The contribution of mesoscale dynamics to the tropical anvil cloud growth rate

Abstract. Tropical anvil cloud life cycle remains a strong source of uncertainty in our understanding of the ice cloud climate feedback. From an object-oriented perspective, the anvil cloud shield of convective systems exhibits a well documented growth and a decay phase. This study focuses on the less understood processes at play in the growing phase. Radiative convective equilibrium (RCE) numerical experiments from km-scale models and a cloud tracking algorithm are used together with an analytical budget equation to decipher the various contributions to the anvil area growth rate. It is first shown that anvil growth rates in the RCE simulations are consistent with satellite observations-derived anvil properties, confirming the fitness for purpose of these simulations. Then, the Minimal ANvil growTh Analytic (MANTA) model for anvil growth rate is introduced. It links the growth rate to the detrainment of cloudy air and a simple cloud sink. The minimal model is shown to perform very well in explaining the simulated growth rates. Following a mechanism denial approach, the minimal model shows that both the convective and non convective, i.e. mesoscale, vertical motions, have to be considered to predict the correct growth rate. The growth rate is balanced by a source term due to overall detrainment, which is three to four times larger than the sink term, depending on the km-scale model used. These relative contributions are furthermore shown to be constant across the whole range of growth rates for all of the simulations.