Review on the study of decadal prediction and coupled data assimilation

Decadal prediction has been a rapidly developing new field in the research on climate change these years. The first and foremost procedure in decadal predictions is initialization, which aims to provide initial conditions which include the observed internal climate variabilities for decadal predictions. One of the biggest challenges in decadal predictions is the design of a high-quality and time-saving initialization approach. A commonly-used kind of initialization approach is coupled data assimilation (i. e., assimilate observations under the framework of the coupled model). During decadal predictions,an initial shock problem often turns up due to model bias and the limitation of initialization method. Currently, the modeling groups around the world achieve high decadal prediction skills of sea surface temperature (SST) in the North Atlantic, tropical eastern and western Pacific and Indian Ocean, but relatively poor decadal prediction skills in forecasting global mean surface air temperature and North Pacific SST. In this paper,we provide a detailed review of the current status of the initialization approaches and decadal predictions. The existing problems and future developments and challenges are also discussed.