Recent & planned developments to the Met Office Global and Regional Ensemble Prediction System (MOGREPS) Richard Swinbank, Warren Tennant, Sarah Beare, Christine Johnson, Neill Bowler, Ken Mylne, Nigel Roberts and Adam Clayton GIFS-TIGGE Working Group meeting #9, Sept 2011 © Crown copyright Met Office

MOGREPS – The Met Office ensemble 24-member ensemble designed for short-range forecasting Regional ensemble over Atlantic and Europe (NAE) to T+54 at 06Z and 18Z (18km grid, 70 levels) Global ensemble to T+72 at 00Z and 12Z (~60 km grid, 70 levels) Medium-range version of MOGREPS-G: MOGREPS-15, used for TIGGE. ETKF for initial condition perturbations Stochastic physics Aim to assess uncertainty in short-range, eg.: Rapid cyclogenesis Local details (wind etc) Precipitation Fog and cloud NAE Starting point for the storm surge ensemble is our short-range atmospheric ensemble. Describes resolutions applicable to results shown here; planned to upgrade to ~18 km this year with new supercomputer. Analysis uncertainty sampled using Ensemble Transform Kalman Filter, which estimates the impact of observations on the background uncertainty estimated by the previous ensemble run, based on the same maths underlying data assimilation. Aims to produce an ensemble correctly calibrated from T+0, unlike initial growth phase of singular vector perturbation (not perfect in achieving this, of course). Stochastic physics to capture some of the errors associated with model evolution. MOGREPS has been running since August 2005, and was made Operational in September 2008. © Crown copyright Met Office

Recent (2010-11) upgrades © Crown copyright Met Office

Increased MOGREPS resolution (2010) Global N144 (~90km) to N216 (~60km) Regional (NAE) 24km to 18km Both systems 38L to 70L: © Crown copyright Met Office

Summary of 2010 MOGREPS upgrades - not just resolution changes Global Regional PS23 (Spring) N144L38 to N216L70 L70 physics changes SKEB2 implementation ETKF vertical localisation MOGREPS-15 as Global NAE 24km L38 to 18km L38 minimal physics changes PS24 (Summer) IAU - Increments added at T+0 ETKF & OPS changes RP2 – additional BL parameters SKEB2 – add KE term NAE 18km L38 to 18km L70 Physics changes for L70 © Crown copyright Met Office

IAU (Incremental Analysis Update) The IAU was originally developed to add unbalanced (3DVar) analysis increments to the background state. MOGREPS uses the technique to add initial perturbations. The increment is added in gradually over time to damp fast gravity waves. © Crown copyright Met Office

MOGREPS global ensemble MOGREPS-G uses the ETKF to generate perturbations. These are then added to the reconfigured global analysis to create the set of the ensemble members. © Crown copyright Met Office

Ranked Probability Score RPS is similar to mean-square-error but measuring probabilities over a range of thresholds. Precip T850 No IAU gives improvement for precip but degradation for T850. control No IAU Shifted IAU © Crown copyright Met Office

Met Office hybrid implementation (Adam Clayton, Dale Barker, Andrew Lorenc, ...) Basic details: “Alpha control variable” hybrid, with localisation in control variable space (streamfunction, velocity potential, unbalanced pressure, humidity). 23 error modes from MOGREPS-G. Static localisation in horizontal and vertical. 80% climatological / 50% ensemble covariance. (Total variance inflated to maintain analysis fit to obs.) Performance: ~1% improvement against obs and ECMWF analyses. Operational implementation: July 2011. Dec uncoupled (29 days) Jun coupled (28 days) RMSE changes vs. obs: © Crown copyright Met Office

Future upgrades © Crown copyright Met Office

Plans for MOGREPS changes following HPC mid-life upgrade Allows further improvements in resolution of operational forecast models For MOGREPS we will use a two-step nesting strategy: Global ensemble MOGREPS-G grid ~40 km Regional ensemble MOGREPS-EU ~12 km UK convective-scale ensemble MOGREPS-UK 2.2 km The short-range ensemble forecasts will run four times a day, with 12 members (1 control + 11 perturbed) Products calculated from pairs of lagged forecasts The ETKF will use 22 (later, more) perturbed members with a 6-hour cycle MOGREPS-15 will continue to run twice a day © Crown copyright Met Office

Proposed (schematic) schedule Each configuration to run 3 hours after driving ensemble to obtain freshest boundary conditions. © Crown copyright Met Office

Proposed new MOGREPS-EU domain Aim to use 12km grid for MOGREPS-EU, so that MOGREPS-EU control run can directly replace 12km NAE – to be retired Adopt new set of 70 levels to improve resolution in lower troposphere Also used for EURO4M reanalysis project, covering EEA countries & Mediterranean. Covers Storm Surge and ocean Atlantic Margin model domains Will investigate sensitivity to western boundary. © Crown copyright Met Office

UKV Model Domain for MOGREPS-UK Variable resolution, 2.2km in inner domain Based on 1.5km UKV model used for convective-scale deterministic forecasting Same 70-level set as MOGREPS-EU © Crown copyright Met Office

Implementation schedule Originally planned as “big bang” implementation at PS29 (Spring 2012), but due to delay in IBM P7 delivery, implementation will be phased: PS28 (Autumn 2011) 4 cycles per day with current models, but using new schedule. PS30 (late Spring 2012) Introduce MOGREPS-UK in time for Olympics PS31 (Autumn 2012) MOGREPS-EU Other resolution & physics changes at PS31 or PS32 © Crown copyright Met Office

Medium-range and Seamless Forecasting Currently the medium-range ensemble, MOGREPS-15 is essentially the same as MOGREPS-G but run to 15 days using UK member-state computer time at ECMWF. Met Office strategy is to make forecasts consistent across different timescales, from short-range NWP to climate prediction. We are planning to bring together ensemble prediction systems on the medium-range and monthly to seasonal timescales, including. Initial condition perturbations from ETKF and, in longer term, Ensemble Data Assimilation System; Coupled model to better represent ocean-atmosphere interactions. © Crown copyright Met Office

Schematic of possible coupled medium-range/ monthly/ seasonal EPS Suite 1 20 members 15 days Suite 2 2 members 2 months Suite 3 2 members 7 months Suite 4 X members Hindcast Medium-range products Monthly products Seasonal products © Crown copyright Met Office

Any Questions? © Crown copyright Met Office