Fig. 4: Relationship between WWB, zonal SST gradient, and NPMM condition. | npj Climate and Atmospheric Science

Fig. 4: Relationship between WWB, zonal SST gradient, and NPMM condition.

From: Diverse NPMM conditions deviate the 2023/24 El Niño from the 1997/1998 and 2015/2016 extreme El Niño events

Fig. 4: Relationship between WWB, zonal SST gradient, and NPMM condition.The alternative text for this image may have been generated using AI.

a Time series showing the relationship between monthly WWB event frequency and zonal SST gradient. The thick black line represents monthly zonal SST gradient values arranged from most positive to negative during 1952–2024. Red bars represent WWB event frequency, calculated as the number of days per month with WWB occurrence (defined as zonal wind anomaly averaged in the WWB region exceeding 1 standard deviation)69, arranged according to the corresponding months of the zonal SST gradient. Red and blue shading denote periods of positive and negative zonal SST gradient, respectively. b Scatter plot showing the normalized spring (MAM) zonal SST gradient averaged over the WWB region (135°E–180°E, 5°S–5°N) versus WWB event frequency, both computed over MAM seasons, from 1952 to 2023. c Scatter plot of the normalized spring (MAM) zonal SST gradient versus normalized NPMM index from 1952 to 2023. The black solid line shows the linear regression for all data points. d Same as (c), but comparing the normalized spring (MAM) NPMM index versus normalized spring (MAM) WWB event frequency. The black solid line in (b–d) indicates the linear regression for all data points.

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