Diurnal Variation of Surface Thermodynamic Fields on the Island of Hawaii

Abstract

The diurnal variation in the surface thermodynamic fields over the island of Hawaii is presented for the first time. The diurnal ranges in temperature and dewpoint vary considerably over the island. In addition to the diurnal heating cycle, the thermodynamic fields over the island are also related to orography, airflow, and distributions of clouds and rains. On the windward side, the onset of upslope (downslope) flow in the morning (evening) is closely related to the thermal contrasts between the slope surface and the upstream air. After sunrise around 0600 HST, the onset of upslope flow occurs at approximately 0730 HST on the upper slopes where the virtual temperature first becomes warmer than the environment. In the early evening, the onset of downslope flow occurs just before sunset about 1900 HST in the windward lowland where the virtual temperature first drops below the environmental value. These results suggest that the diurnal evolution of the surface flow on the windward side is closely controlled by the evolution of the surface thermodynamic fields.