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Observations concerning the distribution of solar diffuse radiation over Romania
Building and Environment, Vol. 24, No. 2, pp. 149-153, 1989. Printed in Great Britain.
0360-1323/8953.00+0.00 (c) 1989 Pergamon Press plc
Observations Concerning the Distribution of Solar Diffuse Radiation over Romania V. BA,DESCU* The model proposed by Barbaro et al. (Sol. Energy 22, 225-228, 1979) was used to compute monthly average values of daily diffuse irradiation of horizontal surfaces in sixteen localities of Romania. The yearly variation of diffuse irradiation ranges between 2.0 M J m -2 day -t in December and 10.25 M J m -2 day -~ in June, The radiative regime has the fastest temporal variation during spring and autumn. During the extended warm season a clear dependence of solar diffuse radiation on latitude, altitude and atmospheric circulation was established.
INTRODUCTION
historical provinces: Moldavia, Valahia and Ardeal (Fig. 1). The mean baric field over Romania is determined by the interference of five action centres [14, 15]. Thus, during the whole year the influences of the Azoric anticyclone can be felt. During the cold season the atmospheric circulation is Controlled by the Syberian anticyclone and by the Icelandic and Mediteranean baric depressions. The fifth action centre is the Iranian baric depression, with important influences during the summer.
K N O W L E D G E of the available diffuse solar radiation has special significance for the proper design of the illumination of civil and industrial buildings [1, 2]. Although there have been elaborate global maps concerning solar radiation [3, 4], they refer especially to the distribution of total radiation. Moreover, they are not detailed enough to be used for the determination of the climatic features in small areas. For such regions special approaches are required [5-7]. Though several studies on the radiative regime of some Romanian sites have been made [8-10], there is little data concerning diffuse radiation. This is due to the fact that the national actinometric network only contains seven stations. The researchers attention was directed especially to the study of beam and global radiation. The aim of this paper is to present some information about the distribution of solar diffuse radiation over Romania. The evaluation of solar radiation availability was performed by using the model proposed by Barbaro et aL [11] (BCLS model), which has as input data relative sunshine, ambient temperature and air humidity. This model has been tested and improved by the author [12, 13] and developed to take into account atmospheric pressure variations.
BCLS M O D E L A P P L I C A T I O N A detailed testing of the BCLS model on Romanian territory showed that it estimates the daily global irradiation on horizontal surface with a root mean square error about 10% [13]. The precision with which BCLS model computes the monthly average values of daily diffuse solar irradiation D on horizontal surfaces was also verified. With this purpose we applied the model in three localities with available diffuse radiation measurement data [9]. As statistical indicators of precision, the mean bias error (MBE) and the root mean square error (RMSE) were employed from : N - - L ~;~ DBCLS'i - - D . . . . . i MBE - N ~ l D ..... ~ ' (1)
G E O G R A P H I C A L AND C L I M A T O L O G I C A L DATA ABOUT R O M A N I A
\
Romania is a small country located in south-east of Europe, between 43°37'07" and 48 ° 15'06"N and 20°15'44" and 29°41'24"E. Its area is 237,500 km 2, of which 30% is mountains (heights over 800 m) and 33% hills and plateaus (heights between 200 and 800 m). The territory of the country is split by the Carpathian chains, which stand as a natural border between the three
D ..... ,
] [
(2)
where DBcLs and Drama,are the computed and measured values, respectively, and N is the number of monthly average daily values. Table 1 shows an acceptable concordance between the computed and measured values. Meteorological data from sixteen localities (Fig. 1) have been used to compute diffuse solar radiation. A thorough presentation of the data measuring, collecting and processing methods has been made [16]. Table 2 shows the main geographical features of the localities
*Energetica, Centrale Electrice, Polytechnic Institute of Bucarest, Bucarest 79590, Romania. 149
V. Bgtdescu
150
÷v
s .m
j
Fig. I. Localities where diffuse solar radiation was computed (numbering according to Table 2).
