Preliminary Evaluations of ENSO-Related Cloud and Water Vapor Feedbacks in FGOALS

Abstract

Previous studies have revealed two common biases in the simulation of the response of cloud and water vapor to El Niño warming in current models: an underestimation of the negative shortwave cloud radiative forcing (SWCRF) feedback and an overestimation of the positive water vapor feedback. In the present study, the performance of the FGOALS models in representing these feedbacks was evaluated. The major characteristics of the SWCRF and water vapor feedbacks over the tropical Pacific regions in response to ENSO forcing are generally well captured by the two FGOALS models. Specifically, FGOAS-g2.0 provides a more realistic simulation of SWCRF feedback than FGOALS-s2.0, particularly in the historical run. The bias of the SWCRF feedback in the FGOALS- s2.0 historical run can be attributed to two factors: the small bias in the FGOALS-s2.0 AMIP run is carried into its coupled counterpart and further amplified, and the excessive cold tongue in the FGOALS-s2.0 historical is another key factor behind the SWCRF feedback bias. Both FGOALS models overestimated the positive water vapor feedback, especially in their AMIP runs. This bias can be traced back to the overestimation of the response of water vapor in the upper troposphere.