Development of the Regional Arctic System Model (RASM): Near-Surface Atmospheric Climate Sensitivity

Abstract

The near-surface climate, including the atmosphere, ocean, sea ice, and land state and fluxes, in the initial version of the Regional Arctic System Model (RASM) are presented. The sensitivity of the RASM near-surface climate to changes in atmosphere, ocean, and sea ice parameters and physics is evaluated in four simulations. The near-surface atmospheric circulation is well simulated in all four RASM simulations but biases in surface temperature are caused by biases in downward surface radiative fluxes. Errors in radiative fluxes are due to biases in simulated clouds with different versions of RASM simulating either too much or too little cloud radiative impact over open ocean regions and all versions simulating too little cloud radiative impact over land areas. Cold surface temperature biases in the central Arctic in winter are likely due to too few or too radiatively thin clouds. The precipitation simulated by RASM is sensitive to changes in evaporation that were linked to sea surface temperature biases. Future work will explore changes in model microphysics aimed at minimizing the cloud and radiation biases identified in this work.

Effects of Model Resolution and Ocean Mixing on Forced Ice‐Ocean Physical and Biogeochemical Simulations Using Global and Regional System Models

“…The RASM sea ice and ocean physical model results have been validated in various previous studies (Cassano et al, ; DuVivier et al, ; Hamman et al, ; Roberts et al, ). However, since the marine ecosystem model results are significantly affected by the simulated sea ice and ocean physical environments, we also include physical model validations and comparisons.…”

“…In this study, we use the ice‐ocean model components of RASM in its native regional domain grid (e.g., Cassano et al, ; Hamman et al, ; Roberts et al, ) and in a global domain grid from CESM. The RASM domain (Figure ) covers the entire Northern Hemisphere marine cryosphere, major oceanic inflow and outflow pathways, with optimal extension into the North Pacific and Atlantic oceans to account for the origin and passage of cyclones over marginal ice zones and into the Arctic.…”

Adaptation of NEMO-LIM3 model for multigrid high resolution Arctic simulation

“…Multi-purpose highresolution models are often based on regional or nested configurations. For example, the nested Arctic-FVCOM model [8] reproduces shallow-water transport, the regional NEMObased configuration RASM [9] provides detailed atmospheric circulation, and the CREG project [10] produces detailed short-term ocean predictions for hazard warning.…”

Reply to Referee 1’s comments

“…The late 20th and early 21st centuries have been marked by dramatic changes in the northern high latitudes. Most notable was the rapid decline in sea ice cover (e.g., Serreze et al, 2007;Comiso and Hall, 2014), that accelerated during the first decade of the 21st century (e.g., Comiso et al, 2008;Stroeve et al, 2012;Swart et al, 2015). Since then, sea ice extent partially recovered in 2013-2015 (Swart et al, 2015), followed by further declines in 2016(http: //nsidc.org/arcticseaicenews, last access: 8 November 2018.…”

“…RASM includes version 3.2 of the Advanced Research WRF (Skamarock et al, 2008) modified for use in the Arctic (Cassano et al, , 2017. In order to successfully couple within RASM, WRF's boundary layer, surface layer, and radiation parameterizations have been adapted.…”