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Hiromasa Ueda

Abstract

The land and sea breeze (LSB) and steady conviction (SC), superimposed on the geostrophic wind U, were analyzed by a linear model, the SC being driven by the diurnal-mean land-sea temperature difference and causing seasonal changes in the climate in the coastal region. An extension of Walsh's model (1974) was made to include SC and the effect of the Prandtl number (Pr). The influences of U, as well as the Coriolis force f/w, mean atmospheric stratification Grr (a form of Grashof number) and Pr on the LSB and SC were investigated.

The LSB and SC are similar in their effects on the flow pattern, the wind speed and spatial dimensions being almost the same as at middle and higher latitudes when U = 0. The vertical dimension, the horizontal dimension and the wind speed are proportional to Gr0 rPr¼, Gr0.387 rPr0. and Gr−½ rPr−⅔, respectively. The f/w effect is very small except for the dimensions of SC. The wind speeds of the LSB and SC created by a unit temperature difference between land and sea, as well as the structure and development of the sea breeze opposing U, were also investigated.

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Hiromasa Ueda, Shigeki Mitsumoto, and Hidemi Kurita

Abstract

Flow mechanism causing nighttime smog was investigated by analyzing 1) continuous records of meteorological data and concentration of Oxidants (Ox) for 15 days and 2) aircraft data along the transportation route of a polluted air mass.

It was found that an air mass which passed over the large emission sources along the coastline was transported inland as a sea breeze in the form of a gravity current. A high concentration layer was created in the upper part of the gravity current. It descended at the rear edge of a gravity-current head due to the internal circulation within the head, thus yielding the highest concentration of Ox near the ground there.

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Shigeki Mitsumoto, Hiromasa Ueda, and Hiroyuki Ozoe

Abstract

The land and sea breeze (LSB) circulation was simulated in a laboratory using a temperature controlled water tank. Flow visualization by tellurium and phenolphthalein and velocity measurement by laser-Doppler velocimeter were carried out in addition to temperature measurements. from similarity considerations, the simulated flow pattern was shown to have good correspondence with that in the atmosphere. It was shown that the overall features of the LSB flow pattern consist of a closed circulating motion caused by the periodically changing horizontal temperature difference between the land and the sea, and several kinds of small-scale motions induced by the periodic variation of the land surface temperature itself. The most important small-scale motion is the cellular convection which occurs all over the land surface due to unsteady heating from below in the morning calm. Other small-scale motions such as longitudinal vortex rows which are formed inland throughout the sea breeze layer, and gravity currents, were also investigated and shown to contribute significantly to the dynamics of the LSB and the transport of a pollutant within it.

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Hidemi Kurita, Hiromasa Ueda, and Shigeki Mitsumoto

Abstract

The meteorological structure and transport mechanism of long-range transport of air pollutants from the coastal region to the mountainous inland region were investigated using joint field observation data. The observations were conducted during 26–30 July 1983 over a wide area from the coastal region around Tokyo Bay to the mountainous region located in central Japan.

Air, polluted around the Tokyo Bay area during the early morning remained there until noon, being transformed by photochemical reactions. It was then transported inland, at first by the extended sea breeze and thereafter by the large-scale wind system, toward the thermal low generated in the mountainous central region. At about 1600 Japan Standard Time (JST), polluted air penetrated into the mountainous region, and after sunset it drained down along the valley in the form of a gravity current. The path of the polluted air was in good agreement with the air trajectory started Tokyo at an altitude of 100 m, calculated from pilot-balloon data. Its transport speed reached a maximum value (7.5 m s−1) at about 1500 JST, when the thermal low was most fully developed.

Daytime temperatures over the mountainous central region (Saku) were higher than those over the Kanto Plain (Takasaki), and the thermal effects of the mountainous central region (average height; 1200 m) extended to more than 3000 m in height. The vertical temperature profiles at these locations showed a linear variation in the daytime. At the 700 m level, the temperature difference between these locations attained 3.6°C when the thermal low was most fully developed. The pressure difference between the mountainous central region (Matsumoto) and the Kanto Plain (Kumagaya) was calculated using the vertical temperature profiles observed at 1500 JST. The pressure difference between these locations decreased with altitude and became almost zero at an altitude of 1900 m, indicating the vertical extent of the thermal low. From these results it became obvious that the creation of the thermal low and the wind blowing toward the thermal low was due to the difference in temperature between the air above the plain and that on the plateau.

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Weiming Sha, Takeshi Kawamura, and Hiromasa Ueda

Abstract

It is demonstrated in this numerical study that prefrontal perturbations may be triggered by a penetrating sea-breeze head into an existing nocturnal temperature inversion. The perturbations consist of the lower-layer wavelike perturbation and the upper-wave motion, both of which are manifested as rotor streaming. However, these prefrontal gravity waves take the form of the weak transient waves of a depression trapped in the ambient compensating flow field.

The sea-breeze head dissipates as it penetrates inland into the nocturnal temperature inversion. At midnight, a horizontal vortex is completely detached from the feeder flow of the sea breeze. This isolated horizontal vortex is identified as the sea-breeze cutoff vortex. It is shown that the sea-breeze cutoff vortex may be evolved from a dissipating sea-breeze head. After the sea-breeze cutoff vortex is formed, it propagates farther inland as an isolated wave-type disturbance. Examination of the force balance suggests that the inertia and radiative energy loss are dominant in the processes of the sea-breeze cutoff vortex.

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Weiming Sha, Takeshi Kawamura, and Hiromasa Ueda

Abstract

A two-dimensional, nonhydrostatic, compressible, and dry numerical model was developed. By using high spatial resolution and an appropriate turbulence model, fine structure and dynamics of the sea-breeze head were investigated.

