Photon path length distributions and broadband heating rate profiles

Broadband heating directly drives the global atmospheric circulation and its vertical profiles strongly depend upon cloud three-dimensional (3D) structures. We used a 3D Monte Carlo radiative transfer model with CRM cloud fields to simulate broadband heating rate profiles (BBHRP) and photon path length distribution and to study the internal relationship between them and the cloud 3D effects on BBHRP. Analysis of principal components (PCs) of BBHRP and the first four moments of photon path length distribution show that these moments and total cloud optical depth are effective factors in defining BBHRP. Further, a statistical fitting between the PCs of BBHRP and the path length moments, using a two-layer neural network, provides a quantitative representation of the linkages, demonstrating the utility of photon path length distribution in estimating cloud 3D effects and evaluating BBHRP.