- 200 hPa geopotential heights in the GDAS analysis arelower than in CDAS between 20oN to the South Pole.

- 200 hPa geopotential heights are consistentlylower for GDAS compared to CDAS since at leastNovember 2004 over the global Tropics.

-200 hPa Errors in the GFS forecasts in excess of 0.5 std. dev. are observed after Day-6 & in the Topics & near the poles.

-The CDAS monthly precipitation differences from CAMS_OPIare similar to May and June 2005: CDAS < observations over the near-equatorial Tropics in the NH, the northern Indian Ocean and “coastal” western Pacific, and = or > observations over much of the Southern Hemisphere near-equatorial Tropics

-GFS precip. >> than obs. over the Atlantic & Pacific ITCZs and the Arabian Sea, and < over parts of SE Asia and Indonesiaat all forecast projections (1-15 days)

-Vertical velocity and upper-level divergence fields are consistent with the precipitation differences over the Pacificnear-equatorial regions in the GDAS/GFS.

-CDAS 2m temperature anomalies are generally within 1K of observed surface temperature and 1-3K cooler where they differ.GDAS sfc. temps much closer to obs. than CDAS.

July 2005 Summary of CDAS/GDAS/GFS

200 hPa geopotential heights in the GDAS analysis arelower than in CDAS between 20oN to the South Pole.The magnitude of the differences over the Tropics areequivalent to about 1 standard deviation in the CDASmonthly means over the 1971-2000 base period. This is the the same basic pattern since March 2005.

Time series of 200 hPa heights for GDAS and CDAS over the Tropics indicate that heights are consistentlylower for GDAS compared to CDAS since at leastNovember 2004, and that this difference occurs overland as well as ocean, although the difference is largest over the oceans.

The zonal 200 hPa hgt errors in the GFS grow with the length of the forecast projection. During July 2005, negative hgt errors in excess of 10m are observed for the day-4 forecasts and beyond at most latitudes. Errors in excess of 0.5 std. dev. (right panel) are observed after Day-6 that grow with forecast projection in the Topics & near the poles. The error south of 60o S are much less than in June 2005.http://www.cpc.ncep.noaa.gov/products/fcst_eval/html/maps_mrf.html

Similar to the past 2 months, the CDAS monthly precipitation accumulations are less than the satellite-gauge (“CAMS_OPI”) observations over most of the near-equatorial Tropics in the Northern Hemisphere and the southern portion of the SPCZ. In contrast, CDAS indicates much heavier accumulations than the observations over the hurricane development region in the tropical Atlantic west of the Caribbean in July 2005.

May 2005 June 2005

The precipitation anomalies between CDAS and the satellite estimates agree well over the Indian subcontinent (positive anomalies) and the Pacific ITCZ (negative anomalies). As obs-erved in the accumulation map (previous slide) CDAS has a 4-5Mm/day positive anomaly for July 2005 that is not in theCAMS-OPI estimates.

GFS precip. muchlarger than obs.over equatorial South America and theArabian Sea at all fcst. projections. GFS rainfall is much lessthan the satellite estimatesover the much of SE Asiaand the equatorial IndianOcean.

Very similar to June 2005

Precip. is much too strong in the Atlantic and Pacific ITCZs at all forecast proj-ections – same as allprevious months.

GFS precipitation forecasts generally too wet (by ~ 100 mm) eastof the Mississippi for the Day1 forecasts, but the sign of the diff-erences is not uniform for the other fcst. projections.Contrary to previous months (but consistent with June), these biases do not shrink or grow steadily with forecast projection.

The CDAS OLR is generally cooler over the continents comparedto observed OLR, although this difference may be due to the factthat observed OLR is from measurements at only a few times of day (0200/1400 LST at the equator). GDAS OLR is substantially closer to the observed OLR compared to CDAS, andthe differences with observed OLR are almost completely positive.

The evolution of near-equatorial OLR anomalies during Nov 2004through July 2005 in CDAS shows negative anomalies for theentire period near the date line. That contrasts with the observed OLR which indicates negative anomalies there during Dec 2004 –Feb 2005 and mid-March-May 2005. The relatively dry periodDuring Jan-Mar 2005 on either side of the date line agrees wellWith the observed OLR. Note that GDAS anomalies are not plotted because a reliable climatology is not available from GDAS due to the many model changes that have occurred during the GDAS record.

The GDAS upward motion at 500 hPa is considerably strongerthan CDAS over the ITCZs in the Atlantic and Pacific which isconsistent with the higher rainfall in GDAS over those areascompared to CDAS (see earlier precip. figs – buttons below). This is also consistent with differences in the upper-levelDivergence (button below).

CDAS precip

GDAS precip

Divergence

GDAS vertical velocity (500 hPa) is consistently higher than CDAS over tropical land regions, in good agreement over thetropical oceans, although consistently lower there since April2005. Both are in good agreement over the NH oceanic storm tracks. We presume that the vertical motion over the Pacific ITCZincreases with forecast projection to be consistent with theheavy precipitation in the 5-15 day GFS forecasts.

CDAS 2m temperatures are generally 1-3K cooler over the landsurfaces than is observed; regions where CDAS is up to1K warmer than the obs. are generally in areas with high terrain.In contrast, GDAS 2m temps. are 1-3K warmer than CDAS over the majority of the continental regions.

In general, the CDAS temperature anomalies are within 1K of the observed anomalies; where they differ, the CDAS anomalies are generally cooler than the CAMS (station) data.

Global Mean precip from GFS is about 25% higher than GPCP.