Abstract
Many cut-off low (COL) climatologies have been done throughout the Southern Hemisphere. Few have focused on COL vertical depth and their link to surface cyclones that often accompany these systems. Here we extend these climatologies in order to gain an understanding of the spatial, mobility, temporal, and seasonal variability of COL extensions towards the surface. Deep COLs (dCOLs), with extension all the way to the surface, are most frequent in the autumn months, are longer lasting, are more mobile and found most frequently situated in the high latitudes. They are usually collocated with Rossby wave breaking (RWB) on multiple isentropic surfaces. These RWB events drive high potential vorticity air into the upper troposphere. The depths of these intrusions are also shown to be critical to the development of COL extensions with dCOLs associated with deeper intrusions into the mid-troposphere. Upper-level PV features are collocated with warm surface potential temperature anomalies which can play a critical role in surface cyclogenesis. The warm surface potential temperature features, when out of phase with coupled upper tropospheric processes (surface features lagging behind upper level processes), can inhibit surfaceward extension and result in shallow COL (sCOL) development. Composite analysis shows that dCOLs that drive their own surface low development result in the simultaneous amplification of troughs throughout the troposphere, with the surface cyclone develo** within a day of the COL.
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MAB, under the supervision, review, and guidance of both TN and WAL, conceived of all the ideas in this manuscript. MAB performed all the analysis for this work and wrote the manuscript. The authors would also like to thank the three anonymous reviewers whose contributions and suggestions added significantly to this work.
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Barnes, M.A., Ndarana, T. & Landman, W.A. Cut-off lows in the Southern Hemisphere and their extension to the surface. Clim Dyn 56, 3709–3732 (2021). https://doi.org/10.1007/s00382-021-05662-7
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DOI: https://doi.org/10.1007/s00382-021-05662-7