The comparison between long-wave solar radiation data at Sri Samrong and model
Boossarasiri THANA, Akkaneewut CHABANGBORN, Michio HASHIZUME and Somchai NAKAPADUNGRAT
Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok 10330 Thailand
E-mail:boossara@geo.sc.chula.ac.th
EXTENDED ABSTRACT
The comparison is carried out to test values of long-wave solar radiation at Sri Samrong
Observatory because the observatory is being relocated to Pimai. So, it is helpful if we are able to find apractical model to use in place of the lacking observation. The radiation data used in this paper are thelong-wave solar radiation observed at Sri Samrong Observatory during 2001-2003. We investigate thepattern of long-wave solar radiation then compare with Idso and Jason model (1969). The result can begrouped into three conditions. The first condition is dry period (January-February). The values oflongwave solar radiation are greater than the model about 100 W/m2. Meanwhile the values from themodel are greater than those of observation about 100-200 W/m2 in the period of March-April. After
July the observation values are greater than model again in such amount of 150-200 W/m2.
Keyword: long-wave solar radiation

1. Introduction
The radiation budget consists of the incident andreflected sunlight and the long-wave (infrared and farinfrared) radiation emitted to space. The source for the
recent spurt in scientific and public interest in thegreenhouse effect and global warming is the alteration of
the radiation budget by the anthropogenic emission oftrace gases into the atmosphere. Solar radiation is themajor source of energy that drives the atmosphericsystem (Ramanathan, 1999). The solar radiation can bemeasured by several kinds of instruments. In many
areas, the solar radiation data are limited. Partly,radiation observation programs are not widely supported
or viewed as the vital part of national meteorologicalobservation network. This results in a few numbers ofradiative instruments being installed in the field. In
Thailand, for example, very few numbers ofmeteorological stations in Thailand are readily installedwith solar radiation instruments. To overcome the lacksof the field solar radiation data, various methodologies
are proposed to estimate the solar radiation in absence ofthe ground data. Among many methods, values ofradiation are estimated by a mathematical radiation
models. One of such models, Idso and Jason (1969),
requires simply surface temperatures as input. Idso andJackson (1969) proposed the solar radiation model basedon the studies previously done by Robinson (1947) andMonteith (1961). They established the linear relationshipbetween the ratio of solar radiation transmitted throughthe atmosphere, a black body and an optical depth ofprecipitable water. Although, many factors, such as watervapor, carbon dioxide, ozone, aerosol and gases in theatmosphere, affect solar radiation in the atmosphere, themost important is water vapor (Exell 1978).
In this paper, the solar radiation data from afield pyrgeometer are collected to be compared with thevalues estimated by the mathematical radiation model,
proposed by Idso and Jackson (1969). The model
calculation requires only surface temperatures; thus,
makes it handy to use for wide applications.
2. Data
The field radiation data are collected from theAtmospheric Observatory at Srisamrong, Observatory inSukhothai (Northern part of Thailand) under GAMETropics project. The data are collected from thepyrgeometer during 2001-2003. During the observation
period the first Pyrgeometer was replaced by the second.
The first Pyrgeometer S/N31504F3 was used in the year
2000 and the second Pyrgeometer S/N 32834F3 wasused in the year 2002. The data are then grouped into 3
categories: clear, cloudy and rainy conditions.
3. Methodology
In this paper we compare the data between thedata measured from the pyrgeometer and the values
calculated from the Idso and Jackson (1969) model asshown below:{R = σT 4 1 − c exp[− d (273 − T )]2}

Where σ = 5.67x10-8 W/m2 K4, c = 0.261, and d =0.000777 K2
From the Idso and Jackson model, the longwave solar radiation is proportional to the air temperature.
4. Results
4.1 Data from Pyrgeometer S/N31504F3

Observed on 7 January 2002
700
650600

Irradiance (W/m^2)

Data in 2003 are selected here because the longwave solar radiation data correspond to the nearby station
were already studied by the others (K. Gopala Peddy,
2003 and Masuda, K. 2004). In rainy season long-wave
solar radiation is about 430 W/m2. It is almost constantin the period. The minimum of long-wave solar radiation
occurred in December which is about 375 W/m2.

550
500
Thermal Flux450

Idso-Jackson

400
350

Irradiance (W/m^2)

300
500

250

450

200
0:00:00

12:00:00

18:00:00

0:00:00

Time (hh:mm:ss)

400
LwObv

350

LwCal

300
250
200
12

34Date (November 2000)

Fig 1. The comparison between the long-wave solar
radiation during 1-4 November 2000 which is clear sky
condition and calculation from Idso and Jackson (1969)
model.
500
450
Irradiance (W/m^2)

6:00:00

400
LwObv
LwCal

350

Fig 3. Downward Long-wave Radiation on 7th January
2002 which is the clear sky condition.
For cloudy condition (Fig. 4), on the 30th June,
2002, the long-wave solar radiation shows a lower ridgearound 9 a.m. to 6 p.m.. The pattern of the observed
long-wave solar radiation shows its maximum value
around 1 p.m. The observed maximum values are about
630 watts per square meters. On the other hand,calculated values from Idso and Jackson (1969) modelusing surface temperature are plotted and show a similar
pattern to the observed one. The calculated maximum
value is 450 watts per square meter. The patterns are thesame as shown in Fig 4. The difference of long-wave
solar radiation between measurement and calculation isbiased about 170 watts per square meter.

