Toshiro Kumakura

Gravity Waves Appearing in a High-Resolution GCM Simulation

Global characteristics of gravity waves in the lower stratosphere are examined using a GCM with high resolution in both the horizontal (T106, corresponding to about 120 km) and the vertical (;600 m). The bottom boundary condition of the model is that of an aquaplanet with perpetual February sea surface temperature. The simulated gravity waves are in good agreement with mesosphere‐stratosphere‐troposphere (MST) radar observations at a middle latitude on the gravity wave structure and on the frequency spectra as a function of height. The frequency spectra of simulated wind and temperature fluctuations are also examined as a function of latitude. Large values of spectral density are observed at frequencies higher than the inertial frequency ( f ) in a weak wind region around 20 km, which is consistent with the characteristics of internal gravity waves. An isolated peak is observed near f for horizontal wind spectra at latitudes higher than 108, while the energy is distributed in a wide range of frequency at lower latitudes where f approaches zero. Further analysis is performed of those fluctuations having periods shorter than 24 h and those having vertical wavelengths smaller than 5 km. These are frequently analyzed as gravity waves using observation data. The distribution of energy and momentum fluxes in the latitude‐height section is examined. The result indicates that short-period waves mostly propagate upward and poleward from the equatorial region. The wave energy reaches about 508 lat at the 27-km altitude. A negative (positive) maximum of vertical flux of meridional momentum (y9w9 ) is seen above the subtropical jet in the Northern (Southern) Hemisphere for small vertical-scale gravity waves. This is consistent with the preferred equatorward propagation of the wave indicated by a statistical analysis based on MST radar observations. The ratio of potential to kinetic energy maximizes over the equator and decreases poleward. The Eliassen‐Palm flux divergence associated with gravity waves is decelerative above the subtropical jet, albeit small.

Dependence of the water retention curve of snow on snow characteristics

Abstract The water retention curve (WRC), which shows the relationship between the volumetric liquid water content, θ v, and suction, h, is a fundamental part of the characterization of hydraulic properties. Therefore, the formulation of the WRC as a function of snow characteristics is essential for establishing a model of water movement through the snow cover. In this study, we measured the WRC of several snow samples, which had different characteristics (grain size, bulk dry density and grain type), using a gravity drainage column experiment and then analysed these data using the Van Genuchten soil physics model (VG model). The shape of the WRC depended strongly on both the sample grain size, d, and bulk dry density, ρ. Therefore, we introduced the parameter ρ/d to model the WRC of snow. The relationships between the parameters α and n of the VG model and ρ/d change with grain type. For melt forms, α, which is related to the inverse value of the air-entry suction, increases quickly as ρ/d decreases, whereas n, which is related to the gradient of θ v vs h, increases with ρ/d. Conversely, neither of these parameters of the VG model for rounded grains showed obvious dependence on ρ/d. These results suggest that water movement through snow cover can be modelled using grain size, bulk dry density and grain type based on the soil physics model.

Developing a photosynthetic sterility model to estimate CO2 fixation through the crop yield in Asia with the aid of MODIS data

Abstract Remote sensing technologies have been advanced continuously to a certain level for multi-scale applications to ease social and political concerns resulting from food security. In this study, an integrated monitoring, sensing and modeling system for estimating CO 2 fixation and grain yields using a photosynthetic sterility model was developed. Input data for model computation include observed meteorological data, numerical prediction reanalysis data, and satellite data such as solar radiation, land-cover and Normalized Difference Vegetation Index (NDVI) on a continental scale. Model validation requires crop yields and the Crop Situation Index (CSI) was provided by the Japanese government. It also demonstrates the application potential of this system to grain fields of paddy rice, winter wheat, and maize in Southeast Asia. The carbon hydrate in grains has the same chemical formula as that of cellulose in grain vegetation. The partition of sequestered CO 2 into grain, straw, and root portions of plant biomass weight was computed. The present photosynthesis model was evaluated using the mass of carbon included in the harvested grains of provincial crop production. Results indicate that the proposed system successfully estimates the photosynthesis fixation of rice reasonably well in Japan and China through the analysis of carbon in grains. However, the model tends to underestimate the photosynthesis rates for winter wheat and maize. The parameterization of radiation response function and the temperature response functions for low-temperature sterility need to be improved in the future.

