Available potential energy of the three-dimensional mean state of the atmosphere and the thermodynamic potential for warm conveyor belts

Abstract. Much of our understanding of the atmospheric circulation comes from relationships between aspects of the circula- tion and the mean state of the atmosphere. In particular, the concept of mean available potential energy (MAPE) has been used previously to relate the strength of the extratropical storm tracks to the zonal-mean temperature and humidity distributions. Here, we calculate for the first time the MAPE of the three-dimensional time-mean state of the atmosphere including the effects of latent heating. We further calculate a local MAPE by restricting the domain to an assumed eddy size, and we partition this local MAPE into convective and nonconvective components. Local nonconvective MAPE has a similar spatial pattern to the Eady growth rate, while local convective MAPE has some similarities in spatial pattern to a high percentile of instanta- neous convective available potential energy. Furthermore, the maximum potential ascent associated with nonconvective local MAPE is strongly related to the frequency of warm conveyor belts (WCBs) which are ascending air streams in extratropical cyclones with large impacts on weather. This maximum potential ascent can be calculated based only on mean temperature and humidity, and it also skillfully identifies the necessary conditions for WCBs at a given location on a specific day. These advances in the use of MAPE are expected to be helpful to connect changes in the mean state of the atmosphere, such as under global warming, to changes in important aspects of the extratropical circulation.