Table 1. MBE and RMSE values (%) of daily diffuse solar radiation computed with BCLS model
Bucarest Iasi Constanta Total
Yearly MBE RMSE
Warm Cold Season Season (Apr.-Sep.) (Oct.-Mar.) MBE RMSE MBE RMSE
3.3 - 0.4 0.4
10.5 9.6 5.8
-4.5 5.0 - 1.2
5.3 6.4 3.1
11.I 4.2 2.1
13.9 11.9 7.6
8.9
- 0.2
5.1
5.8
I 1.4
1.1
we selected as well as the years o f meteorological collecting. In a previous p a p e r the climate type of localities was studied, using only meteorological from the years o f study indicated in Table 2 [17].
data these data As a
climatic indicator, the index o f continentality (Ivanov) was used while the m e t h o d o f analysis was presented in [18]. Results are also given in Table 2. In all cases the climatic type determined is similar to t h a t o b t a i n e d by using meteorological data from a longer time interval [15]. To a certain extent this fact justifies the utilization of a five year interval of meteorological d a t a collection to c o m p u t e long-term averaged diffuse radiation. To improve the accuracy o f result a n albedo correction was performed [13]. F o r g r o u n d albedo the value 0.2 was used as a m e a n o f the values measured in Bucarest a n d Cluj-Napoca, ranging between 0.16 a n d 0.24 [14]. Since there are no measurements of dust content in the atmosphere, the suggestion of B a r b a r o et al. [11] was accepted. Based o n the work of Cole [19], the q u o t e d a u t h o r s considered a dust c o n t e n t o f 200 particles cm 3 for the clean a t m o s p h e r e of Palermo [11]. Similar values were
Table 2. The localities where diffuse solar radiation was computed N 1 2 3 4 5 6 7 8 9 I0 11 12 13 14 15 16
Localities Suceava Iasi Bacau Craiova Caracal Pitesti Tirgoviste C-Lung Muscel Bucarest AF. Constanta Sulina Satu Mare Baia Mare Oradea Arad Brasov
Alt (m)
Lat (°N)
Long (°E)
354 102 185 190 112 307 281 681 90 52 3 127 216 136 108 528
47.649 47.166 46.583 44.233 44.099 44.866 44.933 45.283 44.499 44.166 45.149 47.799 47.666 47.049 46.166 45.666
26.250 27.600 26.967 23.867 24.350 24.867 25.433 25.117 26.217 28.617 29.667 22.883 23.500 21.933 21.317 25.617
123.9 129.9 125.3 135.8 136.2 124.5 125.8 121.0 131.9 112.2 97.3 128.3 121.3 123.0 123.8 127.1
Years 1967 68, 70-72 1967-68, 70-72 1967~ 68, 70-72 1967 68, 70-72 1966~67, 70-72 1966, 68, 70-72 1967~8, 70-72 1967~58, 70-72 1964, 66, 68, 70-71 1964~56. 70-71 1965-66, 68, 70 71 1967, 69- 72 1967 68, 70-72 1967~68, 70--72 1967-68, 70-72 1967, 69-72
* The climatic index of continentality corresponding to the years of collecting meteorological data.
