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Abstract
The Maritime Continent is a region with profound climatic importance on both local and global scales. However, correctly simulating the climate of the Maritime Continent and its interaction with other climate phenomena remains a great challenge for the modelling community.
In this thesis, a range of simulations from a new atmosphere-ocean coupled regional model have been carried out to evaluate the model’s ability to represent the mean state and variability of precipitation. Given the existence of strong surface temperature gradients and the possibility of intense air-sea interactions in this region, targeted numerical simulations are further undertaken to test if air-sea interaction at different spatio-temporal scales can improve the simulation of precipitation from sub-daily to seasonal timescales. In particular, three factors are examined: 1) the coupled model’s horizontal resolution; 2) the coupled model’s coupling frequency and 3) the resolution of SST forcing in an atmosphere only configuration.
An evaluation of the model showed dry biases in mean precipitation that decreased with resolution. However, although the diurnal evolution of across-shore propagation of winds and rainfall improved with resolution, increasing resolution led to little overall improvement in the timing of the diurnal cycle. We found that differences in the processes affecting the coastal diurnal cycle were strongly modulated by the direction of the prevailing winds relative to the coastline.
Coupling frequency sensitivity experiments showed that mean and diurnal precipitation were only affected by sub-daily coupling in localised regions where air-sea interaction is known to be strong. In particular, precipitation changes off western Sumatra were tied to two interacting processes: a wind-thermocline-SST and precipitation-barrier layer-SST feedbacks.
Finally even with large increases in SST resolution that resolve small scale ocean features, little discernible effect was found on either the long-term mean or spatio-temporal variability of precipitation and has only a small influence on daily timescale precipitation over the Maritime Continent.
The thesis suggested that high frequency air-sea coupling frequency might provide significant added value for regional models, but only in certain areas where air-sea coupling is already important. However, the added cost of increased ocean resolution may result in limited improvements for high-resolution atmospheric simulations.