© Crown copyright Met Office From the global to the km-scale: Recent progress with the integration of new verification methods into operations Marion Mittermaier with contributions from Rachel North and Randy Bullock (NCAR)

© Crown copyright Met Office Outline 1.Using feature-based verification for global model evaluation during trialling 2.Implementation of the HiRA framework for km-scale NWP

© Crown copyright Met Office Synoptic evolution: Feature-based assessment of global model forecasts with Rachel North

© Crown copyright Met Office Forecast evolution …. … determined by features and how features affect one another…

© Crown copyright Met Office MODE – Method for Object-based Diagnostic Evaluation Davis et al., MWR, 2006 Two parameters: 1.Convolution radius 2.Threshold Highly configurable Attributes: Centroid difference, Angle difference, Area ratio etc Focus is on spatial properties, especially the spatial biases

© Crown copyright Met Office Setting the scene Comparing the previous operational dynamical core (New Dynamics) to the now operational dynamical core (ENDgame) (as of 15 July 2014) Baseline GA3.1 ND (25 km) for NWP (this was the operational GM version) Assessment of GA 5.0#99.13 N512 EG (25 km) and N768 (17 km) NH winter and NH summer trials. Comparison to an independent ECMWF analysis: N512 ND with N768 EG (current and future operational configurations) N512 EG with N512 ND (impact of changed dynamical core at the same resolution) Considering: 250 hPa jet cores, mslp lows and mslp highs.

© Crown copyright Met Office GA3.1 Temporal evolution Older N320 trial 250 hPa winds > 60 m/s at forecast lead time of t+96h from the 12Z initialisation compared to EC analyses Differences in the size of forecast and analysed objects is not overshadowed by growth of synoptic forecast error, i.e. still able to find matches.

© Crown copyright Met Office Foci for ENDgame assessment Spatial biases – extent of features Changes in intensity – deeper, stronger, higher etc Changes in the number of analysed and forecast objects – hits, false alarms, misses Changes in the attribute distributions – are the forecast attribute distributions closer to perfection?

© Crown copyright Met Office Object-based spatial frequency bias NHW NHS EC analyses too large getting smaller neutral LowsHighsJets too small getting larger too small getting smaller ND neutral -ve EG neutral +ve NHW NHS NG neutral -ve EG neutral +ve

© Crown copyright Met Office Object intensities EC analyses N768 EG v N512 ND Do not look at absolute min/max values in objects. Use the 10 th or 90 th percentile as a more reliable estimate of how the intensity distribution has shifted/changed. Lows are deeper, highs and jets are stronger  sharper gradients and a more active energetic model. Differences in the 00Z and 12Z analyses. 10 th percentile 90 th percentile EG deeper LowsHighs Jets 90 th percentile EG stronger

© Crown copyright Met Office Jets Highs Lows Number of objects Lows  EG more matched objects  Some increase in false alarms with fewer misses  Larger matched and unmatched areas Highs  EG more matched objects  Substantially more false alarms at early lead times with misses steady; impact of diurnal pressure bias  Area of matched objects improved at later lead times Jets  EG more matched objects  Substantial increase in false alarms with comparable misses  Modest increase in matched areas, but substantial increase in unmatched area EC analyses

© Crown copyright Met Office Distribution Difference Skill Score DDSS of attribute A is: F and G are the binned test and control distributions (m bins) H is the perfect distribution of attribute A (Heaviside) Measures the relative improvement in the distribution of an attribute compared to perfect attribute distribution. We know what the perfect attribution looks like. e.g. limited area ratio, intersection-over-union ratio e.g. centroid difference, angle difference EC analyses

© Crown copyright Met Office Distribution Difference Skill Score LowsHighsJets LowsHighs Jets Position errorOverlap ExtentPosition error Rotation error EG better N768 better EG better Mixed EC analyses

© Crown copyright Met Office Tropical depressions below 1005 mb Over two trials, June-Aug 2012, Oct-Nov 2012 CIs depend on attribute but are often very wide. Noisy. Verdict: sample size probably an issue in some cases. EC analyses

© Crown copyright Met Office Conclusions Lows deeper and often larger in extent Highs are too intense and too small – tightening of pressure gradients. Jets stronger and slightly too large (too small before). Generally shows as too strong w.r.t. verifying analysis. Significant shifts in frequency bias (i.t.o. spatial extent) with a negative impact on false alarm rate. Compelling seasonal differences in the Northern Hemisphere which may have to do with the land-atmosphere boundary. Pressure biases in the analyses can be very influential for any threshold-based method.

