Fig. 1: Interdecadal modulation of the relationship between ASO and ENSO.
From: Arctic stratospheric ozone as a precursor of ENSO events since 2000s
a 252-month (21-year) running lead-lagged correlation coefficients between the ASO and Niño3.4 indices for the period 1980–2023 (y-axis). Negative and positive values on the x-axis indicate leads of ASO and Niño3.4 at monthly timescales, respectively. Hatching denotes values significant at the 95% confidence level, based on a two-tailed Student’s t-test, with degrees of freedom set to 60 to account for temporal autocorrelation. b Lagged correlation between the ASO and Niño3.4 indices for the period 2002–2023, where the x-axis indicates the number of months by which the ASO index precedes the Niño-3.4 index; the y-axis indicates the period of November to the following October. The negative maximum is found at 7 (x-axis) during April (y-axis), indicating that the ASO in April negatively precedes ENSO with a lag of 7 months. Hatching indicates the 95% confidence level using a two-tailed Student’s t-test (degree of freedom: 20). c Red and black lines indicate the March-April (MA) ASO index and the November-December (ND) Niño3.4 index from 2002-2023. The correlation coefficient between them is 0.57, significant at the 99% confidence level by student's t-test (degree of freedom: 20). Herein, the purple line indicates the March–April (MA) Arctic total column ozone (TCO) index, obtained by averaging TCO over 70–90°N using OMI (2005–2023).