Distribution of Solar Diffuse Radiation
151
used for the Romanian rural and urban localities (200 and 300 particles cm-3, respectively). RESULTS AND ANALYSIS The monthly average values of daily solar diffuse irradiation on horizontal surfaces for the localities shown in Table 2 were computed. A thorough analysis of the results has drawn some general conclusions. The minimum values of diffuse radiation are always reached in December. This is in good agreement with the measured data at Bucarest, Constanta and Iasi [9]. The minimum values ranges between 2.0 and 3.2 MJ m 2 d a y - ' (Suceava and Constanta, respectively). With only two exceptions, the maximum values of radiation are reached in June, as the measurements at Bucarest and Iasi confirmed [9]. At Constanta the maximum value is reached in May, in good concordance with the experimental data [9]. The other exception is Satu-Mare, where the maximum value is reached in July. The maximum values of diffuse radiation ranges between 8.75 and 10.25 MJ m - 2 d a y - ~ (Craiova and Suceava, respectively). The slowest temporal variation of the radiation regime occurs in summer. Spring and autumn show a much more abrupt transient of radiation. The spatial distribution of diffuse radiation is more differentiated during the extended warm season (April-September). All these conclusions are in good agreement with the available experimental data [9]. The dependence of diffuse radiation level on the following factors was investigated: (1) the climatic index of continentality ; (2) latitude ; (3) atmospheric circulation ; (4) altitude. Firstly, the radiative regime of two pairs of localities with low and high climatic index were compared, respectively (maritime and continental climate). These localities have comparable latitude and altitude and are situated in the same region from the point of view of atmospheric circulation [14]. Figure 2 shows no evident dependence of diffuse irradiation level on the climatic index. The influence of latitude was studied by using two pairs of localities from the south and north of the country, respectively. Each member of a pair corresponds to a member of the other, with comparable climatic index and altitude. Figure 3 shows a clear dependence of diffuse radiation on latitude. So, during the extended warm season the radiation level is higher in the north, in good agreement with the measurements [9]. During the winter the diffuse radiation is higher in the south. This conclusion is in good concordance with the measured data from Bucarest and Iasi but not with those from Constanta, where the combined effect of climate and atmospheric circulation is stronger. Measurements performed in USSR for a large range of latitudes [2] clearly confirms our conclusion. Atmospheric circulation may modify the spatial-temporal distribution of solar diffuse radiation in two ways. Firstly there is the control on the distribution of scattering and absorbtion centers (aerosols, water vapour, gases). Secondly, atmospheric circulation imposes the spatial and temporal variation of cloud cover, thus having a direct effect on diffuse radiation values. Two pairs of localities were selected from the east and west of the
8
7
6
5
Eulina
(Ic Consfanfa (It Ca r a ca l (It Craiova (Ic
• •
J
F
M
4
M
J
= = = =
]
97) 112) 136) 136)
A
S
0
N
D
Months
Fig. 2. The yearly variation of solar diffuse radiation for some localities with different climatic index of continentality.
Ioi
A"
]
d
5
]
F
M
A
• • •
Bucarest Pifesti Safu Mare
(Li" = /,4.499eN) (Lf = 44.8660N) (Lt = 4Z799°N)
•
8aia
(Lf =
M
Mare
J
]
A
4Z666°N)
S
0
N
O
Months
Fig. 3. The yearly variation of solar diffuse radiation for some localities with different latitudes.
152
V. B6descu
7 am
6
~s
5
4~
• • • •
J
F
H
A
Arad Oradea Bac~u Suceava
H
(L ("Lgg (Lg (Lg
J
= 2Z317°E) = 2~933°E) = = 26.250°E1
26967°E)
j
A
• • • •
~ \
S
~ 0
N
i !
O
J
F
H
A
C?mpulung Brasov Pifesfi T;rgoviste
H
J
(h {h (h (h
= 681m) =EZBm) = 307r0) = 281m)
J
A
S
0
N
O
l i o n ths
Months
Fig. 4. The yearly variation of solar diffuse radiation for some localities situated in areas with different atmospheric circulation.
Fig. 5. The yearly variation of solar diffuse radiation for some localities with different altitude.
country, with comparable climatic index, latitude and altitude. Atmospheric circulation has different features in east and west, respectively, especially because of the Carpathians, which separate the two regions [14]. Figure 4 shows a clear dependence of the diffuse irradiation on atmospheric circulation during the extended warm season, when the radiation level is higher in west. In the rest of the year no significant connection could be established. The influence of altitude was studied by selecting two pairs of localities from the plain and hilly areas, respectively, having comparable climatic index and latitude. Figure 5 shows that diffuse irradiation clearly depends on altitude during the extended warm season, when the radiation level is higher in the hilly area. In the rest of the year no significant connection was established.
CONCLUSIONS The yearly variation of diffuse solar radiation on the Romanian territory ranges between about 2.0 M J m - 2 day J in December and 10.25 M J m -2 day -~ in June. The fastest temporal variation of the radiative regime occurs in spring and autumn. The radiation level clearly depends on latitude during the whole year. It is higher in the south during winter as well as in the north during the extended warm season. The dependence of diffuse radiation on altitude and atmospheric circulation is evident only during the extended warm season. N o connection between radiation level and the climatic index of continentality could be established.
