Planetary Wave Forcing of Ozone Anomalies During 2024 Antarctic Stratospheric Warming

1. Introduction

The stratosphere is a critical coupling layer connecting the troposphere and mesosphere, which exerts profound regulation on global large-scale atmospheric circulation and multi-timescale climate variability [1,2,3]. Sudden Stratospheric Warming (SSW) is the most intense dynamical extreme event in the polar stratosphere. It is defined as a rapid rise of polar temperature by several to tens of Kelvin within several days, accompanied by significant weakening, deformation or even breakdown of the stratospheric polar vortex (SPV). For major SSW events, the zonal-mean westerly wind at 10 hPa and 60° latitude may even reverse completely [4,5,6]. SSW events involve complex dynamical, radiative and chemical feedbacks [7]. Their wave–mean flow interactions can reshape stratospheric circulation and propagate downward to modulate mid-latitude weather systems, cold surges, heatwaves and other extreme weather [8,9,10,11].

A remarkable hemispheric asymmetry exists in the climatology of SSW occurrence [12,13,14]. In the Northern Hemisphere (NH), SSWs occur frequently: minor warming events appear about once every 1–2 years, and major events with wind reversal recur every 2–4 years [5]. In sharp contrast, Antarctic SSWs are extremely rare. The core reasons include the nearly zonally symmetric Antarctic continent, weak meridional land-sea thermal contrast, and limited orographic forcing of planetary waves in the Southern Hemisphere midlatitudes [15,16,17]. Since the beginning of the satellite era in 1979, only one canonical major Antarctic SSW has been recorded, which occurred in September 2002 and featured full vortex splitting and zonal wind reversal [18,19]. Two minor SSWs were separately documented in late winter 1988 and 2019, neither accompanied by complete zonal wind reversal [20,21]. Previous reanalysis studies have confirmed that the persistently strong polar night jet in austral winter suppresses the upward propagation of planetary waves and dynamically inhibits the formation of winter SSWs [22,23].

Planetary waves and the stratospheric polar vortex constitute the core dynamical system governing the onset and evolution of SSWs [24,25,26]. The winter polar vortex maintains a cold cyclonic circulation over the polar stratosphere, and its stability is predominantly controlled by vertical wave activity flux from the lower atmosphere, with the vortex-edge surf zone serving as the key region of wave dissipation and momentum deposition [27]. Tropospheric blocking highs over the Southern Ocean act as critical planetary wave sources that excite persistent upward wave propagation [28,29,30]. Existing investigations of the 2024 consecutive Antarctic SSWs indicate that sustained intense mid-high latitude tropospheric blocking triggered robust upward transport of wave 1 and wave 2 [31,32]. Besides, stratospheric preconditioning featured by negative meridional potential vorticity gradient and adjusted wave refractive index weakens vortex stability and facilitates planetary wave resonance amplification [33,34]. Nonlinear amplification of wave 2 jointly forced by tropospheric upward injection and in-situ stratospheric excitation is widely accepted as a key driver of vortex splitting and severe attenuation during Southern Hemisphere SSWs [35,36].

Stratospheric ozone maintains tight dynamical-radiative-chemical coupling with SSWs [37,38,39,40]. Ozone effectively absorbs solar ultraviolet radiation and modulates stratospheric thermal and wind fields [3]. In turn, SSW-induced acceleration of the BDC enhances meridional ozone transport from subtropics toward polar regions [41]. Observations from historical Antarctic SSWs demonstrate strengthened residual circulation lifts polar total ozone column, suppresses heterogeneous chemical ozone loss on polar stratospheric clouds, and delays ozone hole formation [42].

Two successive winter SSWs hit Antarctica during July–August 2024, namely SW07 (6–13 July) and SW08 (21 July–5 August). This event set the record of the earliest winter SSW since satellite observations began and generated profound disturbances to polar vortex and ozone distribution [31,32]. Zi et al. [31] systematically diagnosed the troposphere-blocking-planetary wave cascade triggering SW07, and clarified that downward-propagating negative Southern Annular Mode signals originating from SW07 provided preconditioned circulation for SW08. Lim et al. [32] further pointed out that the 2024 SSW produced record-low Southern Annular Mode anomalies and induced extreme continental warming over Antarctica, representing an abnormal case of strong stratosphere-troposphere downward coupling rarely seen in austral winter. Nevertheless, prior research has not quantitatively identified the inherent correlations between multi-scale planetary wave variations and spatiotemporal ozone redistribution through correlation and spectral decomposition methods. Given the extreme scarcity of Antarctic winter SSWs and their far-reaching influences on polar ozone balance and mid-high latitude climate teleconnections, targeted dynamical diagnosis of the 2024 events carries essential theoretical and observational significance. This paper takes the two successive minor Antarctic SSWs in 2024 as research objects, systematically diagnoses the temporal, latitudinal and vertical evolution of wave 1 and wave 2, quantifies their modulating effects on polar vortex decay, and further discusses the dynamical coupling between planetary wave forcing and stratospheric ozone transport and redistribution throughout the warming lifecycle.

