Sentence:  To avoid the idiosyncraciesSIC of leap years, we propose, as a first approximation to the actual <WSD>yearday</WSD>, a standardized <WSD>yearday</WSD> s that is a function of ( m, d) only, s = S(m) +dl (6) where 5 is a function of m only. 
Meaning of the word marked with <WSD> tags:  A day of the year.