Global Data Assimilation and Prediction System (GDAPS)

I. Data assimilation, objective analysis and initialization

    More than 5,000 synoptic observations and various asynoptic observations, including satellite retrieval data, are used in the GDAPS. Table 1 presents the types and numbers of the observation that are available from the GTS.  The pre-processing procedures such as data acquisition, quality control and decoding, are fully automated.

Table 1.  The types and numbers of observations received through GTS, and the percentage of data used in global data assimilation for 24 hours in 2005.

	data type	numbers of data/day	date used in assimilation[%]
1	SYNOP/ SHIP	42,500	49
2	BUOY	7,782	84
3	TEMP/ PILOT	1,759	91
4	AIREP/ AMDAR/ACARS	219,102	8
5	SATEM	29,289	39
6	SATOB	20,341	87
7	ATOVS	108,347	18
8	AWS	5,518	57
9	PAOB	400	100
10	Wind profiler	332	36

    The global analysis is performed with the 6-hour update cycle. A 6-hour forecast from the previous run provides a first guess for the next analysis. If a typhoon occurs in the Western Pacific, a typhoon bogus profile is calculated and the profile is assimilated in 3dVar as an observation with observation error determined statistically. The best fits of analysis are made with the 3dVar system. The analysis resolution of global 3dVar is T426L40 for the outer loop and T106L40 for the inner loop. The analysis is performed up to 0.4 hPa.

    A Non-linear Normal Mode Initialization (NNMI) with full physics is performed to suppress the amplitude of high-frequency gravity waves. The high frequency component is filtered out for each spherical harmonic component in the eight greatest vertical modes that exceed the critical frequency. Machenhauer's iterative scheme is used for determining the non-linear balanced solution.

II. Model Configuration

Dynamics
Basic equation	Primitive equations in sigma- pressure hybrid vertical coordinate
Numerics	Spectral representation of horizontal variables with triangular truncation of T426, corresponding to a Gaussian grid size of 0.28125 degrees or 30km
Domain	Global
Levels	40 vertical levels ranging from surface to 0.4 hPa
Time integration	Eulerian semi-implicit scheme
Physics
Horizontal diffusion	Second order Laplacian, and Rayleigh friction
Moist processes	Kuo scheme, large-scale condensation, and shallow convection scheme
Radiation	Long wave radiation calculated every three hours Short wave radiation calculated every hour
Gravity wave drag	Long waves (wavelength>100km) Short waves (wavelength 10km)
PBL processes	Non-local diffusion  scheme and similarity theory for surface layer
Land surface	Simple biosphere model
Surface state	NCEP daily SST anomaly added to monthly changing climatological  SST Climatological values are used for the soil moisture, snow depth, roughness length and albedo

III. Operational aspects

    GDAPS for 10-day projection runs at 00 UTC and 12 UTC with 2 hours and 20 minutes data cutoff. The 84-hour projection is used for short-range weather forecasts, and for the provision of lateral boundary condition for a regional model. The 10-day projection is used for weekly forecast. The wind fields predicted by GDAPS is used as an input for the trajectory model of yellow sand and the surface wind is also used as an input for the global wave model.

IV. Recent changes

    1^st December 2005, GDAPS has improved its resolution from T213L30 to T426L40 owing to the complete installation of the new super computer Cray X1E at KMA. The analysis resolution of global 3dVar is increased in accordance with the improvement of model resolution. The outer loop increase its resolution from T213L30 to T426L40 and the inner loop is also improved from T63L30 to T106L40. The analysis top becomes higher from 10 to 0.4 hPa.