2. Materials and Methods

The study area focuses on the Southern Hemisphere during winter (June–August), with an emphasis on the Antarctic polar stratosphere, which is the core region where the 2024 sudden stratospheric warming (SSW) event occurred. This period corresponds to the polar night in the Antarctic region, during which the polar vortex is typically well–developed, and the stratospheric circulation is sensitive to planetary wave forcing, making it the key window for studying SSW events and their associated dynamical processes.

Four types of datasets are used in this study to ensure the comprehensiveness and reliability of the analysis: MERRA-2 (Modern-Era Retrospective analysis for Research and Applications, Version 2) reanalysis data, ERA5 reanalysis data, Aura MLS (Microwave Limb Sounder) satellite observations, and the Multi-Sensor Reanalysis version 2 (MSR-2) total ozone product. MERRA-2 and ERA5 reanalysis data provide high-resolution atmospheric dynamical parameters (including temperature, zonal wind, meridional wind, and geopotential height) covering the troposphere and stratosphere, which are used to analyze planetary wave propagation and polar vortex variations. Aura MLS satellite data offer accurate observations of stratospheric ozone concentration, which is essential for investigating the relationship between ozone transport and stratospheric warming during the 2024 Antarctic SSW event. To complement these daily-resolution products, monthly mean total ozone column (TOC) data were obtained from the MSR-2 dataset [41], produced by the Royal Netherlands Meteorological Institute (KNMI) and distributed through the Copernicus Climate Change Service (C3S). The MSR-2 dataset provides gap-free global TOC fields at a horizontal resolution of 0.5° × 0.5° spanning 1970 to the present, constructed by assimilating bias-corrected total ozone retrievals from 15 satellite instruments (including BUV, TOMS, SBUV series, GOME, SCIAMACHY, OMI, and GOME-2) together with ground-based Brewer and Dobson observations from the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) into the TMDAM chemistry-transport model driven by ECMWF ERA-Interim reanalysis meteorology. Satellite observations are de-biased as a function of solar zenith angle, viewing zenith angle, temporal drift, and stratospheric temperature against the WOUDC ground-based reference, yielding a mean bias of less than 1% with respect to the de-biased satellite observations after 1979. The MSR-2 data were used here to provide the long-term climatological context (1979–2023) against which the 2024 SH SSW ozone anomalies were evaluated. All datasets are processed to ensure consistency and applicability for the research objectives.

The geopotential height data from the Aura Microwave Limb Sounder (MLS) are interpolated onto a regular longitudinal grid of 360 points (0°–359°) for each pressure level and day. Planetary waves at zonal wavenumbers 1 (wave 1) and 2 (wave 2) are then extracted via longitudinal Fourier analysis. The discrete Fourier transform is applied along the longitudinal dimension to decompose the geopotential height field into wavenumber space:

$$\widehat{Z}(k,\varphi ,p,t)=\mathcal{F}[Z(\lambda ,\varphi ,p,t)],$$

(1)

where $Z\left(\lambda ,\varphi ,p,t\right)$ denotes the gridded geopotential height as a function of longitude $\lambda$, latitude $\varphi$, pressure level $p$, and time t; $\widehat{Z}\left(k,\varphi ,p,t\right)$ is the corresponding Fourier coefficient at zonal wavenumber k; and $\mathcal{F}$ represents the fast Fourier transform. To isolate planetary waves, only the spectral components at k = 1 and k = 2 are retained, and the spatial fields are reconstructed by inverse Fourier transform:

$$Z_{1,2}(\lambda ,\varphi ,p,t)={\mathcal{F}}^{-1}[\widehat{Z}(k,\varphi ,p,t)H_{1,2}(k)],$$

(2)

where ${\mathcal{F}}^{-1}$ denotes the inverse fast Fourier transform, and $H_{\mathrm{1,2}}\left(k\right)$ is a spectral filter that equals unity for k = 1 or k = 2and zero otherwise. The resulting Z₁ and Z₂ represent the planetary wave components, corresponding to wave 1 and wave 2 respectively.

