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CloudNET meeting: Malcolm Brooks, April 2005

Observatoire de Paris

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Contents

Cloud fraction means

IWC meansFiltering model IWC to mimic obs problems

Adiabatic LWC meansFiltering model LWC?

Categorizing profiles by Met. Regimes

The presentation covers the following sections

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Cloud fraction means

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IWC means

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Filtering Model IWC

The observations are filtered by removing profiles with rain or unknown liquid water attenuation.

At each model level, we need to characterise the effect this has on the observed IWC distribution – so we can apply the same effect to filter the observations.

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Filtering Model IWC

Step 1:

Observed and model distirutions of IWC are normalised, so as to be comparable.

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Filtering Model IWC

Step 2:

The ratio of the unfiltered IWC to the filtered IWC is calculated in the observations.

The varies with the Normalised IWC

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Filtering Model IWC

Step 3:

Use a fit of this ratio to filter the model IWC, as the normalised IWC varies.

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Filtering Model IWC

Step 5:

Convert the Normalised model IWC back to real units….

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IWC means – After filtering model IWC

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IWC means – Compare with ’99-’00 at Chilbolton

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LWC means

- - - Dashed black line shows adiabatic LWC

The Observed LWC appears higher than all the observations shown.

When radiometers not usable, assumed to be adiabatic: some filtering required equivalent to the work done on the IWC?

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Regimes

• What criteria to use to define the “background meteorology”?

- Vertical velocity (smoothed)

- Boundary layer stability.

• Which models will these be obtained from?

- “ensemble approach”

• How will the thresholds be defined?

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Regimes

Cloud data Source

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

7+ km

-0.16 -0.24 -0.23

0-3 km

-0.11 -0.19 -0.16

ECMWF clouds

7+ km

-0.14 -0.41 -0.26

0-3 km

-0.03 -0.23 -0.12

Correlations between cloud fraction and vertical velocity:

Chilbolton, ’99-’00

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Regimes

Cloud data Source

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

7+ km

-0.16 -0.24 -0.23

0-3 km

-0.11 -0.19 -0.16

ECMWF clouds

7+ km

-0.14 -0.41 -0.26

0-3 km

-0.03 -0.23 -0.12

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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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Regimes – vertical velocity

Regime criteria are normalised to account for the different distributions from the different models.

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←Neutral tercile

Regimes – vertical velocity

←Ascending tercileDescending tercile →

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Regimes – effect of vertical velocity at 500hPa

Descending tercile Neutral tercile Ascending tercile

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Regimes - boundary layer stability

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Regimes – boundary layer stability

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Regimes – effects of boundary layer stability

<< Most Stable Stable/Neutral Convective/Neutral Convective >>

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Regimes – Combined regimes

Vertical Velocity

What is it?750 hPa 300 hPa

Down/Neutral Down/Neutral Anticyclonic conditions

Ascent Down/Neutral Low level fronts

Down/Neutral Ascent Ahead of surface fronts,

Ascent Ascent General Ascent!

Combined with 3 Boundary layer types, gives 12 combinations!

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Regimes – Combined regimes

Convective BL:

Neutral BL:

Stable BL:

300hPa / 750hPa: ↓ / ↓ ↓ / ↑ ↑ / ↓ ↑ / ↑

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Regimes – Combined regimes – DJF only

Convective BL:

Neutral BL:

Stable BL:

300hPa / 750hPa: ↓ / ↓ ↓ / ↑ ↑ / ↓ ↑ / ↑

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Conclusions

• Model IWC can be filtered to mimic instrumental effects:

models do not agree with CloudNET IWC means – algorithm changed since ’99-’00 period.

Comparisons with more radar/lidar algorithms would be useful.

• Comparison of adiabatic LWC with models shows large disagreements

more work needed on what the observations mean.

• Regimes defined using vertical velocity and boundary layer stability are useful.

• Combining the ascent/ descent at 300 and 750 hPa and the boundary layer stability gives a ‘final’ regime definition.