The energetics and magnitude of hydrometeor friction in clouds

As hydrometeors fall within or from a cloud, they reach a terminal velocity because of friction with the air through which they settle. This friction has previously been shown to result in significant vertically integrated dissipation of energy, but the nature and vertical profile of this dissipation warrant further investigation. Here, its energetic origin is discussed. It is confirmed explicitly that the dissipated energy originates from the conversion of hydrometeor potential energy during settling as suggested in an earlier study by Pauluis and Held. The magnitude of this heating is then analyzed in a cloud-resolving model simulation of tropical, aggregated convection. Maximum heating from hydrometeor friction reaches ~10 K h-1. The simulation is compared to one without hydrometeor frictional heating. For the case simulated, hydrometeor frictional heating results in a drier mean state, greater cloud cover, lessened convective mass flux, and a warmer atmosphere throughout much of the troposphere. It is suggested that the heating imparted to the atmosphere by dissipation allows the air to recover most of the energy previously expended in lofting hydrometeors