Miyamoto, Yoshiaki

写真a

Affiliation

Faculty of Environment and Information Studies (Shonan Fujisawa)

Position

Associate Professor

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Career 【 Display / hide 】

  • 2011.04
    -
    2016.03

    RIKEN Advanced Institute for Computational Science

  • 2016.04
    -
    2018.03

    University of Miami

  • 2016.04
    -
    Present

    RIKEN Center for Computational Science

  • 2021.10
    -
    Present

    Yokohama National University

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Papers 【 Display / hide 】

  • Lightning frequency in an idealized hurricane-like vortex from initial to steady-state using a coupled meteorological and explicit bulk lightning model

    Sato Y., Miyamoto Y., Tomita H.

    Monthly Weather Review (Monthly Weather Review)  149 ( 3 ) 753 - 771 2021.02

    ISSN  00270644

    　View Summary

    The dependence of lightning frequency on the life cycle of an idealized tropical cyclone (TC) was investigated using a three-dimensional meteorological model coupled with an explicit lightning model. To investigate this dependence, an idealized numerical simulation covering the initial state to the steady state (SS) of an idealized TC was conducted. The simulation was consistent with the temporal evolution of lightning frequency reported by previous observational studies. Our analyses showed that the dependence originates from changes in the types of convective cloud with lightning over the life cycle of the TC. Before rapid intensification (RI) and in the early stage of RI, convective cloud cells that form under high-convective available potential energy (CAPE) conditions are the main contributors to lightning. As the TC reaches the late stage of RI and approaches SS, the secondary circulation becomes prominent and convective clouds in the eyewall region alongside the secondary circulation gradually become the main contributors to the lightning. In the convective cloud cells formed under high-CAPE conditions, upward velocity is strong and large charge density is provided through noninductive charge separation induced by graupel collisions. This large charge density frequently induces lightning in the clouds. On the other hand, the vertical velocity in the eyewall is weak, and it tends to contribute to lightning only when the TC reaches the mature stage. Our analyses imply that the maximum lightning frequency that occurs before the maximum intensity of a TC corresponds to the stage of a TC's life cycle in which convective cloud cells are generated most frequently and moisten the upper troposphere.

  • Using satellite observations to evaluate the relationships between ice condensate, latent heat release, and tropical cyclone intensification in a mesoscale model

    Wu S.N., Soden B.J., Miyamoto Y., Nolan D.S., Buehler S.A.

    Monthly Weather Review (Monthly Weather Review)  149 ( 1 ) 113 - 129 2020.12

    ISSN  00270644

    　View Summary

    This study examines the relationship between frozen hydrometeors and latent heating in model simulations and evaluates the capability of the Weather Research and Forecasting (WRF) Model to reproduce the observed frozen hydrometeors and their relationship to tropical cyclone (TC) intensification. Previous modeling studies have emphasized the importance of both the amount and location of latent heating inmodulating the evolution of TCintensity.However, the lack of observations limits a full understanding of its importance in the real atmosphere. Idealized simulations usingWRF indicate that latent heating is strongly correlated to the amount of ice water content, suggesting that ice water content can serve as an observable proxy for latent heat release in themid- to upper troposphere.Based on this result, satellite observations are used to create storm-centered composites of ice water path as a function of TC intensity. The model reasonably captures the vertical and horizontal distribution of icewater content and its dependence upon TC intensity, with differences typically less than 20%. The model also captures the signature of increased ice water content for intensifying TCs, suggesting that observations of ice water content provide a useful diagnostic for understanding and evaluating model simulations of TC intensification.

  • An energy balance model for low--level clouds based on a simulation resolving mesoscale motions

    Miyamoto Y., Sato Y., Nishizawa S., Yashiro H., Seiki T., Noda A.T.

