Journal of the Meteorological Society of Japan, Vol. 89A, pp. 225--238, 2011.

225

DOI:10.2151/jmsj.2011-A14

Estimation and Veriﬁcation of Daily Surface Shortwave Flux over China

Jianqing XU, Kooiti MASUDA
Research Institute for Global Change (RIGC),
Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan

Yasushi ISHIGOOKA, Tsuneo KUWAGATA
National Institute for Agro-Environmental Sciences (NIAES), Tsukuba, Japan

Shigenori HAGINOYA
Physical Meteorology Research Department, Meteorological Research Institute (MRI), Tsukuba, Japan

Tadahiro HAYASAKA
Graduate School of Science and Faculty of Science, Tohoku University, Sendai, Japanand
Tetsuzo YASUNARI
Research Institute for Global Change (RIGC),
Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan
Hydrospheric Atmospheric Research Center (HyARC), Nagoya University, Nagoya, Japan(Manuscript received 31 May 2010, in ﬁnal form 19 October 2010)

Abstract
Downward shortwave ﬂux at the surface over China was derived from sunshine duration data using parametersof Jordan sunshine recorders. The sunshine duration data were obtained as routine meteorological data and adjusted as necessary for the e¤ects of topography, station surroundings, altitude, and atmospheric turbidity.
Calculated ﬂux was veriﬁed by in situ observations. Daily ﬂux was calculated at more than 190 stations in China,
Climatic maps (statistical period: 1971–2000) of surface solar radiation were produced and have been made public.
The sunshine duration-based shortwave ﬂux was used to check satellite observation-based datasets. Two versions of satellite-based surface radiation budget datasets (SRB 2.0 and SRB 3.0) from NASA’s Langley ResearchCenter were investigated. Compared with the SRB 2.0 dataset, the SRB 3.0 dataset showed improved shortwave
ﬂux, especially over western China and the Tibetan Plateau.

1. Introduction
Corresponding author: Jianqing Xu, Research Institutefor Global Change (RIGC), Japan Agency for MarineEarth Science and Technology (JAMSTEC), 3173-25
Showa-machi, Kanazawa-ku, Yokohama, 236-0001,
Japan.
E-mail: jxu@jamstec.go.jp
6 2011, Meteorological Society of Japan

Global solar radiation is the energy resource ofliving things. Its variation and distribution are very
important. Although meteorological data have become much more plentiful and accessible in recent
years, daily data of downward shortwave ﬂux at

226

Journal of the Meteorological Society of Japanthe surface over wide areas are still lacking. To
improve modeling, shortwave ﬂux simulated bygeneral circulation models (GCMs) and regional
climate models should be checked using long-term
observation-based data. In agriculture science,models including the photosynthetic process could
also be improved by the use of daily shortwave
ﬂux data. Trenberth et al. (2009) and Kiehl andTrenberth (1997) summarized the Earth’s annual
global mean energy budget from satellite data.
Satellite-based surface radiation budget (SRB)
datasets are also available from NASA’s LangleyResearch Center for the periods 1983–1995 (version2.0) and 1983–2006 (version 3.0). To verify suchsatellite-based datasets, ﬁeld observations of shortwave ﬂux at the ground surface are needed, preferably covering long terms and even the period before
satellite observations began.
In monsoon Asia, including parts of Japan and
China, routine meteorological observations including daily measurements of sunshine duration havebeen recorded over long periods. For example,
sunshine duration data have been recorded formore than 100 years at some stations in Japan,
and many analyses have been conducted (Ichino etal. 2008; Inoue and Matsumoto 2003). In China,
sunshine duration has been observed for more than
50 years. Past studies have used these data to analyze the trend of sunshine duration in China (Cheet al. 2005; Kaiser and Qian 2002; Liang and Xia
2005b; Xu 2001; Xu et al. 2005b, 2009), but quantitative assessment of shortwave ﬂux at the surface
has not been previously reported.
To estimate surface shortwave ﬂux in China, thisstudy used observations of sunshine duration madeusing Jordan sunshine recorders (Fig. 1). This typeof instrument is part of the standard observationequipment at surface meteorological stations in
China and was also used at meteorological stationsin Japan until the 1970s. The Jordan sunshine
recorder determines the daily duration of brightsunshine. It consists of a copper cylinder with two
small holes in its sides. One hole faces east, andthe other faces west. The sunbeam penetrates thesmall holes, hitting light-sensitive paper inside thecopper cylinder. The length of the band of changed
color on the light-sensitive paper is a measure ofsunshine duration. The paper is changed daily.
This is a very simple observation method that needs
no electricity and is easily maintained. The daily
total direct solar radiation (integrated from sunrise
to sunset) has a good statistical relationship with

