Model of Intraseasonal Oscillations in Earth’s Atmosphere

We suggest a way of rationalizing intraseasonal oscillations of Earth’s atmospheric flow as four meteorologically relevant triads of interacting planetary waves, isolated from the system of all of the rest of the planetary waves. Our model is independent of the topography (mountains, etc.) and gives a natural explanation of intraseasonal oscillations in both the Northern and the Southern Hemispheres. Spherical planetary waves are an example of a wave mesoscopic system obeying discrete resonances that also appears in other areas of physics.

Figure 1

Four isolated triads are shown below the diagonal dashed line: $\ell$ along the horizontal axis and $m<\ell$ along the vertical one. The three clusters of two connected triads are shown above the diagonal dashed line (now $\ell$ along the vertical axis and $m\le \ell$ along the horizontal one). The (meteorologically significant) spectral domain is restricted by $0<m$, $\ell \le 21$. Localized modes are shown by solid circles, delocalized ones (with a relatively small interaction amplitude) by empty circles.

Figure 2

Left panel: Time dependence of $A_1$, $A_2$, and $A_3$ [denoted by solid green, dashed red, and dotted-dashed blue lines, respectively] of the triad ${\Delta }_1$, with $\mu =0.89$, corresponding to the observed data. Middle and right panels: Dependence of the triad periods $T(E,h)/T_0(E)$ [Eq. (5a)]. Middle panel: The dashed blue line corresponds to the ${\Delta }_1$ triad, the solid green line to the ${\Delta }_3$ triad. Right panel: Dashed red line—${\Delta }_2$; solid magenta line—${\Delta }_4$ triad. The dashed black lines denote the minimal period: $T\approx 1.3T_0$ for ${\Delta }_1$ and ${\Delta }_3$ and $T\approx 1.18T_0$ for ${\Delta }_2$ and ${\Delta }_4$.