On the Genesis Mechanisms of Tropopause Polar Vortices
Tropopause Polar Vortices, or TPVs, are ubiquitous, traceable features over polar regions with average lifetimes of nearly a week. TPVs are known to be important dynamical predecessors to surface cyclogenesis, but little is known about their genesis mechanisms. Five different theories located within the literature for genesis of TPV-like features are analyzed to determine viability as a potential genesis mechanism. These are:
- Vortices emerge as natural consequence of upscale turbulent energy cascades within the vorticity field of the polar atmosphere (Sanders 1988, Hakim et al. 2002).
- Frictional dissipation due to breaking atmospheric mountain gravity waves leads to PV (potential vorticity) generation in the upper troposphere and lower stratosphere that help generate these vortices (Cavallo and Hakim 2010, Ueda et al 2012).
- Rossby wave breaking on the cyclonic shear side of the polar jet stream allows for the creation of closed PV/isentropic contours which can move poleward (Gabriel and Peters 2008, Cavallo and Hakim 2010).
- Given the atmosphere is a continuous fluid, new vortices will be generated from stretching and filamentation of existing structures that leads to breaking of PV/isentropic contours into separate closed fields (Kew et al. 2010).
- Long wave radiation interactions with Arctic clouds and water vapor lead to diabatic generation of PV along the tropopause (Cavallo and Hakim 2012).
A census of TPV genesis events shows maximum genesis frequency to be just north of Baffin Bay and Greenland near a region known as the TPV well. Further analysis of genesis events within this region reveals splitting of existing TPVs to be a primary mechanism by which new TPVs are created. Daily lag composites around the time of genesis demonstrate splitting events to be commonly associated with interactions between TPVs and the polar jet. The composite split TPV is ejected from the Arctic into North America, leading to possible cyclogenesis which acts to diabatically enhance ridging downstream of the initial interaction between it and the jet.