Fig. 4. Weather to intraseasonal timescale perturbations during the 2023 event.

(A) The Wheeler-Hendon phase diagram for June 1974 to July 2023. The 2023 MJO index is highlighted in color, with February in magenta, March in red, and April in blue. (B) Hovmöller diagrams of equatorial (5°S to 5°N) 200 hPa velocity potential (ϕ, color shading, m²/s) and 850-hPa zonal wind anomalies (line contours with an interval of 1 m/s; positive black and negative gray). (C) Observed 30 to 90 band-filtered anomalies of rainfall (millimeters per day; color shading) and 10-m wind (meters per second, vectors), averaged during 5 to 13 March 2023. (D) Correlation (color shading) of observed v10 with eastern Pacific (EP, 85°W to 100°W, 2°S to 2°N) averaged u10; also shown are 10-m wind regressions (vectors) onto EP u10 (30- to 90-day band-filtered anomalies used for 2012–2023).