#A09 Orographic Rainfall Biases in the ACME/CESM models

Abstract

We will examine serious and long-standing excessive precipitation biases that exist over orography and in particular tropical orography.  These are among the largest precipitation biases present in CESM/ACME.  In addition to their direct negative impact on climate skill scores, excessive precipitation biases over mountains may have significant remote impacts. We show evidence that dry biases over the Amazon basin in CESM/ACME  are connected to the strong positive bias in precipitation over the Andes and that excessive precipitation over Colorado can lead to reduced moisture and downstream suppression of Summertime mesoscale convective systems. .  We will present analyses of this bias in perturbed climate simulations as well as in CAPT forecast runs. In addition we will show detailed process diagnostics accumulated during time-steps of the spectral element dynamical core.