Drizzle comparisons
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![Page 1: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/1.jpg)
Ewan O’Connor, Robin Hogan, Anthony Illingworth
Drizzle comparisons
![Page 2: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/2.jpg)
Overview– Do operational forecast models simulate drizzle correctly?
• Models simulate drizzle through precipitation scheme• Treat coalescence drizzle as light rain
– Observed liquid water content/flux• Cloud LWC retrieval• Drizzle liquid water flux retrieval
– Compare observations and models• Daily basis• Monthly means
– Drizzle drop size• Explicit in Met Office model• Effect of changing drizzle number concentration
![Page 3: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/3.jpg)
Liquid water contentMethod of Albrecht et al. (1990), Boers et al. (2000)
– Use lidar/radar to determine cloud boundaries– Assume linear increase of LWC with height– Scale LWC profile to match LWP from radiometers
LWC
Heig
ht
Cloud base(lidar)
Cloud top (radar)
Modellevels
![Page 4: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/4.jpg)
Liquid water content– LWC not retrieved in rain
![Page 5: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/5.jpg)
Drizzle below cloudDoppler radar and lidar - 4 observables (O’Connor et al. 2005)
• Radar/lidar ratio provides information on particle size
![Page 6: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/6.jpg)
Drizzle below cloudDoppler radar and lidar - 4 observables (O’Connor et al. 2005)
• Radar/lidar ratio provides information on particle size
Retrieve three components of drizzle DSD (N, D, μ).• Can then calculate LWC, LWF and vertical air velocity, w.
![Page 7: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/7.jpg)
Liquid water flux– LWF retrieved below cloud base and in the absence of rain
![Page 8: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/8.jpg)
ECMWF model– Cloud similar to observations
![Page 9: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/9.jpg)
Met Office mesoscale model– Cloud similar to observations
![Page 10: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/10.jpg)
Met Office global model– Has rain at correct time!
![Page 11: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/11.jpg)
Meteo France ARPEGE model– Thin layers - can be one grid box thick
![Page 12: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/12.jpg)
Compare obs/models– Models have similar LWC / LWP– Models overestimate precipitation
![Page 13: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/13.jpg)
Compare daily means– Models have similar LWC / LWP– Models overestimate precipitation
![Page 14: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/14.jpg)
Monthly comparisons
– ECMWF model– Observations
![Page 15: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/15.jpg)
Monthly comparisons
– Met Office mesoscale model– Observations
![Page 16: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/16.jpg)
Monthly comparisons
– Met Office global model– Observations
![Page 17: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/17.jpg)
Monthly comparisons
– Meteo France ARPEGE model– Observations
![Page 18: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/18.jpg)
Drizzle drop size– Met Office model uses explicit size distributions– Treats all precipitation as rain
• Overestimates drop sizes • Underestimates evaporation
Disdrometer
Radar/lidar
Model
![Page 19: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/19.jpg)
Met Office diagnostic precipitation
– Met Office model uses explicit size – Treats all precipitation as rain
![Page 20: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/20.jpg)
Met Office diagnostic precipitation
– Met Office model uses explicit size– Treats all precipitation as rain
![Page 21: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/21.jpg)
Met Office diagnostic precipitation
– Met Office model uses explicit size– Treats all precipitation as rain
![Page 22: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/22.jpg)
Met Office diagnostic precipitation
– Met Office model uses explicit size– Treats all precipitation as rain
![Page 23: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/23.jpg)
Met Office diagnostic precipitation
– Met Office model uses explicit size– Treats all precipitation as rain
![Page 24: Drizzle comparisons](https://reader035.fdocuments.us/reader035/viewer/2022062217/56812dd3550346895d931ca8/html5/thumbnails/24.jpg)
Conclusion– Models have reasonable LWC
• Produce far too much drizzle• Precipitation reaches surface• Underestimate evaporation
– Met Office model• Overestimate of drizzle drop size