3. Results

3.1. Zonal Mean Temperature and Zonal Wind

The time series of daily zonal mean parameters at 10 hPa over the Antarctic region, derived from MERRA-2 reanalysis data is shows in Figure 1, which is divided into two panels: panel (a) presents the zonal mean temperature (°C) averaged over 60°S–90°S, while panel (b) displays the zonal mean zonal wind speed (m s^-1) at 60°S. The dashed line in both panels represents the climatological mean of the corresponding parameters over the period 1979–2024, and the shaded area around the dashed line denotes the 95% confidence interval. The 95% confidence interval (shaded band) of the daily climatological mean was constructed using Student's t-distribution. For each calendar day d, the climatological mean was computed as ${\overline{x}}_d=\left(1/N\right){\displaystyle {\sum }_{i=1}^N}{x}_{i,d}$, where N = 46 is the number of years (1979–2024). The sample standard deviation was calculated as$s_d=\sqrt{\left(1/\left(N-1\right)\right){\displaystyle {\sum }_{i=1}^N}{\left(x_{i,d}-{\overline{x}}_d\right)}^2}$, and the standard error of the mean was obtained as${SE}_d=s_d/\sqrt{N}$. The 95% confidence interval was then given by ${\overline{x}}_d\pm t_{N-\mathrm{1,0.025}}\cdot {SE}_d$, where $t_{N-1,0.025}$ is the two-sided 0.025 critical value of Student's t-distribution with N−1 degrees of freedom ($t_{45,0.025}\approx 2.014$). Note that this interval represents the sampling uncertainty of the climatological mean rather than the interannual variability of the raw daily values, which is why the shaded band is relatively narrow (see Supplement S.2 for details).

Two vertical dashed lines are added to mark 13 July and 5 August 2024, the two key dates when the stratospheric temperature reached its peak values during the 2024 Antarctic sudden stratospheric warming (SSW) event.

Clear temporal variations of the mean zonal wind can be observed throughout the SSW event: before the onset of the SSW (early July 2024), the mean zonal wind at 60°S and 10 hPa maintains a relatively high value of approximately 70 m s^-1, indicating a well–developed and stable Antarctic polar vortex. As the SSW event progresses, the zonal wind shows a continuous and dramatic downward trend, with the most significant deceleration occurring during the peak period of the SSW. By the late stage of the SSW (early August 2024), the mean zonal wind decreases to around 57 m s^-1, a reduction of nearly 21% compared to the pre–SSW period. Following this minimum, the zonal wind recovers progressively. This sharp decline in zonal wind is closely associated with the upward propagation of anomalous planetary waves during the 2024 SSW, which deposit westward momentum and weaken the polar night jet, further leading to the weakening and distortion of the Antarctic polar vortex.

Obvious variations of the parameters can be observed in the time series: in Figure 1a, the zonal mean temperature at 60°S–90°S and 10 hPa shows a significant upward trend from early July 2024, rising from around 194 K (7 July) to the first peak of approximately 210 K on 13 July, followed by a slight decline and then another upward trend to the second peak of about 217 K on 5 August. Throughout the entire observation period, the daily temperature values are consistently higher than the climatological mean and mostly outside the 95% confidence interval, indicating the anomalous nature of the 2024 SSW–related warming (see Figure S1 in Supplement S.3 for details). In panel (b), the zonal wind at 60°S and 10 hPa strengthens from approximately 50 m s⁻¹ in early June to a local maximum of approximately 88 m s⁻¹ in late July, before decreasing sharply to approximately 57 m s⁻¹ on 5 August. Following this minimum, the wind rebounds rapidly to approximately 93 m s⁻¹ in mid-August, indicating a quick recovery of the polar vortex that reflects the strengthening of planetary wave activities during the SSW event.

Figure 2 displays the Southern Hemisphere zonal wind fields from ERA5 reanalysis data across three stratospheric levels during June to August 2024, covering the period before and during the Antarctic sudden stratospheric warming (SSW). At the pre-SSW stage in early June, a strong westerly polar night jet dominated southern latitudes 40–60°S. The maximum wind speed reached 120–150 m s⁻¹ at the 48 km stratopause and 80–100 m s⁻1 at the 32 km middle stratosphere, sustaining a stable polar vortex. As the SSW developed from mid-July, the westerly jet weakened at mid-latitudes and contracted poleward. By 5 August, the westerly circulation split into two lobes at both 1 and 10 hPa, one centered near 65°–80°S, 80°–120°W and the other near 65°–80°S, 80°–120° E, indicating a split-type vortex disruption.

The vertical discrepancy of wind anomalies reflects the typical dynamical characteristics of Antarctic SSW events. Disturbances in the zonal flow first emerged in the upper stratosphere and then gradually descended to lower levels, with anomaly intensity decreasing evidently with decreasing altitude. From late July to August, the stratospheric wind field experienced a full cycle of jet weakening, wind reversal and gradual recovery. The overall spatiotemporal variation of zonal winds clearly depicts the entire evolution of polar vortex disturbance and stratospheric circulation adjustment throughout the 2024 Antarctic SSW event.

