Downstream development during ridging South Atlantic Ocean anticyclones

• Published in: Climate Dynamics
• Main Authors: Ndarana, Thando, Lekoloane, Lesetja E., Rammopo, Tsholanang S., Reason, Chris J.C., Chikoore, Hector, Engelbrecht, Francois A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer 2023
• Subjects: Downstream development; Ridging highs; Jet streaks; SDG-13: Climate Action; Cut-off low (COL); South Atlantic Ocean
• Online Access: http://hdl.handle.net/2263/95765; https://doi.org/10.1007/s00382-023-06717-7

This work is part of a broader project that aims is to understand the underlying dynamical processes of the important synoptic systems in the South Atlantic Ocean/South Africa basin. AVAILABILITY OF DATA AND MATERIALS : This study has been supported by the Water Research Foundation (Grant number: C2020/2021-00653) of South Africa and it is part of a larger project that aims to understand the underlying dynamical processes of the important synoptic systems in the South Atlantic Ocean/South Africa basin. All the data used in the study was obtained are the Fifth Generation European Centre for Medium-Range Weather Forecasts reanalysis (ERA5) can be obtained from. https://www.ecmwf.int/en/forecasts/datasets/reanalysis-datasets/era5 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 ...