Akihiro Hashimoto

Implementation of a Silver Iodide Cloud-Seeding Parameterization in WRF. Part I: Model Description and Idealized 2D Sensitivity Tests

AbstractA silver iodide (AgI) cloud-seeding parameterization has been implemented into the Thompson microphysics scheme of the Weather Research and Forecasting model to investigate glaciogenic cloud-seeding effects. The sensitivity of the parameterization to meteorological conditions, cloud properties, and seeding rates was examined by simulating two-dimensional idealized moist flow over a bell-shaped mountain. The results verified that this parameterization can reasonably simulate the physical processes of cloud seeding with the limitations of the constant cloud droplet concentration assumed in the scheme and the two-dimensional model setup. The results showed the following: 1) Deposition was the dominant nucleation mode of AgI from simulated aircraft seeding, whereas immersion freezing was the most active mode for ground-based seeding. Deposition and condensation freezing were also important for ground-based seeding. Contact freezing was the weakest nucleation mode for both ground-based and airborne see...

Performance of Long-Term Integrations of the Japan Meteorological Agency Nonhydrostatic Model Using the Spectral Boundary Coupling Method

The spectral boundary coupling (SBC) method, which is an approach used to couple a limited-area model with a large-scale model, was introduced into a nonhydrostatic model. To investigate whether the SBC method works well in a long-term integration of a high-resolution nonhydrostatic model, two numerical experiments were conducted with a model having a horizontal grid interval of 5 km. In one experiment, the SBC method was employed, while it was not in the other experiment. The time integration in both experiments was over a 40-day period. The nonhydrostatic model was nested into objectively analyzed fields, instead of the forecasts from an extended-area model. Predicted patterns of sea level pressure and precipitation were compared with objective analyses, and data provided by the Global Precipitation Climatology Project (GPCP), respectively. The predicted rainfall amounts and surface temperature over the Japanese islands were statistically evaluated, making use of the analyzed rainfall and surface data observed by the Japan Meteorological Agency (JMA). All results examined in the present study exhibited better performances with use of the SBC method than those without the SBC method. It was found that the SBC method was highly useful in long-term simulations by a high-resolution nonhydrostatic model.

Optical and Microphysical Properties of Upper Clouds Measured with the Raman Lidar and Hydrometeor Videosonde: A Case Study on 29 March 2004 over Tsukuba, Japan

Abstract Optical and microphysical properties of the upper clouds at an altitude range of 5–11 km were measured over Tsukuba, Japan, on 29–30 March 2004 using a ground-based Raman lidar and a balloon-borne hydrometeor videosonde (HYVIS). The Raman lidar measured the vertical distributions of the particle extinction coefficient, backscattering coefficients, depolarization ratio, and extinction-to-backscatter ratio (lidar ratio) at 532 nm; further, it measured the water vapor mixing ratio. The HYVIS measured the vertical distributions of the particle size, shape, cross-sectional area, and number concentration of the cloud particles by taking microscopic images. The HYVIS measurement showed that the cloud particles were ice crystals whose shapes were columnar, bulletlike, platelike, and irregular, and 7–400 μm in size. The Raman lidar measurement showed that the depolarization ratio ranged from 0% to 35% and the lidar ranged from 0.3 to 30 sr for the clouds in ice-saturated air. The comparison between the me...

Numerical Simulations of the Formation of Melting-Layer Cloud

Abstract A number of previously published observational studies have reported the common occurrence of cloudy layers at around 5-km elevation in the tropics. There are two candidate processes that are able to explain the occurrence of cloudy layers in the middle level: cloud detrainment promoted by the stable layer and enhanced condensation to compensate for melting cooling. In the present study, the authors used a cloud-resolving nonhydrostatic model and conducted numerical simulations of a squall line to clarify the process responsible for the formation of midlevel thin cloud, especially the cloud at the 0°C level. In a two-dimensional control experiment thin cloud was simulated in the middle level, and cloud coverage showed a notable peak just below the 0°C level for environments without a stable layer in the initial temperature profile. Enhanced and weakened stability layers simultaneously appeared above and below the peak level of the cloud coverage. The formation of midlevel thin cloud is associated...

Balloon-borne and Raman lidar observations of Asian dust and cirrus cloud properties over Tsukuba, Japan

The vertical distributions of the microphysical and optical properties of tropospheric aerosols and cirrus cloud were measured using an instrumented balloon and a ground-based Raman lidar over Tsukuba, Japan (36°N, 140°E), during the Asian dust events on 9 and 21 May 2007 to investigate the influence of Asian mineral dust on ice cloud formation in the upper troposphere. The instrumented balloon measured the particle size distribution, ice crystal images, dew/frost point, relative humidity, and temperature. The Raman lidar measured the particle backscattering and extinction coefficients and the depolarization ratio at a wavelength of 532u2009nm. The results of the balloon measurements showed that supermicrometer (0.7 to 2.8u2009µm in optical-equivalent radius) dust particles and ice crystals (10 to 400u2009µm in maximum dimension) were present in the upper troposphere (8 to 12u2009km in altitude), with number concentrations varying from 5u2009×u200910−3 to 0.6u2009cm−3 for dust and from 5u2009×u200910−3 to 0.15u2009cm−3 for ice crystals. The Raman lidar measurement indicated that the particle depolarization ratios were 15 to 35% in the altitude range of 6 to 12u2009km, indicating the predominance of nonspherical particles in the region. The temperature ranged from −33 to −63°C, and the relative humidity with respect to ice (RHi), estimated from the total (vapor plus condensate) water content obtained with the Snow White hygrometer in the cloud, was 130% at maximum on 9 May, which was close to the activation point of Asian mineral dust as ice nuclei to form ice crystals.