REFERENCES
1. V.V. Meshkov, Fundamentals oflllumination Engineering, MIR, Moscow (1981). 2. N.E. Gusev, Iluminatul Natural al Cl6dirilor (from Russian), Ed. Tehnich, Bucure~ti (1963). 3. G.O. L6ff, J. A. Duffle and G. O. Smith, World distribution of solar radiation, Engineering Station Report No. 21, University of Wisconsin (1965). 4. H.E. Landsberg, H. Lippmann, H. H. Paffen and O. Troll, Worm Maps of Climatoloyy (Edited by E. Rodenwaldt and H. J. Jusatz), Springer, Berlin (1965). 5. G. Stanhill, Diffuse sky and cloud radiation in Israel. Sol. Energy 10, 96-101 (1966). 6. R.B. Exell, The solar radiation climate of Thailand. Sol. Energy 18, 349-354 (1976). 7. V.A. Notaridou and D. P. Lalas, The distribution of global and net radiation over Greece. Sol. Energy 22, 505-514 (1979).
Distribution o f Solar Diffuse Radiation 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
N. Andritoiu, 1. Ciocoiu, Unele caracteristici ale gradientului vertical al radiatiei solare directe in regiunea de munte. CuL Lucr. Inst. Meteor., 1968 (1971). C. Oancea et al., Studiu comparativ al aportului de energie solarh pe suprafele plane orientate Sud, Sud-Est, Sud-Vest ~i diferit inclinate in Bucure~ti, Constanla ~i Ia~i. Instalatii fn Constructii 9, 13 (1983). E. Teodoreanu, L'insolation dans le couloir Ruc~r-Bran. Rev. Roum. Geogr 19, 21 l (1979). S. Barbaro, S. Coppolino, C. Leone and E. Sinagra, An atmospheric model for computing direct beam and diffuse solar radiation. Sol. Energy 22, 225-228 (1979). V. B~descu, A verification of the atmospheric model proposed by Barbaro et al. for computing direct and diffuse solar radiation. Sol. Energy 2,6, 459-460 (1981). V. Bhdescu, Can the model proposed by Barbaro et al. be used to compute global solar radiation on the Romanian territory? Sol. Energy 38, 247-254 (1987). Gh. C. BSz~c, Influenta reliefului asupra principalelor caracteristici ale climei Romaniei. Ed. Academiei, Bucure~ti (1983). Atlas Republica Socialist~ Romania. Ed. Academiei, Bucure~ti (1972-1979). V. B~descu et al., Elemente pentru un model climatological RSR util in calculul radiatiei solare, Sesiune ICEMENERG, paper II. 1 (1984). V. B~descu and C. Popa, Criteriu climatic de stabilire a regiunilor omogene din punct de vedere meteorologic si a anului tipic de determinare a disponibilului de radiatie solar~. Hidrotehnica 31,265268 (1986). S. Alterio, S. Barbaro, A. Gullotti, Un abaco indicatore per lo studio del clima. Energie Alternative HTE, Anno 5, No. 22, p. 131 (1983). R . J . Cole, Direct solar radiation data as input into mathematical models describing the thermal performance of buildings, Parts 1 and 2. Bldg Envir. 11, 173-186 (1976).
153
0360-1323/8953.00+0.00 (c) 1989 Pergamon Press plc
Observations Concerning the Distribution of Solar Diffuse Radiation over Romania V. BA,DESCU* The model proposed by Barbaro et al. (Sol. Energy 22, 225-228, 1979) was used to compute monthly average values of daily diffuse irradiation of horizontal surfaces in sixteen localities of Romania. The yearly variation of diffuse irradiation ranges between 2.0 M J m -2 day -t in December and 10.25 M J m -2 day -~ in June, The radiative regime has the fastest temporal variation during spring and autumn. During the extended warm season a clear dependence of solar diffuse radiation on latitude, altitude and atmospheric circulation was established.
INTRODUCTION
historical provinces: Moldavia, Valahia and Ardeal (Fig. 1). The mean baric field over Romania is determined by the interference of five action centres [14, 15]. Thus, during the whole year the influences of the Azoric anticyclone can be felt. During the cold season the atmospheric circulation is Controlled by the Syberian anticyclone and by the Icelandic and Mediteranean baric depressions. The fifth action centre is the Iranian baric depression, with important influences during the summer.
