Fig. 7: Extratropical response to SPCZ precipitation and associated Rossby wave source and waveflux activity.

Step response function (computed from the “linear response theory model”) for anomalous 200-hPa geopotential height (m), forced by an area-averaged precipitation anomaly over the SPCZ box, during austral summer of (a) 1979–1998 and (b) 1999–2018. The correlation between the Rossby wave source anomaly induced by the vorticity advection term and the area-averaged precipitation over the SPCZ box for the austral summer of (c) 1979–1998 and (d) 1999–2018 (shaded, values below 99% confidence interval are masked). Wave activity flux vectors (vectors, in m² s⁻²) computed from the step response function during the austral summer of (c) 1979–1998 and (d) 1999–2018 are overlaid. Thick blue lines show the westerly jet (contours of 22 ms⁻¹ zonal wind). The SPCZ is marked by a magenta box.