More advanced models of climate systems are needed for use in present day weather
forecasting and climate projection, and there is a drive towards the use of coupled
modelling of various processes to achieve this goal. This thesis seeks to investigate
coupled ocean-atmosphere-wave modelling using the latest generation of models.
The test basin for this investigation is the Caspian Sea, where accurate representation
of the water budget is vital for prediction of water level changes, which have
historically seen trends of up to 15 cm/year.
The individual models of atmosphere, waves and ocean are first run separately to
investigate their skill in predicting observed conditions in the Caspian. These models
capture the behaviour of the basin when model results are compared with observed
wind speeds, currents, wave heights, sea-surface temperatures and precipitation.
The coupling of the ROMS ocean and WRF atmosphere models is seen to improve
sea-surface temperature prediction, but, under the Janjic Eta surface layer
scheme used here, increases evaporation above the level expected. The additional
inclusion of wave coupling from the SWAN model decreases strong winds through
wave dependent surface roughness, reduces sea-surface temperatures and increases
precipitation; all leading to better agreement with measurements. Wave prediction
is best when wave-atmosphere coupling is included, but not current-wave coupling
- this is believed to be because of the “double counting” of currents, where they
are included both implicitly in the model formulation and then explicitly through
coupling.
The final part of this study considers near-inertial oscillations, which are frequently
observed in the measured current records. The model is able to accurately
represent the observations, and sees significant near-inertial oscillations over most
of the basin. The amplitude of the oscillations in the model is found to increase
with distance from the coastline. This agrees with the mechanism of barotropic
and baroclinic waves, which are generated by the no flow condition at the coast,
controlling inertial oscillations.