K N O W L E D G E of the available diffuse solar radiation has special significance for the proper design of the illumination of civil and industrial buildings [1, 2]. Although there have been elaborate global maps concerning solar radiation [3, 4], they refer especially to the distribution of total radiation. Moreover, they are not detailed enough to be used for the determination of the climatic features in small areas. For such regions special approaches are required [5-7]. Though several studies on the radiative regime of some Romanian sites have been made [8-10], there is little data concerning diffuse radiation. This is due to the fact that the national actinometric network only contains seven stations. The researchers attention was directed especially to the study of beam and global radiation. The aim of this paper is to present some information about the distribution of solar diffuse radiation over Romania. The evaluation of solar radiation availability was performed by using the model proposed by Barbaro et aL [11] (BCLS model), which has as input data relative sunshine, ambient temperature and air humidity. This model has been tested and improved by the author [12, 13] and developed to take into account atmospheric pressure variations.
BCLS M O D E L A P P L I C A T I O N A detailed testing of the BCLS model on Romanian territory showed that it estimates the daily global irradiation on horizontal surface with a root mean square error about 10% [13]. The precision with which BCLS model computes the monthly average values of daily diffuse solar irradiation D on horizontal surfaces was also verified. With this purpose we applied the model in three localities with available diffuse radiation measurement data [9]. As statistical indicators of precision, the mean bias error (MBE) and the root mean square error (RMSE) were employed from : N - - L ~;~ DBCLS'i - - D . . . . . i MBE - N ~ l D ..... ~ ' (1)
G E O G R A P H I C A L AND C L I M A T O L O G I C A L DATA ABOUT R O M A N I A
\
Romania is a small country located in south-east of Europe, between 43°37'07" and 48 ° 15'06"N and 20°15'44" and 29°41'24"E. Its area is 237,500 km 2, of which 30% is mountains (heights over 800 m) and 33% hills and plateaus (heights between 200 and 800 m). The territory of the country is split by the Carpathian chains, which stand as a natural border between the three
D ..... ,
] [
(2)
where DBcLs and Drama,are the computed and measured values, respectively, and N is the number of monthly average daily values. Table 1 shows an acceptable concordance between the computed and measured values. Meteorological data from sixteen localities (Fig. 1) have been used to compute diffuse solar radiation. A thorough presentation of the data measuring, collecting and processing methods has been made [16]. Table 2 shows the main geographical features of the localities
*Energetica, Centrale Electrice, Polytechnic Institute of Bucarest, Bucarest 79590, Romania. 149
V. Bgtdescu
150
÷v
s .m
j
Fig. I. Localities where diffuse solar radiation was computed (numbering according to Table 2).
Table 1. MBE and RMSE values (%) of daily diffuse solar radiation computed with BCLS model
Bucarest Iasi Constanta Total
Yearly MBE RMSE
Warm Cold Season Season (Apr.-Sep.) (Oct.-Mar.) MBE RMSE MBE RMSE
3.3 - 0.4 0.4
10.5 9.6 5.8
-4.5 5.0 - 1.2
5.3 6.4 3.1
11.I 4.2 2.1
13.9 11.9 7.6
8.9
- 0.2
5.1
5.8
I 1.4
1.1
we selected as well as the years o f meteorological collecting. In a previous p a p e r the climate type of localities was studied, using only meteorological from the years o f study indicated in Table 2 [17].
