Effects of a new radiative transfer model on tropical cyclones and surface temperature

In June 2009, a major upgrade was made to the Canadian global NWP model, GEM. This upgrade involved moving the top of the model to 0.1hPa (from 10hPa), increasing the number of vertical levels to 80 and new physical parameterizations, namely a new radiative transfer scheme.

This new CKD based radiative transfer scheme was developed at the Canadian Centre for Climate Modelling and Analysis CCCma for the GCM4. For its implementation in GEM, many inputs to the radiative transfer scheme were updated. Namely the ozone climatology, the cloud optical properties, the partition of the total condensate into liquid and solid and the concentration of trace gases.

We will show that the new radiative transfer scheme significantly reduced a cold bias in the tropical upper tropospheric temperature which has led to a significant reduction in tropical cyclone false alarms. Furthermore, we will also analyze the impact on surface temperature of the new scheme (reduction of cold bias). We will examine the surface temperature errors and establish some links to errors in radiative fluxes and/or clouds.