1. Convective Scale Modelling Humphrey Lean et. al
Convective Scale Modelling Humphrey Lean et. al. Mesoscale Modelling Research, Reading, UK
COPE meeting, Oct 2012
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2. Aims of Explicit Convection UM work
To determine optimum configuration of UM at various (high) resolutions (gridlength 1.5km – 100m).
Assess what benefits of running model at high resolutions might be (and problems).
Hope to shed light on behaviour of model and improve respresentation at 1.5km.
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3. 1.5km UK Model convection (1)
Currently highest resolution operational UK model (no convection parameterisation).
Beats 4km and 12km models for convective rain (as measured by neighbourhood verification).
Beats 4km model for convective rain as measured subjectively by forecasters.
Many systematic problems arising from convective parameterisation improved (e.g. snow showers penetrating inland in winter).
BUT Problems still remain……
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4. 1.5km UK Model convection (2)
Major source of error is large scale errors (motivation for downscaling ensemble – see Nigel Roberts talk!)
Lack of predictability of small features (probabilistic diagnostics)
Problems with representation of convection (under resolved – hence term “convection permitting”).
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5. “UKV” 1.5km UK Model convection
1.5km model
Radar
15 UTC 12th April 2012
Convective cells too large and too intense.
Not enough light rain.
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6. Average cell sizes (km)
Threshold mm/hr
Radar
1.5km Model
0.125
7.81
16.04
0.5
6.32
13.21
1.0
5.58
11.71
2.0
4.42
9.93
4.0
3.28
7.95
8.0
2.57
5.96
16.0
2.13
3.37
Average cell radius from the precipitation field over 22 convective cases.
Emilie Carter
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7. Gridscale structure in 750 hPa w 13UTC 12/05/2010
500m
1.5km
4km
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8. Emilie Carter 2.2km 1.5km 200m 100m 1km RADAR 500m 4km
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9. Emilie Carter 4km 2.2km 1.5km 500m 200m 100m 1km RADAR
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10. Mass flux- 20110807 1500 UTC Carol Halliwell Carol Halliwell
Aggregated to 200m
Aggregated to 500m
Aggregated to 1.5km
Carol Halliwell
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Carol Halliwell

11. Effect of holding mixing length const at 300m (1.5km value).
Spectra of vertical velocity on 100m domain for all resolutions at approximate heights 1km (left) and 3km (right).
Radar
We were hoping to see the 100m and 200m lines lying almost on top of each other, indicating that the solutions had converged but it looks like this is not the case and there still appears to be significant energy in the grid-scale in the 100m run.
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12. Effect of increasing to 140 levels in vertical
Radar
We were hoping to see the 100m and 200m lines lying almost on top of each other, indicating that the solutions had converged but it looks like this is not the case and there still appears to be significant energy in the grid-scale in the 100m run.
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13. Cross section WE through the BL rolls in the 100m model at 10 UTC 3rd November
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14. Average cell diameters over 8 “small shower” April 2012 cases (140L)
Carol Halliwell
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15. CSIP Modelling Outcomes
Main conclusion was that initiation often very complicated and dependent on many factors. But models can capture this if they have them all.
Back then a major interest was verifying the new 4km model – seemed to do well for many cases.
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16. CSIP IOP1 Observations Model Dartmoor (approx 600m)
Single storm initiated over Dartmoor as
a result of a convergence line and a frontal
Structure.
Grey: Precip
Black: cloud
30 min intervals
Radar/Satellite
1.5km model
Observations
Model
Dartmoor (approx 600m)
Lean et al MWR (2009)
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17. CSIP IOP1: Storm breaking through lid at 11 UTC
1.5km Model
Static Stability
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18. DYMECS project
DYnamical and Microphysical Evolution of Convective Storms (DYMECS).
Hogan, Plant, Lean et. al. University of Reading collaboration with Met Office.
Automated tracking of cells used to control Chilbolton research radar and build up statistics of properties of convection (up to 40 cases). Compare with models.
See Robin Hogan talk!
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19. COPE Need continued detailed measurements for comparisons to model.
Concentrate on development of storms rather than initiation.
Key thing would be ways to constrain updraft characteristics (magnitude, area, depth, fluxes) and cloud sizes, concentrations etc.
High res model runs on COPE cases (original proposal envisaged reference 100m runs).
See Rob Warren talk later for modelling work on a COPE type convergence line case.
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20. Thank you for listening. Any questions?
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