This study concentrates on a numerical case study of a Tropical Cyclone Olivia, one of the strongest cyclones to have crossed the Australian coastline in recent decades. Olivia reached a Category 4 storm with maximum wind gusts up to 250 km h-1 24-h prior to landfall over the North-West Cape region of Western Australia during the evening of 10th April, 1996. As part of the Project for the Intercomparison of Land-surface Parameterisation Schemes (PILPS) Phase 4b, we investigate the impact of several land-surface parameterisation schemes when coupled to the same atmospheric host mesoscale model. The aim of Phase 4b is to investigate the importance of land-surface-atmospheric feedbacks on the short-term forecasts (48-h) and to detail the extent to which the complexity of a land-surface parameterisation scheme may affect the accuracy of the forecast.
The numerical model used is the Australia Bureau of Meteorology Limited Area Prediction System (LAPS, Puri et al., 1998) to which 4 land-surface parameterisation schemes are explicitly coupled; (a) the Manabe (1969) bucket scheme, (b) ISBA (Noilhan and Planton, 1989), (c) BATS (Dickinson et al., 1993) and (d) BASE (Desborough, 1997). These 4 schemes vary in complexity from the simple bucket which has no explicit canopy representation and single level of soil moisture to BASE which explicitly represents the effects of canopy-deep soil- surface-atmospheric interactions using a multi-layer mosaic approach.
Two 48-h simulations are performed. The first (12 UTC 8th April-12 UTC 10th April) is designed to investigate the impact of land-surface schemes on the track and intensity change of Olivia prior to land fall, whilst the second simulation (00 UTC 10th April-00 UTC 12th April) investigates the impact of land-surface schemes in the decay and structure of Olivia after landfall has occurred. This study answers two questions:
1. Does the complexity of the land surface parameterisation scheme have an impact on the accuracy of simulating a landfalling tropical cyclone ?
2. What are the important land-surface-atmospheric interactions which occur during landfall and decay of a tropical cyclone ?