Abstract 137

Abstract ID: 137

Impacts of humidity initialization on MJO prediction: a study in an operational Sub-seasonal to seasonal system

Lead Author: Qing Bao
CAS-IAP, China

Keywords: MJO prediction, Initialization, Humidity, CAS-IAP, FGOALS-f2

Abstract: An operational sub-seasonal to seasonal prediction (S2S) system was used to investigate the impacts of humidity initialization on Madden-Julian Oscillation (MJO) prediction. Based on the recent three-year real-time forcing datasets, two kinds of ensemble numerical experiments are designed using the 2nd finite-volume version of the Flexible Global Ocean-Atmosphere-Land System model (FGOALS-f2) sub-seasonal to seasonal (S2S) prediction system. In the control experiment, there was no humidity initialization, while in the sensitivity experiment, three-dimensional humidity was initialed. The initialization method used nudging technology with the time-varying weighting factor schemes. The multivariate MJO index was used to evaluate the MJO prediction skill, and evaluation results showed that the MJO prediction skill was improved by more than five days and reached up to 23 days in the sensitivity experiments under the real-time forcing. Then, the possible physical linkage between the initialization of humidity and the MJO prediction skill was given. A significant improvement can be accomplished during the second and third phases of MJO perturbation, which exhibits a robust convective humidity coupling behavior. The further analysis illustrated that the improvement of MJO prediction skill was highly related to the realistic horizontal and vertical structure of moisture, which induced the improvement of the corresponding circulations and Outgoing Longwave Radiation (OLR). This study suggested that, as for the S2S prediction, accurate initialization of humidity helps improve the MJO prediction.

Qing Bao, Lingjun Zeng, Yangke Liu, Bian He, Xiaofei Wu, Jing Yang, Yimin Liu and Guoxiong Wu