STORM TRACKS IN A HIGH-RESOLUTION GCM WITH DOUBLED CARBON-DIOXIDE

Transient eddy activity has been diagnosed for the winter season of tw o ten-year equilibrium GCM integrations carried out at the UK Meteorol ogical Office, one with present-day levels of carbon dioxide concentra tion (control) and one with doubled carbon dioxide (2CO2). On synoptic timescales, indicators of storm-track activity such as eddy kinetic e nergy are shifted northwards and intensified downstream in the 2CO2 ex periment relative to the control. This effect is particularly marked f or the Atlantic storm track. These patterns correspond closely to chan ges in relevant diagnostics of the time mean, such as the Eady growth rate and the diabatic heating. In the latter, the downstream intensifi cation is effected by a decrease in the sensible heating and an increa se in the latent heating in a warmer, moister atmosphere. Changes in t he jet structure are consistent with changes in baroclinicity and eddy forcing. The total zonal-mean poleward energy transport is only sligh tly different between the two experiments. However, the component of t his transport due to transient eddies has a different character when t he carbon dioxide is doubled. In particular, the moist contribution to the transient energy flux is enhanced.