300
250

Observed on 30 June 2002

200
101112700

13650

Date (July 2000)

Irradiance (W/m^2)

600

Fig 2. The comparison between the long-wave solar
radiation during 10-13 July 2000 which is cloudy
condition and calculation from Idso and Jackson (1969)
model.

550
500

Thermal Flux450

Idso-Jackson

400
350
300
250

4.2 Data from Pyrgeometer S/N32834F3
On the 7th January, 2002, the clear sky day, thevalues of the observed long-wave solar radiation show
the ridge from 7 a.m. to p.m. (Fig 3.). The maximum
value is observed at about 650 watts per square meteraround 2 to 3 p.m. In the same plot, values calculated
from Idso and Jackson (19169) model show a similar
pattern. The maximum calculated value using surface
temperature is 400 watts per square meter at about thesame time. Both patterns have the similar trends asshown in Fig 3. The average difference long-wave solar
radiation between measurement and calculation shows
bias about 200 watts per square meter.

200
0:00:00

6:00:00

12:00:00

18:00:00

0:00:00

Time (hh:mm:ss)

Fig 4. Downward Long-wave Radiation on 20th June
2002 which is the cloudy sky condition.
For the rainy condition, the pattern of the longwave solar radiation on the 26th June 2002 shows themaximum value in the afternoon (Fig. 5). The maximum
value from the measurement is about 600 watts persquare meter. From Idso and Jackson (1969) model, thecalculated values, using surface temperature, show themaximum at 430 watts per square meter. The patterns
are both similar, as shown in Fig 5. The difference oflong-wave solar radiation values between themeasurement and the calculation is biased about 150
watts per square meter.
The slope of the long-wave radiation curve in therainy condition is quite distinguished from the clear sky
and cloudy conditions. The long-wave solar radiation

emits to the atmosphere more slowly and drops down
sharply in the evening.
Observed on 26 June 2002
700
650

Irradiance (W/m^2)

600
550
500

Thermal Flux450

Idso-Jackson

400
350
300
250
200
0:00:00

6:00:00

12:00:00

18:00:00

ones.
The difference between observation andcalculation is 3.41 W/m2 in clear sky condition
meanwhile the observation will give the value 35.67
W/m2 greater than the calculation in cloudy condition.
Finally data in 2000 are shown in Table 1 asrepresentative data in comparing with the model. TheIdso and Jackson (1969) model can be used in clear skycondition better than cloudy condition. The value ofNormalized Mean Biased Error (NMBE) is 0.0128 andthe Normalized Root Mean Square Error (NRMSE) is0.0577 as shown in table1.

0:00:00

Time (hh:mm:ss)

Fig 5. Downward Long-wave Radiation on 26th January
2002 which is the rainy sky condition.
The long-wave solar radiation patterns of theobserved data from a pyrgeometer S/N32834F3 andthose calculated from Idso and Jackson (1969) model aresimilar and show some bias in all cases. The observedvalues are higher than the calculation about 150-200
watts per square meter. So we try to some number tomodify the Idso and Jackson (1969) model as the bias
values might possibly come from the constant values
used in the Idso and Jackson (1969) model. Therefore
we modified the Idso and Jackson (1969) model bymultiplying the outcome by minus one then the result isvery close to the observed from pyrgeometer
S/N31504F3 in the year 2000 as shown in the Fig 6.
700

NRMSE
0.05771.97

SE
19.95318
16.85891

Table 1. The comparison of long-wave solar radiationbetween Idso and Jacson (1969) model and observation
which are clear sky condition during 1-4 November 2000
and cloudy condition during 10-13 July 2000.

Acknowledgement
We would like to thank the National ResearchCouncil of Thailand for supporting this study from 2001
to present. Prof.Dr.Teruyuki Nakajima (Center for
Climate Research, The University of Tokyo) who supportfor funding at Sri Samrong Observatory.

Reference

650
600
Irradiance (W/m^2)

Clear Sky
CloudyNMBE
0.0128-0.121

550
500
LwMod2001

450

LwObv2000

400
350
300
250
200
12

345678910111213141516171819202122232425262728293031Date (December 2001)

Fig 6. The long-wave solar radiation which observed in2000 by pyrgeometer S/N32834F3 and modified Idso
and Jackson (1969) model which use the data frompyrgeometer S/N31504F3 in 2001.
5. Conclusion
The long-wave solar radiation which observedby pyrgeometer S/N31504F3 in 2000 is about 373-432
W/m2 and pyrgeometer S/NM32834F3 in 2002 is about
500-600 W/m2. The long-wave solar radiation data havesome inherited instrumental errors from pyrgeometer
S/N32834F3 as indicated by the previous work by otherresearches.
The long-wave solar radiation can be estimatedby Idso and Jackson (1969) model in clear sky condition.
The calculated values are greater than the observation

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