Table 2 Evaluation metrics for the annually resolved station-based atmospheric reanalysis for the Southern Annular Mode (compared against the Marshall index⁸³ over 1958–2023), regional near-surface air temperature and precipitation (compared against ERA5 over 1979–2023), and regional sea-ice extent (compared with NSIDC³ over 1979–2023).

	r	RRMSE [%]	ECR
Atmospheric modes
Southern Annular Mode	0.90* ± 0.01	5.46 ± 0.24	0.74 ± 0.25
Near-surface air temperature
West Antarctic Ice Sheet	0.78 * ± 0.05	9.56 ± 0.71	0.58 ± 0.13
East Antarctic Ice Sheet	0.92 * ± 0.02	6.39 ± 0.54	0.88 ± 0.33
Antarctic Peninsula	0.88 * ± 0.03	7.39 ± 0.71	0.46 ± 0.27
Antarctic Ice Sheet	0.92 * ± 0.02	6.07 ± 0.67	0.66 ± 0.30
Precipitation
West Antarctic Ice Sheet	0.68 * ± 0.05	11.45 ± 0.54	1.18 ± 0.47
East Antarctic Ice Sheet	0.65 * ± 0.07	12.18 ± 0.58	1.87 ± 0.79
Antarctic Peninsula	0.86 * ± 0.03	10.43 ± 0.51	3.70 ± 2.41
Antarctic Ice Sheet	0.55 * ± 0.10	12.62 ± 0.85	1.90 ± 0.91
Sea ice
Bellingshausen/Amundsen Sea	0.71 * ± 0.12	10.75 ± 1.57	0.37 ± 0.27
Weddell Sea	0.67 * ± 0.05	11.08 ± 0.64	0.95 ± 0.38
King Hakon	0.59 * ± 0.14	12.10 ± 1.75	0.75 ± 0.90
East Antarctica	0.55 * ± 0.06	12.83 ± 0.80	0.82 ± 0.63
Ross Sea	0.57 * ± 0.16	12.45 ± 1.66	0.67 ± 0.43
Southern Ocean	0.55 * ± 0.09	12.67 ± 0.77	0.79 ± 0.47

The definitions of the regions for near-surface air temperature and precipitation follow Steig et al.¹²²: the West Antarctic Ice Sheet (60–180°W, south of 72°S), the East Antarctic Ice Sheet (60°W–180°E), and the Antarctic Peninsula (60–180°W, north of 72°S). The five sea-ice extent regions are defined as follows: Amundsen/Bellingshausen Seas (110°W-70°W), Weddell Sea (70°W-15°W), King Hakon sector (15°W-70°E), Indian sector (70°E-165°E), and Ross Sea (165°E-110°W). Correlation coefficients (r), RRMSE, and ECR values are presented for the multi-model ensemble mean, along with the standard deviation of the multi-model ensemble. Statistically significant correlations at the 95% confidence level are marked with stars.

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