1. Yochanan Kushnir, LDEO, Columbia University John Chiang, UC Berkeley
The Atlantic ITCZ and related atmospheric features: a model-data comparison
Yochanan Kushnir, LDEO, Columbia University
John Chiang, UC Berkeley

2. Data and Models Observations: SST climatology: Reynolds and Smith V2
Surface wind stress and SST anomalies: NCEP/NCAR CDAS1( )
Precipitation: GPCP
CCM3:
“AMIP” runs: CCM3.10 (T42/L18) forced with HadISST 1.1
ECHAM:
“AMIP” runs: ECHAM 4.5 (T42/L19) forced with NCEP SST

3. Climatology of SST & Precip
Projection on SST PC 1
Projection on SST PC 2

4. Climatology: Observations & CCM3
Projection on SST PC 1
Projection SST PC 2
OBS
CCM3

5. Climatology: Observations & CCM3-OBS
Projection on SST PC 1
Projection SST PC 2
OBS
CCM3-OBS

6. Atlantic ITCZ Rainfall: Mean & Variability
Middle Basin 35°-15°W
Eastern Basin 15°W-10°E
OBS
CCM3
Climatological annual cycle and 1st EOF of interannual variability ( )

7. SWCF-precip relationship, SST > 27C ERBE/CMAP and CCM3 (following C. Bretherton)

8. Total CF-precip relationship, SST > 27C ERBE/CMAP and CCM3

9. A SWCF ‘fix’ for CCM3 Precip vs. SWCF
Ad-hoc change to CCM3 ice and liquid water scattering particle sizes from 20S-20N
Resulting SWCF-precip and Total CF-precip relationship resembles ERBE-CMAP
TOA global radiative balance approximately preserved
Precip vs. total CF

10. CCM3 ‘fix’ - control: projection on the SST mean
Control CCM3 - Obs

11. CCM3‘fix’ - control: projection on the SST first harmonic
Control CCM3 - Obs

12. Climatology: OBS & ECHAM4.5-OBS
Projection on SST PC 1
Projection SST PC 2
OBS
CCM3-ECHAM

13. Atlantic ITCZ Rainfall: Mean & Variability
Middle Basin 35°-15°W
Eastern Basin 15°W-10°E
OBS
ECHAM
Climatological annual cycle and 1st EOF of interannual variability ( )

14. CF-precip relationships for ECHAM 4.5 (SST > 27C)
Pcp vs SWCF
Pcp vs LWCF
Pcp vs total CF

15. Summary
CCM3 exhibits substantial biases in precipitation over the Atlantic ITCZ and neighboring land regions in both the annual mean and seasonal cycle
An ad-hoc adjustment to the CCM3 SWCF-precipitation relationship to match the observed appears to decrease the precipitation biases
ECHAM 4.5 biases appear generally smaller than CCM3, and it exhibits better CF-precip relationship

16. The following are extra slides

17. SWCF-precip relationship - ERBE/CMAP and CCM3, land regions 20S-20N

18. Total CF-precip relationship - ERBE/CMAP and CCM3, land regions 20S-20N