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Junsei Kondo

Abstract

A hypothesis of hydrodynamic similarity is proposed in respect to both the atmospheric and oceanic boundary layers just above and below their interface. Both layers are combined through an identical geometric surface roughness h which is composed of the high-frequency components of waves. The logarithmic current profiles, hitherto measured in the upper ocean and wind-wave facilities, can be satisfactorily interpreted with the present purely turbulent transport hypothesis. The roughness Reynolds number hv*/ν characterizes three surface regimes of the current. The hydrodynamic roughness length and the thermometric and mass transport coefficients are obtained in terms of hv*/ν. The roughness Reynolds numbers of the oceanic boundary layer are found to be about half those of the atmospheric boundary layer, which implies that the transitions of the oceanic boundary layer to various regimes lag behind those of the atmospheric boundary layer.

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Junsei Kondo

Abstract

During the last 300 years, most of the poor rice harvests caused by unusual cool summers and leading to famine conditions in the Tohoku district (the northeastern part of Japan), took place just after the great volcanic eruptions.

An analysis of instrumental observations in the past century on the Kinkasan Island indicates that, though the standard deviation in the summer air temperature is 1.1°C for 1882–1985, the summer air temperature averages 1.3±0.5°C lower than normal during the summer following the great volcanic eruptions, the mid- latitudinal mean surface air temperature in the northern hemisphere decreased only about 0.2°C. This result indicates that the summer air temperature in Tohoku district tends to be particularly sensitive to such eruptions. In all the cool summers a blocking high persisted over the ocean northeast of Japan, and impeded the northward movement of the “Raiu” front (the stagnating polar front during the early summer).

Exceptionally cool summers occurred frequently without great volcanic eruptions during 1931-45. During this period, the sea water temperatures at Tohoku's coastal stations on the Pacific were lower by 1.5°C, on the average, than those of the subsequent period of 1946–79.

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Dai Matsushima and Junsei Kondo

Abstract

A multilayer energy budget model for a horizontal-homogeneous vegetation canopy and a simple radiometric canopy model are developed to estimate sensible heat flux with use of the observed directional radiometric temperature of the canopy surface. Field experiments were carried out in an almost horizontal-homogeneous rice paddy under various canopy conditions to obtain boundary conditions and data to test the models.

A proper method for estimating sensible heat flux is proposed, which is based on model simulations and the observational results. Key parameters required for the estimation of the flux are the aerodynamic conductance and the optimum viewing angle, which are investigated in detail using a rice paddy model. The aerodynamic conductance is a function of three parameters, namely, the leaf-area index (LAI), wind speed, and virtual temperature difference between the canopy and the surface layer. The optimum viewing angle for sensible heat is found to be between 50° and 70° of the nadir angle; its variance with LAI and the dependence on wind speed is relatively small. In the case of latent heat, the optimum angle is systematically smaller than that for sensible heat by about 10°. There is a gap in the estimation of the error in the sensible heat flux according to the viewing angle. During the daytime, an error of over 100 W m−2 would result if the viewing angle is near nadir, while it is around a 30 W m−2 error for an angle of 70° of the nadir angle in spite of LAI. This effect is found to be due to four factors: 1) the difference in the surface temperature between the leaf and the underlying ground; 2) the leaf surface, which plays a comparable role as the underlying ground surface in the thermal exchange; 3) the ratio of leaf area and the underlying ground area in the field of view of an infrared thermometer; and 4) the emissivity of the underlying wet ground surface, which varied with viewing angle, is effective for sparse canopy.

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Junsei Kondo and Naoko Okusa

Abstract

Nocturnal cooling in a basin during a calm, clear night is investigated with a simple model of the cooling. The parcel model of Kondo and Sate is used for describing the slope flow in the basin. Mean fields of potential temperature, the slope wind velocity, and the sensible heat flux are evaluated. The simulated vertical temperature profiles were found to agree with observed profiles.

For typical model basins, the dependence of the nocturnal cooling on topographic parameters are obtained as follows: (i) The governing parameters are the depth of the basin and a shape parameter. The conical basin with a small shape parameter has more air cooling and a weaker slope wind than a flat bottom basin with a large shape parameter; (ii) Mean sensible heat flux during the night is almost proportional to a cube root of the depth of the basin, but little affected by the shape parameter.

Sensitivity to radiational condition, the thermal constant of the ground, and surface roughness are also examined.

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Hiromi Yamazawa and Junsei Kondo

Abstract

An empirical-statistical method to estimate surface wind speed over complex terrain under strong wind condition is proposed. This method is based on the postulation that the surface wind speed depends on a surface roughness parameter and a terrain parameter, namely, the topographical parameter Ω.

The topographical parameters for Automated Meteorological Data Acquisition System observatories in the northeastern part of Japan were determined for strong wind conditions, and an expression for the topographical parameter is expressed as a product of single topographical parameters, each determined from prominent local features.

