Measured Data

The data of major cities of South Korea used 20 years (1986-2005). All meteorological and solar radiation data that are used in this study have been measured at the Korea Meteorological Administration (KMA).

Seoul and other three regions are among the solar measured areas and Ulsan is not. This study involves four regions of Korea and compares the figures from each region; the solar radiation estimations apply the original coefficient substitution method which Kasten and Czeplak (1979) suggested for the estimation of Hamburg, Germany (1964-1973); solar radiation estimated from the solar altitude and amount of clouds actually measured solar radiation. In addition, through the estimated solar radiation coefficient from this process, coefficients from four different cities - of which distances are all different as you can see in Figure. 30.1-were substituted for Ulsan's to estimate the City's solar radiation.

Table 30.1 Five data sets from South Korea.

Data measured at the KMA

Table 30.1 Five data sets from South Korea.

Data measured at the KMA

Regions

Latitude (°N)

Longitude (°N)

Altitude (m)

Solar

Cloud

radiation data

cover data

Seoul

37.34

126.5B

B5.5

O

O

Busan

35.06

129.02

69.2

O

O

Daejeon

36.1B

127.24

77.1

O

O

Gwangju

35.0B

126.55

70.9

O

O

Ulsan

35.33

129.19

31.5

X

O

Korea began to measure its cloud amount since 1904 when it established contemporary weather stations. Currently, central meteorological office, 5 regional offices and 36 weather stations, in total 42 stations serve this purpose. Even today observer's eyes are the tools for this job. Hourly CC data recorded during the 20-year period from 1986 to 2005 within the daytime were gathered for the analysis. Cloud cover data are provided as 3-hour interval, 10 divided method in data provided in KMA. Therefore, in this research, this was converted for the use of the equation used in the preceding research and comparison of data. Data of 3-hour interval produced data through the linear interpolation 1 hour. And 10 divided methods were converted to 8 divided methods (Octas). Skies without any cloud (0 Octas) and heavily covered with cloud (8 Octas) were defined as clear and overcast, respectively. Sky conditions with CC between 1 and 7 Octas were considered partly cloudy.

Hourly CC data from the 20-year measurements were analyzed and the frequency of occurrence is shown in Fig. 30.2. A peak of over 23% is observed at a value of 0 Octas. The second most frequent cloud cover is 8 Octas, accounting for 22%, 21%, respectively. At round 5%, 3 Octas is the least frequent CC. These suggest that the overcast and clear sky conditions occur almost 21%, 23%, respectively, of the time. For the rest of the time (i.e., 65%), partly cloudy sky conditions prevail (Younes and Muneer, 2006; Danny and Joseph, 2001).

In addition, the average amount of clouds in Seoul and three other regions, and Ulsan, which this study decided to compare, was observed as similar between Ulsan and Busan, and Seoul and Daejeon, respectively. However, Gwangju reported relatively larger average amount. I think it is needed to review whether these similar amounts of clouds in Busan and Ulsan have any influence on solar radiation of the two cities, which are in relatively close range.

SEOUL

BUSAN

^rrt

2 3 4 5 6 7 Cloud cover (Octas) Fig. 30.2 Frequency of occurrence of cloud cover (Seoul and Busan).

4.15

4.37

3.95

4.14

3.88

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