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505 results on '"Ohata, T."'

136. Modelling plant canopy effects on annual variability of evapotranspiration and heat fluxes for a semi-arid grassland on the southern periphery of the Eurasian cryosphere in Mongolia.

Author

Yinsheng Zhang, Ohata, T., Zhou, J., and Davaa, G.

Subjects
PLANT canopies, EVAPOTRANSPIRATION, HEAT flux, PLANT transpiration, GRASSLANDS, ARID regions biodiversity, SOIL temperature
Abstract

The ability to predict vegetation cover effects on thermal/water regimes can enhance our understanding of canopy controls on evapotranspiration. The Simultaneous Heat and Water (SHAW) model is a detailed process model of heat and water movement in a snow-residue-soil system. This paper describes provisions added to the SHAW model for vegetation cover and simulation of heat and water transfer through the soil-plant-air continuum. The model was applied to four full years (May 2003-April 2007) of data collected on sparse grassland at Nalaikh in north-eastern Mongolia. Simulated soil temperature and radiation components agreed reasonably well with measured values. The absolute differences between simulated and measured soil temperatures were larger at both the surface layer and deeper layer, but relatively smaller in the layer from 0·8 to 2·4 m. Radiation components were mimicked by the SHAW model with model efficiency (ME) reaching 0·93-0·72. Latent and sensible heat fluxes were simulated well with MEs of 0·93 and 0·87, respectively. The vegetation control on evapotranspiration was investigated by sensitivity experiments of model performance with changing leaf area index (LAI) values but constant of other variables. The results suggest that annual evapotranspiration ranged from 16 to − 22% in response to extremes of doubled and zero LAI. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Published
2011
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140. Sublimation from thin snow cover at the edge of the Eurasian cryosphere in Mongolia.

Author

Yinsheng Zhang, Ishikawa, M., Ohata, T., and Oyunbaatar, D.

Subjects
CLIMATE change, SEASONS, SNOW, WIND-snow interaction, SUBLIMATION (Chemistry), WIND speed, UPPER air temperature, EVAPOTRANSPIRATION, METEOROLOGICAL observations, GLACIOLOGY
Abstract

The article presents a study on the variation of snow sublimation at three sites representing a variety of geographic and vegetative cover conditions in Mongolia. The snow sublimation values were calculated using the aerodynamic profile method and the results were verified by eddy covariance observations. Results show that sublimation variability was dominated by intense sublimation events characterized by daily sublimation exceeding 0-4 mm. Wind speed and air temperature are the dominant meteorological elements affecting sublimation. Annual sublimation averaged 11-7 mm at the flat plain meteorological station and 15-7 mm at the site in the mountains. The sum of snow sublimation and snowmelt evaporation represented 17 to 20% of annual evapotranspiration in a couple of observation years.

Published
2008
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141. Environmental controls on evapotranspiration from sparse grassland in Mongolia.

Author

Yinsheng Zhang, Kadota, T., Ohata, T., and Oyunbaatar, D.

Subjects
HYDROLOGY, EVAPOTRANSPIRATION, WATER supply, EVAPORATION (Meteorology), PLANT transpiration, ECOLOGY, GRASSLANDS, GROUNDWATER, RAINFALL, SOIL infiltration
Abstract

Environmental controls on evapotranspiration were investigated at a sparse grassland in Mongolia during 2003 and 2004. The study site was located on the southern periphery of the Eurasian cryosphere. Data from Eddy covariance, aerodynamic, and manual measurements were used in the analysis. A decoupling factor (Ω) was calculated to determine the relative importance of surface conductance and radiation to change in evapotranspiration rates. Higher evapotranspiration rates associated with a higher frequency of large Ω values revealed the importance of radiation forcing on evapotranspiration at this study site. As Ω increases', the aerodynamic conductance (ga) increased correspondingly but vegetation conductance (gc) decreased. Aerodynamic conductance (ga) was well fitted to an exponential function of the wind stress; gc clearly decreased as the vapour pressure deficit (all increased; gc related to air temperature through d. Although grass cover was sparse at the study site, the anticipated effect of soil moisture on E and gs was only slightly suggested and thus not deducible. On the 10-day-interval time scale, the effect of vegetation cover on evapotranspiration was insignificant compared to that of surface soil moisture. Changes in soil evaporation, related to precipitation, mainly caused the very large inter-annual differences in evapotranspiration. The relationship between evapotranspiration and surface bulk resistance at the study site could therefore be fit to an exponential function. [ABSTRACT FROM AUTHOR]

Published
2007
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143. Land surface identification near Yakutsk in eastern Siberia using video images taken from a hedgehopping aircraft.

