18.3
Error growth at the convective scale
PAPER WITHDRAWN
Giovanni Leoncini, University of Reading, Reading, Berks., United Kingdom; and R. S. Plant and S. Gray
Severe convection in the United Kingdom is the primary cause of flash
flooding. Increasing computational power has made possible the use of grid spacings of
the order of 1 km over large domains, with potential great benefit for the forecasting of
such storms. However, the error doubling times are short (hours) compared
to the lead times necessary for useful warnings. The flood of August 16 2004
over the coastal town of Boscastle, UK is a particularly interesting case not
only because of the extremely high accumulations (200 mm over 5 hours) but also
because it was characterised by the almost continuous formation, over the coast,
of new cells that moved over the small river catchment where the town is
located. The predictability of the event is investigated by running the Met Office Unified
Model with a horizontal grid spacing of 1 km. Ensemble members are
generated by perturbing the potential temperature as the simulation progresses and by
altering the microphysics parameterisation and the surface roughness. The
predictability of the event is then assessed by comparison with the control run of the accumulations
over the duration of the event simulated by the different ensemble members.
Session 18, Mesoscale predictability and data assimilation II
Thursday, 20 August 2009, 3:45 PM-5:00 PM, The Canyons
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