Exploratory High-Resolution Climate Simulations using the Community Atmosphere Model (CAM)

Abstract

Extended, high-resolution (0.23° latitude × 0.31° longitude) simulations with Community Atmosphere Model versions 4 and 5 (CAM4 and CAM5) are examined and compared with results from climate simulations conducted at a more typical resolution of 0.9° latitude × 1.25° longitude. Overall, the simulated climate of the high-resolution experiments is not dramatically better than that of their low-resolution counterparts. Improvements appear primarily where topographic effects may be playing a role, including a substantially improved summertime Indian monsoon simulation in CAM4 at high resolution. Significant sensitivity to resolution is found in simulated precipitation over the southeast United States during winter. Some aspects of the simulated seasonal mean precipitation deteriorate notably at high resolution. Prominent among these is an exacerbated Pacific “double ITCZ” bias in both models. Nevertheless, while large-scale seasonal means are not dramatically better at high resolution, realistic tropical cyclone (TC) distributions are obtained. Some skill in reproducing interannual variability in TC statistics also appears.

The resolution sensitivity of the South Asian monsoon and Indo-Pacific in a global 0.35° AGCM

“…In each case, very little resolution sensitivity was seen, consistent with other resolution sensitivity studies (Bacmeister et al 2014). …”

“…The increase in precipitation over India in the MetUM is consistent with the resolution sensitivity of the annual precipitation range over India in the CMIP3 models (Kim et al 2008). In other resolution sensitivity studies using individual GCMs, orographic rain bands over India tend to become more well defined, but the sign of precipitation changes over India are highly variable (Sperber et al 1994;Stephenson et al 1998;Delworth et al 2012;Sabin et al 2013;Bacmeister et al 2014). This is also true within MetUM configurations.…”

“…Both of these reductions are likely due to a combination of increased precipitation windward of orography decreasing moisture in the flow and decreased circulation strength due to the decreased latent heating associated with the reduced precipitation over the northern Maritime Continent. Similar shifts in precipitation over the Maritime Continent are seen in other GCMs (Bacmeister et al 2014), perhaps suggesting that many GCMs are sensitive to increased resolution of orography in the Maritime Continent region.…”

“…The Somali Jet, due to its reliance on the orography in east Africa, often shows resolution improvements in speed and position (Sperber et al 1994;Stephenson et al 1998;Sabin et al 2013). Studies in multiple versions of the MetUM Johnson et al in preparation) as well as other GCMs (Sabin et al 2013;Bacmeister et al 2014) show similar precipitation changes over the Maritime Continent. The increase in precipitation over India in the MetUM is consistent with the resolution sensitivity of the annual precipitation range over India in the CMIP3 models (Kim et al 2008).…”

The heated condensation framework as a convective trigger in the NCEP Climate Forecast System version 2

“…Recent advancements in high performance computing represent an exciting opportunity for global climate model development, pushing the limits of representing clouds and convection in a global atmospheric model [Chen and Lin, 2011;Dirmeyer et al, 2012;Manganello et al, 2012;Murakami et al, 2012;Bacmeister et al, 2014;Wehner et al, 2014]. As a consequence, atmospheric moist convection can now be represented in sophisticated schemes such as global cloud-resolving models and super parameterization schemes [Grabowski, 2001;Khairoutdinov and Randall, 2001;Randall et al, 2003;Tomita and Satoh, 2004;Satoh et al, 2008Satoh et al, , 2014Stan et al, 2010].…”