MIXING INDUCED MERIDIONAL MOTION OF MODONS

The effect of mixing on a zonally stationary modon (Stern's modon) and rider is analysed using the method of multiple scales. Cases in which only the rider contributes to the mixing, or only the modon mixes, or a combination of both, are considered separately. In each case the mi xing is shown to establish a dipole field aligned in such a manner to drive meridional motion in a direction dependent on the type of mixing . Moreover, the radius and amplitude of the modon and rider field are shown to decrease in response to mixing. The rule by which they decrea se is dependent on the type of mixing. For the particular case when bo th the modon and rider fields contribute equally to the mixing, it is shown that cyclones propagate north and anticyclones propagate south.