Convergence Associated With Cyclones
extra-tropical and tropical cyclones

In extra-tropical cyclones, surface winds are deflected by friction towards the center of the low pressure system (red "L" below).

Coupled with divergence aloft, (blue arrows), surface convergence (red arrows) can generate rising motion (green arrow) that leads to the condensation of water vapor.

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Credits and Acknowledgments for WW2010.
Department of Atmospheric Sciences (DAS) at
the University of Illinois at Urbana-Champaign.