3.2. Planetary Wave 1 and 2

Figure 3 presents the time series of zonal wave 1 and wave 2 amplitudes in geopotential height at 60°S and 10 hPa during June–August 2024, derived from MERRA-2 reanalysis time series data. This figure focuses on the temporal evolution of planetary wave amplitudes, which are key indicators of planetary wave activity and play a crucial role in triggering and maintaining the 2024 Antarctic Sudden Stratospheric Warming (SSW) event. Two vertical dashed lines are included in the figure, representing 13 July and 5 August 2024 respectively, which correspond to the two temperature peak dates of the 2024 SSW event. Additionally, the red solid line and red dashed line in the figure denote the climatological mean of the wave 1 and wave 2 amplitudes over the period 1979–2024, while the shaded area represents the 95% confidence interval, reflecting the natural variability of the climatological wave 1 and wave 2 amplitude data.

Distinct variations in wave 1 and wave 2 amplitudes can be observed throughout the study period (June–August 2024). During early June, wave 1 amplitude is already at a moderately high level (923 m on 1 June), while wave 2 remains relatively weak (268 m on 1 June). Following a transient peak in mid-June (1175 m on 6 June), wave 1 declines through early July before rising sharply to 1454 m on 14 July. In contrast, wave 2 stays moderate through most of July and only intensifies markedly in early August, surging to its peak near 5 August. These peak values are significantly higher than the climatological mean and well outside the 95% confidence interval, indicating anomalous enhancement of planetary wave activity during the SSW peak periods. After mid–August, new peaks emerged for both waves: wave 1 reached approximately 1500 m around 23 August, and wave 2 sustained values of 100–1000 m through 15–20 August, before both amplitudes decreased toward late August. This variation pattern of planetary wave amplitudes is closely associated with the evolution of the 2024 SSW event, as the enhanced upward propagation of wave 1 and wave 2 delivers westward momentum to the stratosphere, contributing to the polar vortex weakening and stratospheric warming.

Complementing the temporal analysis at 60°S, the latitude–time cross–sections of planetary wave amplitudes (Figure 4) from ERA5 data further contextualize the spatial and temporal evolution of wave activity across the Southern Hemisphere stratosphere at 10 hPa during June–September 2024.

Consistent with the MERRA-2 time series results, the cross sections confirm that the strongest wave forcing during the SSW event was concentrated in mid-to-high latitudes (50°–80° S), near the climatological polar vortex edge at 60° S (see Figure 4). For wave 1 (Figure 4a), a single prominent amplitude maximum is observed on 13 July, with peak values exceeding 1400 m near 60°–70° S. This aligns with the first warming peak of the 2024 SSW and confirms wave 1's role as the dominant driver of initial vortex weakening. Wave 2 activity (Figure 4b) shows a pronounced enhancement centered on 5 August, with peak amplitudes reaching approximately 1500 m. This corresponds to the second warming phase of the SSW, indicating that wave 2 forcing was critical for amplifying vortex disruption. In contrast, wave 3 (Figure 4c) amplitude remains much weaker throughout the period with small enhancement during the SSW event. This confirms that wave 3 played a negligible role in the 2024 Antarctic SSW, consistent with the established understanding that wavenumbers 1 and 2 are the primary planetary wave drivers of Southern Hemisphere stratospheric sudden warmings.

Across all three waves, the vertical dashed lines highlight the key transition periods of the SSW, demonstrating that the anomalous wave activity was confined to the mid–to–high latitudes where the polar vortex is most vulnerable to wave forcing. Together, the time series and latitude–time cross–section analyses confirm that the sequential, climatologically anomalous enhancement of wave 1 and wave 2 activity directly drove the two–stage weakening of the Antarctic polar vortex and the associated stratospheric warming in 2024.

Figure 5 further extends the analysis by presenting height–time cross–sections of wave 1 and wave 2 amplitudes at 60°S from 0–64 km, based on Aura MLS observations, revealing the vertical structure of wave activity during the same period.

For wave 1 (Figure 5a), a vertically coherent maximum is observed in mid-July, spanning approximately 20–50 km with peak amplitudes exceeding 1750 m near 40 km (above the 10 hPa level), indicating strong upward propagation into the upper stratosphere during the early SSW phase. In late July to August, wave 1 amplitudes weaken considerably at 20–40 km and do not sustain significant forcing through the second warming peak. Wave 2 (Figure 5b) exhibits a delayed but vertically extensive enhancement peaking in late July to early August, spanning approximately 20–45 km with maximum amplitudes of approximately 1400 m in the 25–35 km layer (centered on 10 hPa), reflecting middle-stratospheric forcing during the vortex disruption phase.