Vol. 89A

Fig. 1. Photograph of a Jordan sunshine
recorder.

the observed daily duration of sunshine. Because
most of the energy of daily mean downward shortwave ﬂux at the surface (global solar radiation) isfrom direct solar radiation, shortwave ﬂux at thesurface can be estimated empirically from the daily
duration of sunshine. This relationship was developed by means of both Jordan daily sunshine
duration data and pyranometer instantaneous
measurements of solar radiation (Kondo 1994).
However, the Jordan recorder may not record times
when the Sun is at low altitudes (about 5 in a cityand 2 in a rural area). Yoshida (1970) analyzed
this problem statistically and developed a revised
method. Kondo and Xu (1996c) and Kondo et al.
(1996) later revised the method for applications athigh altitudes.
In this paper, we introduce a shortwave ﬂux estimation method that adjusts for the e¤ects of the
topography, surroundings, and altitude of anobservatory, as well as atmospheric turbidity.
Satellite-based surface radiation budget (SRB)

February 2011

J. XU et al.

datasets from NASA’s Langley Research Center
were also compared to estimations produced inthis study. We discuss the method for calculating
shortwave ﬂux in section 2. Data adjustments aredescribed in section 3, and results and comparisonswith the satellite-based SRB data are presented in
section 4. Section 5 contains a summary and conclusions.
2. Method of estimating downward shortwave
radiation ﬂux from sunshine durationN¼ as þ bs
;
#
N0
S0

N
0<
a 1;
N0

S0#

¼ cs ;

N¼ 0;
N0

where N0 is the possible duration of sunshine, andS0# the daily mean of the downward shortwave ﬂux
at the top of the atmosphere. as , bs , and cs are empirical coe‰cients and depend on the type of thesunshine recorder, elevation, atmospheric turbidity,
etc. These coe‰cients are decided empirically inJapan where the elevation is lower than 100 m asl(Kondo 1994). The elevation of observation stations in China varies from 0 m asl to more than
4,500 m asl. Thus, the e¤ect of elevation was considered, following observation results over the
Tibetan Plateau (Kondo et al. 1996). The coe‰cients as , bs , and cs depend on the surface pressure
ps as follows:ps
as ¼ 0:179 þ 0:32 1 
;
ð3Þ
1000
bs ¼ 0:55;

ð4Þ


ps
cs ¼ 0:114 þ 0:32 1 :1000

z ¼ cos1ð5ÞHere, N0 is determined by the latitude. N0 and S0#
are given by

ð6Þ




sin a  sin f sin d;cos f cos d

ð7Þ

and
S00
dðz sin f sin d þ cos f cos d sin zÞ;
p

ð8Þ

where
d ¼ 1:00011 þ 0:034221 cos h þ 0:00128 sin hþ 0:000719 cos 2h þ 0:000077 sin 2h;

ð9Þ

1

d ¼ sin ð0:398  sinð4:871 þ h þ 0:033 sin hÞÞ;
ð10Þ
and

ð1Þ

ð2Þ

24
2z
¼
;
2p 0:2618

where

h¼

and
#
SM

N0 ¼ 2z

S0# ¼

The method to estimate downward shortwave
radiation ﬂux at the surface from records of sunshine duration has been developed and describedby Kondo (1994), Kondo and Xu (1996a, 1996b,
1996c), and Kondo et al. (1996). We summarize
the method here.
The daily mean downward shortwave ﬂux at the#surface SM
can be derived from sunshine duration
N using parameters obtained from a Jordan sunshine recorder:
#
SM

