Verification of the approximated formula for the sensitivity of precipitation to RSST. Scatterplot of Precip_clim (monthly GPCP precipitation; units: mm day⁻¹) to RSST_clim (monthly OISST, regridded on GPCP grid; units: K) in the equatorial Pacific (5°N–5°S, 120°E–80°W). The default fit in blue is P(RSST) = 2e^0.56RSST, the factor 0.56 inspired by the Tippett et al. cyclogenesis index. Tests using other exponential forms, e.g., P(RSST) = 2e^0.4RSST (green) or P(RSST) = 2e^{0.8(RSST−0.5)} (red) show that the default approximation is qualitatively reasonable. Figures 2c and 2d redone with these other forms lead to qualitatively similar results, with delayed term contribution increasing if the factor in the exponential increases, as it gives more weight to regions with higher climatological RSST (vice versa if it decreases).

Citation: Journal of Climate 37, 9; 10.1175/JCLI-D-23-0127.1