COPE: The COnvective Precipitation Experiment. Met Office interests Phil Brown 26/10/2012

Table of Contents Aims Background Modelling Summary

Aims and Background

Aims of COPE To study the production of precipitation in organized convective systems over SW England To improve the exploitation of data used for operational assimilation To improve the representation of microphysical processes in operational km-scale NWP Leading to the improvement of quantitative precipitation forecasts

Some science questions What are the impacts of large- and meso-scale dynamics on convective precipitation? What is the representivity of line-of-sight Doppler winds from network radars and what can we learn to improve the way they are assimilated? What is the role of supercooled rain in the growth of precipitation in UK summertime convection? Which ice nucleation processes are active in these clouds, and why is -10C a magic number? What are the impacts of aerosol changes on precipitation formation and how well are these represented in the UM? Does the UM generate realistic precipitation-driven downdrafts and cold pools? Does it evaporate rain correctly? What are the relative importances of resolution, microphysics and other sub-grid processes in producing good forecasts?

Background: Boscastle floods, 16 Aug 2004 Meteosat, high-res visible 1530Z 1130Z Convergence line over N.Cornwall Downdrafts triggering new convection 1330Z 1530Z

Background: Boscastle floods, 16 Aug 2004 Golding et al Background: Boscastle floods, 16 Aug 2004 Golding et al., 2005, Weather High accumulations resulted from intensity and duration of precipitation Slow-moving cells organized in along-wind lines These were not spectacular convective clouds – tops probably reaching -15 to -20C Significant involvement of both warm-rain and ice-phase processes New convection triggered by downdrafts

Background: ICEPIC B200, 18/05/2006 Lack of precip in the upwind end of shower line – probably warm rain Excessive precip rates from cells further downwind – probably ice-phase

Background: ICEPIC B200, 18/05/2006 Region of flight operations, 1100-1330Z UM – 4km UM – 1.5km Radar

Background: ICEPIC B200, 18/05/2006 Liquid -10 -5 +5 -10 -5 +5 -10 -5 +5 -10 -5 +5 Ice -10 -5 +5 -10 -5 +5 Rain Tracking single cells in a 1.5km UM simulation

Background: ICEPIC B200, 18/05/2006 Insufficient warm-rain in early stages of cloud growth Excessive precipitation rates following onset of ice-phase Ice-phase transition occurs very rapidly in 1.5km model – within 10 min similar to Phillips et al. (2001) LES study of orographically-triggered convections Aircraft observations continue to show largely unglaciated updrafts Resolution or microphysics?

Modelling

Models UKV UKV Ensemble (2.2km) resolution High-resolution UM 36hr forecasts every 6hr 3D-VAR UKV Ensemble (2.2km) resolution High-resolution UM 100m resolution for case studies Nowcasting Demonstration Project 1.5km resolution 12hr forecasts every hour 4D-VAR

NDP domain Focus on Olympics sites and period, 2012 Doppler weather radars in S.England 1.5km resolution Run every hour, for 12hr duration 4D-VAR with sharper error covariance matrices NDP UKV

NDP: 29/08/2012 06Z cycle T+8

Questions and answers