Page 1© Crown copyright 2005 The convective-scale Unified Model: Results from UK case studies Richard Forbes (JCMM, Met Office) October 2005

Page 2© Crown copyright 2005 Talk Outline 1.The high resolution UM in action  An example UK case this summer from CSIP. 2.How are we doing ?  Verifying the high resolution UM convective rainfall. 3.Improving the model  Examples of recent model developments

Page 3© Crown copyright The high resolution UM in action  An example UK case this summer from CSIP. 2.How are we doing ?  Verifying the high resolution UM convective rainfall. 3.Improving the model  Recent model developments. Peter Clark, Humphrey Lean

Page 4© Crown copyright 2005 HRTM Domains Note that operational UK 4km model uses larger (whole UK) domain

Page 5© Crown copyright 2005 CSIP Alan Blyth, Keith Browning, Lindsay Bennett, Karl Beswick, Karen Bozier, Barbara Brooks, Peter Clark, Fay Davies, Wendy Garland, Charles Kilburn, Darcy Ladd, John Marsham, Cyril Morcrette, Emily Norton, Doug Parker, Ed Pavelin, Nigel Roberts, Ann Webb.

Page 6© Crown copyright 2005 Salford Doppler Lidar Aberystwyth Wind Profiler Leeds AWS Leeds Sodar Reading JCMM, Forecast Centre Met Office Radiosonde Radiosondes UMIST Cessna Chilbolton Radars and Lidar Met Office Unified Model Forecasts Cyril Morcrette, University of Reading

Page 7© Crown copyright 2005 CSIP IOP 18 – 25 th August Water Vapour 850 hPa  w, 300 hPa height 1200

Page 8© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 Network radar – 1/2/4 km Composite 09 UTC

Page 9© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 Network radar – 1/2/4 km Composite 10 UTC

Page 10© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 Network radar – 1/2/4 km Composite 11 UTC

Page 11© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 Network radar – 1/2/4 km Composite 12 UTC

Page 12© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 Network radar – 1/2/4 km Composite 13 UTC

Page 13© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 Network radar – 1/2/4 km Composite 14 UTC

Page 14© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 MSG High Resolution Visible

Page 15© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 MSG High Resolution Visible

Page 16© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 MSG High Resolution Visible

Page 17© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 MSG High Resolution Visible

Page 18© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 Observations Chilbolton Rainfall Rate Timeseries Chilbolton 1.5m Temperature Timeseries 8 K drop Peak 40 mm/hr Sferics 11Z to 13Z

Page 19© Crown copyright 2005 A convective-scale NWP System Animation of surface rain rates for 12km, 4km, 1km and radar from 0800 UTC to 1500 UTC on 25/08/2005 UM 12kmUM 4kmUM 1km Radar 300 km

Page 20© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 – 12 UTC 4 km model 10 m wind and convergenceRainfall rate

Page 21© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 – 12 UTC 4 km 12 km Screen Temperature

Page 22© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 – 14 UTC 4 km Divergence Screen Temperature

Page 23© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 – 14 UTC 4 km 8hr f/cRadar Surface Rainfall Rate

Page 24© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 – 14 UTC Visible Sat Image 4 km 8hr f/c High/Med/Low Cloud

Page 25© Crown copyright 2005 Summary – CSIP case study Showed high resolution UM results for one convective case study this summer (25 th Aug 2005) Secondary generation of convective storms by cold pools is an important process that needs to be captured by the model for a good forecast. A 12km resolution model is poor at representing this aspect of the dynamics, but 4km and 1km models with explicit convection are able to do so.

Page 26© Crown copyright The high resolution UM in action  An example UK case this summer from CSIP. 2.How are we doing ?  Verifying the high resolution UM rainfall. 3.Improving the model  Recent model developments. Nigel Roberts, Humphrey Lean, Peter Clark

Page 27© Crown copyright 2005 Background - What do we want to know? 1km model – should improve precipitation forecasts In some circumstances (e.g. strong orographic forcing) small scales can be relatively predictable, but most of the time small scales are less predictable. Can a 1-km model provide more accurate and useful forecasts of rainfall events on the scales of river catchments? On what scales should the output be presented?

Page 28© Crown copyright 2005 Verification approach Verify over different spatial scales using a conceptually simple approach. Fractions/probabilities from nearest neighbouring points. Verify against radar – good spatial coverage. Stable network over UK. Verify accumulations - smooth out temporal noise. Use accumulation exceedance thresholds e.g. > 4 mm, > 8 mm ….