data these data As a
climatic indicator, the index o f continentality (Ivanov) was used while the m e t h o d o f analysis was presented in [18]. Results are also given in Table 2. In all cases the climatic type determined is similar to t h a t o b t a i n e d by using meteorological data from a longer time interval [15]. To a certain extent this fact justifies the utilization of a five year interval of meteorological d a t a collection to c o m p u t e long-term averaged diffuse radiation. To improve the accuracy o f result a n albedo correction was performed [13]. F o r g r o u n d albedo the value 0.2 was used as a m e a n o f the values measured in Bucarest a n d Cluj-Napoca, ranging between 0.16 a n d 0.24 [14]. Since there are no measurements of dust content in the atmosphere, the suggestion of B a r b a r o et al. [11] was accepted. Based o n the work of Cole [19], the q u o t e d a u t h o r s considered a dust c o n t e n t o f 200 particles cm 3 for the clean a t m o s p h e r e of Palermo [11]. Similar values were
Table 2. The localities where diffuse solar radiation was computed N 1 2 3 4 5 6 7 8 9 I0 11 12 13 14 15 16
Localities Suceava Iasi Bacau Craiova Caracal Pitesti Tirgoviste C-Lung Muscel Bucarest AF. Constanta Sulina Satu Mare Baia Mare Oradea Arad Brasov
Alt (m)
Lat (°N)
Long (°E)
354 102 185 190 112 307 281 681 90 52 3 127 216 136 108 528
47.649 47.166 46.583 44.233 44.099 44.866 44.933 45.283 44.499 44.166 45.149 47.799 47.666 47.049 46.166 45.666
26.250 27.600 26.967 23.867 24.350 24.867 25.433 25.117 26.217 28.617 29.667 22.883 23.500 21.933 21.317 25.617
123.9 129.9 125.3 135.8 136.2 124.5 125.8 121.0 131.9 112.2 97.3 128.3 121.3 123.0 123.8 127.1
Years 1967 68, 70-72 1967-68, 70-72 1967~ 68, 70-72 1967 68, 70-72 1966~67, 70-72 1966, 68, 70-72 1967~8, 70-72 1967~58, 70-72 1964, 66, 68, 70-71 1964~56. 70-71 1965-66, 68, 70 71 1967, 69- 72 1967 68, 70-72 1967~68, 70--72 1967-68, 70-72 1967, 69-72
* The climatic index of continentality corresponding to the years of collecting meteorological data.
Distribution of Solar Diffuse Radiation
151
used for the Romanian rural and urban localities (200 and 300 particles cm-3, respectively). RESULTS AND ANALYSIS The monthly average values of daily solar diffuse irradiation on horizontal surfaces for the localities shown in Table 2 were computed. A thorough analysis of the results has drawn some general conclusions. The minimum values of diffuse radiation are always reached in December. This is in good agreement with the measured data at Bucarest, Constanta and Iasi [9]. The minimum values ranges between 2.0 and 3.2 MJ m 2 d a y - ' (Suceava and Constanta, respectively). With only two exceptions, the maximum values of radiation are reached in June, as the measurements at Bucarest and Iasi confirmed [9]. At Constanta the maximum value is reached in May, in good concordance with the experimental data [9]. The other exception is Satu-Mare, where the maximum value is reached in July. The maximum values of diffuse radiation ranges between 8.75 and 10.25 MJ m - 2 d a y - ~ (Craiova and Suceava, respectively). The slowest temporal variation of the radiation regime occurs in summer. Spring and autumn show a much more abrupt transient of radiation. The spatial distribution of diffuse radiation is more differentiated during the extended warm season (April-September). All these conclusions are in good agreement with the available experimental data [9]. The dependence of diffuse radiation level on the following factors was investigated: (1) the climatic index of continentality ; (2) latitude ; (3) atmospheric circulation ; (4) altitude. Firstly, the radiative regime of two pairs of localities with low and high climatic index were compared, respectively (maritime and continental climate). These localities have comparable latitude and altitude and are situated in the same region from the point of view of atmospheric circulation [14]. Figure 2 shows no evident dependence of diffuse irradiation level on the climatic index. The influence of latitude was studied by using two pairs of localities from the south and north of the country, respectively. Each member of a pair corresponds to a member of the other, with comparable climatic index and altitude. Figure 3 shows a clear dependence of diffuse radiation on latitude. So, during the extended warm season the radiation level is higher in the north, in good agreement with the measurements [9]. During the winter the diffuse radiation is higher in the south. This conclusion is in good concordance with the measured data from Bucarest and Iasi but not with those from Constanta, where the combined effect of climate and atmospheric circulation is stronger. Measurements performed in USSR for a large range of latitudes [2] clearly confirms our conclusion. Atmospheric circulation may modify the spatial-temporal distribution of solar diffuse radiation in two ways. Firstly there is the control on the distribution of scattering and absorbtion centers (aerosols, water vapour, gases). Secondly, atmospheric circulation imposes the spatial and temporal variation of cloud cover, thus having a direct effect on diffuse radiation values. Two pairs of localities were selected from the east and west of the
8
7
6
5
Eulina
(Ic Consfanfa (It Ca r a ca l (It Craiova (Ic
• •
J
F
M
4
M
J
= = = =
]
97) 112) 136) 136)
A
S
0
N
D
Months
Fig. 2. The yearly variation of solar diffuse radiation for some localities with different climatic index of continentality.