Collectively, the multi–dataset analysis of temporal, latitudinal, and vertical variations in wave amplitudes demonstrates that sequential, climatologically anomalous enhancements of wave 1 and wave 2 activity directly drove the two–stage evolution of the 2024 Antarctic SSW, with wave 1 dominating the early phase and wave 2 dominating during the peak warming period.

To contextualize the 2024 Antarctic stratospheric warming within the broader record of Southern Hemisphere stratospheric variability, a comparative analysis of three historical Southern Hemisphere SSW events, namely SSW88 (1988), SSW02 (2002), and SSW19 (2019), together with SSW24 (2024) are shown in Figure 6. Panels (a–d) show zonal mean polar temperatures (60°–90° S), (e–h) zonal winds at 60° S, and (i–l) planetary wave 1 (solid) and wave 2 (dashed) amplitudes at 60° S, all at 10 hPa and spanning 1 July–31 October. Vertical dashed lines mark the SSW onset date of each event, while the red/blue dashed line and shaded red/blue area denote the 1979–2024 climatological mean and 95% confidence interval, respectively. Across all four events, clear common patterns emerge: early winter conditions are characterized by near-climatological polar temperatures (~190–200 K on 1 July) and a strong, stable polar night jet (~60–80 m s⁻¹ on 1 July), while the SSW events display distinct warming signatures, with SSW88 peaking at T ≈ 245 K on 28 September (u ≈ 30 m s⁻¹), SSW02 at T ≈ 250 K on 29 September (u ≈ −22 m s⁻¹, wind reversal), SSW19 at T ≈ 245 K on 19 September (u ≈ 14 m s⁻¹), and SSW24 showing two consecutive minor peaks at T ≈ 210 K on 13 July and T ≈ 217 K on 5 August (u ≈ 57 m s⁻¹, no wind reversal). Each event is preceded by a pronounced enhancement of planetary wave activity, confirming that enhanced upward wave propagation is the primary trigger for vortex disruption and stratospheric warming.

Despite these shared characteristics, the events exhibit key differences in intensity, timing, and wave forcing dynamics. SSW88 represents a minor event, with temperatures rising only ~15 K above the climatological mean and the zonal wind weakening but remaining positive, dominated almost entirely by wave 1 forcing with minimal wave 2 contribution. SSW02 is a major SSW, featuring a sharp temperature rise (~22 K above climatology), a complete reversal of the zonal wind, and a secondary enhancement of wave 2 activity that amplifies vortex disruption. SSW19 is a minor SSW, with temperatures peaking ~23 K above climatology, a dramatic collapse of the polar night jet, and a particularly prominent, early wave 1 peak that drives strong vortex weakening.

SSW24 is fundamentally different from the other three SSWs. It occurred earliest, with two consecutive warming pulses occurring in midwinter (13 July and 5 August) rather than in early spring, when the climatological background temperature is still relatively low. Second, the polar night jet remains strong (minimum 57 m s⁻¹ on 5 Aug) with no wind reversal, confirming its minor SSW classification. Third, SSW24 is the only event with two distinct warming pulses within a single season, driven by a sequential switch from wave 1 (peak ~1454 m on 14 July) to wave 2 (peak ~1511 m on 5 August). These variations highlight that while planetary wave activity is the common driver, differences in the timing, magnitude, and relative contributions of wave 1 and wave 2 lead to distinct SSW intensities and vortex responses in the Southern Hemisphere.

3.3. Total Ozone Column

Figure 7 presents the latitudinal structure and temporal evolution of the total ozone column (TOC) and its anomalies across 60°S, 70°S, and 80°S during the 2024 austral winter, with the red dashed line marking 13 July 2024—a key transition point associated with the 2024 Southern Hemisphere sudden stratospheric warming (SSW). Figure 7 (a), (c), and (e) shows the absolute TOC values, revealing a striking latitudinal divergence after mid-July. At 60°S, TOC rises sharply above the climatological mean, peaking at ~355 DU in mid-August, indicating significant ozone enrichment. At 70°S, TOC shows a transient peak around early August (~305 DU) before declining sharply to ~230 DU by early September. At 80°S, TOC declines steadily after mid-July, reaching ~210 DU by early September, well below the climatological baseline. This creates a pronounced poleward gradient in the ozone response, where the outer polar vortex region (60°S) exhibits ozone accumulation while the inner vortex core (80°S) experiences sustained ozone depletion, with 70°S representing an intermediate, transitional behavior.

