Observed Changes in Organized Tropical Deep Convection as Identified by Cloud Regime Analysis

The fact that organized deep convection provides half the tropical rainfall despite its comparatively low occurrence is a striking example of its importance in the climate system. However, how organized deep convection will change in a warming climate remains an open question, one that cannot be convincingly answered by climate models due to their inability to produce such organization. As a consequence, we will need to rely on observations to infer its behavior under climate change.

The International Satellite Cloud Climatology Project enables the creation of tropical cloud regimes, which allows us to identify organized deep convection on scales of a few hundred kilometers. This provides an avenue for investigating how organized deep convection has changed in the past twenty-five years. Previous work has identified an increase in the occurrence of the cloud regime associated with organized deep convection, assuming that the regime structure does not change in time. We extend this work by investigating the structural variation within this regime over the ocean to dissect the internal changes in organized deep convection.

We find a decline in the mean cloud top pressure of the organized deep convective regime. This largely results from an increase in the population of deep convective clouds within the regime. Our results support the Fixed Anvil Temperature hypothesis, which predicts an increase in cloud top height in a warming climate. Furthermore, the geographical distribution of this increase agrees with observed trends in precipitation, thereby identifying organized deep convection as an important source of precipitation changes. We conclude that organized deep convection has not only become more frequent but also changed structurally. This implies we will witness more organized deep convection that gives rise to more intense rainfall in a warming climate.