Evaluation of cirrus microphysics in CAM5 using aircraft data

C. Bardeen, A. Gettelman, E. Jensen

ATTREX Science Team MeetingOctober 24, 2013

Ice Water Path

Bardeen et al., [2013]

IWP: Tropical Bias

GlobalTropics

IWP: Tropics, JF

Cloud Fraction & Ice Water Content

IWC Bias

Low Z, High IWC: 2C-ICE > DARDAR

High Z, Low IWC: DARDAR > 2C-ICE

SPartICus

Deng et al., [2012]

SD-CAM: Tropical T, H2O, RH

CAM5 relative humidity too high

RH: Tropics, JF, 100 hPa

ATTREX2: T, Q, RH, March 1, 2013

ATTREX2: CF, N, M, March 1, 2013

Clear Sky: RH vs T

Krämer et al., [2009] ATTREX 1 & 2

Don’t see higher frequencies of RH > 100% when T < 190 K like Krämer et al. [2009]

Cloudy: RH vs T

Krämer et al., [2009] ATTREX 1 & 2

Don’t see as much higher frequencies of RH > 100% when T < 190 K like Krämer et al. [2009].

Cloud N & Re vs TKrämer et al., [2009] ATTREX 1 & 2

Subgrid Scale Clouds

• Cloud Fraction– Wilson & Ballard [1999]– CF α ice mass

• Subgrid Saturation– Nucleation– Growth– Sice α 1/CF

Many clouds should fill the gridbox, but never get CF = 1.0 in model

Model: RH vs TATTREX 1 & 2 CAM/CARMA

Clear

Cloudy

Gridbox Avg

Model: In-Cloud N & Re vs TATTREX 1 & 2 CAM/CARMA

Concentration much lower and effective radius too big

Summary

• Significant difference between DARDAR and 2C-ICE IWP, but clear tropical bias in the models

• Relative humidity too high in CAM5• ATTREX RHvsT looks like Krämer et al., but not as

high at low T• Model low in ice concentration and high in

effective radius• How to deal with subgrid scale clouds: saturation,

cloud fraction, …?