Page 29© Crown copyright 2005 Radar12 km forecast1 km forecast mm The problem we face 0100 km Six hour accumulations 10 to 16 UTC 13th May 2003

Page 30© Crown copyright 2005 Schematic example - different scales

Page 31© Crown copyright km forecastRadar mm Six hour accumulations 10 to 16 UTC 13th May 2003

Page 32© Crown copyright mm threshold, Fractions at grid scale (1 or 0) ModelRadar > 4 mm Fraction

Page 33© Crown copyright 2005 ModelRadar > 4 mm Fraction 4 mm threshold, Fractions within 35x35 km squares

Page 34© Crown copyright 2005 ModelRadar Fraction 4 mm threshold, Fractions within 75x75 km squares

Page 35© Crown copyright 2005 ModelRadar Fraction 4 mm threshold, Fractions within 105x105 km squares

Page 36© Crown copyright 2005 Brier score for comparing fractions Skill score for fractions/probabilities - Fractions Skill Score (FSS) A score for comparing fractions with fractions

Page 37© Crown copyright 2005 Graphical behaviour of the Fractions Skill Score

Page 38© Crown copyright 2005 Summer 2004 Trial Run seven cases from 2004 period (mostly convective) For each case run 4 forecasts at 3 hour intervals Run one suite with 4km, 1km assimilation and a second initialising 4km, 1km from 12km analyses. Forecasts out to T+7 for 1km model Aggregate statistics over forecasts and cases.

Page 39© Crown copyright 2005 HRTM Domains Note that operational UK 4km model uses larger (whole UK) domain

Page 40© Crown copyright 2005 Assimilation Configuration 12km 3d-Var, MOPS/LHN 4km 3d-Var (scale selective), MOPS/LHN 1km 4km increments, MOPS/LHN 3 hour cycles all models

Page 41© Crown copyright 2005 Scores for 6 hour accums 1, 4 and 16mm thresholds Solid: Assim Dotted: Spinup Blue 12km Green 4km Red 1km 1mm / 6hr threshold 4mm / 6hr threshold 16mm / 6hr threshold

Page 42© Crown copyright 2005 Area average rain rates over 2004 summer trial Solid: Assim Dotted: Spinup Blue 12km Green 4km Red 1km Black Radar

Page 43© Crown copyright 2005 Scores for 1 hour accums 1 and 4mm threshold Solid: Assim Dotted: Spinup Blue 12km Green 4km Red 1km

Page 44© Crown copyright 2005 Summary - Verification Verifying high resolution precipitation forecasts on the grid scale is not always very helpful given the chaotic nature of convection. A skill score for an area is found to be a useful measure of rainfall forecast performance. Verification from seven cases during the summer of 2004 shows there is increasing skill for higher rainrates as the resolution is increased. Bias in the precipitation is still an issue (too much at high resolution) but this is being addressed.

Page 45© Crown copyright The high resolution UM in action  An example UK case this summer from CSIP. 2.How are we doing ?  Verifying the high resolution UM rainfall. 3.Improving the model  Recent model developments. Carol Halliwell, Richard Forbes, Peter Clark, Terry Davies, Yongming Tang

Page 46© Crown copyright 2005 Parametrization of sub-grid turbulent mixing Carol Halliwell, Peter Clark, Richard Forbes

Page 47© Crown copyright 2005 Parametrization of sub-grid mixing in the UM  Existing parametrizations in UM:  In the vertical  Convection scheme  1D non-local boundary layer scheme  In the horizontal  First order conservative operator with constant diffusion coefficient  For high resolution, require a 3D turbulence parametrization  First order scheme may be sufficient  We have implemented a variant of Smagorinsky-Lilly subgrid model.  Eddy-viscosity and eddy-diffusivity computed from resolved strain-rate, scalar gradients and certain prescribed length scales.

Page 48© Crown copyright 2005 Subgrid turbulence scheme in UM ( 0 is basic mixing length) Smagorinsky-Lilly subgrid-turbulence scheme with Richardson number based stability factor

Page 49© Crown copyright 2005 Impact of turbulence scheme on convective forecast (4 th July 2005) ReferenceWith Turbulence Param. 1km UM 6 hour forecast surface rainfall rate.

Page 50© Crown copyright 2005 Impact of turbulence scheme on convective forecast (4 th July 2005) Number of cells Reference With Turbulence Histogram of cell sizes Average cell size Time →

Page 51© Crown copyright 2005 Summary – Turbulent Mixing  3D sub-grid turbulent mixing parametrization introduced into the UM (based on Smagorinsky-Lilly).  Tested in idealised and real case studies and can have a very significant impact on convective initiation and evolution.  Reduces overprediction of small convective cells at 1km. Reduces excessive rain rates in larger storms.  Work is ongoing into most appropriate formulation for different resolutions, and enhancing the scheme (e.g. stochastic backscatter).

