Surface energy balance studies in Australia's seasonally wet tropics: results from AMEX Phase I and II

The diurnal variation of the surface energy balance of savannah grassland on Cape York during Phase I and Phase II of the Australian Monsoon Experiment is presented. Each of the components of the energy balance was measured directly, with the exception of sensible heal transfer from the surface which was determined as a residual. The results indicate that available surface energy for partitioning into the convective fluxes is much less during the late dry season than during the wet season, and that the difference is due mainly to enhanced surface albedo, enhanced surface long-wave emission and increased soil heat flux during the pre-monsoon period. Despite reduced available surface energy, daytime sensible heat inputs to the lower atmosphere are generally greater during the dry season than during the wet; conversely, daytime evaporative heat inputs to the lower atmosphere are far larger during the wet season. These seasonal energetic characteristics are reflected in the more standard meteorological parameters, with the pre-monsoon period having much higher daytime surface and air temperatures than the monsoon period, and a lower atmospheric water vapour content.