    Journal of the Meteorological Society of Japan (Journal of the Meteorological Society of Japan)  98 ( 5 ) 987 - 1004 2020.10

    ISSN  00261165

    　View Summary

    This study proposes a new energy balance model to determine the cloud fraction of low-level clouds. It is assumed that the horizontal cloud field consists of several individual cloud cells with a similar structure. Using a high–resolution simulation dataset with a wide numerical domain, we conducted an energy budget analysis. Here we show that the energy injected into the domain by surface flux is approximately balanced with that loss due to radiation and advection due to large–scale motion. The analysis of cloud cells within the simulated cloud field showed that the cloud field consists of a number of cloud cells with similar structures. We developed a simple model for the cloud fraction from the energy conservation equation. The cloud fraction determined using the model developed in this study was able to quantitatively captured the simulated cloud fraction.

  • Impacts of number of cloud condensation nuclei on two-dimensional moist rayleigh convection

    Miyamoto Y., Nishizawa S., Tomita H.

    Journal of the Meteorological Society of Japan (Journal of the Meteorological Society of Japan)  98 ( 2 ) 437 - 453 2020

    ISSN  00261165

    　View Summary

    The impacts of the number density of cloud condensation nuclei (CCN) and other thermodynamic quantities on moist Rayleigh convection were examined. A numerical model, consisting of a simple two–dimensional equation for Boussinesq air and a sophisticated double moment microphysics scheme, was developed. The impact of the number of CCN is most prominent in the initially formed convection, whereas the convection in the quasi–steady state does not significantly depend on the number of CCN. It is suggested that the former convection is driven by a mechanism without a background circulation, such as parcel theory. In contrast, the latter convection appears to be driven by the statically unstable background layer. Incorporating the cloud microphysics reduces the integrated kinetic energy and number of convective cells (increases the distance between the cells), with some exceptions, which are consistent with previous studies. These features are not largely sensitive to the number of CCN. It is shown in this study that the reduction in kinetic energy is mainly due to condensation (evaporation) in the upper (lower) layer, which tends to stabilize the fluid. The ensemble simulation shows that the sensitivity of the moist processes to changes in the temperature at the bottom boundary, temperature lapse rate, water vapor mixing ratio, and CCN is qualitatively similar to that in the control simulation. The impact becomes strong with increasing temperature lapse rate. The number of convective cells in a domain decreases with the degree of supersaturation or an increase in the domain-integrated condensate.

  • Large dependency of charge distribution in a tropical cyclone inner core upon aerosol number concentration

    Sato Y., Miyamoto Y., Tomita H.

    Progress in Earth and Planetary Science (Progress in Earth and Planetary Science)  6 ( 1 )  2019.12

    　View Summary

    The impacts of aerosols on the charge distribution of hydrometeors and lightning flash density in a tropical cyclone (TC) were investigated using a meteorological model coupled with an explicit lightning model. The meteorological model successfully simulated the tripole structure of charge density distribution in a TC, as reported by previous studies. The impacts of aerosols were investigated through a sensitivity experiment with changing the aerosol number concentration. The tripole structure became unclear with increasing aerosol number concentrations. The positive charge distribution located in the lower layer was not seen, and raindrops with negative charge distribution reached the surface. As a result, the vertical structure of the charge density was dipolar in the polluted case. As the tripole structure shifted to dipole, the magnitude of the electric field tended to be large, and the flash number was large. By contrast, in the pristine case, the tripole structure was dominant, and the flash number was much smaller than in the polluted case. [Figure not available: see fulltext.].

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Papers, etc., Registered in KOARA 【 Display / hide 】

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Research Projects of Competitive Funds, etc. 【 Display / hide 】

  • 台風の強度・構造に対するエアロゾルの影響

    2019.04
    -
    2020.03

    MEXT,JSPS, Grant-in-Aid for Scientific Research, Grant-in-Aid for Research Activity Start-up , Principal investigator

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Courses Taught 【 Display / hide 】

  • THEORY OF GLOBAL ENVIRONMENT TECHNOLOGY

    2024

  • THEORY OF ENVIRONMENT SENSING TECHNOLOGY

    2024

  • SPECIAL RESEARCH PROJECT B

    2024

  • SEMINAR A

    2024

  • PRACTICE IN TEACHING 2

    2024

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