227

2p
Day:
365

ð11Þ

In the above equations, S00 is the solar constant, z
is the half-day angle, a (radians) is the solar altitude, f is the latitude, d is the solar declination,
and Day is the number of days from 1 January to
the observation day.
The daily mean of the downward shortwave ﬂux#
at the surface under clear skies (SMf
) is (Kondo
1994)
#
SMf

S0#

¼ ðC1 þ 0:7  10k3 mnoon F1 Þð1  i3 Þð1 þ j1 Þ;
ð12Þ

where
i3 ¼ 0:014ðk3 mnoon þ 7 þ 2 log10 wÞ log10 w;
mnoon ¼ ð ps =p0 Þ secðf  dÞ;
mnoon ¼ y;

f  d < p=2;

f  d b p=2;

ð13Þ
ð14Þ
ð15Þ

k3 ¼ 1:042  0:06 log10 ðbDUST þ 0:02Þ
 0:1ðsecðf  dÞ  0:091Þ 1=2 ;C1 ¼ 0:21  0:2bDUST ;C1 ¼ 0:15;

b DUST < 0:3;

bDUST b 0:3;

F1 ¼ 0:056 þ 0:16ðbDUST Þ 1=2 ;

ð16Þ
ð17Þ
ð18Þ
ð19Þ

and
j1 ¼ ½0:066 þ 0:34ðb DUST Þ 1=2 ðref  0:15Þ:ð20Þ

Journal of the Meteorological Society of Japan228

where p0 (¼ 1,013 hPa) is the standard atmosphericpressure, ref the ground surface albedo, b DUST is
the atmospheric turbidity deﬁned by Robinson(1966), and w the precipitable water (cm) estimatedaslog10 w A log10 w  þ 0:10:

ð21Þ



Here, w is the e¤ective precipitable water,ð
1 ps p
w ¼
q dp:
ð22Þ
g 0 p0
Where q is the speciﬁc humidity of air. Because
we had no observed aerological q data, an empirical method (Kondo and Xu 1996c) was used here.
The method was developed from observed aerological data of China. Dew point TDEW can be calculated from the surface air vapor pressure e,
TDEW ¼

237:3  log10 ðe=6:1078Þ
;
7:5  log10 ðe=6:1078Þ

ð23Þ

and,
log10 w  ¼ 0:027TDEW  0:15  x0 ;TDEW < 5 C;

ð24Þ

log10 w  ¼ 0:031TDEW  0:13  x0 ;
5 C a TDEW < 23 C;

ð25Þ

log10 w  ¼ 0:015TDEW þ 0:238  x0 ;23 C a TDEW < 30 C;

ð26Þ

Here,

x0 ¼ 1 

0:5
ps:
1013:2

ð27Þ

If the change in precipitable water with elevationis considered (in this paper, where the elevation ishigher than 100 m asl), as can be expressed as,
as ¼ ð0:21 þ 0:7  100:056Y Þð1  i3 Þ  bs ;where
Y ¼ 1:45

