PSD amplitudes near maximum wavenumbers by superposition of subgrid scale perturbations, in contrast, slightly counteracted in the average data owing to weak attenuation of PSD amplitudes near maximum wavenumbers by smoothing. Hence, variation of observed wave spectrum may stem from resolution as well as data sampling technique, rather than only geophysical causes.