© Crown copyright Met Office Implementation of a new dynamical core in the Met Office Unified Model Andy Brown, Director of Science

Met Office science strategy: Unified science and modelling for unified prediction

© Crown copyright Met Office DePreSys TIGGE ensemble GloSea4 MOGREPS-R ensemble Coupled atmos/ocean Earth System Timescale 36hrs48hrs5 days 15 days 6 months 10 years 30 years >100 years 1.5km 4km 12km 24km 40km 80km 150km 300km Complexity UKV UK4 NAE Global HadCM3 HadGEM1 HadGEM2 Global atmosphere-only Regional atmosphere-only HadGEM3-RA regional HadGEM3 Atmospheric grid length

© Crown copyright Met Office A new dynamical core: ENDGame Atmos Physics 1 Advection Atmos Physics 2 Helmholtz Solver x2 Evolution of existing dynamics Same equation set & variables Same horizontal staggering (Arakawa C-grid) Same vertical staggering (Charney-Phillips) Iterative Semi-implicit semi-Lagrangian Simpler solver Less damping ( = 0.55) Fully 3D advection for θ Reformulated continuity equation  More scalable  More stable  More accurate

A possible timeline for a major model upgrade Quality Time (years) Operational Development Model

© Crown copyright Met Office Model changes alongside ENDGame Package of physics changes ENDGame+physics= GA6.0 (climate) GA6.1 (weather) GA6.0 and 6.1 extremely similar (more seamless than ever) For global NWP Model N512 (≈25km) → N768 (≈17km) 4D-Var inner loop N216 (≈60km) → N320 (≈40km) Satellite package

ENDGame results

© Crown copyright Met Office Eddy Kinetic Energy T+72hr EKE from 10 x ECMWF cases Paul Earnshaw N96N216N512N768

© Crown copyright Met Office Extra-tropical circulation Equivalent plots from PS32-based trials See poster by David Walters July 2012

© Crown copyright Met Office Tropical circulation Significant increases in variability Equatorial precip frequency/wavenumber spectrum from 20yr climate runs: Prince Xavier GA4.0GA6.0TRMM obs

© Crown copyright Met Office Tropical circulation Major improvements in Tropical Cyclone forecasts Impact of science upgrade N512 GA6.1 vs N512 GA3.1 Impact of science + resol’n N768 GA6.1 vs N512 GA3.1 Mean abs. PMSL error reduction3.0 hPa3.6 hPa Central pressure reduction7.1 hPa11.1 hPa Mean abs. |v| error reductions6.7 kt9.0 kt Mean max. |v| increase8.9 kt13.4 kt 850hPa vorticity increase79%155% Track error reduction7.3% 8.6%* Track skill score increase3.8%4.5% Julian Heming, Keith Williams * Biggest reduction in TC track error in a single UM upgrade for 20 years! Average impacts from PS32-based trials:

© Crown copyright Met Office Hermite Cubic Control minus ERA-InterimHermite minus ERA-Interim Vertical advection of tropopause by small amplitude oscillations Cubic Lagrange = 3 rd order upwind scheme (cf. ND = 2 nd order centred)  opposite phases of oscillation do not cancel: θ[z + dt*w - dt*w] ≠ θ(z)  biased increments Remedy: Cubic Hermite  enforce continuity of interpolation gradient Bias now close to that of New Dynamics

© Crown copyright Met Office New global versus 12km regional model Surface weather impacts (Temperature, cloud cover, cloud base, ppn, visibility) New global versus old global Significant improvement in near-surface weather measures Global outperforms 12km Limited Area Model – now retired Global significantly behind 1.5km model for UK

© Crown copyright Met Office N. Atlantic SST bias in GloSea hindcasts GA3 (coupled) GC2 Ruth Comer

© Crown copyright Met Office Outgoing SW radiation New New minus Old Old minus climatology New minus climatology Dan Copsey

ENSO © Crown copyright Met Office

Kilometre-scale modelling Closer to a centred semi-implicit approach Impact in UKV Lee Wave test: New Dynamics ENDGame Simon Vosper

© Crown copyright Met Office DePreSys TIGGE ensemble GloSea4 MOGREPS-R ensemble Coupled atmos/ocean Earth System Timescale 36hrs48hrs5 days 15 days 6 months 10 years 30 years >100 years 1.5km 4km 12km 24km 40km 80km 150km 300km Complexity UKV UK4 NAE Global HadCM3 HadGEM1 HadGEM2 Global atmosphere-only Regional atmosphere-only HadGEM3-RA regional HadGEM3 Atmospheric grid length Dynamics matters! Extremely significant model upgrade achieved in seamless framework

© Crown copyright Met Office Questions?

© Crown copyright Met Office Physics changes Significant physics differences between GA3.1 and GA6.1: Total of 66 tickets (including ENDGame) in GA4, GA5 and GA6

© Crown copyright Met Office ENDGame in a nutshell Example of scalability vs New Dynamics ENDGame required for 17km in PS34 N768 GA6.1 on 96 nodes currently runs in ≈ 40 mins Allows further resolution upgrades over next 10 years Andy Malcolm, Paul Selwood