THORPEX is a ten-year international research programme to accelerate
improvements in the accuracy of high-impact weather forecasts. A
key part of the THORPEX programme entails extending the range of
skilful weather forecasts to time scales of value in decision-making
(up to 14 days) using probabilistic ensemble forecast techniques.
As explained in more detail on the ensemble
forecasting pages, probabilistic techniques give the potential
to forecast possible high-impact events further ahead than is feasible
using conventional, deterministic, weather forecasts.
The THORPEX Interactive Grand Global Ensemble (TIGGE)
is a framework for international collaboration in development
and testing of ensemble prediction systems. Along with several
other weather forecast centres, the Met Office is running regular
medium-range ensemble forecasts that contribute to TIGGE. The
forecast results are being collected in near real time in the
TIGGE database, to be used for research on ensemble prediction.
The Met Office medium-range ensemble forecasts are produced using
a version of the Met Office Global and Regional Ensemble Prediction
System (MOGREPS). MOGREPS was originally developed to produce short-range
ensemble forecasts for the UK and Europe. For THORPEX, the global
model forecast part of MOGREPS has been extended to 15 days. Initial
conditions are produced by adding perturbations (generated using
an Ensemble Transform Kalman Filter method) to the operational
global analysis. A 24-member ensemble is run twice a day, starting
from 0 and 12 UTC.
The forecast model is a lower resolution configuration of the
model used for operational deterministic weather forecasts for
the globe. It is a version of the Unified
Model with a resolution of 1.25 degrees E-W by 0.83 degrees
N-S (i.e. a grid-length of about 90 km), with 38 levels. In order
to ensure that the forecasts have the best possible skill, work
is in hand to evaluate improvements to the model, which will be
introduced into the 15-day ensemble forecasts in the future.
The medium-range ensemble forecasts are currently being run on
the ECMWF supercomputer, using part of the UK member-state allocation
of computer resources. The ensemble forecasts are added to the
TIGGE database at ECMWF and also transferred to other TIGGE
archive centres. Output fields are returned to the Met Office
where they are the basis for much of our THORPEX research work.
This includes the development and evaluation of products to forecast
high-impact weather, assessment of societal and economic weather
impacts, development of observation targeting methods, and research
on techniques for multi-model ensemble forecasting.
Relevant links:
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