pssecðf  dÞ ;
1013

ð28Þ



ð29Þ

where i3 is shown in Eq. 13.
3. Data, data adjustments, and veriﬁcations

Vol. 89A

produced by the SRB team led by Paul Stackhouseof NASA’s Langley Research Center, Hampton,
Virginia. Information about the dataset is available at http://eosweb.larc.nasa.gov/PRODOCS/
srb/table_srb.html.
The time resolution is 3 hours, and the spatial
resolution is 1 degree latitude/longitude. The SRB
Shortwave (SW) Release 2.0 covers July 1983 to
October 1995, and Release 3.0 covers July 1983 toJune 2006. Both versions are based on cloud information compiled as the pixel-level (DX) dataset of
the International Satellite Cloud Climatology Project (ISCCP, Rossow and Schi¤er 1999) and thealgorithm developed by Pinker and Laszlo (1992).
However, many practical improvements were madebetween the two versions.
From SRB 2.0 to 3.0, several steps were entailed
in updating the versions, for example, ﬁxing thedeﬁcits in the polar night, using the cloud amountin the calculation, reforming the solar zenith angle,
etc. In particular, comparison with experimental
ground-based observations revealed substantial underestimation over the Tibetan Plateau in SRB SW
Release 2.5 (Yang et al. 2006); the lessons learned
have been incorporated in the revision of the algorithm. A major di¤erence between SRB 2.5 and
SRB 2.81 is that the lookup tables in the radiativetransfer code of SRB 2.5 do not account for levation and its e¤ect on Rayleigh scattering, whereas
this e¤ect was included in SRB 2.81 (Yang et al.
2008).
In the present study, monthly climatologicalvalues of both SRB 2.0 and 3.0 were calculated using all available months. Then, values at the gridboxes nearest to observation stations were extracted
and compared with those estimated at the stationsin the present study.
2)

Routine meteorological data
The routine meteorological data were provided
by the China Meteorological Data Sharing Service
System (http://cdc.cma.gov.cn/) of the China Meteorological Administration for a period from the
1950s to 2006. The data used in the present study
include the following:sunshine duration N (hour)
daily mean vapor pressure e (hPa) surface pressure p (hPa)s

3.1 Data
1) Satellite-based data
Among several global satellite-based data products of radiation at the surface, we use the NASA/GEWEX Surface Radiation Budget (SRB) data set

Atmospheric turbidity bDUST , as deﬁned byRobinson (1966), was assumed in the calculation#of SMf.

February 2011

J. XU et al.

229

Fig. 2. Picture of the Deqen observatory (28 29 0 N, 98 55 0 , 3,320 m asl), which is located in a valley surrounded by high mountains. Raw sunshine duration data for Deqen were revised.

3.2 Data adjustments
Some observatories are located in valleys (Fig.
2), such as Deqen (31 25 0 N, 95 36 0 E, 3,875 m asl)
observatory, which is located in a valley surrounded by mountains, while others are situatedin urban canyons. When discussing the trend ofsunshine duration, problems associated with suchlocations can be ignored. However, if we want toquantitatively assess the distribution of shortwave
ﬂux at the surface, the raw data should be revised.
Thus, we considered the e¤ects of topography, andsurroundings to adjust the data of sunshine duration.
If a meteorological station is located in a valleyor surrounded by high buildings, the observed sunshine duration NObs may be less than its true value.
Under clear sky condition, NObs =N0 should be near
1.0, but the Jordan sunshine recorder records only
the duration of bright sunshine. If the solar altitude

is too low (about 5 in the city and 2 in rural
areas), the sunlight will be too weak to be recordedby the light-sensitive paper. Generally, the maximum of the ratio NObs =N0 is 0.92–1.00. We modiﬁed the observed sunshine duration NObs to derive
the representative value N, which was then applied to Eq. 1. For such a case, we assumed that
N ¼ NObs . The reference of the minimum direct
solar radiation is deﬁned as 120 W m2 because
the shadow of objects is hard to recognize when
direct solar radiation is less than 120 W m2 . However, if the ratio of NObs =N0 under clear-sky condition is always shows a low value, for example, lessthan 0.9, the station may be in a valley or surrounded by high buildings and the observed raw
data NObs should be adjusted.
The theoretical possible duration of sunshine N0
can be calculated from Eq. 6 when the latitude is
known. In Eq. 7, a is the solar altitude and repre-

Journal of the Meteorological Society of Japan

230

Vol. 89A

sents the time of sunset in a valley. The half-day
angle z can be obtained, and the possible durationof sunshine N00 in a valley can be calculated from
Eq. 6. The ratio NObs =N00 is used to revise thedataset through the following empirical formulas(Kondo et al. 1996):
N
NObs
¼
 D;
N0
N00

ð30Þ

D ¼ f f1  exp½0:085ðe  2Þg;