© Crown copyright Met Office Conclusions (cont’d) Analysis has added a new dimension to the traditional root-mean- square method of assessing global NWP performance. The features that drive our synoptic weather patterns are linked and analysing them as such provides potentially useful information for understanding and resolving model deficiencies. Feature-based output is also a lot closer to the way in which forecasters (meteorologists) use and interpret model output on a daily basis and should provide more meaningful objective guidance for forecasting applications.

© Crown copyright Met Office The High Resolution Assessment framework: Comparing ensemble and deterministic performance

© Crown copyright Met Office Low Small uncertainty at large scales = large uncertainty at small scales 5% error at 1000 km = 100% error at 50 km Link to larger scale: Russell et al Hanley et al. 2011, 2012 Justifies the use of a downscaling ensemble (MOGREPS-UK)

© Crown copyright Met Office 3 x 3 Spatial sampling 7 x 7 17 x 17 Only ~ km grid points in > domain used to assess entire forecast! Note the variability in the neighbourhoods. Represents a fundamental departure from our current verification system strategy where the emphasis is on extracting the nearest GP or bilinear interpolation to get matched forecast-ob pair. Make use of spatial verification methods which compare single observations to a forecast neighbourhood around the observation location.  SO-NF Forecast neighbourhood Observation x NOT upscaling/ smoothing!

© Crown copyright Met Office High Resolution Assessment (HiRA) framework Use standard synoptic observations and a range of neighbourhood sizes Use 24h persisted observations as reference The method needs to be able to compare:  Deterministic vs deterministic (different resolutions, and test vs control of the same resolution)  Deterministic vs EPS  EPS vs EPS  Test whether differences are statistically significant (Wilcoxon) [“s” denotes significant at 5%]  Grid scale calculated for reference  NOT main focus. Mittermaier 2014, WAF. VariableOldNew Temp RMSESSCRPSS Vector wind (wind speed) RMSVESSRPSS Cloud cover ETSBSS CBH ETSBSS Visibility ETSBSS 1h precip ETSBSS RMS(V)ESS = Root Mean Square (Vector) Error Skill Score ETS = Equitable Threat Score BSS = Brier Skill Score RPSS = Ranked Probability Skill Score CRPSS = Continuous Ranked Probability Skill Score MAE = Mean Absolute Error PC = Proportion Correct MAE grid scale Ready for operational trialling Jan 2015

© Crown copyright Met Office Deterministic vs EPS 1 st 5 weeks of 03Z MOGREPS-UK +ve = MOGREPS-UK ensemble better “none” = 12 nearest GP values MOGREPS-UK vs 1 nearest GP UKV 2.2 km 1.5 km Benefit of ensemble Need neighbourhood for convective precip neighbourhood greater benefit for UKV

© Crown copyright Met Office Skill against persistence 2.2 km 1.5 km

© Crown copyright Met Office Conclusions New verification framework illustrates benefit of km-scale ensemble over deterministic. Bigger neighbourhoods will improve forecast skill (for the most part) but the UKV needs (and benefits more from) neighbourhood processing, i.e. better “harvesting” of information content. The ensemble is more reliable to begin with and requires a smaller neighbourhood to achieve reliability. There is a trade-off between resolution and reliability as a function of neighbourhood size, and therefore simple neighbourhood processing for the ensemble is possibly not optimal.

© Crown copyright Met Office Questions? Mittermaier MP, 2014: A strategy for verifying near-convection-resolving forecasts at observing sites. Wea. Forecasting. 29(2), Mittermaier M.P., 2014: Quantifying the difference in MODE object attribute distributions for comparing different NWP configurations. In internal review. Mittermaier M.P., R. North and A. Semple, 2014: Feature-based diagnostic assessment of global NWP forecasts, in preparation for QJRMS.