Abstract

Over 30 year ago, it was discovered that deep convection in idealized
simulations of radiative-convective equilibrium (RCE) using convection
permitting models could could undergo a spontaneous transition from a
random state to a highly organised state in which convection is
clustered in one part of the domain.  In the intervening period, we
have understood how this clustering can affect the tropical energy
budget and how diabatic forcing, in particular cloud-long wave
radiative forcing, can lead to clustering.  However, the details and
onset characteristic of clustering remain highly model-specific. In
this talk, we will show how the characteristics of the bistable
random/clustered states can be reproduced in a simple stochastic toy
model, and use this to derive a dimensionless parameter that predicts
whether a given model will cluster. We will then move to examining
aspects of organisation in tropical observations, showing how both
clustered and random type situations can be found on the mesoscale in
the warm pool region, and how these states relate to tropical wave
dynamics.  We will argue that understanding convection organisation on
the mesoscale is important for understanding basin-wide tropical
energy budgets.
 

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