Abstract: Proceeding from frequency equations of waves in the tropical atmosphere, a detailed analysis of approximate frequency formula of low-frequency Rossby wave given by Matsuno is done in this paper. Results show that the approximate formula
ω=-βκ/[(2n+1)(β/c₀+κ²)]
misrepresents Rossby wave in the tropical atmosphere in some degree. In view of this problem, we restudy the frequency equations and obtain another approximate frequency formula
ω=-βκ/[(2n+1)(β/c₀+(4n(n+1)/(2n+1))κ²)]
that represents tropical Rossby wave more precisely than the above formula. Then, by using iteration method we further expound and prove this approximate formula. Finally, a comparison of disperisive relations between the liner and the solitary Rossby wave in the tropical atmosphere is done simply.