Remote sensing datasets of water vapor isotopic composition are used along with objective measures of convective aggregation to better understand the impact of convective aggregation on the atmospheric hydrologic cycle in the global tropics ($30^{\circ}$N to $30^{\circ}$S) for the period 2015-2020. When convection is unaggregated, vertical velocity profiles are top-heavy, mixing ratios increase and water vapor $\delta D$ decreases as the mean precipitation rate increases, consistent with partial hydrometeor evaporation below anvils into a relatively humid atmospheric column. Aggregated convection is associated with bottom-heavy vertical velocity profiles and a positive correlation between mixing ratio and $\delta D$, a result that is consistent with isotopic enrichment from detrainment of shallow convection near the observation level. Intermediate degrees of aggregation do not display significant variation in $\delta D$ with mixing ratio or precipitation rate. Convective aggregation provides a useful paradigm for understanding the relationships between mixing ratio and isotopic composition across a range of convective settings. The results presented here may have utility for a variety of applications including the interpretation of paleoclimate archives and the evaluation of numerical simulations of convection.

We investigate how interactive surface feedbacks impact convective clustering in a cloud resolving model coupled to a slab ocean, where the domain-mean temperature is controlled with an adaptive Q-flux. In the first investigation, with constant domain-mean surface temperature, progressively thinner ocean layers slow the onset of clustering by up to a month through surface feedback. Enhanced solar radiation in nascent dry, cloud-free areas leads to local surface warming, increasing latent heat fluxes in regions distant from convection. Once the magnitude of humidity anomalies increases, longwave emission dominates and the ocean cools rapidly under the dry patches. In this stage the surface feedback reverses and favors clustering. In the second investigation using a 1 meter mixed layer, the ocean undergoes a diurnal cycle in response to solar forcing, with a diurnal range of 2.5$^o$C in the domain mean. This leads to convective rainfall shifting from a weak broad nocturnal maximum to a sharper afternoon peak. The consequent daytime anvil shielding reduces the spatial SST variance, but the sharper rainfall peak results from more concurrent convective towers, which are distributed throughout the domain due to coldpools. This reduces the upper tropospheric water vapor variance and causes a slight delay in clustering onset, despite the reduced spatial SST variance. We find that the onset time is deterministic when strong forcing causes clustering to occur quickly (after 25 days), whereas it is highly stochastic when surface feedback weakens the diabatic forcing and delays clustering past 40 days.