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CMIP1, CMIP2 and CDAS Comparisons. Vernon E. Kousky December 2007. CMIP1-CDAS Circulation and Temperature Differences. Average 200-hPa wind and 850-hPa temperature were computed for JFM and JJA over the last 50 years of the CMIP1 free run.
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CMIP1, CMIP2 and CDAS Comparisons Vernon E. Kousky December 2007
CMIP1-CDAS Circulation and Temperature Differences • Average 200-hPa wind and 850-hPa temperature were computed for JFM and JJA over the last 50 years of the CMIP1 free run. • The differences between those fields and the 1971-2000 CDAS1 mean fields are used to evaluate the performance of the CFS (CMIP1 run). • Differences are considered to be biases in the model climatology.
JFM 200-hPa Wind • During JFM, the NH westerlies in the CMIP1 run are shifted poleward with respect to CDAS1. • In addition, the NH flow is more zonally symmetric, and the eastern Pacific low-latitude troughs (in both hemispheres) are weaker in CMIP1
JJA 200-hPa Wind • During JJA the flow is more zonally symmetric in the SH. • Again, the low-latitude troughs are weaker than in CDAS1 over the eastern Pacific. • In addition, the westerlies are too strong over the NH subtropics.
The upper-level ridge over the western US is too weak in CMIP1 and the westerlies are too strong over the hurricane development regions in the Gulf of Mexico, off the Southeast US coast and over the northwestern Caribbean.
The low-level flow is too strong from the NW over the region of the Gulf of California during summer, and the easterlies are too weak over the Caribbean.
JFM 850-hPa Temperature • The 850-hPa temperatures, relative to CDAS, are too cold over the central and eastern N. Pacific, southern US, and central North Atlantic, and too warm over the eastern tropical Pacific. • The 200-hPa circulation differences, shown in slide 3 are consistent with this pattern.
JJA 850-hPa Temperature • During JJA, the 850-hPa temperatures are generally colder in the mid-latitudes than depicted in CDAS1. • This pattern is consistent with the 200-hPa circulation differences shown in slide 4. • Again, the tropical eastern Pacific is too warm in the CMIP simulation run.
CMIP1(2)-CDAS 200-hPa Wind and v-Variance Differences • Average 200-hPa winds and v-variance were computed for each month over the last 98 years of the CMIP1, CMIP2 free runs. • The differences between those fields and the 1971-2000 CDAS1 mean fields are used to evaluate the performance of the CFS (CMIP1 and CMIP2 runs). • Differences are considered to be biases in the model climatology. • Both CMIP1 and CMIP2 show nearly identical difference patterns for all months, when compared to CDAS1.
Summary • The CFS has a number of biases when compared to CDAS. • The 850-hPa temperatures are too cold over many mid-latitude locations and too warm over the eastern tropical Pacific. • The wintertime westerlies are shifted poleward and the east-Pacific low-latitude troughs are too weak in the CMIP runs. • The meridional wind variance is too high over the NH middle latitudes during winter and too high over the middle and high latitudes of the SH throughout the year. • The summertime upper-level ridge over the SW US is weaker in the CMIP run and low-level flow is too strong from the NW over the region of the Gulf of California, indicating a weaker SW monsoon in the CFS.
Summary • The CFS precipitation has substantial biases when compared to CAMS-OPI. • The precipitation in the ITCZ over the North Pacific is too strong. • The CFS displays a strong SH ITCZ over the Pacific, which is not evident in the CAMS-OPI analyses. • The CFS has too much precipitation over Brazil during the SH summer, and the precipitation pattern over the Equatorial Atlantic is markedly different from that depicted in CAMS-OPI.
