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Met Office Africa Limited Area L38 Model (Africa-LAM) deployed on Met Office supercomputer (Exeter)

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This computation involved: Met Office Africa Limited Area L38 Model (Africa-LAM) deployed on Met Office supercomputer (Exeter). The Africa Limited Area Model is a configuration of the Met Office Unified Model, which is a non-hydrostatic finite difference model with height as the vertical coordinate. It uses the full equations with virtually no approximations. This is the L38 configuration.

Abbreviation: africa-lam38
Keywords: Not defined

inputDescription:      None
outputDescription:      None
softwareReference:      None
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More Information (under review)

The model has three runs per day - 06Z, 12Z and 18Z. The 06Z forecast is a cold start from an interpolated global model state. The 12Z and 18Z runs perform 3D-Var data assimilation using output from the previous cycle as the forecast background fields. The 06Z and 12Z forecasts are as short as they can be (out to T+9) to provide the fields required for the next cycle. The 18Z is the main run and goes out to T+54. There is no 00Z run. The whole process starts again in the 06Z run the next day."

The horizontal grid is square, consisting of 432 rows by 432 columns which span the latitude range 37.5° S to 40.1° N and the longitude range 20.0° W to 57.6° E. The horizontal resolution is 0.18° (approximately 20 km). The time-step is 7.5 minutes.

There are 38 levels in the vertical. These follow the terrain at the surface but level out to constant heights further up. The lowest model level is at 10 m, the highest at 39 km.

The boundary conditions are provided by the Met Office global model. They are applied in an eight-point rim around the edge of the area which is visible as a discontinuity in some of the fields.

The sea-surface temperature is held constant throughout the course of a run. Lakes are given surface temperatures equal to that of their nearest sea-point.

The model does not use diffusion.

Model specification:

Model ID: MJ
Grid-points: 432 x 432
Horizontal Resolution: 0.18° x0.18°
(20 km x 20 km)
Unrotated pole: 90° N 180° W
1st point (lat, lon): (-37.5000°,340°)
Vertical Levels: 38 (details)
13 BL levels
Model Lid: 40 km
Model Timestep: 7.5 minutes
Radiation Timestep: 1 hour
Forecast Range: T+54
Main Forecast Time: 18Z
Data Assimilation: 3D-Var (window T-3→T+3)
Assimilation-only cycles: 12Z and 18Z (i.e. intermittent DA)
Driving Model: Global Model
Reconfigure from global cycle: 06Z
LBCs: 3-hourly from T-3
5 point halo
8 point rim (weights, 1,1,1,1,1,0.75,0.5,0.25)
Dates: June 2006 - 15th March 2011

Model Description

This configuration of the Africa LAM uses intermittent data assimilation and thus has just three runs a day: QJ06, QJ12 and QJ18. The QJ06 cycle obtains its UM start dump by interpolation (reconfiguration) from the global model and takes no inputs from any previous QJ cycle, i.e. it is a "cold start" from the global model. It runs a nine hour forecast (from T+0 to T+9) which is used to initialise the next cycle, QJ12. This cycle uses 3DVAR in the conventional way and serves to provide some data assimilation spin-up for the main cycle, QJ18. Like the QJ06 cycle, the QJ12 does not provide any forecast products and runs for the minimum forecast time required (12 hours from T-3 to T+9 in this case). It is the QJ18 cycle that runs the main forecast and provides the products. This runs 3DVAR and does a 54 hour forecast from T-3 to T+51. There is no QJ00 cycle and the whole process starts all over again from scratch the next day.

Since March 2011, a higher resolution Africa-LAM model (0.11 deg x0.11 deg - 70 levels - continuous 3D-VAR) is routinely producing data.

More details to follow
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