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A numerical weather model is the computer program that simulates an atmospheric motion in space and time. A variety of weather phenomena can be analyzed and predicted by the different types of numerical weather prediction models.

In the model the atmosphere is assumed to be composed of a number of lumps in which corner points are called as the grid points. The more number of lumps indicates the more elaborate simulation. Simulation by the model generates the future state of the model atmosphere at all grid points from its initial state.

Products of numerical models are serviced to forecasters as well as public on the web-site through Internet dedicated as a delivery system. In particular, forecasters use these products as guidance with their expertise and experiences for an issue of weather forecasting. Besides, many other models such as statistical model, ocean wave model, and typhoon model, etc., are employed to exploit the output produced from the weather forecast model for their purposes.

With the operational supercomputer NEC/SX-5, the KMA could run several numerical models in 1999. Recently, KMA introduced Unified Model (UM) and data assimilation (4DVAR) system from UK Met Office to improve NWP performance. UM-based global and regional NWP system installed on a new supercomputer CRAY/XE6 are being operated since May 2010.

Model	Horizontal Resolution (Vertical Layers)	Simulation/day	Prediction Period	Remarks
Global Prediction Model(GDAPS)	25 km(70)	2(00,12UTC)	10 days	Global domain
		2(06,18UTC)	3 days
	40 km(70)	2	10 days	Ensemble forecasting
	110 km(21), T106	1	120 days	Seasonal Forecasting
Regional Prediction Model(RDAPS)	UM 12 km(70)	4	3 days	East-Asia domain
	WRF 10 km(40)	4	3 days	East-Asia domain
Korea Local Analysis and Prediction System (KLAPS)	5 km(40)	24	12 hours	Korea domain
Typhoon Model (DBAR)	35 km(1)	4 (when Typhoon generated)	3 days	Typhoon tracks
Wave Model	1 km	2	1 day	6 Coastal domains along Korean peninsula
	8 km	2	3 days	Asia domain
	50 km	2	10days	Global domain
Regional Tide/Surge Model (RTSM)	8 km	2	3 days	Asia domain
Asian Dust Aerosol Model (ADAM)	30 km(29)	2	3 days	Asia domain
Statistical Model	-	2	2-10days	Temperature, precipitation probability

I. Model Configuration

Dynamics
Basic equation	Complete equation
Horizontal Resolution	Grid points of horizontal resolution with N512, corresponding to a grid size of 0.352Ⅹ0.234 degrees or 25km
Prediction Period	10days
Levels	70 vertical levels ranging from sfc. to 80km
Time Integration	Semi-implicit /Semi-Lagrangian scheme
Physics
Convection process	Mass flux convection with CAPE closure
Microphysics processes	Mixed-phase precipitation
Radiation	Edwards-Slingo general 2-stream scheme
Gravity wave drag	G.W. drag due to orography(GWDO)
PBL processes	MOSES-Ⅱ Non-local PBL
Land surface	MOSES-Ⅱ land-surface scheme
Data Assimilation
Method	4DVAR(4 Dimensional Variational method)
Observation time window	-3hr ~ 3hr
VAR Innerloop /levels	N144(90km) / 70 layers (Top : 80km)
Observation species	Surface, Sonde, Aircraft ,ATOVS, Satwind, Scatwind, SSMIS, IASI, AIRS, GPSRO, etc.
Typhoon bogus	Observation bogussing for wind and MSLP

II. Operational aspects

Global Model (GDAPS) for 10-day forecast runs at 00UTC and 12UTC with 2 hours and 25 minutes data cutoff. The 3-day forecast is also provided at 06UTC and 18UTC. The 3-day projection is used for the provision of lateral boundary condition for regional models, and prognostic/diagnostic variables from the global model are used as input for the application models such as yellow dust model and global wave model.

III. Recent changes

The GDAPS which is based on the Unified Model (UM) introduced from Met Office has been operated on KMA’s 3^rd supercomputer (Cray XE6) since 14^th May 2010. The horizontal and vertical resolution of the global model was enhanced from 40km/50 layers to 25km/70 layers in May 2011.