A Comparative Study on Reanalysis Data between GAME and NCEP/NCAR
During the Period of HUBEX in 1998
*Weijing Li 1, Rongqing Han 1, Guoquan Hu 1, Jinhai He 2
(1: China National Climate Centre, China, 100081, 2: Nanjing Institute of Meteorology, China, 210044)*China National Climate Centre, Beijing, China, 100081. E-mail: liwj@cma.gov.cn
Abstract

1. Introduction
This paper is about a comparison of the GAME reanalysis
data(GRD) with the NCEP/NCAR reanalysis data(NRD) ondiscrepancy for the both sets of reanalysis data but not thedifferent assimilation systems employed by both sets ofreanalysis data.

2.5×2.5° horizontal resolution in 1998, which GRD

The aforementioned judgment supported by anotherassimilated more raw data observed by HUBEX and TIPEX,

proof that the discrepancy of both sets of reanalysis data reaches

etc, than NRD. So what differences exist between the both sets

the maximum value in experimental regions (seeing the contrastof reanalysis data in the experimental regions of GAME? Andof mid-latitude in Fig. 1).

what good qualities are there in GRD? Whether the main causeexperimental raw data used by GRD? These problems are theaims of the paper, and have been gotten satisfactory answers in
the paper, meanwhile which indicate that the HUBEX as theEastern Asia part of the GAME is necessary to continue, andincreasing the temporal and spatial resolution of observed
meteorological elements is important to improve our forecasting

Contrast ( % )of good qualities is the different assimilation system or the850hPa
700hPa500hPa100hPa(a)accuracy of the weather and climate.

2. The comparative analysis
On the basis of the weather processes of Huaihe Riverbasin from June to August in 1998, the difference and reliability
derivative, precipitation，and surface flux were studied bydynamic diagnosis and statistics methods.

2.1 The comparisons in the basic element andderivative fields

Contrast ( % )of the two reanalysis data from the fields of basic element，(b)

00:00UTC
06:00UTC
12:00UTC
18:00UTC

Fig. 1 includes the comparisons of daily mean height fields
for different pressure levels (Fig. 1(a)) and the height field of
850hPa pressure level for 4 times of daily (Fig. 1(b), other levels
omitted), between both sets of reanalysis data. It is obvious thatthe bigger contrast exists in lower and upper troposphere,Fig. 1. The relative contrast lies in GAME and NCEP data inhowever in which the contrasts of 06:00 and 18:00 UTC areheight field. The contrast is defined as 100 ×100

more distinct than other two times. Then it is easy to be

H GAME − H NCEP

(H GAME + H NCEP ) 2

understood that 4 times observed raw data assimilated in GRD,(a) Height averaged from June-August and 100~120°Ei.e. 0Z, 06Z, 12Z, and 18Z, vs. only 2 times observed raw data

respectively in pressure levels

assimilated in NRD, i.e. 0Z, and 18Z, is the root of the(b) Averaged as (a) but only 850hPa height at different times

Pressure ( hPa )(a)aPressure ( hPa )(b)b
Fig.2. Longitude-pressure section of vertical velocity(fromcalculation; 06:00UTC; contour, units: Pa ﹒S-1) and 24hobserved rainfall (black bars, units: mm)along 27.5°N.
(a)GAME vertical velocity data.

Fig.3. Time-longitude section of negative divergence (implies(b)NCEP vertical velocity data.
The vertical velocity (contour) calculated from the equationr∇ ﹒ (Ps Vh )in б coordinate, б=0.75; contour, units: Pa﹒S-1)

of conservation of mass in P coordinate and the 24h observed

and 24h observed rainfall (shaded area, units: mm)along 30°N.

rainfall (black bars and the values underlined) are showed inFig.2, and then the strongly ascending motion ( negative verticalvelocity) was accompanied with rainfall while weak ascending
motion and downdraft matched the rainless zones in GRD(seeing a), whereas the vertical motions namely not only
ascending motion but also downdraft can not accord with theactually observed state in particular for NRD (seeing b).
The aforementioned situation is only at 06Z, and the same as
at 18Z, however no so remarkable differences at other two times(Fig. omitted). So the evidences emphasize again the fact that
intensive observation is important in GAME.

(a)

GAME divergence data.

(b)

NCEP divergence data.
The divergence evolution for lower troposphere of Tibet

plateau to Yangtze River basin in summer is presented on samechart at б coordinate, in which GRD took on the development ofsouthwest vortexes, but did not NRD. Furthermore GRD
detected apparently its origin of southeast of Tibet, which isdiffer from the traditional opinions.

2.2 The comparisons in precipitation and surface flux
fields
The regional mean daily-rainfall comparative analysis hasbeen done among two sets of reanalysis data and observed

actual rainfall changes, e.g. seeing Fig.4 (a), in July13th noprecipitation in Huaihe River basin (32.5°-35.0°N ，obvious rainfall occurred, but the net moisture flux of NCEP

112.5°-120.0°E), and the results denoted that GRD precipitation

increased rapidly. There are the same examples in July16th

is more close to the observed precipitation in evidence (Figseeing (a) and (b), etc.

omitted).

The latent and sensible heat flux always decrease

By calculating the instantaneous moisture flux for four

markedly in rainy days, and subsequently increase greatly invertical sections of south, north, east and west surface of Huaihe

sunny days, so that the comparisons of regional mean latent andRiver basin respectively, then the instantaneous net moisturesensible heat flux respectively between GRD and NRD influx can be obtained. At 0Z and 12Z, the differences for theHuaihe River basin are valid, and the results indicate that theinstantaneous net moisture fluxes of two sets of reanalysis datachanges of latent and sensible heat flux of GRD are moreare small (Fig omitted), but the differences are rather large atreasonable according to the actual precipitation processes during

06Z and 18Z (seeing Fig.4).

HUBEX period (Fig. omitted).

3. Conclusion(a)

06:00UTC

1. The results showed that the GRD is more reliable than NRD

Net moisture flux / kg﹒s-1﹒km-2

at the bottom and mid-high levels of troposphere, and at theprecipitation and surface flux fields the case is just the same.
2. The paper revealed that the GRD can show the evolution of
the southwest vortex but the NRD can not do so. In addition,
GRD detected apparently the origin of southwest vortexes insoutheast of Tibet, which is differ from the traditional opinions.
3. Meanwhile the main cause of which the GRD being better
than the NRD is GRD including the sonde data of the GAME
but not the different assimilation modes used by the tworeanalysis data because the advantages of GRD excelling toNRD exist chiefly at 06Z and 18Z, and are not evident at 0Z and12Z.
4. It is very necessary to continue carrying out the HUBEX as(b)18:00UTCthe Eastern Asia part of the GAME, and it is considerably

Net moisture flux / kg﹒s-1﹒km-2

important that increasing the temporal and spatial resolution ofobserved meteorological elements lead to improve ourforecasting accuracy of the weather and climate.
Keyword: HUBEX, Reanalysis data, Comparison analysis

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Fig.4. Instantaneous net moisture flux for day to day change

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