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- Author or Editor: Yasushi Mitsuta x
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Abstract
Based on the precipitable water data provided by Scanning Multichannel Microwave Radiometer (SMMR), and wind data by Geostationary Meteorological Satellite (GMS) and Geostationary Operational Environment Satellite (GOES), the monthly averaged water vapor flux and flux divergence have been estimated over the equatorial Pacific area for July 1980.
The main flow pattern of water vapor transport is essentially the combination of meridional convergence and westward flow. The intertropical convergence zone (ITCZ) in the northern part of the equatorial Pacific around 10°N, is characterized by water vapor convergence, which indicates that precipitation exceeds evaporation. The largest convergence areas of about 500 mm month−1 are seen over the ITCZ.
Evaporation can be estimated from the water vapor convergence if precipitation data, such as island rainfall data, are available. Over the eastern Pacific, where rainfall is nearly zero, evaporation is about 150 mm month−1 averaged over 0°-20S, 170°-90W. While precipitation is obtained if evaporation can be estimated by an independent method. Precipitation of more than 400 mm month−1 is seen around the ITCZ by the use of evaporation by bulk method.
Abstract
Based on the precipitable water data provided by Scanning Multichannel Microwave Radiometer (SMMR), and wind data by Geostationary Meteorological Satellite (GMS) and Geostationary Operational Environment Satellite (GOES), the monthly averaged water vapor flux and flux divergence have been estimated over the equatorial Pacific area for July 1980.
The main flow pattern of water vapor transport is essentially the combination of meridional convergence and westward flow. The intertropical convergence zone (ITCZ) in the northern part of the equatorial Pacific around 10°N, is characterized by water vapor convergence, which indicates that precipitation exceeds evaporation. The largest convergence areas of about 500 mm month−1 are seen over the ITCZ.
Evaporation can be estimated from the water vapor convergence if precipitation data, such as island rainfall data, are available. Over the eastern Pacific, where rainfall is nearly zero, evaporation is about 150 mm month−1 averaged over 0°-20S, 170°-90W. While precipitation is obtained if evaporation can be estimated by an independent method. Precipitation of more than 400 mm month−1 is seen around the ITCZ by the use of evaporation by bulk method.
Abstract
The peak gust speed is often used to evaluate the maximum wind tome acting on the structure in wind engineering. To evaluate this peak gust speed, the ratio of the peak gust speed over the mean wind speed (called gust factor) is defined. The peak gust is an averaged value of wind speed over a very short duration and small space and is the function of those averaging parameters as well as turbulent conditions. Experimental relation of the gust factor on the averaging time and space was studied by the results of a typhoon wind experiment made on Tarama Island in the Southwest Islands of Japan. The gust factor is independent from mean wind speed in winds higher than 14 m s−1. The dependence of the gust factor on the averaging time is well described by a formula proposed previously by one of the authors and can be explained as the mean normal extreme of wind fluctuations. The space averaging the gust factor is also described by a new experimental formula of exponential form.
Abstract
The peak gust speed is often used to evaluate the maximum wind tome acting on the structure in wind engineering. To evaluate this peak gust speed, the ratio of the peak gust speed over the mean wind speed (called gust factor) is defined. The peak gust is an averaged value of wind speed over a very short duration and small space and is the function of those averaging parameters as well as turbulent conditions. Experimental relation of the gust factor on the averaging time and space was studied by the results of a typhoon wind experiment made on Tarama Island in the Southwest Islands of Japan. The gust factor is independent from mean wind speed in winds higher than 14 m s−1. The dependence of the gust factor on the averaging time is well described by a formula proposed previously by one of the authors and can be explained as the mean normal extreme of wind fluctuations. The space averaging the gust factor is also described by a new experimental formula of exponential form.
Abstract
An observational study of convective motion in the cumulus subcloud layer was made by remote sensing from the ground. The vertical distributions of three-dimensional wind components are observed by a Doppler acoustic sounder (Sodar); the cloud base temperature is detected by a radiation thermometer; and cloud form was recorded by a fish-eye camera. Three cases of cumulus cloud passage were observed during the period of August and September 1981. In the case of a small developing cumulus cloud, an updraft in the boundary layer preceded the cloud passage. However, in the case of a little larger and more mature cloud, an updraft area trails from the cloud. This trailing updraft area consists of a horizontally rotating wind system in the boundary layer. In the case of a roll cloud, no systematic relation between cloud and boundary layer air flow was found. In all three cases no evidence of cloud passage was seen in the surface meteorological parameters.
