Long-Term Behaviour of Kelvin Waves and Mixed Rassby.Gravity Waves

Abstract

By spectral analyses of upper winds and temperature at Canton Island (S 02°46', W 171°43') from July 1957 to June 1960, two types of disturbances were shown to occur remarkably in the equatorial lower stratosphere: One is considered to be Kelvin waves and the other is to be mixed Rossby-gravity waves. Occurrence of the two types of disturbances have close relations with the quasi-biennial oscillation. Kelvin waves appear predominantly when the basic westerly momentum is rapidly increasing, while mixed Rossby-gravity waves appear when the absolute value of the basic wind speed is decreasing. Both types of disturbances were shown to carry westerly momentum upward. The upward flux of westerly momentum due to mixed Rossby-gravity waves is of the same amount as that due to Kelvin waves.