Close Window

Univ. of Hawaii: "High resolution simulations of high wind and heavy rainfall events"

Final Report


The objectives of this project are to compile the surface parameters for the nested mesoscale regional spectral model, to analyze the data collected during the aerosonde (unmanned aircraft) experiment for model verifications and to collect data for high wind or heavy rainfall events to compare with model results.

The aerosonde experiment was conducted in May 1999. A report on the aerosonde field testing in Hawaii was prepared by the Insitu group (McGeer 1999). There were two operation areas: windward and leeward. For the windward option, the focus is to study the island blocking, offshore flow deceleration and the arc-shape cloud band offshore in the morning. For the leeward option, the emphasis is on the atmospheric conditions in the wake and the wake clouds.

Data collected from the aforementioned Hawaii Aerosonde experiment and HaRP (Hawaiian Rain Project) during July-August 1990 were used to assess the model performance under the normal trade-wind conditions with weak synoptic-scale forcing. Our analyses show that the model simulated the island-induced airflow reasonably well, including upstream decelerating flow, splitting flow along the windward coasts, orographically enhanced strong winds within the channels between the islands, and lee side vortices. However, our results suggest that (i) the amplitude of the simulated diurnal surface temperature range is much smaller than observed during the HaRP experiment; and (ii) the simulated nighttime offshore flow is weaker, in some cases even missing, as compared to the HaRP observations. These two drawbacks may be related to the fact that the current MSM model version only contains one soil type, sandy-clay loam, and one vegetation type, broadleaf trees, for the major Hawaiian islands. Besides, vegetation fraction at every grid point is a constant (= 0.70) in the current RSM/MSM model. These results strongly suggest the need to couple an advanced land surface model with the MSM with improved surface conditions. Using the high resolution (~ 200 m) USGS (U.S. Geological Survey) land use, land cover data sets for the Hawaiian islands (USGS, 1986; Anderson et al., 1976), we compiled surface parameters (e.g., soil type, vegetation type and vegetation fraction) at every grid point for the nested Oahu domain. The original USGS land use, land cover data were classified into 9 first-level categories and 37 second-level categories. We re-classified the data into 9 soil types and 13 vegetation types (F. Chen and Dudhia, 1996 and F. Chen et al., 2000) after consulting Dr. F. Chen (NCAR). The vegetation type and soil type at every grid point in the new data set are designated to be the dominant vegetation and soil type within each grid point. The vegetation fraction at every grid point is simply the ratio of the grid points which contain vegetation to the total grid points within the domain.

The simulated trade-wind inversion is weaker than observed. There are discrepancies in altitude between the simulated and the observed inversion height as well. These differences could be attributed to the fact that the trade-wind inversion may not be well resolved by the Global Spectral Model (GSM or AVN).

We conducted a case study of a high wind event which occurred on 30 March 1998 for all three model domains: Kauai domain with a resolution of 1.5 km, Oahu domain with a resolution of 1.5 km, and Maui-Hawaii domain with a resolution of 3.0 km. The downslope wind storms were simulated on the lee side of mountain ridges with tops below the trade-wind inversion. The results also show that, on the lee side of mountain ridges with tops above the trade-wind inversion, winds are considerably weaker than the upstream values because of island blocking. Enhanced winds were also simulated within the channels and immediately off the coast of the northernmost and southernmost tips of the islands. Mary Ann Esteban was supported by this project for two months as an undergraduate student assistant to collect and plot the surface data for this high wind event.

We also studied a heavy rainfall case which occurred in 3-4 November 1995 with MSM. Our results show that, while the simulated precipitation patterns vary depending on the model precipitation physics, the prognostic cloud scheme with three predicted water substances (water vapor, cloud/ice, and snow/rain) appears to be superior to the other precipitation schemes in simulating the rainfall location and rainfall rate for this particular case.

The nonhydrostatic meso-eta model is not available yet.


Anderson, J. R., E. E. Hardy, J. T. Roach and R. E. Witmer, 1976: A land use and land cover Classification System for Use with Remote Sensor Data. U.S. Geological Survey, Professional Paper 964, Reston, VA, 28 pp.

USGS, 1986: Land use and land cover digital data from 1:250,000- and 1:100,000-scale Maps: Data User Guide 4, U.S. Geological Survey, DOE, Reston, VA, 36 pp.

Chen, F., K. Mitchell, J. Schaake, Y. Xue, H.-L. Pan, V. Koren, Q. Y. Duan, M. Ek and A. Betts, 1996: Modeling of land surface evaporation by four schemes and comparison with FIFE
observations. J. Geophs. Res., 101, 7251-7268.

Chen, F. and J. Dudhia, 2000: Coupling an Advanced Land-Surface/Hydrology Model with the Penn State/NCAR MM5 Modeling System. Part I: Model Implementation and Sensitivity. Mon. Wea. Rev., (in press).

McGeer, T, 1999: Field testing of aerosondes in offshore meteorological reconnaissance. Final Project Report to the NOAA, The Insitu Group, Bingen, WA, 40 pp.


The base for aerosonde operations was the Upolu airport at the northern tip of the island of Hawaii. The control center for aerosonde operations was set up at NWSFO-HNL. The travel funds budgeted for the field operations were used to support Y.-L. Chen and two students (Mary Ann Esteban and Yongxin Zhang) to attend the First International Regional Spectral Model Workshop held at the Maui High Performance Computer Center (MHPCC), Maui, Hawaii during 9-13 August, 1999 and to invite H. H.-M. Juang to stop over to work with us during 15-17 August after the workshop.

NWS provided working space for the aerosonde project and assisted in preparing forecasts for the aerosonde project and determining the flight paths. NWS staff participated in pre-project planning with Aerosonde staff and the FAA to get flight approval. The UH team worked closely with the NWSFO-HNL and the Insitu group on the planning and execution of the aerosonde experiment as well as preliminary analysis of the data collected.


Zhang, Y.-X., Y.-L. Chen, H.-M. Juang, S.-Y. Hong, K. Kodama, and R. Farrell, 2000: Validation and sensitivity tests of Mesoscale Spectral Model simulations over the Hawaiian islands. The 2nd International RSM Workshop, 17-21 July, MHPCC, Maui, HI.

Kodama, K. and H.-M. H. Juang, 1999: An assessment of regional spectral model forecasts for the Hawaii islands. The 1st Regional Spectral Model Workshop, Maui, Hawaii, 9-13 August, 1999.

Chen, Y.-L., J. Li, H.-M. H. Juang, P. Jendrowski and K. Kodama, 1999: Application of the NCEP nonhydrostatic spectral model to improve weather forecasting in Hawaii. The 1st Regional Spectral Model Workshop, Maui, Hawaii, 9-13 August, 1999.

Li, J and Y.-L. Chen, 1999: A case study of nocturnal rainshowers over the windward coastal region of the island of Hawaii. Mon. Wea. Rev., 11, 2674-2692.


4.1 University:

The primary benefits to the university are the opportunity to participate in the first aerosonde field testing in Hawaii and the exposure of our students to the execution and data collection process from aerosondes and operational forecasting.

4.2 NWS:

During the Aerosonde project, NWS staff meteorologists interacted with the Aerosonde staff and were able to view real time vertical profiles of winds and temperature data.