An assessment of radiative impacts of CO2 on baroclinic instability using idealized life cycles

Abstract

AbstractInteraction between CO2 and atmospheric radiation has a significant part in changing horizontal and vertical temperature distributions, through which it can affect the midlatitude atmospheric dynamics. Baroclinic instability, which is the energy source of large‐scale eddy formation in midlatitudes, depends on meridional and vertical eddy fluxes of heat. While several studies have been devoted to the impact of CO2 concentration present in the atmosphere on baroclinic eddies in climate time‐scales, the current work aims to determine the corresponding impact over a period of 10 to 20 days relevant to the duration of baroclinic life cycles when the flow is deterministically predictable. To this end, the radiative parametrization scheme called RRTMG (Rapid Radiative Transfer Model for General Circulation Models) has been coupled with the Diabatic Contour‐Advective Semi‐Lagrangian (DCASL) dynamical core. Except for parametrization of radiation as well as surface processes to represent radiative interaction with the surface, no other physics parametrizations are included in the model. The idealized life‐cycle experiments are carried out for both the predominantly anticyclonic (LC1) and cyclonic (LC2) Rossby wave breaking with the same initialization but five different CO2 concentrations (0, 250, 500, 750 and 1,000 ppmv). The impacts of different CO2 concentrations on eddy growth, mean flow and eddy–mean flow interaction are discussed. Results show that the presence of CO2 has a damping effect on instability in the baroclinic growth stage, amounting to about 7% and 4% reduction in the peak value of domain area‐average eddy kinetic energy for LC1 and LC2, respectively. In addition, increase in CO2 concentration has a small negative impact on the growth rate, vertical eddy propagation and jet intensification.