ð31Þ

f ¼

NObs
0:23

 NObs  10 :
N00
1 þ tan 0  0:2

ð32Þ

N0

where e is the emissivity of ground-surface. Figure 3
shows examples of observed raw sunshine duration
data. The solid lines show seasonal changes at different solar altitudes ð2 ; 4 ; . . . ; 20 Þ. The upper
panel is for Jiuquan (39 46 0 N, 98 29 0 E, 1,477 masl), and the lower panel is for Baingoin (31 22 0 N,
90 01 0 E, 4,700 m asl). At Jiuquan, NObs =N0 exceeds 0.9 and is plotted around 2 –4 of the solar
altitude. The meteorological observatory at Jiuquan is in an open area without nearby mountains
or buildings, and thus N ¼ NObs at this station. In
contrast, at Baingoin, NObs =N0 is sometimes lessthan 0.9 and is plotted between 4 and 7 . Sunlightis blocked when the solar altitude is less than about
5 . Baingoin may be in a valley on the Tibetan
Plateau, where N 0 NObs .
Figure 4 shows seasonal changes in the ratios ofsunshine duration. The top panel presents observed
raw data, the middle panel shows adjusted data,
and the bottom panel gives precipitation at Baingoin in 1998. The revised sunshine duration is reasonable. This kind of data checking was conducted
for all of the stations.
3.3

Veriﬁcations of the downward shortwave ﬂux
at the surface
1) Shortwave ﬂux at the surface under clear-sky#
conditions SMf
The calculation of daily mean downward shortwave ﬂux at the surface under clear-sky conditions#
SMf
used atmospheric turbidity bDUST as deﬁned byRobinson (1966). In fact, atmospheric turbidity has
its seasonal change. In this study, we assumed it asa constant. Assuming that the atmospheric turbidity bDUST as a constant changes between 0 and 0.1#(for example, bDUST ¼ 0:01; 0:02; . . . ; 0:10), SMf
can be obtained for di¤erent bDUST when the latitude is known. If the calculated daily mean of#shortwave ﬂux SM(input data is N only) underFig. 3. Checking of sunshine duration data.
Solid lines show the seasonal changes atdi¤erent solar altitudes ð2 ; 4 ; . . . ; 20 Þ.
The upper panel is for Jiuquan (39 46 0 N,
98 29 0 E, 1,477 m asl), and the lower panel
is for Baingoin (31 22 0 N, 90 01 0 E, 4,700 m
asl). The circles mark NObs =N0 on ﬁne
days.

clear sky conditions (when N=N0 b 0:9) is adjusted#with the most suitable SMf, then b DUST can be determined.
Figure 5 shows the seasonal changes of calculated shortwave ﬂux at Jiuquan in 1985. The solid#line is the daily mean shortwave ﬂux SM
estimatedfrom sunshine duration N. The dotted line is theFebruary 2011

J. XU et al.

231

daily mean shortwave ﬂux under clear-sky condi#
tions SMf
when bDUST ¼ 0:1. The broken line is##
SMf when bDUST ¼ 0:03. The dashed line is SMf#
when bDUST ¼ 0:0. When b DUST ¼ 0:03, SMf ad#
justs SMwell, and bDUST is assumed to be 0.03 in
Jiuquan. In the winter time, bDUST may be lessthan 0.03, but the solar energy in the winter time isless than that in the summer time.
Atmospheric turbidity b DUST was estimated forevery meteorological station for determination of#a suitable SMf. b DUST ranges between 0.01 and##0.10 in present study. This SMf
and calculated SM
are independent under clear-sky conditions (when#
N=N0 b 0:9). The calculated SM
was checked by##
SMf . If SM (observed N) is over its theoretical value#), it is replaced by the climatic value (30-year(SMfmean value in 1971–2000) for the same day.
2)

Fig. 4. Seasonal changes in the ratios ofsunshine duration N=N0 . The top panelpresents raw observed data, and the bottom panel shows revised data Baingoin in
1998.

