Monsoons and tropical rainfall in the MetUM general circulation model
Dr. Gill Martin
Met Office Hadley Centre, UK
Despite considerable efforts worldwide to improve model simulations of monsoon systems, significant biases still remain in climatological seasonal mean rainfall distribution and circulation strength, timing of onset, and inter-annual and intra-seasonal variations. Generally, models often fail to reproduce the observed spatial and temporal distributions of tropical precipitation. The need for improved understanding of how a warming climate may change precipitation variability and extremes has focused model developers' attention on the inability of convection parameterizations to represent the observed range of deep convective processes. Under particular scrutiny are the consequences of poorly simulated sub-daily, grid-point precipitation variability on rainfall distributions at longer (e.g., daily, seasonal, decadal) timescales and larger spatial scales.
The Met Office benefits from a unified modelling strategy where essentially the same modelling system is used across timescales ranging from days to centuries. This allows errors in the monsoon simulation to be examined as they develop, and the relationship between problems with short-timescale variability and longer-term systematic biases to be established. Various areas of study are being pursued at the Met Office, in conjunction with our many collaborators in the UK and worldwide. These include: analysis of South Asian and East Asian monsoon simulations in various global configurations and resolutions of the MetUM, the representation of synoptic-scale systems such as monsoon depressions, and the temporal and spatial intermittency of sub-daily precipitation. Examples of some of this research are given in this talk.