Development of Data Assimilation Systems for
Short-Term Numerical Weather Prediction at JMA

Tadashi Fujita
Numerical Prediction Division, Japan Meteorological Agency

Japan Meteorological Agency (JMA) operates Mesoscale Model (MSM) aimed at assisting warning and short-range forecast services (15/33-h forecast, every 3 hours). MSM, based on the JMA non-hydrostatic model (JMA-NHM, Saito et al. 2006), runs over a domain covering Japan and its surrounding areas at a resolution of 5km. Initial condition of MSM is produced by the 4DVar system of JNoVA (JMA Non-hydrostatic model-based Variational Data Assimilation, Honda et al. 2005) in Mesoscale Analysis (MA). JNoVA-4DVar has forward and adjoint models based on JMA-NHM. The inner model runs at a resolution of 15km with simplified physical processes, and the outer model runs at a resolution of 5km with the same configuration as MSM. New developments of MA have been implemented to improve MSM forecast, such as recent introduction of satellite (brightness temperature) and radar (relative humidity retrieved from reflectivity) observations.

In order to help producing sophisticated disaster-prevention and aviation information services, development of NWP at a higher resolution (Local Forecast Model, LFM) also is in progress at JMA. A trial operation of 9-hour LFM forecast at a resolution of 2km was performed in FY2010, and operation is scheduled to start in FY2012. LFM also uses JMA-NHM as a forecast model, and its initial condition is generated from a 3DVar rapid update cycle. The cycle uses the MSM forecast as the first guess, and performs JNoVA-3DVar (a degenerate version of JNoVA-4DVar) analysis and 1-hour JMA-NHM forecast in turn over 3 hours at a resolution of 5km. Impact of assimilating observations including data from surface stations (temperature and wind) and ground based GPS stations (total column water vapor) has been tested in various cases in the trial operation.

The paper presents current status and recent developments of these data assimilation systems for short-term NWP at JMA.

Honda, Y., M. Nishijima, K. Koizumi, Y. Ohta, K. Tamiya, T. Kawabata and T. Tsuyuki, 2005: A pre-operational variational data assimilation system for a non-hydrostatic model at the Japan Meteorological Agency: Formulation and preliminary results. Q. J. R. Meteorol. Soc., 131, 3465 – 3475.

Saito, K., T. Fujita, Y. Yamada, J. Ishida, Y. Kumagai, K. Aranami, S. Ohmori, R. Nagasawa, S. Kumagai, C. Muroi, T. Kato, H. Eito and Y. Yamazaki, 2006: The operational JMA Nonhydrostatic Mesoscale Model. Mon. Wea. Rev., 134, 1266 – 1298.