Abstract
An observational study of convective motion in the cumulus subcloud layer was made by remote sensing from the ground. The vertical distributions of three-dimensional wind components are observed by a Doppler acoustic sounder (Sodar); the cloud base temperature is detected by a radiation thermometer; and cloud form was recorded by a fish-eye camera. Three cases of cumulus cloud passage were observed during the period of August and September 1981. In the case of a small developing cumulus cloud, an updraft in the boundary layer preceded the cloud passage. However, in the case of a little larger and more mature cloud, an updraft area trails from the cloud. This trailing updraft area consists of a horizontally rotating wind system in the boundary layer. In the case of a roll cloud, no systematic relation between cloud and boundary layer air flow was found. In all three cases no evidence of cloud passage was seen in the surface meteorological parameters.
Abstract
During the field observation period of the Air Mass Transformation Experiment in 1975 (AMTEX ‘75), one of the boundary-layer research flights of the National Center for Atmospheric Research (NCAR) Electra aircraft was conducted in the vicinity of Tarama Island. A 50-m onshore observation tower was located on the southwestern coast of Tarama Island, and a 12-m offshore observation tower on the northern reef. We compare and discuss mean profiles of dry- and wet-bulb temperature, wind speed and direction, and turbulent fluxes of latent and sensible heat and momentum observed by these three observing platforms. We found that the 50.m onshore tower, which was about 3.5 km downwind of the shoreline, and the airplane flight legs over the island at 140 and 160 m height were in the island-modified air. This resulted in large differences between ocean and island measured fluxes, smaller differences in the variances and almost no differences in the means. Thus, we found that for the conditions of this experiment it is feasible to use the island-measured values of mean quantities as characteristic of the ocean. but the fluxes and variances are characteristic of the island.
Abstract
During the field observation period of the Air Mass Transformation Experiment in 1975 (AMTEX ‘75), one of the boundary-layer research flights of the National Center for Atmospheric Research (NCAR) Electra aircraft was conducted in the vicinity of Tarama Island. A 50-m onshore observation tower was located on the southwestern coast of Tarama Island, and a 12-m offshore observation tower on the northern reef. We compare and discuss mean profiles of dry- and wet-bulb temperature, wind speed and direction, and turbulent fluxes of latent and sensible heat and momentum observed by these three observing platforms. We found that the 50.m onshore tower, which was about 3.5 km downwind of the shoreline, and the airplane flight legs over the island at 140 and 160 m height were in the island-modified air. This resulted in large differences between ocean and island measured fluxes, smaller differences in the variances and almost no differences in the means. Thus, we found that for the conditions of this experiment it is feasible to use the island-measured values of mean quantities as characteristic of the ocean. but the fluxes and variances are characteristic of the island.
Abstract
The present study group has developed a new wind profiling sodar with a phased array antenna. This system is superior to usual ones with parabolic reflectors in its portability. Preliminary experiments have shown the expected acoustic performance by theoretical estimations. A new simplified homodyne complex covariance method has been introduced and tested to estimate the Doppler frequency shifts. Doppler wind measurement based on the five-beam system was used to get free from acoustic refraction effect and contamination of vertical component on the horizontal wind estimates. The test observations were successful but the data are too small in number at this stage to discuss the instrumentation error or the error due to inhomogeneity.
Abstract
The present study group has developed a new wind profiling sodar with a phased array antenna. This system is superior to usual ones with parabolic reflectors in its portability. Preliminary experiments have shown the expected acoustic performance by theoretical estimations. A new simplified homodyne complex covariance method has been introduced and tested to estimate the Doppler frequency shifts. Doppler wind measurement based on the five-beam system was used to get free from acoustic refraction effect and contamination of vertical component on the horizontal wind estimates. The test observations were successful but the data are too small in number at this stage to discuss the instrumentation error or the error due to inhomogeneity.
