1. Cloud fraction and Ice Water Content in Various Weather Regimes
Malcolm Brooks
CloudNET Final Symposium, 12 October 2005
Beeskow, Germany
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2. Contents Cloud fraction means Categorizing profiles by Met. Regimes
Defining Regimes
Results
Further Applications?
eg. Damian Wilson’s talk on Tuesday
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3. Mean Cloud fraction profiles
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4. Regimes What criteria to use to define the “background meteorology”?
- Vertical velocity (smoothed in time)
- Boundary layer stability.
Which models will these be obtained from?
- “ensemble approach”
How will the thresholds be defined?
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5. Regimes Cloud data Source Observed clouds -0.17 -0.22 -0.23 -0.06
ω data source (Pa s-1)
Met Office
ECMWF
Mean (UKMO, ECMWF)
Observed clouds
7+ km
-0.17
-0.22
-0.23
0-3 km
-0.06
-0.09
-0.07
Met Office clouds
-0.16
-0.24
-0.11
-0.19
ECMWF clouds
-0.14
-0.41
-0.26
-0.03
-0.12
Correlations between cloud fraction and vertical velocity:
Chilbolton, ’99-’00
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6. Regimes – vertical velocity
Not all models are included to define regimes:
RACMO – uses ECMWF analyses
Met Office Global model – too similar to the Mesoscale model
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7. Regimes – vertical velocity
Regime criteria are normalised to account for the different distributions from the different models.
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8. Regimes – vertical velocity
←Neutral tercile
Descending tercile →
←Ascending tercile
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9. Regimes – effect of vertical velocity at 500hPa
Descending tercile Neutral tercile Ascending tercile
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10. Regimes – boundary layer stability
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11. Regimes – effects of boundary layer stability
<< Most Stable Stable/Neutral Convective/Neutral Convective >>
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12. Regimes – Combined regimes
Vertical Velocity
What is it?
750 hPa
300 hPa
Down/Neutral
Anticyclonic conditions
Ascent
Low level fronts
Ahead of surface fronts,
General Ascent!
Combined with 3 Boundary layer types, gives 12 combinations!
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13. Regimes – Combined regimes
300hPa / 750hPa: ↓ / ↓ ↓ / ↑ ↑ / ↓ ↑ / ↑
Convective BL:
Neutral BL:
Stable BL:
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14. Application to Met Office Global Data
Ascent 300,750 hPa Neutral BL
Descent 300,750 hPa Stable BL
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15. Conclusions
Mean model cloud fractions in rough agreement with the observations.
Defining Meteorological regimes combining the vertical velocities in the upper and lower troposphere, and boundary layer stability can be a useful tool.
eg ECMWF does not over predict cloud in convective boundary layer.
The method can be applied beyond single profiles.
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