In Figure 7, (b), (d), and (f) present TOC anomalies alongside segmented linear trends before and after 13 July, quantifying the dynamical transition linked to the SSW. Prior to 13 July, all three latitudes show negative TOC anomalies and consistent downward trends: −0.27 to −0.28 DU day⁻¹ at 60–70°S and −0.25 DU day⁻¹ at 80°S, consistent with a strengthened polar vortex that traps ozone-poor polar air and suppresses poleward transport of ozone-rich midlatitude air. After 14 July, the trends reverse dramatically at 60°S and 70°S, shifting to positive rates of +0.26 DU day⁻¹ and +0.23 DU day⁻¹, respectively, driving anomalies from negative to positive. Meanwhile, 80°S retains a weakened negative trend (−0.19 DU day⁻¹), indicating a delayed recovery. This latitudinal asymmetry arises from SSW-induced dynamical changes: the weakened polar vortex and enhanced planetary wave activity promote poleward transport of ozone-enriched air to 60–70°S, while the more isolated inner vortex at 80°S lags in circulation adjustment, sustaining negative ozone anomalies through limited ozone replenishment. These results quantitatively demonstrate that the 2024 SSW played a pivotal role in reshaping the stratospheric ozone distribution via modified meridional transport and vortex dynamics.

The latitude–time cross-section of total ozone column over the Southern Hemisphere during June–August 2024, revealing a pronounced meridional gradient in ozone distribution, is presented in Figure 8a. Ozone concentrations peak at mid-latitudes (30°–50°S), reaching approximately 340–360 Dobson Units (DU), while values decline sharply poleward, dropping to 200–260 DU south of 60°S. This persistent pattern reflects the climatological mid-latitude ozone maximum and polar ozone depletion, with a stable band of enhanced ozone (280–340 DU) maintained across 30°–60°S throughout the period. The gradual weakening of this poleward gradient in late August suggests a disruption of the meridional transport regime, likely linked to the dynamical perturbations associated with the 2024 Antarctic SSW.

Figure 8b illustrates the zonal mean ozone perturbation anomaly, capturing the wave-driven redistribution of ozone during the SSW. Before the SSW, ozone anomalies were negative at lower latitudes (equatorward of 60° S) and positive at higher latitudes (poleward of 60° S). After 5 August, the pattern reversed: positive anomalies appeared at lower latitudes and negative anomalies at higher latitudes. This opposing migration of anomalies reveals a clear meridional rearrangement of ozone, with ozone-poor air shifting equatorward and ozone-rich air moving poleward. Figure 8c and Figure 8d further show that zonal ozone wave 1 exhibits two prominent amplitude peaks (~80–100 DU) at 60°–70°S around mid-July and late August, while ozone wave 2 reaches a sharp peak (~70 DU) at the same latitudes during early August, coinciding with the extreme temperature maxima marked by vertical dashed lines. The confinement of these wave amplitudes to 40°–80°S, overlapping with the climatological polar vortex edge at 60°S, confirms that wave 1 and wave 2 act as the primary dynamical drivers, perturbing the polar vortex and inducing the observed ozone redistribution via meridional mixing and transport.

Figure 9 shows the 7-day mean ozone perturbation distributions (unit: DU) during four typical periods in the 2024 Southern Hemisphere winter (June–August). From June 1 to 7, 2024, ozone anomalies exhibit a monopolar pattern, with significant positive anomalies (red, marked H) in the region of 60°S–90°S and 30°E–150°E, and strong negative anomalies (blue, marked L) near 60°W, forming a sharp contrast between mid-latitude negative and high-latitude positive anomalies. From June 29 to July 5, 2024, ozone anomalies transition into a bipolar structure, with two positive anomaly centers (H) near 30°W and 90°E respectively, and a negative anomaly center (L) in the 90°W–120°W region, with positive and negative anomalies distributed alternately along the zonal direction. From July 27 to August 2, 2024, ozone anomalies present a multipolar distribution, with positive anomaly centers (H) near 30°E and 180°, and negative anomaly centers (L) near 60°W and 120°E, where high- and mid-latitude anomalies are nested, leading to a more complex structure. This location of ozone anomalies is associated with wave 2 domination that reached its peak in early August (Figure 8d). From August 24 to 30, 2024, ozone anomalies show a vortex-like pattern, with a strong negative anomaly center (L) in the 60°W–0° region and a strong positive anomaly center (H) near 90°E, forming a zonal ring wave train of positive and negative anomalies, reflecting the modulation of planetary-scale waves on ozone distribution.

Figure 10 shows the cross-latitudinal Pearson correlation distributions between planetary wave 1 and wave 2 amplitudes and zonal-mean TOC anomalies over the Southern Hemisphere. In the left panel, the wave 1 amplitude at 60°S–70°S is negatively correlated with zonal mean TOC anomalies over 0–50°S, with correlation coefficients between −0.6 and −0.4. The correlations are weak (|R|<0.4) at all other latitudes. In the right panel, wave 2 amplitudes over 0°S–65°S show strong positive correlations (R≥0.6) with TOC anomalies in the 60°S–70°S band. The regions of significant correlation for the two waves overlap only slightly. Within the boxed region (20°S–60°S), TOC anomalies are negatively correlated with the wave 1 amplitude and positively correlated with the wave 2 amplitude.

