Influence of the trade-wind inversion on the climate of a leeward mountain slope in Hawaii

The climate of oceanic islands in the trade-wind belts is strongly influenced by the persistent subsidence inversion characteristic of the regions. In the middle and upper elevations of high volcanic peaks in Hawaii, climate is directly affected by the presence and movement of the inversion. The natural vegetation and wildlife of these areas are vulnerable to long-term shifts in the inversion height that may accompany global climate change. Better understanding of the climatic effects of the inversion will allow prediction of global-warming-induced changes in tropical mountain climate. To evaluate the influence of the inversion on the present climate of the mountain, solar radiation, net radiation, air temperature, humidity, and wind measurements were taken along a transect on the leeward slope of Haleakala, Maui. Much of the diurnal and annual variability at a given location is related to proximity to the inversion level, where moist surface air grades rapidly into dry upper air. The diurnal cycle of upslope and downslope winds on the mountain is evident in all measurements. Measurements indicate that the climate of Haleakala can be described with reference to 4 zones: a marine zone, below about 1200 m, of moist well-mixed air in contact with the oceanic moisture source; a fog zone found approximately between 1200 and 1800 m, where the cloud layer is frequently in contact with the surface; a transitional zone, from about 1800 to 2400 m, with a highly variable climate; and an arid zone, above 2400 m, usually above the inversion where air is extremely dry due to its isolation from the oceanic moisture source.