Kelvin–Helmholtz (KH) instability was found to occur in the foremost part of the head. Consequently KH billows were generated there and grew in amplitude while travelling backward relative to the advancing front along the “zero-velocity boundary.” The KH billows entrained the upper air into the sea breeze. The resultant turbulent mixing and wave perturbations induced a top friction force acting on the sea-breeze head. Structure of the KH billow and the wavelike motion induced by it near the ground were also investigated and compared with the results obtained in laboratory density currents, linear theories, and observations.

The KH instability (KHI) did not occur at all stages of the sea breeze, and this resulted in a diurnal variation of the fine structure and dynamics of the head. Rather, the KHI was produced only in the middle part of the day and the induced top friction force decelerated the inland penetration of the sea-breeze front. By estimating all the controlling forces acting on the head, it was concluded that the increasing top friction force is associated with the slowing of the sea-breeze penetration.

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Hidemi Kurita, Kazutoshi Sasaki, Hisao Muroga, Hiromasa Ueda, and Shinji Wakamatsu

Abstract

The long-range transport of air pollution on clew days under light gradient wind conditions is investigated from an analysis of all days with high oxidant concentrations in 1979 at locations in central Japan that are far from pollutant sources. Surface-level wind and pressure distributions over a 300×300 km area were analyzed, together with concentration isopleths of oxidants and suspended particles produced by photochemical reactions.

It was found that the transport mechanism consists of. 1) land/sea breezes; 2) a steady onshore wind driven by the diurnal-mean land–sea temperature difference; 3) the generation of a strong thermal low in the inland mountainous region in the daytime; and 4) a subsidence inversion accompanied by a synoptic-scale high pressure system. The last three mechanisms work to combine land/sea breezes and slope and valley winds into one large-scale high-speed wind field that transports pollutants a long distance inland into the mountainous region.

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Hiroyuki Katayama, Takashi Karasudani, Koji Ishii, Kenji Marubayashi, and Hiromasa Ueda

Abstract

A system for measuring partial pressure of CO2 in seawater (pCO2) has been developed as a part of a missing-sink elucidation study. The most important part of this system is the multistage bubbling gas–liquid equilibrator. This equilibrator has four independent equilibrate cells in parallel. Seawater flows into each cell in parallel, while the bubbled carrier gas stream passes through every cell in series. The carrier gas circuit of a nondispersive infrared gas analyzer is opened to the atmosphere to keep the pressure of carrier gas at a barometric pressure. The present system can measure pCO2 continuity with sample water of 24 L min−1.

Furthermore, a performance test was carried out to examine the degree of equilibrium achieved. The results showed an 83% equilibrium per cell. This indicates that the uncertainty of this equilibrator is 1 μatm. The correlation coefficient between the deviation of pH and that of pCO2 observed with this system was −0.96.

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Genki Katata, Haruyasu Nagai, Hiromasa Ueda, Nurit Agam, and Pedro R. Berliner

Abstract

A one-dimensional soil model has been developed to better predict heat and water exchanges in arid and semiarid regions. New schemes to calculate evaporation and adsorption in the soil were incorporated in the model. High performance of the model was confirmed by comparison of predicted surface fluxes, soil temperature, and volumetric soil water content with those measured in the Negev Desert, Israel. Evaporation and adsorption processes in the soil have a large impact on the heat and water exchange between the atmosphere and land surface and are necessary to accurately predict them.

Numerical experiments concerning the drying process of soil are performed using the presented model and a commonly used land surface model. The results indicated that, when the dry soil layer (DSL) develops, water vapor flux to the atmosphere is caused by evaporation in the soil rather than evaporation at the ground surface. Moreover, the adsorption process has some impact on the water and heat balance at the ground surface. The upward water vapor flux during the daytime is due to evaporation of soil water in the DSL, which is stored during the night due to adsorption. When the DSL progresses sufficiently, almost the same amounts of water are exchanged between the air and the soil surface by daytime evaporation and nighttime adsorption. In such conditions, latent heat due to evaporation and adsorption in the soil also work to reduce the diurnal variation of surface temperature.

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Hiromasa Ueda, Tetsuo Fukui, Mizuo Kajino, Mitsuaki Horiguchi, Hiroyuki Hashiguchi, and Shoichiro Fukao

Abstract

Recently, middle- and upper-atmosphere Doppler radar (MU radar) has enabled the measurement of middle-atmosphere turbulence from radar backscatter Doppler spectra. In this work, eddy diffusivities for momentum Km in the upper troposphere and lower stratosphere during clear-air conditions were derived from direct measurements of the Reynolds stress and vertical gradient of mean wind velocity measured by MU radar. Eddy diffusivity for heat Kh below 8 km was determined from measurements of temperature fluctuations by the Radio Acoustic Sounding System (RASS) attached to the MU radar. The eddy diffusivity for momentum was on the order of 10 m2 s−1 in the upper troposphere and decreased gradually in the stratosphere by an order of magnitude or more. The eddy diffusivity for heat was almost of the same order of magnitude as Km.

Estimates of eddy diffusivity from the radar echo power spectral width give fairly good values compared with the direct measurement of Km. Applicability of three turbulence models—the spectral width method, the k–ε model modified for stratified flows, and the algebraic stress model—were also examined, using radar observation values of turbulent kinetic energy k and turbulent energy dissipation rate ε together with atmospheric stability observations from rawinsonde data. It is concluded that the algebraic stress model shows the best fit with the direct measurement of Km, even in the free atmosphere above the atmospheric boundary layer once k and ε values are obtained from observations or a model.

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