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Junsei Kondo and Sachinobu Ishida

Abstract

A value for the exchange speed of sensible heat C H U under natural convective conditions was determined by both indoor and field experiments. Regardless of the type of experiment, the relationships for the C H U were obtained as C H U = b(T ST)1/3. For a wet surface, ΔT v should be substituted for (T ST). Here, T S is the ground surface temperature, T the air temperature, and ΔT v the virtual temperature difference. In addition, b is a coefficient having a value of 0.0011 m s−1 K−1/3 for a smooth surface and 0.0038 m s−1 K−1/3 over a rough surface. From the field observation data, it was concluded that under strongly unstable conditions (−1 > ζ > −477) the best pair of stability profile functions was proposed.

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Junsei Kondo and Takeshi Yamazaki

Abstract

A snowmelt model based on a heat balance method has been developed. This model takes into account both the heat balance at the snow surface and that of the entire snow cover and simultaneously predicts the snow surface temperature and freezing depth. Observed or estimated incident radiation data are required for operation of the model.

Calculated amounts of snowmelt and snow surface temperatures were in agreement with those observed. Dependency of snowmelt on several parameters including maximum liquid water content, thermal conductivity and albedo of the snow was examined. It was found that as liquid water content or thermal conductivity increases, snowmelt decreases. Albedo is very influential in evaluating snowmelt.

Runoff from a basin having an area of 583 km2 was estimated using the present model, and was verified by the inflow data to a dam.

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Junsei Kondo and Jianqing Xu

Abstract

A model is presented for estimating the seasonal variations of evaporation, soil-water content, and soil temperature over nonvegetated land surfaces, especially in arid and semiarid regions. In the model, several types of soil are taken into consideration. Verification of the model has been achieved by comparing the observed and calculated results for the volcanic ash soil surface in Tsukuba and a sand dune field in Tottori. Using the routine data of 30 observatories including moist, semiarid, and arid regions at different elevations in China, the heat and water balances are estimated by the model.

At a station in a semiarid region such as Lanzhou, the sensible heat flux is found to be considerably greater than the latent heat flux during the dry season. Both fluxes, however, have comparable magnitudes during the rainy season. The annual mean value of the soil-water content increases with depth, and the rate of increase grows larger as the amount of annual precipitation increases. But for an arid station such as in Turpan, the profile of annual mean value of soil-water content does not increase with depth, and the soil-water evaporated from the soil surface during the day and came back to the soil surface at night. At a station having a snowfall during the winter in Altay, the ground-surface temperature begins to rise just after the disappearance of the snow cover. Consequently, the sensible and latent heat fluxes increase abruptly from negative values to positive values. Soil-water content becomes abundant due to the melted snow.

It is found that the annual amount of evaporation depends on the annual amount of precipitation. That is, in the arid region, it is proportional to the annual amount of precipitation. On the other hand, in the humid region, it tends to have a limited upper value, determined as functions of the potential evaporation and soil type. The water retentivity of loamy soil is better than that for sandy soil while the water permeability of sand is the best. These differences yield the result that the loamy soil has larger annual evaporation than the sandy soil. In arid and semiarid regions, a greater portion of rainwater is lost to evaporation within a few days after rainfall, so water resources become scarce. For a region having a snow cover during the winter, however, a considerable amount of melted water formed in the spring, resulting in a remarkable contribution to water resources.

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Takesh Yamazaki and Junsei Kondo

Abstract

The snowmelt and heat balance in snow-covered formed areas have been studied with the use of a canopy model. It was found that, in general, as the canopy density increased the snowmelt decreased. However, with conditions of high air temperature, weak winds, and large snow albedo, a greater degree of snowmelt occurred under a dense canopy due to infrared radiation from the canopy elements than under a sparse canopy. Although the snow temperature was never higher than 0°C while the air temperature was greater than 0°C, an upward sensible heat flux was supplied from the forest canopy, resulting in the atmospheric heating.

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Junsei Kondo and Tsutomu Watanabe

Abstract

A multilayer energy budget model for vegetation canopy is developed to describe the fluxes of sensible and latent heat exchanged between the vegetated surface and the atmosphere. The model gives satisfactory results when the calculated radiative surface temperature TR and fluxes of sensible and latent heat are compared with experimental data. This model illustrates that values of the bulk transfer coefficients CH and CE are sensitive to meteorological conditions (incident radiation, wind speed, air humidity) when their values are evaluated using TR as the mean surface temperature. Therefore, the use of TR is inadequate to determine the bulk transfer coefficients. As an alternative, the effective surface temperatures for the energy exchange are defined and the values of CH and CE are determined with these temperatures. These values of CH and CE are only dependent on the vegetation parameters: vegetation type and density, the leaf transfer coefficients (or stomatal resistance), and the moisture availability of the ground. Incorporating the values of CH and CE into the surface energy budget equation, the surface energy exchange and the effective surface temperature can be estimated when the available energy (the incident radiation minus the soil heat storage) is given. Also, an example of the method to determine the surface moisture availability β = CE/CH is shown with use of the measured radiative surface temperature.

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