1. The evaluation of updrafts in the Unified Model using single-Doppler radar measurements Nicol JC a, Hogan RJ b, Stein THM b, Hanley KE c, Lean HW c, Plant RS b, Clark PA b and Halliwell CE c a National Centre for Atmospheric Science (NCAS), University of Reading, Reading, UK b University of Reading, Reading, UK c MetOffice@Reading, Reading, UK

2. Estimation of vertical velocities from mass continuity DYMECS project (Dynamical and Microphysical Evolution of Convective Storms) Vertical cross-sections (RHIs) are typically made at low elevations (e.g. < 10°), so radial velocities provide an accurate estimate of the horizontal winds Assume vertical winds are zero at the surface or echo top Working upwards (or downwards), changes in horizontal winds at a given level increment the vertical wind to that point based on flow continuity Need to account for density change with height and integrate throughout the column Assumes no divergence into plane from cross-radial winds; only true for rain bands orientated perpendicular to the radar scan but not for rain cells

3. Reflectivity (dBZ) Actual vertical velocity (m/s) Vertical velocity estimated from 1D convergence (m/s) Unified Model (UM) Radar

4. Top-downGround-up TrueMerged Use weighted average of ground-up and top-down calculations based on the propagation of errors (due to density changes) 500-m gridlength Unified Model Log pdfs of vertical velocity as a function of height

5. 500-m model (1D conv.) Radar observations (1D conv.) 500-m model Radar observations Actual vertical velocity Transformed vertical velocity Radar observations using 1D conv. (dashed) and best estimate (solid) using transform function obtained from model results Radar data with dBZ>0 within 90 km of the radar Log pdf of model vertical velocity showing estimate from 1D conv. (dashed) and ‘true’ velocity (solid) between 7 and 8 km

7. 100-m 200-m 500-m UKV (1500-m) Radar Updraft profiles Reflectivity profiles Primary peak profiles

8. Updraft profiles Reflectivity profiles Multi-peaked profiles UKV (1500-m) 500-m 200-m 100-m Radar Updraft profiles Reflectivity profiles

9. Radar UKV (1500-m) 500-m 200-m 100-m Primary peak profile widthMulti-peaked profile width Updraft profile width (> 1 m/s) vs. Reflectivity profile width (> 20 dBZ) 2-3 km height 25 th August 2012 5-6 km height 25 th August 2012

10. Radar UKV (1500-m) 500-m 200-m 100-m Primary peak profile widthMulti-peaked profile width Updraft profile width (> 1 m/s) vs. Reflectivity profile width (> 20 dBZ) 2-3 km height 20 th April 2012 4-5 km height

11. 500-m UM 200-m UM Mixing length: λ=300m λ=100m λ=40m Primary peak profile widthMulti-peaked profile width Updraft profile width (> 1 m/s) vs. Reflectivity profile width (> 20 dBZ) 5-6 km height 25 th August 2012

12. Conclusions  Updraft widths decrease with model gridlength  200-m model has best agreement with observations  Updrafts are typically single-peaked profiles whose widths correspond to the primary reflectivity peak  Reflectivity profiles are often multi-peaked (combining precipitation from multiple updrafts?), though only very high resolution models tend to display this behaviour  Updrafts (precipitation cells) may be broadened or narrowed by increasing or decreasing the mixing length parameter; perhaps can improve how the size of cells is represented in the model for the wrong reasons

13. Perspectives for COPE  Similar approach using closely stacked PPIs from X-band  Compare with dual-Doppler retrievals from X-band, Met Office radars and Chilbolton radar  Independent validation from aircraft obs.  Contrast cases exhibiting deep (IOPs 4, 9, 10, 11 and 12) and shallow convection (IOPs 6, 8, 13, 15 and 16)  Evolution of individual storms  Interested in any collaborations which can utilise estimates of vertical velocities