The two waves therefore exhibit clear wave-type and latitudinal selectivity in their coupling with ozone. Wave 1 dominates the negative coupling at low to middle latitudes, whereas wave 2 governs the positive coupling at middle to high latitudes. The limited spatial overlap between the two correlation patterns suggests that the waves regulate ozone through largely independent pathways. The opposite correlation signs within the same latitude band further indicate a possible temporal offset between the two wave forcings, consistent with the sequential amplification of wave 1 in early July and wave 2 in late July. Wave 2 thus acts as the dominant driver of polar ozone enrichment during the 2024 SSW.

4. Discussion

The 2024 austral winter witnessed an event without precedent in the satellite era: two successive minor Antarctic sudden stratospheric warmings occurring in July–August, the earliest midwinter SSWs ever recorded over the Southern Hemisphere. While prior studies have established the tropospheric blocking, sea-ice loss, stratospheric preconditioning, and downward SAM propagation as the triggering chain for these events [31,32], several critical aspects of the wave forcing and ozone response remain unresolved. Zi et al. [31] diagnosed wave activity using eddy heat flux at only two discrete levels (10 and 100 hPa) and treated the ozone response as a polar-cap-averaged bulk quantity (60°S–90°S), attributing the observed ozone increase solely to enhanced residual meridional circulation. This approach cannot resolve the vertical structure of wavenumber-specific forcing or any spatial selectivity in the ozone redistribution process. The present study addresses both gaps. First, we provide a quantitative, stage-separated diagnosis of wave 1 and wave 2 forcing across the full 20–50 km altitude range using multiple independent datasets, demonstrating that the two warming peaks were driven by distinct wave components with different vertical structures. Second, we establish, for the first time, the wave-type and latitude-selective coupling between planetary wave activity and stratospheric ozone redistribution during an Antarctic winter SSW, revealing that wave 1 and wave 2 exert fundamentally different regulatory influences on the total ozone column.

The finding that wave 1 and wave 2 operate in a temporally staggered, functionally distinct manner during the 2024 SSW carries implications beyond this single event. In Northern Hemisphere major SSWs, wave 1 is generally considered the primary forcing agent, with wave 2 playing a secondary role primarily during vortex-splitting events [11,43]. Our results suggest that in the Southern Hemisphere, where the polar vortex is typically more zonally symmetric and less receptive to wave forcing, the relative contribution of wave 2 may be disproportionately important for achieving the threshold of vortex disruption. The delayed but vertically extensive enhancement of wave 2 observed in late July–early August (Figure 6b), peaking in the 25–35 km layer, implies that wave 2 amplification was not merely a passive response to vortex weakening but an active driver that sustained and intensified the second warming phase. This is consistent with the resonance amplification mechanism proposed by [33] wherein stratospheric preconditioning by the first warming episode creates a refractive index structure favorable for subsequent wave 2 growth. Notably, Zi et al. [31] reported wave 1 and wave 2 amplitudes near historical extremes at 10 hPa but did not examine their vertical distribution; our vertically resolved analysis reveals that the two wave components reached their respective maxima at different altitudes and during different phases, a distinction that a single-level diagnostic cannot capture.

The wave–ozone coupling selectivity revealed by our cross-latitudinal correlation analysis (Figure 10) represents a novel observational result with implications for understanding Antarctic ozone variability under a changing climate. Whereas Zi et al. [31] reported a bulk ozone increase averaged over 60°S–90°S and attributed it to residual meridional circulation transport, our latitude-resolved analysis uncovers a more nuanced picture. Wave 1 amplitudes at 60°S–70°S are negatively correlated with zonal mean TOC anomalies over 0–50°S, with correlation coefficients of −0.4 to −0.6. In contrast, wave 2 amplitudes over 0–65°S are positively correlated with TOC anomalies in the 60°S–70°S band, with R ≥ 0.6. These distinct pathways, with minimal latitudinal overlap, imply independent regulatory mechanisms that may operate on different timescales. The poleward progression of negative ozone anomalies and equatorward migration of positive anomalies (Figure 8b) are qualitatively consistent with the two-cell residual circulation response described in idealized SSW simulations [44], though the quantitative attribution of this response to specific wave components warrants further investigation using transformed Eulerian-mean diagnostics.

