Energetics of wave propagation leading to frost events in South America: extratropical latitudes

Müller, Gabriela V.; Gan, Manoel Alonso; Piva, Everson Dal

doi:10.1002/asl.762

Cited by 6 publications

(1 citation statement)

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“…One approach that previous studies have employed in understanding upper level dynamical processes is the local energetics framework (Orlanski and Katzfey 1991) to diagnose the evolution of baroclinic waves (Orlanski and Sheldon 1995), which gives rise to the notion of downstream development Sheldon 1993, 1995). The local energetics framework has since been applied to a broad range of atmospheric dynamical settings, beyond the evolution of baroclinic waves, including intensifying jet streaks (Lackmann et al 1999), surface cyclolysis (McLay and Martin 2002), life cycles of conservative extratropical cyclones that exhibit explosive deepening behaviour (Decker and Martin 2005), extratropical transitions of tropical cyclones (Harr and Dea 2009), travelling mid-tropospheric troughs (Piva et al 2010), the evolution of cut-off low (COL) pressure systems Piva 2013, 2016;Ndarana et al 2021b;Pinheiro et al 2022), dynamical processes that lead to the formation of frost events (Müller et al 2017), the processes that maintain jet wave trains (Li 2021) and dust storms (Rivière et al 2015); to name a few. Some studies (e.g.…”

Section: Introductionmentioning

confidence: 99%

Downstream development during ridging South Atlantic Ocean anticyclones

et al. 2023

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Ridging South Atlantic high pressure systems (ridging highs) are often accompanied by cut-off low (COL) pressure systems aloft, but may also occur without them, in which case a linear baroclinic wave would be observed propagating across the South African domain in the upper troposphere. Using 41 years of ERA-5 reanalysis data, this study documents differences between the characteristics of the prevailing dynamical processes and associated local eddy kinetic energy generation, its downstream transfer and dissipation during these two scenarios. The study shows that when COLs are present then baroclinic conversion is strong and it is confined east of the Greenwich Meridian, whereas it is located downstream of South Africa and it is much weaker, when ridging occurs without COLs. The differences in strength and locations of the baroclinic conversion are associated with the differing jet streak configurations between the two scenarios; which lead to Rossby wave breaking and the absence thereof when there are COLs and when ridging occurs without COLs, respectively. The presence of breaking during COLs leads to trans-ridge downstream development that facilitates energy transfer from the midlatitudes into the South African domain. When there are no COLs present, the trans-trough downstream development is stronger than it is across the upstream ridge. Barotropic conversion from eddy kinetic energy to mean kinetic energy occurs in the South African domain during COLs, but occurs much further downstream when there are no COLs during ridging highs. The difference in the characteristics identified in this study can be traced back to the differences in the potential vorticity anomaly structures, which are largely due to whether the waves break or do not during the evolution of ridging events in the South African domain.

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