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[AAS08-03] Resolution dependency of the charge structure of a convective cloud in a bulk lightning model
In this study, we investigated the dependency of the charge structure in a summer convective cloud (Takayama et al., 1997) on the horizontal resolution of a bulk lightning model (BLM; Sato et al., 2019) coupled with a meteorological model Scalable Computing for Advanced Library and Environment (SCALE; Nishizawa et al., 2015; Sato et al., 2015). For investigating the dependency, we implemented a multigrid (MG) solver (Wesseling, 1995), which can efficiently solve inversion problems even when the problem size is large, into SCALE. MG solver enabled us to perform the simulations with sweeping the horizontal grid resolution including high-resolution, which cannot be conducted without MG solver.
The results of the simulation indicate that the numerical convergence of total lightning frequency and the charge separation rate of graupel was achieved with a resolution of 200 m. The reason for this convergence is that with finer resolution, the strong vertical updraft actively transports liquid water to higher altitudes, generating an environment conducive to riming, with sufficient supercooled water present at altitudes of 9–11 km. Consequently, with higher resolution, the graupel mixing ratio increases at these altitudes. This sequence of processes is achieved with resolutions higher than 200 m and converged numerically with a resolution of 200 m. The formation of graupel at these altitudes led to an increase in the charge separation of graupel, resulting in higher lightning frequency with higher resolutions. It is also confirmed that the numerical convergence of the graupel mixing ratio is accompanied by the numerical convergence of the total lightning frequency and the charge separation of graupel with a resolution of 200 m. These results suggest that a resolution of 200 m or higher is necessary to accurately reproduce the lightning frequency in a numerical weather model coupled with BLM.
Reference
・Nishizawa, S., Yashiro, H., Sato, Y., Miyamoto, Y., Tomita, H., 2015: Influence of grid aspect ratio on planetary boundary layer turbulence in large-eddy simulations. Geosci. Model Dev., 8, 3393–3419, doi:10.5194/ gmd-8-3393-2015
・Sato, Y., Nishizawa, S., Yashiro, H., Miyamoto, Y., Kajikawa, Y., and Tomita, H., 2015: Impacts of cloud microphysics on trade wind cumulus: Which cloud microphysics processes contribute to the diversity in a large eddy simulation?. Prog. Earth Planet. Sci., 2, 1-16, doi: 10.1186/s40645-015-0053-6
・Sato, Y., Miyamoto, Y., Tomita, H., 2019: Large dependency of charge distribution in a tropical cyclone inner core upon aerosol number concentration, Prog. Earth Planet. Sci., 6(62), doi:10.1186/s40645-019-0309-7
・Takayama, H., Niino, H., Watanabe, S., Sugaya, J., Studies, Members of Tsukuba Area Precipitation Studies, 1997: Downbursts in the northwestern part of Saitama Prefecture on 8 September 1994. J. Meteorol. Soc. Jpn. Ser. II, 75(4), 885–905. https://doi.org/10.2151/JMSJ1965.75.4_885
・Wesseling, P., 1995: Introduction to MultiGrid solvers, No. NASA-CR-195045, 134 pp.
The results of the simulation indicate that the numerical convergence of total lightning frequency and the charge separation rate of graupel was achieved with a resolution of 200 m. The reason for this convergence is that with finer resolution, the strong vertical updraft actively transports liquid water to higher altitudes, generating an environment conducive to riming, with sufficient supercooled water present at altitudes of 9–11 km. Consequently, with higher resolution, the graupel mixing ratio increases at these altitudes. This sequence of processes is achieved with resolutions higher than 200 m and converged numerically with a resolution of 200 m. The formation of graupel at these altitudes led to an increase in the charge separation of graupel, resulting in higher lightning frequency with higher resolutions. It is also confirmed that the numerical convergence of the graupel mixing ratio is accompanied by the numerical convergence of the total lightning frequency and the charge separation of graupel with a resolution of 200 m. These results suggest that a resolution of 200 m or higher is necessary to accurately reproduce the lightning frequency in a numerical weather model coupled with BLM.
Reference
・Nishizawa, S., Yashiro, H., Sato, Y., Miyamoto, Y., Tomita, H., 2015: Influence of grid aspect ratio on planetary boundary layer turbulence in large-eddy simulations. Geosci. Model Dev., 8, 3393–3419, doi:10.5194/ gmd-8-3393-2015
・Sato, Y., Nishizawa, S., Yashiro, H., Miyamoto, Y., Kajikawa, Y., and Tomita, H., 2015: Impacts of cloud microphysics on trade wind cumulus: Which cloud microphysics processes contribute to the diversity in a large eddy simulation?. Prog. Earth Planet. Sci., 2, 1-16, doi: 10.1186/s40645-015-0053-6
・Sato, Y., Miyamoto, Y., Tomita, H., 2019: Large dependency of charge distribution in a tropical cyclone inner core upon aerosol number concentration, Prog. Earth Planet. Sci., 6(62), doi:10.1186/s40645-019-0309-7
・Takayama, H., Niino, H., Watanabe, S., Sugaya, J., Studies, Members of Tsukuba Area Precipitation Studies, 1997: Downbursts in the northwestern part of Saitama Prefecture on 8 September 1994. J. Meteorol. Soc. Jpn. Ser. II, 75(4), 885–905. https://doi.org/10.2151/JMSJ1965.75.4_885
・Wesseling, P., 1995: Introduction to MultiGrid solvers, No. NASA-CR-195045, 134 pp.