Atmospheric methane, nonmethane hydrocarbons, and carbon monoxide were measured at the Mauna Loa Observatory on the island of Hawaii in May and June 1988. The daily island upslope/downslope circulation resulted in a variable mixture of boundary layer and free tropospheric air at the observatory. Mixing ratios of these gases were higher during upslope flow than during downslope flow. Mixing ratios characteristic of the free troposphere at this altitude were most often measured during nighttime, downslope flow. Local marine emissions of ethylene and propylene and emissions of isoprene from island vegetation were detected during upslope circulation, but ethylene and propylene were also often detected at night during downslope circulation, indicating that air sampled during nighttime downslope flow may have included some air recently transported from the marine boundary layer. Comparison of data for methane, carbon monoxide, ethane, and propane from in situ measurements with measurements made from canister samples collected during the experiment showed very good agreement. Fluxes of isoprene from selected dominant island flora were also measured.

Diurnal variability of atmospheric methane, nonmethane hydrocarbons, and carbon monoxide at Mauna Loa

The Weather Research and Forecasting (WRF) model V3.3 has been configured for the Hawaiian Islands as a regional climate model for the region (HRCM). This paper documents the model configuration and presents a preliminary evaluation based on a continuous 1-yr simulation forced by observed boundary conditions with 3-km horizontal grid spacing in the inner nested domain. The simulated vertical structure of the temperature and humidity are compared with twice-daily radiosonde observations at two stations. Generally the trade wind inversion (TWI) height and occurrence days are well represented. The simulation over the islands is compared with observations from nine surface climatological stations and a dense network of precipitation stations. The model simulation has generally small biases in the simulated surface temperature, relative humidity, and wind speed. The model realistically simulated the magnitude and geographical distribution of the mean rainfall over the Hawaiian Islands. In addition, the...

Configuration and Evaluation of the WRF Model for the Study of Hawaiian Regional Climate

Heavy rainfall and the associated floods occur frequently in the Hawaiian Islands and have caused huge economic losses as well as social problems. Extreme rainfall events in this study are defined by three different methods based on 1) the mean annual number of days on which 24-h accumulation exceeds a given daily rainfall amount, 2) the value associated with a specific daily rainfall percentile, and 3) the annual maximum daily rainfall values associated with a specific return period. For estimating the statistics of return periods, the three-parameter generalized extreme value distribution is fit using the method of L-moments. Spatial patterns of heavy and very heavy rainfall events across the islands are mapped separately based on the aforementioned three methods. Among all islands, the pattern on the island of Hawaii is most distinguishable, with a high frequency of events along the eastern slopes of Mauna Kea and a low frequency of events on the western portion so that a sharp gradient in ext...

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Extreme Rainfall Events in the Hawaiian Islands

Owing to the increasing power demand and the environmental concerns of the conventional power sources, power generation from wind is receiving due attention from majority of power planners. Since wind is an intermittent energy source and to find the economic viability of wind project, a proper wind resource assessment (WRA) and analysis of the data collected is very important. An extensive literature survey on WRA is carried out and the different techniques of WRA are discussed. The methodology includes discussions on preliminary wind survey to choose the best site for installing wind data instruments, selecting the optimum wind turbine suitable for a site and the uncertainties involved in estimating the wind speed using the different WRA techniques.

Some of the design and methodology considerations in wind resource assessment

[1] Changes in the frequency and intensity of the prevailing northeast and east trade winds from 1973-2009 are analyzed from four land stations in the Hawaiian Islands. A nonparametric robust trend analysis indicates a downward trend in northeast trade wind frequency since 1973. At the Honolulu International Airport, northeast trade wind days usually occurred 291 days per year 37 years ago are observed to occur only 210 days per year in 2009. In contrast, the frequency of the east trade winds has increased over the past 37 years. Comparison of observations from four ocean buoys with land stations for the last 26 years (1984–2009) is presented. The northeast trade frequency is found to decrease for all eight stations while the east trade winds are found to increase in frequency. These results are similar to the longer (1973–2009) data set. Most buoys revealed an increase in trade wind speeds since 1984. The NCEP/NCAR reanalysis II data are used to analyze surface winds and sea level pressure (SLP) over the north Pacific. A northeast to east shifting of winds and an increase in SLP is found to occur from the 1980s to the 2000s epoch. Linear trends in reanalysis II from 1980 to 2009 indicated a strengthening of northeast trade winds over the Hawaiian Islands and in the subtropical eastern North Pacific with an extension of increased northerlies off the California coast. Meanwhile, southeast trades in the eastern North Pacific reduced their strength. Changes in trades in the western Pacific are relatively small.

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Changes of the prevailing trade winds over the islands of Hawaii and the North Pacific

During the period 22–29 June 1978, meteorological data were collected at six stations arranged in nearly linear transection extending from the coast at Anaehoomalu, Hawaii to Waimea Airport, 25 km inland and 800 m higher Sea breeze response to synoptic-scale weather patterns was documented Within the six days of 24 h measurements, two disturbances embedded in the prevailing trade winds passed over the island Three different types of sea breeze development ensued Sea breeze variability appears to be related to both synoptic-scale cloud and wind distributions and to the thermal properties of lava surfaces situated within the transection Days of maximum insolation corresponded to minimum sea breeze advance through the network It is suggested that numerical models be employed with this data set to test the sensitivity of sea breezes to soil and cloud conditions

Characteristics of local winds in northwest Hawaii

Low-level winds in the central valley of the island of Maui were investigated in a field program during August 1976. Forty-one sites were occupied using three mobile stations during a period of persistent trade winds. Contemporaneous data from the Kahului Weather Service Office as well as other Hawaiian stations were collected to relate field observations to large-scale events. Streamline analyses reflect the diurnal variation of the low-level circulation which is profoundly influenced by Haleakala and West Maui volcanoes. The field survey was utilized in planning new fixed stations to monitor wind characteristics for wind power applications. Preliminary fixed station results are discussed. The importance of diurnal mesoscale patterns on wind power planning was emphasized.

Thomas A. Schroeder

Papers

Characteristics of local winds in northwest Hawaii

Air Flow in the Central Valley of Maui, Hawaii