Fig. 5. Seasonal changes in calculated downward shortwave ﬂuxes at Jiuquan in 1985.
The solid line represents the daily short#wave ﬂux SM
as estimated from sunshine duration. The dotted line represents the daily downward shortwave#
ﬂuxes under clear-sky conditions SMf#
when b DUST ¼ 0:1. The broken line is SMf
when bDUST ¼ 0:03, and the dashed line is#SMfwhen b DUST ¼ 0:0.

Veriﬁcation of the downward shortwave ﬂux atthe surface from observed data
The calculated shortwave ﬂux has been comparedwith observations at Beijing (39 48 0 N, 116 28 0 E,
54 m asl) and Lhasa (29 40 0 N, 91 08 0 E, 3650 m#
asl). The observed SM
of Beijing was downloaded
from the China Meteorological Data Sharing Service System (http://cdc.cma.gov.cn/) of the China
Meteorological Administration. Lhasa is located at
a high altitude, 3650 m, and no observed shortwave
ﬂux data were available from routine meteorological station records. Pyranometers (Ishikawa Industry, A2-S-180) were installed at Lhasa, whereobservations were conducted in cooperation withspecialists from Ishikawa Industry. The pyranometers were exchanged every year and recalibrated in
the factory. Sunshine duration N was observed at
the Lhasa meteorological station. These observations were part of the automated weather station(AWS) observations of the Global Energy andWater Cycle Experiment (GEWEX) Asian Monsoon Experiment (GAME)-Tibet project. Data
from these pyranometers have been utilized by Xu
and Haginoya (2001), and Xu et al. 2005a.
Figure 6 shows the shortwave ﬂux as observedand calculated (from sunshine duration N) at
Lhasa in 1996 (Fig. 6a,b) and Beijing in 1999 (Fig.
6c,d). The same parameters were used to estimate
shortwave ﬂux at both stations. bDUST was 0.01 at
both stations. The annual mean shortwave ﬂux
was 240 W m2 at Lhasa and 160 W m2 at Beijing. From the regression analysis, the observed
value was larger than the calculated value when
the shortwave ﬂux was small, and the situation

232

Journal of the Meteorological Society of Japan

Vol. 89A

Fig. 6. Calculated and observed daily mean shortwave ﬂux at the surface in Lhasa (1996) and Beijing (1999).
a) seasonal variation in shortwave ﬂux at the surface by pyranometer observations and calculations from##from N. The dotted line is SMf
sunshine duration N for Lhasa in 1996. The solid line is the calculated SM#
under clear-sky conditions with Robinson’s atmospheric turbidity b dust of 0.01. Circles represent SM ob#
served by pyranometer; b) regression analysis of the observed and calculated SM; c) the same as a) except
for Beijing 1999; d ) the same as b) except for Beijing 1999.

was reversed when the shortwave ﬂux became
large. The maximum di¤erences between the observed and calculated values were about 10 W m2
at Lhasa and 3–5 W m2 in Beijing. The maximum
estimation errors were less than 10% at both stations. These results indicate that the calculated
values well matched the observations. The coe‰cient of correlation was 0.98 at Beijing and 0.95 at
Lhasa. The range of daily mean shortwave ﬂux was
about 80 W m2 –380 W m2 at Lhasa and about
20 W m2 –320 W m2 at Beijing.
So far, all of the data have been checked, and thecalculation method has been veriﬁed. Calculation
results (see the solid lines in Fig. 6a,c as examples)for the period from the 1950s to 2006 were obtained
daily for 194 stations in China, including the Tibetan Plateau. This data set was derived from sun-shine duration data, with the time resolution set as
daily because the daily data of downward shortwave ﬂux at the surface over wide areas are needed
for recent years.
4. Estimation results
Of course, the climatic distribution of the solar
radiation can be drawn directly from the observed
sunshine duration time, and its unit will be hours.
This kind of dataset is inconvenient for checking
the shortwave ﬂux results from the GCMs or for
use as the input data for agricultural models. In
this study, we provide the absolute value of thesolar radiation ﬂux in W m2 units.
Here, we only show the climatological normal
values of downward shortwave ﬂux at the surface
during 1971 to 2000.