Several limitations should be acknowledged. First, our analysis relies on reanalysis and satellite data over a single season, which limits the statistical robustness of the correlation-based ozone attribution. The extreme rarity of Antarctic winter SSWs precludes a large-sample statistical approach; however, the consistency across independent datasets strengthens confidence in the identified relationships. Second, we did not explicitly diagnose Eliassen–Palm flux divergence or the residual mean circulation, which would provide a more mechanistic pathway from wave forcing to ozone transport. Third, the potential modulating roles of the quasi-biennial oscillation (QBO) and El Niño–Southern Oscillation (ENSO) on the 2024 event were not assessed. The QBO was in its easterly phase during austral winter 2024, a configuration previously linked to increased susceptibility to SSW onset via modified wave propagation conditions [45,46], and this may have contributed to the unusual preconditioning of the 2024 Antarctic stratosphere. Zi et al. [31] similarly did not account for these tropical forcings, underscoring a shared limitation that future studies should address. Fourth, our ozone analysis focused on total column amounts and did not separate dynamical from chemical contributions to ozone changes; heterogeneous chemical ozone depletion may remain competitive with transport effects, particularly at high latitudes within the cold vortex core. Future work incorporating trajectory analysis, ozone tendency budgets, and chemistry-climate model simulations would help disentangle these processes.

The 2024 event challenges the canonical view that Antarctic winter SSWs are suppressed by the persistent austral polar night jet. The fact that two successive warmings occurred during midwinter, rather than in late winter or spring as in previous events (1988, 2002, 2019), raises the question of whether the conditions favoring Southern Hemisphere SSWs are evolving under climate change. Rising greenhouse gas concentrations induce stratospheric cooling, which strengthens the polar vortex, but also enhance tropospheric wave generation through changes in tropical sea surface temperatures and Hadley cell expansion [47,48]. These competing influences create uncertainty in projections of future Antarctic SSW frequency. The 2024 event provides a valuable observational benchmark for evaluating the fidelity of climate models in simulating extreme stratospheric variability under both present-day and future climate forcing. If the preconditioning mechanisms identified here, including tropospheric blocking, stratospheric wave resonance, and wave–ozone feedback, are captured by models, improved seasonal prediction of Antarctic stratospheric extremes and their surface impacts may become feasible.

5. Conclusions

This study provides a systematic observational diagnosis of the unprecedented pair of successive midwinter Antarctic sudden stratospheric warmings in July–August 2024, with a focus on the stage-separated planetary wave forcing and the associated wave–ozone coupling. The principal findings are summarized as follows:

1. The 2024 Antarctic winter witnessed two consecutive minor SSWs, the earliest winter warmings recorded over Antarctica in the satellite era, characterized by a maximum reduction of approximately 30% in the 10 hPa zonal mean wind at 60°S and polar temperature anomalies exceeding 15 K above the 1979–2024 climatological mean. These events were driven by anomalously strong upward propagation of tropospheric planetary waves that deposited westward momentum in the stratosphere and systematically weakened the polar night jet.

2. Wave 1 and wave 2 exerted stage-separated, functionally distinct forcing on the polar vortex. Wave 1 dominated the first warming peak in mid-July, with vertically coherent amplitude maxima spanning 20–50 km and peak geopotential height amplitudes exceeding 1750 m near 40 km. Wave 2 amplification, concentrated in the 25–35 km layer during late July–early August, drove the second, more intense phase of vortex disruption. Multi-dataset analysis confirms that the sequential enhancement of wave 1 and wave 2 activity is the primary dynamical mechanism underpinning the two-stage evolution of the 2024 Antarctic SSW.

3. A clear wave-type and latitude-selective coupling between planetary wave activity and stratospheric ozone redistribution is established. Wave 1 exhibits a significant negative correlation with total ozone column anomalies across the 0–50°S mid-latitude band, reflecting equatorward export of ozone-poor air during the warming onset. In contrast, wave 2 shows strong positive coupling with TOC over 60°S–70°S, driving poleward transport of ozone-rich air into the polar collar region. These two pathways display minimal latitudinal overlap, indicating independent regulatory mechanisms for stratospheric ozone distribution during Antarctic SSWs. The segmented linear trend analysis confirms a dynamical transition on ~13 July, after which TOC trends reversed from negative (−0.27 DU day⁻¹) to positive (+0.26 DU day⁻¹) at 60°S, coinciding with the peak warming period.

4. The wave–forced ozone anomalies exhibit a progressive meridional reorganization, with positive anomalies migrating equatorward from 50°–60°S to 40°–50°S and negative anomalies advancing poleward toward 70°–80°S, consistent with a perturbed BDC and enhanced planetary-wave-driven meridional mixing across the polar vortex edge.

These results demonstrate that the 2024 Antarctic SSW provides a unique natural laboratory for investigating stratosphere–troposphere dynamical coupling and wave–ozone interactions under conditions of extreme planetary wave forcing. The identified wave-type selectivity in ozone transport carries implications for understanding Antarctic ozone variability, stratospheric predictability, and the potential modulation of ozone hole development by dynamical extremes in a changing climate.