Cloud radiative interactions and their effects on oceanic tropical deep convection evolution and organization

Cloud radiative heating plays a crucial role in the diurnal cycle of tropical oceanic convection and influences convective organization. Here, we investigate its impact on the mesoscale convective lifecycle and the diurnal cycle of precipitation. To do so, the Weather Research and Forecasting (WRF) model is run over the East Pacific at 3 km resolution and forced by European Center for Medium Range Weather Forecasting (ECMWF) ERA5 reanalysis with cloud radiation interactions (CRI) disabled by making (a) clouds entirely transparent to radiation, (b) transparent to only the longwave, and (c) transparent to only the shortwave. First, the domain mean diurnal cycle range and phase are preserved when CRIs are disabled, but disabling the longwave reduces the domain average precipitation. The effects of CRIs on precipitation intensity are more pronounced for larger mesoscale convective systems (MCSs) than for smaller isolated deep convection (IDC). As for the domain mean, disabling the longwave reduces the precipitation intensity of both MCSs and isolated deep convection, while disabling the shortwave substantially increases the precipitation intensity of daytime MCSs but does little to affect isolated deep convection. The effect of CRIs on precipitation intensity can be directly linked to the effects of the radiation on the stability. Moreover, evidence suggests that disabling the longwave lengthens the time it takes for isolated deep convection to grow upscale into MCSs in the overnight hours, underscoring the importance of the longwave CRIs for deep convective organization, consistent with results from idealized modeling studies. Finally, disabling the shortwave interactions increases the percentage of MCSs occurring with respect to the isolated systems, and MCSs become larger and longer-lived. This result suggests that the shortwave is also important for deep convective organization, playing a critical role in discouraging the organization of deep convection in the daylight hours.