February 2011

J. XU et al.

4.1

Climatic distribution of shortwave ﬂux at thesurface in China
Figure 7 shows the distribution of shortwave ﬂux
at the surface annually, in January, and in July.
The annual and monthly data are made public at
the daily shortwave ﬂux during 1971–2000 (http://
www.jamstec.go.jp/drc/maps/d/kadai/mon/mon_ea.html). Annual shortwave ﬂux is small over the
Sichuan Basin (120–140 W m2 ) and large over
the Tibetan Plateau (240–260 W m2 ) because Sichuan Basin is always covered by cloud, and thesunshine duration is shorter than other places atthe same latitude. From the Tibet Plateau to northwest China, the climate is arid or semi-arid and ismarked by many clear days. The sunshine duration
is longer in these areas.
In winter (January), shortwave ﬂux is less than
80 W m2 in the Sichuan Basin and about
150 W m2 in southeastern Tibetan Plateau. The
contrast in the distribution of shortwave ﬂux between the Sichuan Basin and the Plateau becomes
more obvious in the winter time.
In summer (July), from Sichuan Basin throughsoutheast China to the southern part of northeast
China, the shortwave ﬂux is relatively small because
the Asian monsoon brings cloudy and rainy days,
and the sunshine duration is short in this season.
4.2

Comparison with solar radiation ﬂux from
Langley SRB datasets
We compared both the Langley SRB2.0 and
SRB3.0 datasets to our calculated shortwave ﬂux
at the surface. Figure 8a presents the distributionof data from the observatories. In the case of theLangley SRB2.0 dataset, data performances arepoor in both the Tibetan and western China areas(Fig. 8b,c). However, the newer Langley SRB3.0
dataset agrees with our dataset well in winter (January, Fig. 8d) and shows improved performancecompared with SRB2.0 in summer (July, Fig. 8e).
The dataset produced in this study provides a relatively standard dataset (daily) for checking otherdatasets. SRB3.0 products di¤er substantially from
SRB2.0 owing to numerous improvements of thealgorithms and input data sets (http://eosweb.larc.nasa.gov/PRODOCS/srb/table_srb.html).
4.3

Comparison of interannual variations between
calculated shortwave ﬂux and SRBs
SRB3.0 products have been improved from
SRB2.0, and its value are more closer to the calculated shortwave ﬂux in the present study, especiallyin the areas of Tibet and western China.

233

Beijing is located in the eastern region, andLhasa in the Tibetan region. The values from both
SRB 2.0 and 3.0 were extracted at the grid boxes
nearest to observation stations. Figure 9 shows the#monthly mean value of shortwave ﬂux (SM: solidline) for Beijing (lower panel) and Lhasa (upper
panel) from 1984 to 1994 (the period of SRB 2.0).
#
The variation of satellite based SM(SRB2.0 and#
SRB 3.0) matches that of calculated SMwell inevery month in Beijing, but values of calculated##SM
are smaller than those of SRB SM. Averaged##
value of calculated SM is 164 W m2 , SRB 2.0 SM#
is 180 W m2 , and SRB 3.0 SM is 183 W m2 during 1984–1994.
In the case of Lhasa (upper panel in Fig. 9), the#averaged value of calculated SM
is 242 W m2 ,##2
SRB 2.0 SM 202 W m , and SRB 3.0 SM
231 W m2 during 1984–1994. The SRB 2.0 value
was too small, and the SRB 3.0 value was better#
than SRB 2.0 if the calculated SM
was consideredas the standard value. As mentioned in Section
3.a.1, the improvement from SRB2.0 to SRB 3.0
was mainly observed considering the inﬂuence of
the Tibetan Plateau (Yang et al. 2006, 2008). For
plain-ﬁeld areas such as Beijing, no improvement
was apparent.
5. Summary and conclusion
A method to estimate downward shortwave
ﬂux has been developed and applied over awide area of China. Shortwave ﬂux was estimatedfrom sunshine duration data using parameters
measured by Jordan sunshine recorders. The raw
data of sunshine duration were revised, considering the e¤ects of the topography, surroundings, and altitudes of observation stations. The
inﬂuence of atmospheric turbidity was also considered. Calculated values were veriﬁed by in situ
observations.
The results show the climatic distribution ofshortwave ﬂux. The estimated daily shortwave ﬂux
has many research uses, such as for veriﬁcation ofother databases. Two Langley SRB datasets werechecked using the shortwave ﬂux obtained in thisstudy. The SRB3.0 dataset was improved comparedwith the SRB2.0 dataset for a high altitude area
(Tibet) and an arid area (West China). Our dataset
can also be compared with the output from GCMs
and regional climatic models. In agricultural research, models incorporating the photosynthetic
process of vegetation can also be improved by using
these daily shortwave ﬂux data.

