Development of a 5-km-Mesh Cloud-System-Resolving Regional Climate Model at the Meteorological Research Institute

Abstract

A 5-km-mesh nonhydrostatic cloud-system-resolving regional climate model (NHM-5km) has been developed at the Meteorological Research Institute (MRI) of the Japan Meteorological Agency (JMA) by improving upon the JMA operational mesoscale model (MSM). Three major changes have been made to MSM: the Kain-Frisch convective parameterization scheme has been improved to reduce the incidence of false predictions of rainfall areas along coastlines during the warm season, a spectral nudging method has been introduced to avoid phasegap between the inner model (NHM-5km) and the outer model, and a Simple Biosphere model has been applied for sophisticated representation of land surface processes. This article presents details of the first two of these modifications.A present-day climate simulation is performed using NHM-5km by nesting within the results of a 20-kmmesh atmospheric global climate model (MRI-AGCM3.2S). Taylor's skill score is used to compare the performances of NHM-5km and MRI-AGCM3.2S in terms of reproducing the spatial pattern of precipitation-based extreme indices over the Japanese Islands. The comparison shows that NHM-5km yields a significant improvement in reproducing the present-day climatology (e.g., the maximum number of consecutive dry days and the simple daily precipitation intensity index), suggesting that NHM-5km is a reliable tool for accurately predicting future changes in extreme weather at a fine spatial resolution.

Projection of Future Climate Change over Japan in Ensemble Simulations with a High-Resolution Regional Climate Model

“…Sasaki et al (2008) and Nakano et al (2012) describe the specifications of NHRCM except for recent improvements that include a revised version of the Kain-Fritsch convection parameterization, developed by one of the present authors (T. Kato). This revision was intended to correct an underestimated precipitation at a small island.…”

“…Height for which an ascending air parcel originates depends on area of an island when the area is between 100 and 1000 km 2 . NHRCM includes a spectral nudging scheme (Nakano et al 2012), based on a spectral boundary coupling scheme (Kida et al 1991;Sasaki et al 2000) for climate simulations. NHRCM has successfully been used for previous studies (e.g., Sasaki et al 2011, hereafter S11;Nakano et al 2012;Murata et al 2013).…”

“…For Japan, simulations should be prepared at much finer spatial scales because of its complex topography and coastlines, which lead to considerable climate variability. Nakano et al (2012) captured such small spatial and temporal variations in projected future climate change over Japan in summertime (from June to October) with a non-hydrostatic regional climate model (NHRCM) with a grid spacing of 5 km. Sasaki et al (2012; hereafter S12) achieved all-season downscaling results around Japan by integrating an NHRCM (5-km grid spacing) over 20 years at the end of the 21st century.…”

A Geographic Information System (GIS)-based approach to adaptation to regional climate change: a case study of Okutama-machi, Tokyo, Japan

“…These studies indicate that the NHRCM-5 km significantly improves the reproduction of the present climate. In particular, the bias of models with observations for daily mean temperatures in June, July, August, September and October was within 0.5 K (700 samples covering Japan) for the present climate Nakano et al 2012). Thus, we used only NHRCM-5 km output data for summertime (July to October data).…”

“…We used a high-quality daily dataset from the JMA, and projections from the NHRCM-5 km following an SRES-A1B scenario. The MRI-AGCM3.2S supported by KAKUSHIN Project, is used as initial and lateral boundary conditions (Kitoh et al 2009;Sasaki et al 2012;Nakano et al 2012). MRI-AGCM3.2S output is successful in simulating characteristic features of the seasonal cycle of the East Asian summer monsoon and topographyregulated precipitation data has good agreement with observations (Mizuta et al 2012).…”