A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering of the Asian Institute of Technology, Bangkok, Thailand

Thesis (M.Eng.) - Asian Institute of Technology, 1977

The existing time series analysis of the daily totals of solar radiation at Bangkok was refined by dividing the daily totals of solar radiation into six classes of width 100 cal.cm-2.d-1. Comparisons of the simulations by the purely random model and the Markov chain model with the observed series of six radiation classes for different seasons of the year were made. The better representation by second order theory (Markov chain model) shows spells of fine weather with higher radiation amounts in the spring, and spells of bad weather in the summer and autumn. The hourly radiation amounts in five year s of measurements at Bangkok and Chiang Mai were converted from zone mean time to apparent solar time by taking into account the effect of the equation of time and the station latitude and longitude. Dividing the daily totals of solar radiation into classes of width 100 cal.cm-2.d-1 and the hourly radiation into classes of width 10 cal.cm-2.d-1 , fluctuations in the hourly solar radiation among these classes were examined for different seasons of the year. During the dry season in spring and winter uniformly high radiation amounts were found. During the wet season in summer and autumn, the distributions were more dispersed. The percentage distributions of a cloudiness factor K, defined to be the ratio between the hourly observed radiation amounts and the maximum possible hourly radiation amounts under clear sky conditions, were determined for different daily radiation classes and seasons. For high daily radiation classes, the K-values during the middle of the day are in the range 0.7-1.0 in spring and 0. 4-1.0 in autumn, and for low radiation classes, the K-values are in the range 0.4-0.9 in spring and 0.1-0.9 in autumn, which shows that the cloud amounts are less in spring. The average morning and afternoon distributions of the cloudiness factor were al so calculated. In winter the morning and afternoon distributions of the cloudiness factor are nearly the same both at Bangkok and Chiang Mai. In all other seasons cloud amounts in the afternoon hours are higher than those in the morning hours.