Island-scale circulations of the island of Hawaii during HaRP and the summer of 2004.

摘要

The island-scale circulations of the island of Hawaii have been studied with emphasis on the leeside from the analyses of HaRP data and the MM5/LSM simulations for the HaRP period and the summer of 2004 with improved land surface conditions. With better surface conditions in the model, the simulated thermal forcing over land is improved, which lead to better simulations of the strength of land/sea breezes and diurnal rainfall variations over the island.; The temperature maxima (mixing ratio minima) on the northwestern and southwestern leeside areas of the island are larger (smaller) for strong trade-wind cases than for weak trade-wind cases, due to more significant descent of trade-wind flow aloft there for strong trade-wind cases. The low-level westerly return flow in the wake has larger mixing ratio than other leeside areas with a maximum over the ocean near the Kona coast. The PV maxima associated with the lee vortices are found on the northwestern and southwestern leeside areas with larger PV values when trades are stronger. The wake circulations are more significant with a stronger westerly mean return flow with higher mixing ratio when trades are stronger.; The convergence between the return flow and the katabatic/offshore flow in the evening over the ocean accounts for the evening rainfall maximum along the central Kona coast. The offshore convergence is larger with a stronger upward motion when trades are stronger. As a result, more rainfall tends to occur there in the evening under strong trade-wind flow regime. The rainfall production on the Kona slope is mainly caused by the persistent orographic lifting due to the development of anabatic winds in the late afternoon.; Model sensitivity tests are also conducted for different terrain heights and for a smaller island size. The terrain height affects not only island blocking, but also the land surface thermal forcing during the diurnal cycle, which can feedback to the island-scale circulations and weather. Besides the mountain height, the island size is another factor to affect the rainfall production and distribution.