Abstract/Summary

Attributing sources of tropical cyclogenesis (TCG) bias to large-scale circulation in global circulation models is challenging. Here, we propose the use of empirical orthogonal functions as an approach to understand model bias of TCG. Two leading modes of large-scale wind circulations in the West Pacific can explain the TCG frequency and location in both climate reanalysis and the MetUM model. In the reanalysis, the two modes distinguish the summer monsoon trough position and the strength of the north Pacific subtropical high. However, in the model, the wind circulations are biased towards the positive phase of simulated modes thus overestimating TCG in the entire Main Development Region. This bias is further related to the north-eastward shifted monsoon trough and a weakened subtropical high, and overly strong tropics-subtropics connections. This approach could be deployed more widely to other basins and models to diagnose the causes of TCG bias.