A New Explicit and Computationally Efficient Sub-grid Convective Initiation Scheme

It is well documented that most convective parameterizations produce too frequent and less intense precipitation events, and often use convective closure schemes that depend on moisture convergence or convective instability derived from lifting a parcel from a specified level. Here we implement a new convective triggering mechanism in the Community Earth System Model (CESM) that directly makes use of sub-grid, plant functional type (pft) level potential temperature information to explicitly represent convective initiation and intensity. This is done by calculating a convective initiation threshold derived from temperature and humidity profiles (referred to as the buoyant mixing temperature, θBM) following the Heated Condensation Framework (HCF) introduced by Tawfik and Dirmeyer (2014) at the atmospheric grid level. This threshold, θBM, is then passed to each pft-level where convection is triggered when θ2m is greater than or equal to θBM and passed back to the convective scheme to scale the cloud base mass flux. Preliminary results show improvements in the frequency and intensity distribution of precipitation globally and regionally, especially over semi-arid regions.