The evaluation of updrafts in the
Unified Model using single-Doppler
radar measurements
Nicol JCa, Hogan RJb, Stein THMb, Hanley KE c, Lean HW c, Plant RSb, Clark PAb and Halliwell CE c
a
National Centre for Atmospheric Science (NCAS), University of Reading, Reading, UK
b
c
University of Reading, Reading, UK
MetOffice@Reading, Reading, UK
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
Unified Model (UM)
Radar
Reflectivity (dBZ)
Vertical velocity estimated from 1D convergence (m/s)
Actual vertical velocity (m/s)
500-m gridlength Unified Model
Top-down
Ground-up
True
Merged
Log pdfs of vertical velocity as a function of height
Use weighted average of
ground-up and top-down
calculations based on the
propagation of errors
(due to density changes)
Log pdf of model vertical velocity
showing estimate from 1D conv.
(dashed) and ‘true’ velocity (solid)
between 7 and 8 km
500-m model (1D conv.)
Radar observations (1D conv.)
Radar observations using 1D
conv. (dashed) and best estimate
(solid) using transform function
obtained from model results
500-m model
Actual vertical velocity
Radar observations
Transformed vertical velocity
Radar data with dBZ>0 within 90 km of the radar
Updraft profiles
Reflectivity profiles
Updraft profiles
Reflectivity profiles
UKV (1500-m)
100-m
500-m
Radar
Primary peak
profiles
200-m
Updraft profiles
Reflectivity profiles
Updraft profiles
Reflectivity profiles
UKV (1500-m)
100-m
500-m
Radar
Multi-peaked
profiles
200-m
Updraft profile width (> 1 m/s) vs. Reflectivity profile width (> 20 dBZ)
Primary peak profile width
Multi-peaked profile width
25th August 2012
2-3 km height
Radar
UKV (1500-m)
500-m
200-m
100-m
25th August 2012
5-6 km height
Updraft profile width (> 1 m/s) vs. Reflectivity profile width (> 20 dBZ)
Primary peak profile width
Multi-peaked profile width
20th April 2012
2-3 km height
Radar
UKV (1500-m)
500-m
200-m
100-m
20th April 2012
4-5 km height
Updraft profile width (> 1 m/s) vs. Reflectivity profile width (> 20 dBZ)
Primary peak profile width
Multi-peaked profile width
500-m UM
25th August 2012
5-6 km height
200-m UM
25th August 2012
Mixing length: λ=300m
λ=100m
λ=40m
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
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