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The Atlantic ITCZ and related atmospheric features: a model-data comparison

The Atlantic ITCZ and related atmospheric features: a model-data comparison. Yochanan Kushnir, LDEO, Columbia University John Chiang, UC Berkeley. Data and Models. Observations: SST climatology: Reynolds and Smith V2 Surface wind stress and SST anomalies: NCEP/NCAR CDAS1(1979-2001)

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The Atlantic ITCZ and related atmospheric features: a model-data comparison

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  1. 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(1979-2001) • Precipitation: GPCP 1979-2001 • CCM3: • “AMIP” runs: CCM3.10 (T42/L18) forced withHadISST 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. CCM3 Atlantic ITCZ Rainfall: Mean & Variability Middle Basin 35°-15°W Eastern Basin 15°W-10°E OBS Climatological annual cycle and 1st EOF of interannual variability (1979-2001)

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

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

  9. 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 A SWCF ‘fix’ for CCM3 Precip vs. SWCF Precip vs. total CF

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

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

  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 (1979-2001)

  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 ERBE/CMAP CCM3

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

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