P32 Revisions to RRTMG cloud radiative transfer in HWRF

Henderson, John, Michael Iacono, Atmospheric and Environmental Research, and Mrinal Biswas, Developmental Testbed Center and National Center for Atmospheric Research

The main objective of this DTC Visitor Program project was to implement and test revisions to HWRF related to the treatment of cloud radiative transfer in the RRTMG radiation code developed at AER. The default assumption in RRTMG related to the radiative coupling of clouds and the treatment of vertical cloud overlap, known as maximum-random (MR), was compared to an improved exponential-random (ER) method that relaxes the strict assumption in MR of maximum overlap through adjacent cloud layers by allowing the vertical correlation of clouds to transition exponentially from maximum to random with distance through the cloud. Preliminary simulations designed to test the effect of using ER on Tropical Cyclones were completed in conjunction with DTC for multiple forecast cycles of Atlantic Hurricanes Gonzalo (2014) and Joaquin (2015), and Pacific Hurricane Dolores (2015).

Diagnostic HWRF radiative heating rate profiles illustrated details of the changes to the inner structure of tropical cyclones related to the use of the ER technique. These radiative heating changes in turn modify the atmospheric state both within the TC and in the surrounding environment over time.