The Regional Arctic System Model (RASM) is a fully coupled regional climate model developed by a group of U.S. institutions as a regional counterpart to the Community Earth System Model (CESM), and incorporates the Los Alamos Sea Ice Model (CICE), Parallel Ocean Program (POP), Variable Infiltration Capacity (VIC) hydrology model and the Weather Research and Forecasting (WRF) Model. The model is coupled using the same coupling infrastructure as CESM (CPL), with version 1.0 of RASM configured with a 1/12è_ ice-ocean mesh and 50km land-atmosphere grid. Development of a 1/48è_ - 25km version is also underway. During development of RASM, we encountered several obstacles in simulating high-resolution sea ice evolution in the Arctic, including a strong sea ice sensitivity relating to atmospheric aerosols and a previously undetected physical instability that arises from delayed ice-ocean-atmosphere coupling in the presence of strong mesoscale wind regimes. We detail these and other sensitivities in RASM 1.0 simulations. As part of this we highlight an improved dynamic CICE coupling that has been established in CPL based on a theoretical set of stability criteria, now also being applied to CESM in a series of tests that suggest a significant climatological difference when compared to existing CESM coupling methods. This is now being tested in combination with the latest version of CICE (Version 5), which itself is being incorporated jointly into RASM and CESM in collaboration with Los Alamos National Laboratory and the National Center for Atmospheric Research.