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Diabatic Rossby waves in the Southern Hemisphere.

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Publication date 2015
Author Boettcher M. and H. Wernli,
Project The dynamics of North Atlantic warm conveyor belts and their impact on downstream wave propagation and European weather systems
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Original article (peer-reviewed)

Journal Quart. J. Roy. Meteorol. Soc.
Volume (Issue) 141
Page(s) 3106 - 3117
Title of proceedings Quart. J. Roy. Meteorol. Soc.
DOI 10.1002/qj.2595


Diabatic Rossbywaves(DRWs)are a special type of low-level cyclone with a self-maintaining mechanism given an environment of moderate or strong baroclinicity and abundant moisture. Under certain conditions, these shallow cyclones associated with a cyclonic low-level PV anomaly can serve as precursors for explosive cyclone intensification. The present study is the first to investigate DRWs in the Southern Hemisphere (SH). Two typical DRW casestudies are presented and a sophisticated algorithm is used to detect DRWs in operational analysis data from 2001 to 2012. DRWs occur in all ocean basins and seasons with a maximum in summer. On average, about four DRWs are found per month and 12% intensify explosively. Thereby, they contribute 6% to the total set of explosively deepening extratropical cyclones in the SH.DRWtracks originate slightly closer to the Equator than normal extratropical cyclones, and they follow the convergence zones eastward and poleward. This results in a climatological DRW track density similar to a spiral, from the western South Pacific ending in the eastern South IndianOcean, broken only by the Andes. Typical synoptic situations associated withDRWgenesis are identified.Thecategories include (i) low-levelPV generation by upper-level induced lifting, (ii) low-level jet-induced diabatic PV generation, and (iii) transformation of the low-tropospheric PV anomaly from another system.