The Effect of Vertical Resolution on Zonal

Wind Stress in AMIP Runs

Glenn.White@noaa.gov

An evaluation of

monthly means

from Suru Saha’s AMIP runs

with observed SST 1979-2001 PRX

28 versus 64 levels

Validation NCEP Reanalyses

CDAS, NCEP2

FSU Stresses 1978-2000

SOC flux climatology 1980-93

SOC 1980-83

Zonal mean

Ocean

5S-5N 1980-93

SOC

5S-5N

Pacific FSU

1980-93 SOC

Time-mean

Us

Pacific FSU

1979-2000

Time-mean zonal wind stress

Annual Cycle

1980-93

Pacific

SOC

FSU

CDAS

NCEP2

28 levels

64 levels

28 levels-NCEP2

64-NCEP2

64-28 levels

CDAS-NCEP2

Time-mean zonal wind stress 1980-93 SOC

Magnitude of systematic difference

CDAS

NCEP2

CDAS-SOC

NCEP2-SOC

28 levels

64 levels

28 levels minus SOC

64-SOC

Systematic difference from

FSU 1980-93 Mean

Tropical Pacific

JJA 1980-93 Time mean zonal wind stress

FSU

28

64

JJA 1980-93 Time mean zonal wind stress

SOC

CDAS

NCEP2

28-FSU

64-FSU

64-28JJA 1980-93 Time mean zonal wind stress

FSU-SOC

FSU-NCEP2

CDAS-NCEP2

JJA 1980-93 Time mean zonal wind stress

Anomaly correlation with NCEP2

28

64

CDAS

The reanalyses correlate better in time with FSU stresses than the AMIP runs, after the time-mean annual cycles are removed.

Monthly anomalies 1979-2000

Pacific

Anomaly correlation with FSU--Pacific

CDAS

NCEP2

28 levels

64 levels

Merid. Wind Stress

CDAS

NCEP2

28 levels

64 levels

Anomaly correlation with FSU merid. Wind stress

1979-2000

Difference in anomaly correlation with FSU

28 – NCEP2

64-NCEP2

64-28

FSU

Standard deviation of monthly anomalies

28 levels

64 levels

1979-2000

28-FSU

64-FSU

64-28

Difference in standard deviation

Standard deviation of monthly anomalies

1979-2000

CDAS

NCEP2

CDAS-FSU

NCEP2-FSUCDAS-NCEP2

1979-2000

64 levels do not produce better zonal wind stress than 28 levels.

Reanalyses display more agreement with SOC, FSU than AMIP runs.

64 level AMIP run too strong easterly stress in JJA, too strong westerly stress in JFM.