A GLOBAL RADIATIVE-CONVECTIVE FEEDBACK

We have investigated the sensitivity of the intensity of convective ac tivity and atmospheric radiative cooling to radiatively thick upper-tr opospheric clouds using a new version of the Colorado State University General Circulation Model. The model includes a bulk cloud microphysi cs scheme to predict the formation of cloud water, cloud ice, rain, an d snow. The cloud optical properties are interactive and dependent upo n the cloud water and cloud ice paths. We find that the formation of a persistent upper tropospheric cloud ice shield leads to decreased atm ospheric radiative cooling and increased static stability. Convective activity is then strongly suppressed. In this way, upper-tropospheric clouds act as regulators of the global hydrologic cycle, and provide a negative feedback between atmospheric radiative cooling and convectiv e activity.