Cam3 composite cyclone comparison
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CAM3 composite cyclone comparison. Paul Field, A. Gettelman, R. Neale, P. Rasch, R. Wood. Satellite Observations. All data over ocean AMSR – WVP, Rainfall, SST Quikscat – 10m winds NCEP/NCAR – mslp, T-profile 2003, 2004, 1500 midlatitude cyclones from NP, NA, SP, SA

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CAM3 composite cyclone comparison

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Cam3 composite cyclone comparison

CAM3 composite cyclone comparison

Paul Field, A. Gettelman,

R. Neale, P. Rasch, R. Wood


Satellite observations

Satellite Observations

  • All data over ocean

  • AMSR – WVP, Rainfall, SST

  • Quikscat – 10m winds

  • NCEP/NCAR – mslp, T-profile

  • 2003, 2004, 1500 midlatitude cyclones from NP, NA, SP, SA

  • Field and Wood JCLI 2007


Cam3 composite cyclone comparison

Compositing

cyclone

center


Compositing

Compositing

  • Locate low center onto 4000x4000 km grid

  • 100x100 km ‘pixels’

  • Subsample composites based on mean windspeed and mean wvp


Strength and moisture

Strength and Moisture


Models

Models

  • 10 yr runs, analyze last 3 years

  • Control: CAM3 0.9x1.25deg Finite Volume

  • SSAT: Modify Slingo cloud fraction curve

  • 4x5 : 4 by 5 degree grid spacing

1

CF

0

1.0

RHice


Cam3 composite cyclone comparison

Satellite

Control

High Cloud

All show positive correlation with cyclone strength

Control ~+3% bias in high cloud fraction

Ssat ~no bias, slightly more dependence on wvp that obs

4x5 ~+10% bias

ssat

4x5


Cam3 composite cyclone comparison

Satellite

Control

Rainfall

All show positive correlation with cyclone strength

All show greater dependency of rainfall on cyclone strength than obs

ssat

4x5


Cam3 composite cyclone comparison

Satellite

Control

RHcol

Obs shows no correlation with cyclone strength or wvp

Model runs show positive correlation with cyclone strength

Control & ssat ~ -7% bias

4x5 less bias

ssat

4x5


Cam3 composite cyclone comparison

Satellite

Control

High Cloud Composite (max strength, med wvp)

All show high cloud to east and se

Model runs greater means and extent

Ssat is better than control

4x5 is worse than control

ssat

4x5


Cam3 composite cyclone comparison

Satellite

Control

Rainfall composite (max strength, med wvp)

All show max rain to east and se

Model runs greater means and extent

ssat

4x5


Warm conveyor belt

Warm Conveyor Belt

thermodynamic dynamic

R = WVPV

W

V

S

q0 = WVP / S


Cam3 composite cyclone comparison

Satellite

Control

Warm Conveyor Belt

All show positive correlation

Models show greater dependency of rainfall on cyclone strength than obs

ssat

4x5


No convection

No Convection

  • No deep or shallow or midlevel convection

  • Unbalanced

  • 5 year run – analyse last 3 years


Cam3 composite cyclone comparison

Satellite

Control

High Cloud Composite (max strength, med wvp)

No conv: much less high cloud

No conv


Cam3 composite cyclone comparison

Control (NP)

Obs (NA)

Cloud top temperature

pdf slices

No convection:

much less high cloud

reduction in mid-level cloud

better agreement with obs

No conv (NP)


Cam3 composite cyclone comparison

Satellite

Control

Warm Conveyor Belt

No convection:

Still shows more dependence on cyclone strength

Still RHcol correlation with strength (not shown)

No conv


Cam3 composite cyclone comparison

Quikscat wind divergence (10m)

Increasing moisture

Increasing cyclone strength


Cam3 composite cyclone comparison

Horizontal wind divergence (10m)

Satellite

Control

Obs: width of pdf increases with strength

Model: no obvious increase in pdf width with strength

weak

med

strong

4x5

ssat


Conclusions so far

Conclusions (so far)

  • Rainfall behavior largely unaffected by differences in models

  • RHcol dependence on strength in model – not obs (related to div/dynamics?)

  • High cloud is better in ssat run. Introduction of scheme that allows supersat should be improvement

  • No conv – improves high cloud representation (fix midlat cyc clouds with improved conv)


To do list

To do list

  • Provide physical arguments for observed variations

  • Compare results from

    • New microphysics

    • New conv. schemes


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