Flood caused by driftwood accumulation at a bridge

Purpose n n n n nExtreme weather events introduced by climate change have been frequent across the world for the past decade. For example, Takeda City, a mountainous area in the south-western Japan, experienced a severe river flood event caused by the factors of high flow, presence of bridges and driftwood accumulation in July 2012. This study aims to focus on this event (hereafter, Takeda flood) because the unique factors of driftwood and bridges were involved. In the Takeda flood, high flow, driftwood and bridge were the potential key factors that caused the flood. The authors studied to reveal the physical processes of the Takeda flood. n n n n nDesign/methodology/approach n n n n nThe authors conducted a fundamental laboratory experiment with a miniature bridge, open channel flow and idealized driftwood accumulation. They also performed a numerical simulation by using a smoothed particle hydrodynamics (SPH) method, which can treat fluid as particle elements. This model was chosen because the SPH method is capable of treating a complex flow such as a spray of water around a bridge. n n n n nFindings n n n n nThe numerical simulation successfully reproduced the bridge- and driftwood-induced floods of the laboratory experiment. Then, the contribution of the studied key factors to the flood mechanism based on the fluid forces generated by high flow, bridge and driftwood (i.e. pressure distributions) was quantitatively assessed. The results showed that the driftwood accumulation and high flow conditions are potentially important factors that can cause a severe flood like the Takeda flood. n n n n nOriginality/value n n n n nSimulated results with high flow conditions may be helpful to consider the countermeasure for future floods under climate change even though the test was simple and fundamental.

Development of spaceborne radar simulator by NICT and JAXA using JMA cloud-resolving model

This study demonstrated preliminary results in diagnosis of the numerical model with reference to the TRMM/PR, examples of the GPM/DPR synthetic data, and application of the synthetic data to the algorithm development in the nonuniform beamfilling correction method. These were performed using a satellite radar simulation algorithm by the National Institute of Information and Communications Technology (NICT) and the Japan Aerospace Exploration Agency (JAXA) named as the Integrated Satellite Observation Simulator for Radar (ISOSIM-Radar) and a cloud-resolving model by the Japan Meteorological Agency (JMA-NHM).

EXPELIMENTAL STUDY ON THE ABILITY TO INDUCE A UNIDERECTIONAL FLOW BY A PIPE WITH A FLANGE

In order to activate water exchange between a semi-enclosed bay and its open sea, a water purification method, called One-Way Pipe, is proposed. One-Way Pipe is a pipe attached asymmetrical structures inside, and can generate residual currents in oscillatory flow fields due to their directional resistance properties. This method is more economic and eco-friendly because it utilizes waves as energy sources. In this study, the optimum size and the position of the flange to generate residual currents were experimentally investigated under several wave conditions. Furthermore, the mechanisms for producing a unidirectional flow inside the pipe were discussed. The flange forms separation vortices behind it and generate a low pressure region behind the outlet of the pipe. This low pressure region due to separation vortices draws mass flow inside the pipe.

Residual Currents Around Plural Asymmetrical Structures in Oscillatory Flow Fields

In the resent years, water deterioration by pollution in a stagnant sea area like a semi-enclosed bay occurs mainly due to the lack of water exchange with the open sea. [KYG97] suggested to use unidirectional residual currents generated by asymmetrical structures which are put on the sea bottom in order to activate substance transport in a tidal field. In addition, [KSK01] also proposed to apply this method to control sediment transport in wave fields. [KHF06] proposed the specific pipe called One-Way Pipe, which can generate residual currents in a wave field by a number of asymmetrical structures set inside the pipe. It is expected to activate water exchange with the open sea by putting a series of One-Way Pipes from the inside end of the bay to the baymouth.

Simulations of Forecast and Climate Modes Using Non-Hydrostatic Regional Models

Two applications with a cloud-resolving model are shown utilizing the Earth Simulator. The first application is a case in the winter cold-air outbreak situation observed over the Sea of Japan as a forecast mode. Detailed structures of the convergence zone (JPCZ) and formation of mechanism of transverse convective clouds (T-modes) are discussed. A wide domain in the horizontal (2000 × 2000) was used with a horizontal resolution of 1 km, and could reproduce detailed structures of the JPCZ as well as the cloud streets in the right positions. It is also found that the cloud streets of T-modes are parallel to the vertical wind shears and, thus, similar to the ordinary formation mechanism as longitudinal convective ones. The second application is changes in the Baiu frontal activity in the future warming climate from the present one as a climate mode. At the future warming climate, the Baiu front is more active over southern Japan, and the precipitation amounts increase there. On the other hand, the frequency of occurrence of heavy rainfall greater than 30 mm h-1 increases over the Japan Islands.