A new computer, CRAY SV1-1A with 16 CPU’s and a peak performance of 19.2 Gflop/s, was commissioned in 1999 at the Hong Kong Observatory (HKO). The Regional Spectral Model (RSM) became operational on the new computer by the end of the year with an outer horizontal domain of 60km nesting into a 20km inner domain. Rainfall information from radar and rain gauges was routinely incorporated into the RSM through a physical initialization process.

Current systems at the HKO with their major characteristics are listed below:

The CRAY SV1-1A is used to run the analysis and forecast system for both the inner and outer domains of the RSM.

The SGI Origin 2000 is also deployed to support the operation of the RSM. It is mainly used for data pre-processing and product generation based on the output of the RSM.

One of the SUN E450 is used for provision of NWP products to support aviation operations and for development of the RSM. The other is for running the rainstorm nowcasting system to support the Central Forecasting Office (CFO). Two O2 are used as graphics display workstations for visualization of nowcasting products and staging the web server for RSM products.

One of the IBM 590 servers is used for running the operational database, generating diagnostic products, plotting weather charts and producing graphics displays to support the operations of the CFO and Airport Meteorological Office (AMO). The other 590 servers are configured to take up the operational tasks in case the first one breaks down. They are also used for the processing of climatological data and research.

The number of reports received from GTS circuits on a typical day in 1999 are given below:

SYNOP/SHIP 20 000

TEMP/PILOT 4 000

AIREP 3 000

SATEM/SATOB 2 000

About 900 GRID bulletins and 20 T6 fax charts are received each day on the GTS.

On days with tropical cyclones in the region, additional GTS bulletins (e.g. RADOB) and radio facsimile charts are also received.

Automated.

For quality control of incoming data, adherence to prescribed coding formats, internal consistency, and physical and climatological limits are checked automatically.

External consistency check against the first guess field provided by the forecast from the RSM is also carried out automatically.

Quality control of outgoing observational data originating from Hong Kong is implemented to ensure conformity to WMO coding formats and to enforce checking against internal consistency, time consistency as well as physical and climatological limits.

Monitoring on the territorial level.

For short-range (0-72 hours) forecasting, the HKO commenced operation of the RSM by the end of 1999, replacing the Observatory Limited Area Model (OLAM), the one degree resolution model adapted from the Very Fine Mesh Model (VFM65) of Japan Meteorological Agency (JMA).

The outer 60km-RSM is run four times a day to produce 48-hour forecasts for the area 9S - 59N, 65-152 E based on 00, 06, 12 and 18 UTC analysis data. The inner 20km-RSM is run 8 times a day for 24-hour forecasts for the area 10–35 N, 100-128E based on 00, 03, 06, 09, 12, 15, 18 and 21 UTC analyses.

Not implemented.

Meteorological data assimilated by the analysis scheme of the RSM are as follows:

(A) From GTS

SYNOP, SHIP surface data and ship data

TEMP, PILOT radiosonde and pilot data

AIREP aircraft data

SATEM satellite thickness data

TOVS, ATOVS virtual temperature profiles

SATOB satellite wind data

(B) From RSMC Data Serving System (DSS) of JMA

GMS digital data - total cloud amount, mean cloud top temperature and its standard deviation for moisture bogus

GMS cloud motion vectors during tropical cyclone situations

(C) From NCEP data server

Daily sea surface temperature analysis at 1 degree resolution

(D) Locally generated data

Tropical cyclone bogus data during tropical cyclone situations

Three-dimensional multivariate optimal interpolation is performed four times a day based on 00, 06, 12 and 18 UTC data for the 60km outer domain. Data cut-off time is about three hours after the observation time. For the inner domain, the same objective analysis scheme is performed 8 times a day based on 00, 03, 06, 09, 12, 15, 18, and 21 UTC. Data cut-off time is about 2 hours. All analyses are applied to 36 vertical levels.

The horizontal domains of both inner and outer models compose of 151 x 145 model grids in Mercator projection. The first guess fields of the models are provided by their respective latest forecasts.

Hourly rainfall information derived from real-time calibration of radar reflectivity with rain gauge data as well as from the GMS digital cloud data, are incorporated into the model through a physical initialization process. In this process, the moisture of the initial field (between the lifting condensation level and the cloud top inferred from the cloud top temperature) at the point where rain is observed is adjusted to allow precipitation process to be switched on. The heating rate of the precipitation process is also adjusted to correspond to the rainfall amount observed. The rainfall information in the hour preceding analysis time is used in the outer model. For the inner model, pre-runs for 3 hours preceding analysis time are performed to incorporate the rainfall information.

Non-linear normal mode initialization is performed before the forecast model is run.

The RSM is adapted from JMA with the following characteristics:

Further details on the formulation of the RSM are given in JMA(1997).

For the outer 60km domain, the RSM produces primarily 3-hourly numerical products which include pressure/ geopotential heights, wind, temperature, dew point depression at 15 pressure levels ( 1000, 925, 850, 700, 500, 400, 300, 250, 200, 100, 70, 50, 30, 20, 10 hPa ) and the surface. Accumulated rainfall at the surface is also produced. For the inner 20km domain, the same forecast elements as the above are produced but at hourly intervals.

Post-processing of RSM prognostic data are performed and over 400 GIF products are generated per model run which are made available to the forecasters for reference through a web-based display.

These products include forecast time cross-section and tephigrams as well as forecast rainfall distribution charts for Hong Kong. Local text forecasts based on RSM prognostic data with warnings of thunderstorms and rainstorms, are generated automatically. Pre-defined 3-D products of forecast temperature and cloud cover using VIS5D are also produced.

Kalman filtering technique is employed to provide daily minimum and maximum temperature forecasts in Hong Kong based on 60 km RSM prognostic data.

A weather map algorithm is employed in the RSM to produce hourly weather map (fine area, cloudy area, cumulated rainfall contours) based on RSM prognostic data. The actual IR satellite imagery for the same time, when available, is also superimposed on the forecast weather map to facilitate visual verification of the weather map product by forecasters.

The verification of the RSM forecasts, particularly the prediction of rainfall, will be focused. The feasibility of operating a local model at resolution of below 20km is being studied.

Arakawa, A. and W.H. Schubert. 1974: Interaction of a Cumulus Cloud Ensemble with the Large-Scale Environment, Part I. J. Atmos. Sci., 31: 674-701.

Benwell, G.R.R. and F.H. Bushby, 1970: A case study of frontal behavior using a 10-level primitive equation model. Quart. Jour. Roy. Meteor. Soc., 96,287-296.

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Japan Meteorological Agency (JMA) : Progress report on numerical weather prediction 1997. Appendix. 126 pp.

Sugi, M., K. Kuma, K. Tada, K. Tamiya, N. Hasegawa, T. Iwasaki, S. Yamada and T. Kitade, 1990: Description and performance of the JMA operational global spectral model (JMA-GSM88). Geophys. Mag., 43, 105-130.

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