Relevance to Climate Variability and Future Perspectives

In this article, the authors' research results in the past 15 years in the tropics are highlighted. Reviewed are convective-radiative processes including climate equilibrium study, tropical convective responses to radiative and microphysical processes, the diurnal cycle, cloud clustering and associated cloud-microphysical processes, precipitation efficiency, air-sea exchanges and ocean mixing processes at diurnal-to-intraseasonal scales, and coupled boundary layer and forced oceanic responses. These physical processes coupled with the tropical wave dynamics have been recognized as key mechanisms in maintaining climate variability in the tropical ocean atmosphere, as exemplified in the following scientific issues.

One of the important issues is the response of water vapor and clouds to anthropogenic changes of greenhouse gases and aerosols. While many observational analyses and GCM simulations support a positive water vapor feedback on a global scale (e.g. Zhang et al., 1996; Soden, 1997; Inamdar and Ramanathan, 1998), some studies suggest that this water vapor feedback may be overestimated or even negative (Lindzen, 1990; Lindzen et al., 2001). Being inseparable from water vapor feedback, cloud-radiative forcing is another important climate feedback process. However, the effect of cloud feedback on climate change is equally if not more controversial than water vapor feedback. Studies of cirrus (or high) clouds and associated radiative effect on tropical climate do not even agree on the sign of the cloud feedbacks (e.g. Prabhakara et al., 1993; Ramanathan and Collins, 1991; Kiehl, 1994). A synthesis of the above studies reveals that water vapor and cloud feedbacks depend on the relative areas of cloudy/moist regions versus clear/dry regions, as well as on cloud properties (type, height, optical thickness) and water vapor distribution within the clear and cloudy regimes.

Another issue is the impact on the simulations of global mean climate and climate variability through the improved representation of cloud-related processes in GCM's using the CRM simulations. Wu and Moncrieff (2001) used the CRM to identify the biases in the radiation and cloud scheme used in the GCM. Liang and Wu (2005) used the CRM to evaluate the treatment of subgrid cloud distribution in the radiation scheme; Wu and Liang (2005) used the CRM results to improve the climate simulations with the inclusion of effects of sub-grid cloud-radiation interaction. With the inclusion of the convective momentum transport (CMT) scheme derived from the CRM simulations, the tropical convection and the Hadley circulation are better-represented in GCM's (Zhang and Wu, 2003; Wu et al., 2003).

The other issue is the multiscale air-sea interaction processes associated with the

Intraseasonal Oscillation Multiscale Cloud Clusters

Intraseasonal Oscillation Multiscale Cloud Clusters

vapor/cloud radiative forcing

Tropical Atmosphere vapor/cloud radiative forcing

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