Masahide Ishizuka

Further development of a parameterization for convective turbulent dust emission and evaluation based on field observations

Further developments of a parameterization scheme for convective turbulent dust emission (CTDE) are presented. The scheme is advanced by including (1) a new statistical description of instantaneous momentum flux, (2) a correction function for cohesive force to account for the effect of soil moisture, and (3) a correction function for lifting force to consider the effect of vegetation roughness elements. The probability density function describing instantaneous momentum flux is now derived from large-eddy simulations for different atmospheric stabilities. The vegetation correction function is based on a drag partition theory. Additional improvements on the representations of interparticle cohesive force and particle size distribution are introduced. The new CTDE scheme is tested against the field data obtained at a sand storm monitoring station in the Horqin Sandy Land in China in 2011 and during the Japan-Australia Dust Experiment in Australia in 2006.

Use of a size-resolved 1-D resuspension scheme to evaluate resuspended radioactive material associated with mineral dust particles from the ground surface.

A size-resolved, one-dimensional resuspension scheme for soil particles from the ground surface is proposed to evaluate the concentration of radioactivity in the atmosphere due to the secondary emission of radioactive material. The particle size distributions of radioactive particles at a sampling point were measured and compared with the results evaluated by the scheme using four different soil textures: sand, loamy sand, sandy loam, and silty loam. For sandy loam and silty loam, the results were in good agreement with the size-resolved atmospheric radioactivity concentrations observed at a school ground in Tsushima District, Namie Town, Fukushima, which was heavily contaminated after the Fukushima Dai-ichi Nuclear Power Plant accident in March 2011. Though various assumptions were incorporated into both the scheme and evaluation conditions, this study shows that the proposed scheme can be applied to evaluate secondary emissions caused by aeolian resuspension of radioactive materials associated with mineral dust particles from the ground surface. The results underscore the importance of taking soil texture into account when evaluating the concentrations of resuspended, size-resolved atmospheric radioactivity.

Topographical and hydrological effects on meso-scale vegetation in desert steppe, Mongolia

This study investigated the seasonal variations of the normalized difference vegetation index (NDVI) and its relationships with climatic variables and topography in a small-scale (20 km×20 km) area (i.e., Tsogt-Ovoo village) within the desert steppe zone of Mongolia using in-situ observed climate data and satellite remote sensing data. We found that the topography is very important for vegetation growth in the desert steppe although the summer precipitation is the constraining factor. The unexpectedly high NDVI (up to 0.56), as well as the high aboveground biomass, in the valley bottom was primarily resulted from the topography-modulated redistribution of overland flow after relatively heavy precipitation events during the growing season. This makes the valley bottoms in desert steppes not only reliable feeding resources for livestock but also heavens for wild lives. But, the detected large standard deviation of annual maximum NDVI (NDVImax) from 2000 to 2013 in the valley bottom in response to rather variable precipitation implies that the valley bottoms under desert steppe climates are more vulnerable to climatic change.

ESTIMATION OF BOD LOADS CONSIDERING WATER TEMPERATURE IN THE YAMATO RIVER CATCHMENTS

Calculated Pollutant load per unit production and actual pollutant load of Yamato River were estimated. The actual pollutant load was determined from measured flow rates and concentrations. As a result, actual BOD load showed seasonal changes with low values of summer and high values of winter. The change depended on temperature because a rate of decomposition of organic compound depends on temperature. The actual BOD loads between two pints along the Yamato River with no branch river and no drainage were measured and a rate of decomposition between them was calculated. The calculated seasonal BOD load from pollutant load unit production method including rate of decomposition showed the same pattern of the actual BOD load. The total BOD load value by unit production including decomposition calculated method was 4 times of the actual load. As BOD was not measured at flood condition, the actual BOD did not include floating material at the condition of high flow rate and then was smaller than the calculated load per unit production.

CHARACTER OF COD VALUES WITH FLOW RATE CLAFIED BY ONE HOUR AUTOMATIC MEASUREMENT IN THE YAMATOGAWA RIVER

COD was previously measured from sampled water. Then 1 month measurement does not include flood condition because of safety for sampling. 1 hour measurement is automatically sampled and measured in situ at station and then includes flood condition. To clarify difference between 1 month measurement and 1 hour measurement , using both measuring results of flow rate, COD, TB and EC values of the Yamatogawa river, effect of flow rate on COD , TB and EC values was clarified. COD and TB values increased with flow rate. EC value decreased as flow rate increased . The relationships between COD and flow rate, TB and flow rate were very similar. Therefore , COD was more strongly influenced by floating material than soluble substances because TB was concentration of floating material . Using the relationships between COD and flow rate, COD loads were calculated. As a result , the COD load calculated by the 1 hour measurement was more about 2 times than the COD load calculated by the 1 month measurement.

CHANGES OF SUBSTANCES DERIVED FROM DOMESTIC SEWAGE IN YAMATOGAWA RIVER BASIN

Seasonal Concentrations of BOD, NH4+-N and interfacial active agent derived from domestic sewage were high in winter and low in summer. The concentrations decreased with an increase in water temperature. Generally, river water contains organic compounds and Cl- derived from domestic sewage and Cl- was quite stable in rivers. As the ratios of BOD/Cl- and NH4+-N/Cl- decreased down the stream and changed seasonally, organic compounds were thought to be decomposed during flow. NO3--N/Cl- which organic compounds were finally decomposed into, also decreased down the stream and were high in winter and low in summer. NO3--N was thought to be used for photosynthesis because pH, DO values and chlorophyll concentration of the Yamato river increased with temperature and decrease of NO3--N concentration.

SURFACE FLOW MEASUREMENT USING VHF OCEAN RADAR IN A STRATIFIED COASTAL WATER AND DATA ASSIMILATION INTO A 3-D BAROCLINIC FLOW MODEL

Doppler ocean radar is being increasingly used in estuarine research. The advantage of using this instrument is that it can measure sea surface flow velocity field in all weather conditions due to its remote sensing capability. In the present study, the accuracy of the surface current velocities in Osaka Bay measured by very high-frequency (VHF) Doppler radar is investigated. The radar system uses a frequency of 41.9 MHz and allows a radial range resolution of 500 m at ranges up to 20 km from a coastline. Data from VHF ocean radar are compared with that using Acoustic Doppler Current Profilers (ADCP) in order to quantitatively verify the surface shear and wind-induced current. They are also used to enhance an assimilation technique in order to assimilate the observed surface flow velocities into a three-dimensional baroclinic flow model. The correlation coefficient and rms difference between the velocities measured by the VHF ocean radar and the in situ current profiler axe in the order of 0.69 and 6.4 cm/s, respectively. Assimilation of the surface velocity is carried out using ocean radar observations. Two assimilation schemes, blending and nudging, are examined. The blending scheme including the vertical mixing induced by wind stress and with a logarithmic profile for the decrease in surface velocity downward performs better than the nudging scheme. Application of the assimilation model shows good agreement with the in situ current and salinity data.