RADIATION CLIMATOLOGY THROUGH THE TRADE-WIND INVERSION ON THE LEE SLOPE OF HALEAKALA, MAUI, HAWAII

Abstract

Two years of global and net radiation measurements in Hawaii were used to analyze annual and diurnal radiation patterns between 950 and 3000 m on a tropical island mountain. This layer includes the usual altitude of a subsidence inversion over the islands. Maximum average monthly depletion of solar irradiance ranged from between 38% in December to 52% in April at 1650 m, just below the average level of the inversion. It reached a minimum of 6% in May at 3000 m, well above the average inversion level. Climatological average values strongly reflect the diurnal weather pattern on the mountain. Attenuation of solar irradiance peaked near 1300 to 1400 hours in summer and later, near 1500 to 1600 hours, in winter. The coefficient of variation in hourly solar irradiance values was greatest (50% to 60%) at 1650 m in the afternoon in summer. In winter, the coefficient of variation was nearly equal for sites between 950 and 2130 m, ranging from 40% to 60%. Net radiation followed the solar irradiance pattern during daylight hours. At night longwave loss increased with elevation; for example, from 25 W m^-2 at 950 m to 74 W m^-2 at 3000 m on average at midnight in June. Examples of specific synoptic weather events are given to illustrate the source of variability in the radiation climate and to show associated changes in other climatological variables.