Information

In June 2014, a new coupled model was started to operate as the operational long-range forecast system of the Korea Meteorological Administration (KMA) from sub-seasonal to seasonal time scale. The system, named Global Seasonal forecast system version 5 (GloSea5), is a join seasonal forecasting system with UK Met Office and consists of the following components:

• Atmosphere: Met Office Unified Model (UM; Brown et al., 2012), Global Atmosphere 3.0

• Land surface: Joint UK Land Environment Simulator (JULES; Best et al., 2011), Global Land 3.0

• Ocean: Nucleus for European Modeling of the Ocean (NEMO; Madec, 2008), Global Ocean 3.0

• Sea-ice: The Los Alamos Sea Ice Model (CICE; Hunke and Lipscomb, 2010), Global Sea-Ice 3.0

Detailed descriptions about the GloSea5 can be found in MacLachlan et al. (2014).

 

A model configuration of the GloSea5

Fig. 1. A model configuration of the GloSea5

 

 

• Basic Propetries
 

The dynamical core of the UM uses a semi-implicit semi-Lagrangian discretization to solve the fully compressible, non-hydrostatic atmospheric equations of motion. The stochastic physics scheme Stochastic Kinetic Energy Backscatter v2 (SKEB2; Bowler et al., 2009) is included to represent unresolved processes and provide small grid-level perturbations during the model integration. The GloSea5 features a higher horizontal resolution model than other operational models. The atmosphere and land surface resolution is 0.833◦×0.556◦, about 60 km at mid-latitude region. The grid spacing in the ocean and sea-ice models is about 0.25◦. The model top is about 85 km that can fully resolve the interaction between troposphere and stratosphere.

 

 

• Prescribed climate forcing
 
 

Climate forcings (e.g. methane, CO2, etc.) are set to observed values up to the year 2005; after this point the emissions follow the Intergovernmental Panel on Climate Change (IPCC) RCP4.5 scenario. Climatologies with a seasonal variation are used for other aerosols (biogenic aerosols, biomass burning, black-carbon, sea salt, sulphates, dust, and organic carbon fossil fuels). These climatologies have been generated from a climate simulation using HadGEM2 (except dust which is from a HadGEM1a run). The Stratosphere–troposphere Processes And their Role in Climate (SPARC; Cionni et al., 2011) observational climatology is used for ozone, which includes a seasonal cycle. The solar forcing is the same in the forecast and hindcast, with an inter-annual variation.

 

 

• Initialization
 
 

The initial atmospheric conditions for the forecast members are generated by the KMA operational numerical weather prediction (NWP) 4D-Var data assimilation system. The ocean and sea-ice initial conditions are generated by the NEMOVAR assimilation scheme developed jointly by the UK Met Office and other centers. Reanalyses from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim project are used to initialize the atmosphere and land surface in the hindcast members. The soil moisture in both the forecast and hindcast are initialized with climatological values.

The initial atmospheric conditions for the forecast members are generated by the KMA operational numerical weather prediction (NWP) 4D-Var data assimilation system. The ocean and sea-ice initial conditions are generated by the NEMOVAR assimilation scheme developed jointly by the UK Met Office and other centers. Reanalyses from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim project are used to initialize the atmosphere and land surface in the hindcast members. The soil moisture in both the forecast and hindcast are initialized with climatological values.

 

 

• Ensemble prediction system
 
 

GloSea5 is a sub-seasonal to seasonal forecast system comprising three parts: an sub-seasonal forecast, a seasonal forecast, and a hindcast. Each day we complete four members initialized with 0000 UTC analyses from the NWP global data assimilation and the ocean–sea-ice data assimilation system. Two of these members are run out to about 7 months (seasonal forecast members) and two are run out to about 60 days (sub-seasonal forecast members). The first 60 days of all forecast members are used in the creation of sub-seasonal products. The hindcasts are initialized from the following set of start dates: (1, 9, 17, and 25 in each calendar month) for 14 years from 1996 to 2009. Spread between members initialized on the same date is achieved through the use of a stochastic physics scheme.

For sub-seasonal forecasts, the bias corrected seasonal and sub-seasonal members from the last seven days are combined to form a lagged ensemble containing 28 forecast members. The sub-seasonal forecast products are produced on a weekly basis and are used in KMA’s operational 1-month outlook. Seasonal forecast members from the previous three weeks are combined, resulting in a 42-member ensemble for the next six months. These products are updated on a monthly basis.