Ioi
A"
]
d
5
]
F
M
A
• • •
Bucarest Pifesti Safu Mare
(Li" = /,4.499eN) (Lf = 44.8660N) (Lt = 4Z799°N)
•
8aia
(Lf =
M
Mare
J
]
A
4Z666°N)
S
0
N
O
Months
Fig. 3. The yearly variation of solar diffuse radiation for some localities with different latitudes.
152
V. B6descu
7 am
6
~s
5
4~
• • • •
J
F
H
A
Arad Oradea Bac~u Suceava
H
(L ("Lgg (Lg (Lg
J
= 2Z317°E) = 2~933°E) = = 26.250°E1
26967°E)
j
A
• • • •
~ \
S
~ 0
N
i !
O
J
F
H
A
C?mpulung Brasov Pifesfi T;rgoviste
H
J
(h {h (h (h
= 681m) =EZBm) = 307r0) = 281m)
J
A
S
0
N
O
l i o n ths
Months
Fig. 4. The yearly variation of solar diffuse radiation for some localities situated in areas with different atmospheric circulation.
Fig. 5. The yearly variation of solar diffuse radiation for some localities with different altitude.
country, with comparable climatic index, latitude and altitude. Atmospheric circulation has different features in east and west, respectively, especially because of the Carpathians, which separate the two regions [14]. Figure 4 shows a clear dependence of the diffuse irradiation on atmospheric circulation during the extended warm season, when the radiation level is higher in west. In the rest of the year no significant connection could be established. The influence of altitude was studied by selecting two pairs of localities from the plain and hilly areas, respectively, having comparable climatic index and latitude. Figure 5 shows that diffuse irradiation clearly depends on altitude during the extended warm season, when the radiation level is higher in the hilly area. In the rest of the year no significant connection was established.
CONCLUSIONS The yearly variation of diffuse solar radiation on the Romanian territory ranges between about 2.0 M J m - 2 day J in December and 10.25 M J m -2 day -~ in June. The fastest temporal variation of the radiative regime occurs in spring and autumn. The radiation level clearly depends on latitude during the whole year. It is higher in the south during winter as well as in the north during the extended warm season. The dependence of diffuse radiation on altitude and atmospheric circulation is evident only during the extended warm season. N o connection between radiation level and the climatic index of continentality could be established.
REFERENCES
1. V.V. Meshkov, Fundamentals oflllumination Engineering, MIR, Moscow (1981). 2. N.E. Gusev, Iluminatul Natural al Cl6dirilor (from Russian), Ed. Tehnich, Bucure~ti (1963). 3. G.O. L6ff, J. A. Duffle and G. O. Smith, World distribution of solar radiation, Engineering Station Report No. 21, University of Wisconsin (1965). 4. H.E. Landsberg, H. Lippmann, H. H. Paffen and O. Troll, Worm Maps of Climatoloyy (Edited by E. Rodenwaldt and H. J. Jusatz), Springer, Berlin (1965). 5. G. Stanhill, Diffuse sky and cloud radiation in Israel. Sol. Energy 10, 96-101 (1966). 6. R.B. Exell, The solar radiation climate of Thailand. Sol. Energy 18, 349-354 (1976). 7. V.A. Notaridou and D. P. Lalas, The distribution of global and net radiation over Greece. Sol. Energy 22, 505-514 (1979).
Distribution o f Solar Diffuse Radiation 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
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