eastern Turkey has many days of the year where the sky is overcast due to high elevations reaching up to 6500 m above the sea level. The cold period of the year lasts almost 9 months. In contrast, from the Aegean Sea coast in the west toward central Anatolia, days with a cloudless sky are encountered much more frequently. In Fig. 4.7b the regional variation of b' coefficient has just the opposite trend to the east-west variation of a' and this is the expected meteorological situation as explained above. In order to support these conclusions in detail, Fig. 4.8 and 4.9 show the regional variations of the same parameters but this time with elevation instead of longitude as the abscissa.
Figures 4.7-4.9 relate the geographical (regional, spatial) information to solar radiation variations over the country. Figure 4.10 shows the relation between a' and b' for values calculated for all over Turkey.
There_appears an inverse relationshipbetween these two parameters. It means that low b' values are coupled with high a' values and vice versa. The general trend
relationship between a' and b' is a = —0.61b7 + 0.52 . (4.38)
The empirical relative frequency distributions of average a' and b' values on a regional basis are shown in Fig. 4.11. It is to be noticed from Table 4.4 that a' and b' values are confined between zero and one. This piece of information implies that a beta-type of theoretical probability distribution function (PDF) is suitable for the parameters regional estimation (Bucciarelli 1984). Figure 4.11 shows both observed and beta-type PDF for a' and b'.
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