NMOC Quarterly Summary April-June 2002

Notes on NWP systems

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GASP

On 25 July a change was made to the convection scheme in the operational GASP system based on positive results from a parallel trial. The maximum convection area permitted for a grid box has been reduced from 100% to 10% and middle level convection is restricted. The impact on verification scores was slightly positive, but the rainfall distribution and surface pressure field in the tropics are much less noisy with the change in this setting.

LAPS

From 1 Aug 2002 NMOC is commencing an operational trial of a new version of the LAPS_PT375 system. The main changes are:

• Variational analysis of TOVS radiances within the LAPS assimilation
• 1-hourly radiation calculations (was 3-hourly)
• Improved land surface climatology, e.g. Henderson-Sellers 1x1 degree albedo
• New surface wind extrapolation algorithm to address low wind-speed bias over land
• Reduced atmospheric diffusion to produce deeper systems
• Forecast period extended to 72 hours (was 48 hours).

Cold running (starting from GASP first guess) is still being used except for the soil moisture field which is set in warm running mode (i.e. using previous LAPS forecast field) and then nudged using the ECMWF adjustment scheme.

The Met Office (UK)

The Met Office has advised that a new version (version 5) of the Met Office Unified Model was introduced with effect from 1200 UTC on 7 August 2002. Version 5 of the model incorporates new dynamics and new physics, allowing new configurations to be run on higher resolution grids, as well as data to be assimilated more effectively. Details of the changes can be found in the June 2002 NWP Gazette at:
http://www.metoffice.gov.uk/research/nwp/publications/nwp_gazette/jun02/um.html

The changes have added new features to the model, including a non-hydrostatic formulation for high resolution mesoscale modelling. Overall performance of the suite of models based on the Unified Model has improved, although verification scores in the trial period showed slight degradation in the global model predictions for the southern hemisphere. This deficiency is being investigated.

ECMWF

The Spring edition of the ECMWF Newsletter lists some recent model changes:

4 March - a new black-listing procedure to avoid using satellite Air Motion Vectors (AMVs) during time-slots likely to be affected by solar-eclipse problems.

9 April - an upgrade to the model including:

• revised short-wave radiation scheme
• retuning of the land-surface parameterisation scheme to reduce warm biases over land
• improved physics for the ocean wave model
• inclusion of some new data types in the analysis (such as water vapour radiances, ozone measurements and European wind profilers).

Ensemble Prediction System Products
ECMWF has recently restructured its web pages ( www.ecmwf.int). Some products from the Ensemble Prediction System (EPS) are included on a page accessible by WMO Members. The EPS products are probability maps of strong wind gusts and heavy precipitation for the northern and southern hemispheres (excluding the tropics) for forecast ranges of 72 hours and beyond. Many charts from the high resolution deterministic prediction system are also on the web site.