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JMA Numerical Weather Prediction

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Japan Meteorological Agency Numerical Weather Prediction
Japan Meteorological Agency (JMA) numerical weather prediction (NWP) has advanced significantly since its introduction in June 1959 thanks to the rapid development of computer resources/telecommunications and other fields in earth sciences and information technology,especially those involving the use of meteorological and earth-observing satellites.

JMA currently operates several NWP models to cover various types of prediction, including very-short-range forecasts, short-/medium-range forecasts, typhoon track forecasts and aviation forecasts. Ensemble prediction systems (EPSs) and a coupled ocean-atmosphere model are operated for other predictions, including one-week/one-month/seasonal predictions and El-Niño forecasts.

As part of Agency's commitment to the ongoing enhancement of its NWP systems, a Meso-Scale Model with increased horizontal resolution was introduced in March 2006 along with more frequent operation. The resolution of the global model was enhanced in November 2007, and one-week EPS based on global model products was also improved. In February 2008, a new EPS targeting typhoon forecasts was launched.
In August 2012, the Local Forecast Model covering the eastern part of Japan was put into operation.
In May 2013, the model's forecast domain was expanded to cover the whole of Japan, and its operational frequency was raised from every three hours to every hour. In March 2013, the forecast domain of the Meso-Scale Model was also enlarged, and the range of forecast runs made by the Global Spectral Model at 12UTC and the One-week Ensemble Prediction System was extended from 216 to 264 hours. In May 2013, the Meso-Scale Model's forecast period was extended to 39 hours for all eight daily operations (once every three hours).
In February 2014, the horizontal resolution of the One-week Ensemble Prediction System was enhanced from 55 to 40 km, and the operational frequency/number of ensemble members per day were increased. In March 2014, the Global Spectral Model was also enhanced by increasing the number of vertical layers from 60 to 100, raising the top level from 0.1 to 0.01 hPa and revising the physical processes involved. The Typhoon Ensemble Prediction System was also improved by enhancing horizontal resolution from 55 to 40 km and the number of ensemble members from 11 to 25.
In March 2017, the Global Ensemble Prediction System was introduced as a unification of the Typhoon Ensemble Prediction System, the One-week Ensemble Prediction System and the One-month Ensemble Prediction System.
In June 2018, the range of forecast runs conducted at 00, 06 and 18 UTC was extended from 84 to 132 hours for the Global Spectral Model.
In March 2019, the Meso-Scale Model's forecast range was extended from 39 to 51 hours for daily operations at 00 and 12 UTC, and the Local Forecast Model's forecast range was extended from 9 to 10 hours for all 24 daily operations (every hour).
In December 2020, the range of forecast runs conducted at 00 UTC was extended from 132 to 264 hours for the Global Spectral Model.
In March 2021, the number of vertical layers was increased from 100 to 128 for the Global Spectral Model and the Global Ensemble Prediction System, and from 58 to 76 for the Local Forecast Model. The number of ensemble members for the Global Ensemble Prediction System per initial time was also increased from 27 to 51 for 11-day forecasts, from 13 to 51 for two-week forecasts and from 13 to 25 for one-month forecasts. At the same time, the frequency of two-week and one-month forecasts was changed from twice a day (00, 12 UTC) to once a day (12 UTC).

Data assimilation systems for NWP are based on variation, with four-dimensional variational (4D-Var) systems being introduced for Meso-Scale Analysis and Global Analysis in March 2002 and February 2005, respectively. The Local Forecast Model is initialized with an hourly assimilation-forecast cycle running three-dimensional variational (3D-Var) analysis and one-hour forecasts in turn over periods of three hours.

In August 2011, JMA began operation as a Data Collection or Production Centre (DCPC) under the WMO Information System to provide regional analysis and short-term forecasts based on the global model.