Moisture–Precipitation Couplings for Mesoscale Convective Systems in Tracking Data and Idealized Simulations

An increase in extreme precipitation has been well established in the transition from disorganized to organized convection, but studies conflict about how precipitation changes with the degree of clustering in organized convection. Mesoscale convective systems (MCSs) are one form of organized convection, and we examine here how precipitation intensities and various moisture–precipitation couplings change with MCS morphology, in both a multidecade tracking dataset and idealized radiative–convective equilibrium (RCE) simulations. Both in general and for a given column saturation fraction (CSF), mean and extreme precipitation robustly increase for larger MCSs in the tracking dataset but show limited changes or decrease for larger MCSs in the RCE simulation output. In an attempt to explain this discrepancy, we examine other moisture–precipitation relationships within the two datasets, including how insufficient moisture suppresses precipitation, how saturation deficit generates convective available potential energy (CAPE), how CAPE generates ascent, and how much condensate the systems contain. In both datasets, reduced CAPE production at MCS margins and higher stability from a warmer upper troposphere reduce vertical velocities within the larger MCSs. ... mehrIn both datasets, larger MCSs also contain less condensate, especially above 500 hPa. We then explain how sampling and model biases could contribute to the different responses of precipitation to MCS extent and suggest that a “dual role” of vertical velocity—in determining both condensate formation and sedimentation—should be considered in future studies of precipitation intensity from mesoscale clusters.