200 hPa geopotential heights in the GDAS analysis are

1
July 2005 Summary of CDAS/GDAS/GFS

• - 200 hPa geopotential heights in the GDAS
  analysis are
• lower than in CDAS between 20oN to the South
  Pole.
• - 200 hPa geopotential heights are consistently
• lower for GDAS compared to CDAS since at least
• November 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_OPI
• are similar to May and June 2005
• CDAS lt observations over the near-equatorial
  Tropics in the
• NH, the northern Indian Ocean and coastal
  western Pacific,
• and or gt observations over much of the
  Southern Hemisphere
• near-equatorial Tropics
• GFS precip. gtgt than obs. over the Atlantic
  Pacific ITCZs
• and the Arabian Sea, and lt over parts of SE Asia
  and Indonesia

2
200 hPa geopotential heights in the GDAS analysis
are lower than in CDAS between 20oN to the South
Pole. The magnitude of the differences over the
Tropics are equivalent to about 1 standard
deviation in the CDAS monthly means over the
1971-2000 base period. This is the the same
basic pattern since March 2005.
3
Time series of 200 hPa heights for GDAS and CDAS
over the Tropics indicate that heights are
consistently lower for GDAS compared to CDAS
since at least November 2004, and that this
difference occurs over land as well as ocean,
although the difference is largest over the
oceans.
4
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.n
oaa.gov/products/fcst_eval/html/maps_mrf.html
5
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.
June 2005
May 2005
6
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 4-5 Mm/day positive anomaly for
July 2005 that is not in the CAMS-OPI estimates.
7
Precip. is much too strong in the Atlantic and
Pacific ITCZs at all forecast proj- ections
same as all previous months.
GFS precip. much larger than obs. over equatorial
South America and the Arabian Sea at all fcst.
projections. GFS rainfall is much less than
the satellite estimates over the much of SE
Asia and the equatorial Indian Ocean. Very
similar to June 2005
8
GFS precipitation forecasts generally too wet (by
100 mm) east of 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.
9
The CDAS OLR is generally cooler over the
continents compared to observed OLR, although
this difference may be due to the fact that
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, and the
differences with observed OLR are almost
completely positive.
10
The evolution of near-equatorial OLR anomalies
during Nov 2004 through July 2005 in CDAS shows
negative anomalies for the entire 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 period During Jan-Mar
2005 on either side of the date line agrees
well With 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.
11
The GDAS upward motion at 500 hPa is considerably
stronger than CDAS over the ITCZs in the Atlantic
and Pacific which is consistent with the higher
rainfall in GDAS over those areas compared to
CDAS (see earlier precip. figs buttons below).
This is also consistent with differences in the
upper-level Divergence (button below).
CDAS precip
GDAS precip
Divergence
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• GDAS vertical velocity (500 hPa) is consistently
  higher than
• CDAS over tropical land regions, in good
  agreement over the
• tropical oceans, although consistently lower
  there since April
• Both are in good agreement over the NH oceanic
  storm
• tracks. We presume that the vertical motion over
  the Pacific ITCZ
• increases with forecast projection to be
  consistent with the
• heavy precipitation in the 5-15 day GFS forecasts.

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CDAS 2m temperatures are generally 1-3K cooler
over the land surfaces than is observed regions
where CDAS is up to 1K 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.
16
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.
17
Global Mean precip from GFS is about 25 higher
than GPCP.