Yasushi Mitsuta

Mineral particles collected in China and Japan during the same Asian dust-storm event

Aerosol particles were collected at China and Japan in the same spring Asian dust-storm event of 1991 in order to study the change in composition of mineral aerosol particles during long range transport. It was found on the basis of a microchemical analysis that dust particles containing Mg, Al, Si, K, Ca and Fe were a major fraction of the aerosol particles collected at Hohhot and Beijing, China, and Nagasaki, Japan. A large fraction of the mineral aerosol particles was internally mixed with sea salt in Nagasaki. Present study suggests that the internal mixed particles were mainly produced by cloud processes through droplet coalescence.

Evaporation from the desert : some preliminary results of HEIFE

As part of a feasibility study for HEIFE, a Sino-Japanese Cooperative Research Program on Atmosphere-Land Surface Processes in Heihe River Basin, fluxes of water vapour are estimated above and below the sand surface. It is found that during the daytime under clear skies, the water vapour flux is directed towards the surface from both the atmosphere above and the sand below.

Intraseasonal variation of monsoon activities associated with the rainfall over Bangladesh during the 1995 summer monsoon season

The rainfall over Bangladesh during the 1995 summer monsoon season has been investigated in terms of the intraseasonal variation of monsoon activities. The rainfall over Bangladesh is basically dominated by the north-south oscillation of the monsoon trough. The rainfall increases when the monsoon trough is located at the foot of the Himalayas, because synoptic-scale convective activity is much more vigorous to the south of the monsoon trough axis than to the north of it. In addition, the strong southwesterly wind to the south of the monsoon trough intensifies local convective activity owing to the effects of the orography to the north and east of the country. It is also found that the monsoon rainfall over Bangladesh in 1995 varies with a periodicity of ∼20 days, and this rainfall variation is closely associated with synoptic-scale monsoon activities spreading over South and Southeast Asia. The active/break cycle of the rainfall variation during the 1995 summer monsoon season can be mostly explained by the northward propagation of what is called the 10–20 day variation of monsoon activities.

Direct measurement of turbulent fluxes on a cruising ship

The result of an attempt at the direct measurement of turbulent fluxes on the top of the mast of a cruising ship is presented. The three-dimensional components of wind relative to the ship measured by a sonic anemometer are corrected for ship motion; from these the fluxes of momentum, sensible heat and water vapor are computed using the outputs of a fine-wire thermocouple psychrometer. The observations were made by this method on the Northwestern Pacific. The results indicate that this technique is usable for determining the distribution of fluxes over the ocean.

Studies on Spatial Structure of Wind Gust

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.

Development of Wind Profiling Sodar

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.

Stability dependence of the drag and bulk transfer coefficients over a coastal sea surface

Bulk transfer coefficients were evaluated from eddy correlation flux measurements on a fixed pier during onshore winds. The mean values are CD = 1.69 × 10-3, CH = 2.58 × 10-3 and CE = 1.51 × 10-3. The drag coefficient, CD, gradually increases with wind speed but CH and CE are independent of wind speed. According to theory and empirical formulas based on experimental results over flat grassland, the transfer coefficients should gradually increase with increasing instability. This is confirmed experimentally in the stable region in our case. However, the drag coefficient appears to decrease with increasing instability, which is against the theoretical result. A stability dependence is not clearly observed for CH or CE.

An evaluation of evaporation over the tropical Pacific Ocean as observed from satellites

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. Whil...

Convective Motion in the Cumulus Subcloud Layer

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.

A TATSUMAKI IN TOKYO ON FEBRUARY 28TH, 1978

ABSTRACT In the evening of Feb. 28th, 1978, a strong wind caused severe damages in the area along the north-west coast of Tokyo Bay. The damage was distributed in a straight belt area beginning at Kawasaki, Kanagawa and ending at Kamagaya, Chiba. The length of the damaged area was about 40 km (25 miles) and the width 0.4 km (0.25 miles). Most outstanding damages of all were that a train (Tozai-line) was turned over on the bridge over the Arakawa River in Tokyo and that a prefabricated onestory school building (floor area 539 m2) was lifted about 5 m up and carried over the next building and crashed over the third building