A study on mechanics of polar lows developed by cold vortex aloft using idealized numerical experiments and potential vorticity analysis

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We investigated the mechanism of the development of polar lows excited by cold vortex aloft, through numerical experiments using meso-scale atmosphere model under idealized simple conditions. When the level of the cold vortex is low and the atmosphere is weakly stratified, the dynamic effect that the vortex aloft directly excites the surface disturbance is dominant. On the other hand, when the cold vortex is situated high and the stratification is strong, the thermal effect that the stratification of the lower-level atmosphere weakened by the cold air aloft enhances the convective motions becomes evident. As for the dynamical effect, the mechanism that the surface vortex is stretched by the upward motion driven by the advection of potential vorticity aloft is more significant than the mechanism that the advection at the sea-surface level interacts with the potential vorticity gradient.