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Fig. 7. Distributions of climatological shortwave ﬂux at the surface annually (upper panel), in January (middle panel), and in July (bottom panel). Black spots show the distribution of the stations.

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#
Fig. 8. a) Distribution of the SMdata at the observatories. Blue circles represent the Tibetan area (high altitude), and red circles denote western China (arid). Relationships between b) Langley SRB2.0 data and thepresent data in January, c) Langley SRB3.0 data and the present data in January, d) Langley SRB2.0 data
and the present data in July, and e) Langley SRB3.0 data and the present data in July.

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Fig. 9. Interannual variations in the downward shortwave expressed by monthly mean values at Beijing(lower panel) and Lhasa (upper panel) during 1984–1994. The solid lines represent the calculated monthly#
mean value of downward shortwave ﬂux SM, the triangles with dashed lines show the downward shortwave
ﬂux from Langley SRB2.0, and the plus signs with broken line are from Langley SRB3.0 data. Numbers on
the upper x-axis show years and are placed at the beginning of individual years. Numbers on the lower
x-axis represent the sequential number of months, where 1 corresponds to January 1984.

Acknowledgments
The authors thank Dr. Kazuyo Fukuda of theJapan Agency for Marine Earth Science and Technology (JAMSTEC) for making the ﬁgures for theinternet publication of this dataset. We also thankthe China Meteorological Data Sharing Service
System (http://cdc.cma.gov.cn/) of the China
Meteorological Administration for providing thedata. Thanks are also extended to NASA’s
Langley Research Center Atmospheric Sciences
Data Center NASA/GEWEX SRB Project forproving the SRB datasets. We thank the referee
for providing constructive comments and help in

improving the contents of this paper. This study
was supported by data Integration and Analysis
System (DIAS). The study was also supported
by JSPS and China NSFC under the Japan–China
Scientiﬁc Cooperation Program ‘A study of waterand heat circulation in the Nam Co Basin using remote sensing and in situ observation data,’ Grantsin-Aid for Scientiﬁc Research of JSPS (No.
22310016), and ‘Impact of Asian Megacity Development on Local to Global Climate Change’ under
the Strategic Japanese–Chinese Cooperative
Program on Climate Change between JST and
MOST.

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Appendix
Notationasbscse (hPa)N (hour)
NObs (hour)
N0 (hour)ps (hPa)qref#
SM(Wm2 )#
SMf
(Wm2 )#
S0 (Wm2 )S00 (Wm2 )TDEW ( C)
w (cm)a (rad)bDUSTed (rad)z (rad)f (rad)one of the coe‰cients of Jordan sunshine recorder
one of the coe‰cients of Jordan sunshine recorder
one of the coe‰cients of Jordan sunshine recorderobserved daily mean vapor pressure
observed sunshine duration
observed sunshine duration (rawdata)
duration of possible sunshine
observed surface pressure
speciﬁc humidity of air
albedo of ground surface
daily mean downward surface shortwave radiation ﬂux#
SMunder clear sky
downward surface shortwave radiation ﬂux at the top of the atmosphere
solar constant (1365 Wm2 )dew point
precipitable water
sun’s altitude
Robinson’s atmospheric turbidity
emissivity of ground-surface
solar declination
half-day angle
latitude
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