![]() ![]() Trends in extreme rainfall are less subject to energetic constraints (Allen & Ingram, 2002) and often explained in terms of a Clausius-Clapeyron (CC) scaling of 7% increase in the moisture holding capacity of air per degree of surface warming. Although trends of storm occurrence are less clear, intensification of tropical cyclones and hurricanes is fairly well established (e.g., Emanuel, 2005 Held & Zhao, 2011 Knutson & Tuleya, 2004 Lau & Zhou, 2012 Stephens et al., 2018). Many studies have looked at changes in storm occurrence or strength with ENSO or greenhouse warming. Given their association with flooding, strong winds, and hail, it is important to understand how these systems will adjust to tropical sea surface temperature (SST) gradients during different phases of the El Niño–Southern Oscillation (ENSO), a dominant mode of climate variability. This organization can have important radiative and dynamical impacts on climate via outflow cirrus and adjustments to the vertical latent heating profile (Bouniol et al., 2016 Roca et al., 2014 Schumacher et al., 2004), while associated precipitation contributes disproportionately to the tropics-wide accumulation (Nesbitt & Zipser, 2003 Tao & Chern, 2017). We define organized convection here as meso- α systems with a cold cloud shield of infrared (IR) brightness temperature 245 K or less over an area of at least 90-km equivalent radius and with at least one convective core of IR brightness temperature 220 K or less, following Machado et al. These systems include mesoscale convective systems (MCS), mesoscale convective complexes, and superclusters and are generally characterized by strong vertical motions and intense precipitation in a localized area (Houze, 2004). Under the right conditions, individual deep convective cells can develop into larger-scale systems with long lifetimes and self-sustaining circulations. Rain intensity and amount increase for a given system size during El Niño, but a given rain amount may actually fall with higher intensity during La Niña. Finally, with collocated precipitation data, we see that rainfall attributable to convective organization jumps up to 5% with warming. 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. 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. 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. The occurrence of organized deep convection becomes more concentrated, increasing threefold in the eastern and central Pacific during El Niño and decreasing twofold outside of these regions. Here, we construct multidecade satellite climatologies of occurrence of tropical convective organization and its properties and assess changes with ENSO phase. The degree of this convective organization changes with modes of climate variability like the El Niño–Southern Oscillation (ENSO), but because organization is not represented in current climate models, a quantitative assessment of these shifts has not been possible. Convective organization has a large impact on precipitation and feeds back on larger-scale circulations in the tropics. ![]()
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