Page 52© Crown copyright 2005 Variable Resolution Grids Yongming Tang, Peter Clark, Terry Davies

Page 53© Crown copyright 2005 Variable Resolution An alternative approach to 1-way nesting. Grid varies from coarse resolution at the outer boundaries smoothly to a uniform fine resolution in the interior of the domain Benefits close to hires domain boundary, e.g. reduces spin-up of convection at inflow boundaries Uniform High Res zone Var-Res 2 Var-Res 1 Uniform Coarse Res 1 Uniform Coarse Res 2 Typically, there are 3 regions, and inflation ratio R 1 = R 2 = 5~10% R2R2 R1R1

Page 54© Crown copyright 2005 May Case - Variable Resolution Model Rainfall at 14 UTC. The three regions of the variable resolution domain are shown

Page 55© Crown copyright 2005 Summary – Variable Resolution  Variable resolution grid capability implemented in the UM.  Tested in idealised and real case studies with a nesting ratio of 1 : 4 and results look promising.  Currently working on the model parametrizations to make them depend appropriately on the local grid-length in different parts of the domain (e.g. grid-length dependent convection scheme).

Page 56© Crown copyright 2005 Summary – Variable Resolution  Variable resolution grid capability implemented in the UM.  Tested in idealised and real case studies with a nesting ratio of 1 : 4 and results look promising.  Currently working on the model parametrizations to make them depend appropriately on the local grid-length in different parts of the domain (e.g. grid-length dependent convection scheme).

Page 57© Crown copyright 2005 Summary

Page 58© Crown copyright 2005 Summary 1.4km UM now operational for the UK (since May 2005) 2.Performed many case studies with 1km/4km models over UK as well as idealised studies (diurnal cycle of convection) and other regions of the world (Alps, Africa, NewZealand) 3.Convective rainfall is of particular interest (for flooding) and 4km/1km models show skill in forecasting higher rain rates (better than 12 km model) 4.But …there are still improvements to be made !!!  Including missing processes in the model (e.g. turbulence, radiation on slopes, microphysics, improved representation of urban areas, other surface characteristics, lakes, snow)  Different approaches to modelling (e.g. variable resolution)  Understanding high resolution processes (convective initiation – CSIP)  Data assimilation (3D/4DVAR ?)  New applications (air quality)

Page 59© Crown copyright 2005 The End

Page 60© Crown copyright 2005 A convective-scale NWP System Surface rainfall rate (mm/hr) at 13:00 UTC on 04/07/2005 from the 1km UM and radar. UM 1kmUM 1km on 5km radar grid Radar 5km 300 km

Page 61© Crown copyright 2005 Scores for 1 hour accums 10% and 1% threshold Solid: Assim Dotted: Spinup Blue 12km Green 4km Red 1km Threshold is rainrate for which 10% of rainy grid points are higher Threshold is rainrate for which 1% of rainy grid points are higher

Page 62© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 Radar 4 km 12 km 1 km Rainfall Accumulations over 300x300 km box

Page 63© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 – 12 UTC

Page 64© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 Reflectivity Doppler Radial Velocity 1227 UTC 120  RHI

Page 65© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 – 12 UTC 10 m wind and convergenceRainfall rate

Page 66© Crown copyright 2005 CSIP IOP 18 – 25 th August 2005 – 12 UTC 2 gridlengths Cross section through 4 km model gust front Wind speed along section

Page 67© Crown copyright 2005 Incoming solar radiation on orographic slopes James Manners

Page 68© Crown copyright 2005 Surface radiation interactions Real situation is complex: Sloped surfaces, shadowed regions, reflection in valleys... Non-isotropic diffuse radiation... …and this is just the SW. Current 2-stream parametrization: SW and LW up and down. Direct SW incoming at angle of Sun Assumes flat surface.

Page 69© Crown copyright 2005 Orographic features important to radiation Oliphant et. al. 2003, ‘Spatial variability of surface radiation fluxes in mountainous terrain’ Characteristics in order of importance: slope aspect, slope angle, elevation, albedo, shading, sky view factor, leaf area index The most important factor is the area presented by each grid-box to the incoming direct SW radiation

Page 70© Crown copyright 2005 Grid-box mean slope aspect and angle Slope aspect: Slope angle:

Page 71© Crown copyright km Mesoscale Unified Model: 8 hr forecast Extra direct SW surface flux:Temperature difference at 1.5 metres:

Page 72© Crown copyright km Mesoscale Unified Model: 16 hr forecast Extra direct SW surface flux:Temperature difference at 1.5 metres:

Page 73© Crown copyright 2005 Summary – Orography and Radiation  Included slope aspect and angle into the incoming direct short-wave radiation scheme.  Tested in UM with grid resolutions ranging from 60km (global) to 1km (over the southern UK).  At high resolution, small (0.5K) surface temperature changes resulting from the scheme can lead to differences in convective initiation and evolution.

Page 74© Crown copyright 2005 Scales of Motion & Predictability Hail shaft Thunderstor m Front Extratropica l Cyclone Space Scale Lifetime Predictability? 10mins1 hr12hrs3 days 30mins3 hrs36hrs9 days 1000km 100km 10km 1km MCS

Page 75© Crown copyright 2005 Boscastle accumulations