Radar Attenuation and Reflectivity Measurements of Snow With Dual Ka-Band Radar

There is insufficient understanding of backscattering and attenuation for the radiowave remote sensing of snow because ground measurements of snow in the Ka-band are limited. This study estimates the equivalent radar reflectivity factor (Ze) and specific attenuation (k) of snow using a dual Ka-band radar (KaR) system comprising two identical Ka-band instruments. To evaluate the estimations, estimated k-Ze plots of rain events are compared with plots estimated from the raindrop size distribution. The two k-Ze plots have similar power-law relations. In contrast, k-Ze plots of snow have complex tendencies. Among snow events, the tendencies of k-Ze relations depend on surface temperature. When surface temperature exceeds 0 °C during snow events, k-Ze data are scattered and there are k values higher than those of rain. In contrast, when surface temperature is below 0 °C during snow events, both k and Ze are low and the k-Ze plots show no relation. In the former (latter) cases, wet (dry) snow is probably dominant. The differences in k-Ze relations of snow are attributed to the differences in backscattering and attenuation characteristics between wet and dry snow. To confirm the existence of wet/dry snow, snow particle data obtained using a two-dimensional video disdrometer on the ground are analyzed. Velocity-size distributions are clearly different in wet- and dry-snow cases. For dry-snow cases, snow particles of dry snow and graupel occasionally coexisted.

Snow measurement using a dual Ka-band radar system for GPM/DPR algorithm development

Both equivalent radar reflectivity factor (Ze) and specific attenuation (k) in several snow events are measured using a dual Ka-band radar system. Different k-Ze relations are obtained depending on surface air temperature. When surface air temperature is just above 0 °C, k-Ze relations scatter and larger k values than those of rain appear. On the other hand, when surface air temperature is below 0 °C, both k and Ze are small and a slight positive trend appears in the k-Ze relations. The difference of k-Ze relations can be attributed to the difference of the backscattering and attenuation characteristics between wet and dry snow. To confirm wet/dry snow existences, 2D-video-disdrometer data are analyzed. Velocity-size distributions of wet snow events are different from those of dry snow events. Graupels also show different velocity-size distributions from wet and dry snow particles with different k-Ze relations.

Development of rice photosynthesis model for monitoring yields and carbon sequestration using multi-satellite data

The forth IPCC report pointed out grain production as one of the highest vulnerability by which climate change is expected to impart the most severe effects. The recent concern about food scarcity motivates the development of the present system named Remote Sensing Environmental Monitor (RSEM) for crop yield monitoring. The authors have developed a photosynthesis model for rice production to address such issues. The system includes a photosynthetic sterility yield model using meteorological re-analysis data and precise land use and cover (LULC) classification of crop field in Asian countries. The validation concept is based on the fact that the carbon hydrate in grains has the same chemical formula as cellulose in grain vegetation. The both photosynthesis and sterility models are validated by carbon partitioning method associated with particular rice species in Japan and China.

Carbon partitioning as validation methods for crop yields and CO 2 sequestration monitoring in Asia using a photosynthetic-sterility model

Sustainability of world crop production and food security has become uncertain. The authors have developed an environmental research system called Remote Sensing Environmental Monitor (RSEM) for treating carbon sequestration by vegetation, grain production, desertification of Eurasian grassland, and CDM afforestation/ reforestation to a background of climate change and economic growth in rising Asian nations. The RSEM system involves vegetation photosynthesis and crop yield models for grains, including land-use classification, stomatal evaluation by surface energy fluxes, and daily monitoring for early warning. This paper presents a validation method for RSEM based on carbon partitioning in plants, focusing in particular on the effects of area sizes used in crop production statistics on carbon fixation and on sterility-based corrections to accumulated carbon sequestration values simulated using the RSEM photosynthesis model. The carbonhydrate in grains has the same chemical formula as cellulose in grain plants. The method proposed by partitioning the fixed carbon in harvested grains was used to investigate estimates of the amounts of carbon fixed, using the satellite-based RSEM model.

Crop yield and CO2 fixation monitoring over Asia by a photosynthetic-sterility model comparing with MODIS and carbon amounts in grain yields

The authors have developed a photosynthesis crop model for grain production under the background of climate change and Asian economic growth in developing countries. This paper presents an application of the model to grain fields of paddy rice, winter wheat, and maize in China and Southeast Asia. The carbon hydrate in grains has the same chemical formula as that of cellulose in grain vegetation. The partitioning of carbon in grain plants can validate fixation amounts of computed carbon using a satellite-based photosynthesis model. The model estimates the photosynthesis fixation of rice reasonably in Japan and China. Results were validated through examination of carbon in grains, but the model tends to underestimate results for winter wheat and maize. This study also provides daily distributions of the PSN, which is the CO2 fixation in Asian areas combined with a land-cover distribution classified from MODIS data, NDVI from SPOT VEGETATION, and meteorological re-analysis data by European Centre for Medium-Range Forecasts (ECMWF). The mean CO2 and carbon fixation rates in paddy areas were 25.92 (t CO2/ha) and 5.28 (t/ha) in Japan, respectively. The method is based on routine observation data, enabling automated monitoring of crop yields.