资源环境科技发展态势分析平台

Convective organization has a large impact on precipitation and feeds back on larger-scale circulations in the tropics. The degree of this convective organization changes with modes of climate variability like the El Nino-Southern Oscillation (ENSO), but because organization is not represented in current climate models, a quantitative assessment of these shifts has not been possible. Here, we construct multidecade satellite climatologies of occurrence of tropical convective organization and its properties and assess changes with ENSO phase. The occurrence of organized deep convection becomes more concentrated, increasing threefold in the eastern and central Pacific during El Nino and decreasing twofold outside of these regions. Both horizontal extent of the cold cloud shield and convective depth increase in regions of positive sea surface temperature anomaly (SSTa); however, the regions of greatest convective deepening are those of large-scale ascent, rather than those of warmest SSTa. Extent decreases with SSTa at a rate of about 20 km/K, while the SSTa dependence of depth is only about 0.2 K/K. We introduce two values to describe convective changes with ENSO more succinctly: (1) an information entropy metric to quantify the clustering of convective system occurrences and (2) a growth metric to quantify deepening relative to spreading over the system lifetime. Finally, with collocated precipitation data, we see that rainfall attributable to convective organization jumps up to 5% with warming. Rain intensity and amount increase for a given system size during El Nino, but a given rain amount may actually fall with higher intensity during La Nina.

Plain Language Summary Tropical storms at an intermediate scale between individual thunderstorms and cyclones or hurricanes are not represented by climate models. As the satellite data record now spans several decades, we can use these observations to understand how large storms change during El Nino periods. Here, we find that warmer waters in the central and eastern Pacific during El Nino cause a dramatic increase in storm occurrence. Storms are more likely to occur near to other storms and to become larger in both the vertical and horizontal. Changes to large-scale winds are more influential on these structural factors than locally warmer ocean water. The hydrological impact of these storms is also important because they bring the majority of precipitation in some regions. We see that a storm of a certain extent brings larger volume and intensity of rain during El Nino. But a certain rain volume may actually fall with greater intensity during La Nino.