A Three-Dimensional Simulation of Airflow and Orographic Rain over the Island of Hawaii

Abstract

A three-dimensional mesoscale numerical model is presented, designed with the capability of simulating the airflow and orographically-induced rain in the presence of steep irregular terrain. The model utilizes a fourth-order accurate version of Arakawa's potential enstrophy and total energy conserving scheme to improve the simulation of nonlinear aspects of the airflow over steep topography, along with an adiabatic reference atmosphere to reduce the effects of orographic truncation errors. The precipitation processes are represented by large-scale condensation.The model is applied to the island of Hawaii. The results of a 24-h simulation indicate the model is generally successful in reproducing leeward eddies depicted in the composite surface airflow patterns.A nondimensional analysis of vortex parameters suggests that the simulated vortex pattern is an atmospheric analog of the Karman vortex street and compares favorably with an observed case of Hawaii vortices. Spatial distribution of simulated rainfall is also generally in good agreement with observations. However, the lack of precipitation in the lowland along the windward as well as leeward coast is apparent.The excess rainfall over the southern peninsula suggests the need for an finer grid mesh to improve representation of the effects of subgrid-scale mountain forcing. An application of the model to regional climate modeling through the use of large-scale objective analyses is also discussed.

The 0.125 degree finite‐volume general circulation model on the NASA Columbia supercomputer: Preliminary simulations of mesoscale vortices

“…However, it has been found that other factors such as changes in upstream wind, boundary layer frictions, complexity of terrains, Coriolis force, and diurnal heating could also change the final appearance of the vortices/wakes [e.g., Reisner and Smolarkiewicz , 1994]. Due to the limited computing resources, the above effects were studied separately with limited domain sizes and short integration periods (12–24 hours) [e.g., Ueyoshi and Han , 1991].…”

Numerical Simulation of the Maui Vortex in the Trade Winds

“…Numerical simulations of Hawaii's wake by Smolarkiewicz et al (1988) and Ueyoshi and Han (1991) both predict shedding eddies behind Hawaii. In the latter simulation, the Froude number upstream of Hawaii, calculated from the composite wind and temperature profiles fixed in time and space, was Fr<0.4.…”

“…It is suggested that the above discrepancy between observations and simulations may be due to the simplified topography included in the models. One problem with the simulation by Ueyoshi and Han (1991) is that the island of Maui was not included in the model topography, which would have further accelerated the trade wind moving through Alenuihaha Channel between Maui and Hawaii. We speculate that this exclusion of Maui may have had a significant influence on simulated vortex shedding behind Hawaii because the accelerated northeasterly trade wind through the Channel might have deterred vortex shedding in a mechanism similar to that in the Maui Vortex case.…”

“…On the other hand, a variety of attempts has been made to model air flow over the islands of Hawaii and Oahu (Lavoie, 1974;Nickerson, 1979;Smolarkiewicz et al, 1988;Rasmussen et al, 1989;Ueyoshi and Han, 1991;Rasmussen and Smolarkiewicz, 1993;Reisnerx and Smolarkiewicz, 1994). These works have contributed significantly to our understanding of the effects of topographic barriers on air flow structure and precipitation over and around these islands by filling the spatial as well as temporal gaps in observational data analyses.…”

Effects of Trade-Wind Strength and Direction on the Leeside Circulations and Rainfall of the Island of Hawaii

“…In the past, many numerical studies for the island of Hawaii have been conducted (Nickerson 1979;Fett and Bury, 1981;Smolarkiewicz et al 1988;Rasmussen et al 1989;Ueyoshi and Han 1991;Reisner and Smolarkiewicz 1994;and others); however, the diurnal thermal forcing from the land surface was crudely estimated in these studies. Feng and Chen (2001) used the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5), version 1, to successfully simulate the nocturnal regime on the windward side of the island of Hawaii with the land surface specified as tropical rain forest over the entire island.…”