Author

Suzuki, R., Hiyama**, T., Asanuma, J., and Ohata, T.

Subjects
REMOTE-sensing images, AERIAL photographs, SURVEYING (Engineering), RADAR in surveying, GEOGRAPHY
Abstract

Aircraft-based remote sensing was carried out over the Lena River region (approximately 100 km horizontal scale) near Yakutsk, in eastern Siberia, on nine days between 24 April and 19 June 2000. A home-use video camera was installed on the aircraft and aerial images of the land surface were recorded. By flying at very low altitudes (100 m and 150 m), we compensated for the low resolution of the camera. In all, 5515 scenes were sampled at 10-s intervals from the video, visually interpreted, and classified. The snow/ice and water cover conditions were also interpreted. The results showed that grassland covers the riverine lowland (RLL) of the Lena River, while the principal form of land cover over the terraces is larch forest (about 61%). There was a remarkable contrast between the left (LBT) and right (RBT) bank terraces of the Lena River, no-forest areas covered 28.8% of the RBT, whereas no-forest areas covered only 13.8% of the LBT. In addition, the LBT had a greater proportion of birch forest than the RBT (15.2% vs 2.5%). The video data over eight days showed that the snow thawed first in the RLL and last in the forested areas of the LBT and RBT. An increase in the area covered by water in the RLL in mid-May was probably due to flooding by the Lena River. Distinguishing insolated from cloud-shadowed scenes of the land surface revealed that the insolation rate was lower over the LBT and RBT than over the RLL. The land-cover database created in this analysis will play an important role as basic, reliable ground-truth information for studies using satellite images. [ABSTRACT FROM AUTHOR]

Published
2004
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147. Inhibition by 1'-acetoxychavicol acetate of lipopolysaccharide- and interferon-γ-induced nitric oxide production through suppression of inducible nitric oxide synthase gene expression in RAW264 cells.

Author

Ohata, T, Fukuda, K, Murakami, A, Ohigashi, H, Sugimura, T, and Wakabayashi, K

Abstract

Although nitric oxide (NO) is an important biological mediator, excessive production in inflammation is thought to be a causative factor of cellular injury and cancer in the long term. In the present study the effects of 1'-acetoxychavicol acetate (ACA), which has anticarcinogenic properties, on NO production in murine macrophage cell line RAW264 cells stimulated with lipopolysaccharide or interferon-γ were examined. ACA suppressed NO production dose dependently with an IC50 of 160 ng/ml (680 nM). The decrease in NO production was shown to parallel reduced expression of iNOS mRNA and protein. The influence of ACA on transcription factors, such as NF-κB, AP-1 and Stat1, which are involved in expression of the iNOS gene was assessed. ACA was found to suppress degradation of IκB, and NF-κB inhibitor factor, and consequently inhibit NF-κB activation. Activation of AP-1 and Stat1 was also blocked by ACA treatment. Thus we demonstrate that ACA exerts potent inhibitory effects on NO production, apparently mediated by modulation of activation of several transcription factors. This could contribute to the anticarcinogenic properties of ACA. [ABSTRACT FROM PUBLISHER]

Published
1998
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149. Role of nitric oxide in a temperature dependent regulation of systemic vascular resistance in cardiopulmonary bypass.

Author

Ohata, T, Sawa, Y, Kadoba, K, Kagisaki, K, Suzuki, K, and Matsuda, H

Abstract

Nitric oxide is the most potent vasodilator among inflammation-mediated vasoactive substances. Tepid cardiopulmonary bypass has been known to maintain low vascular resistance and nitric oxide may also be involved. There has been no previous clinical study elucidating a role of nitric oxide in a temperature dependent regulation of systemic vascular resistance in cardiopulmonary bypass.

Published
2000
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