An Investigation of the Dynamics of Coherent Tropopause Disturbances Using a High Resolution Global Model

Jet streams and jet streaks play a significant role in many different aspects of mesoscale and synoptic-scale weather systems. Recent studies have demonstrated that jet streaks are frequently associated with the superposition of large-amplitude, localized potential vorticity (PV) maxima of mesoscale dimensions with the enhanced PV gradients associated with the jet stream. In many cases, these PV maxima can be interpreted dynamically as coherent monopolar vortices that are based on or near the tropopause; an observational climatology of these vortices has recently been performed, and a dynamical framework has been established for their association with jet streaks. Nevertheless, the dynamics of the origin and life cycles of coherent tropopause vortices have yet to be determined. The role of these vortices in extratropical cyclogenesis and jet streak amplification, and their interactions with smaller- and larger-scale flows, also remain to be investigated and are worthy of further examination. To this end, a high-resolution global circulation model will be used to examine the life cycles of coherent tropopause vortices from a dynamic perspective, including their origins, their interactions with the larger-scale flow, and their role in the low-frequency variability of the atmosphere.

In order to gain insight into the life cycles of coherent tropopause vortices, preliminary simulations have been conducted using the NCAR Community Climate Model (CCM) at high horizontal resolution (T213) for conditions representative of the Northern Hemisphere winter. These preliminary simulations exhibit wind speed maxima that are consistent with climatology, and these wind speed maxima coincide with gradients in PV. Localized PV maxima are frequently found on the poleward side of the wind speed maxima, with PV minima found less frequently on the equatorward side. Following previous observational studies, potential temperature extrema will be mapped and tracked on a constant PV surface representing the dynamic tropopause, in order to further examine coherent tropopause vortices in a materially conserved framework. Initial simulations with the high-resolution CCM have shown results that are consistent with recent observational studies and climatology, indicating that the CCM may be a useful tool for a detailed investigation of the dynamics and life cycles of coherent tropopause vortices.