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Drizzle comparisons. Ewan O’Connor, Robin Hogan, Anthony Illingworth. 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

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drizzle comparisons
Drizzle comparisons

Ewan O’Connor, Robin Hogan, Anthony Illingworth

overview
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
liquid water content
Liquid water content

Model

levels

Method 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

Cloud top

(radar)

Height

Cloud base

(lidar)

LWC

liquid water content1
Liquid water content
  • LWC not retrieved in rain
drizzle below cloud
Drizzle below cloud

Doppler radar and lidar - 4 observables(O’Connor et al. 2005)

  • Radar/lidar ratio provides information on particle size
drizzle below cloud1
Drizzle below cloud

Doppler 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.
liquid water flux
Liquid water flux
  • LWF retrieved below cloud base and in the absence of rain
ecmwf model
ECMWF model
  • Cloud similar to observations
met office mesoscale model
Met Office mesoscale model
  • Cloud similar to observations
met office global model
Met Office global model
  • Has rain at correct time!
meteo france arpege model
Meteo France ARPEGE model
  • Thin layers - can be one grid box thick
compare obs models
Compare obs/models
  • Models have similar LWC / LWP
  • Models overestimate precipitation
compare daily means
Compare daily means
  • Models have similar LWC / LWP
  • Models overestimate precipitation
monthly comparisons
Monthly comparisons
  • ECMWF model
  • Observations
monthly comparisons1
Monthly comparisons
  • Met Office mesoscale model
  • Observations
monthly comparisons2
Monthly comparisons
  • Met Office global model
  • Observations
monthly comparisons3
Monthly comparisons
  • Meteo France ARPEGE model
  • Observations
drizzle drop size
Drizzle drop size
  • Met Office model uses explicit size distributions
  • Treats all precipitation as rain
    • Overestimates drop sizes
    • Underestimates evaporation

Disdrometer

Radar/lidar

Model

met office diagnostic precipitation
Met Office diagnostic precipitation
  • Met Office model uses explicit size
  • Treats all precipitation as rain
met office diagnostic precipitation1
Met Office diagnostic precipitation
  • Met Office model uses explicit size
  • Treats all precipitation as rain
met office diagnostic precipitation2
Met Office diagnostic precipitation
  • Met Office model uses explicit size
  • Treats all precipitation as rain
met office diagnostic precipitation3
Met Office diagnostic precipitation
  • Met Office model uses explicit size
  • Treats all precipitation as rain
met office diagnostic precipitation4
Met Office diagnostic precipitation
  • Met Office model uses explicit size
  • Treats all precipitation as rain
conclusion
Conclusion
  • Models have reasonable LWC
    • Produce far too much drizzle
    • Precipitation reaches surface
    • Underestimate evaporation
  • Met Office model
    • Overestimate of drizzle drop size
ad