El Niño Southern Oscillation teleconnections and their effects on the Amundsen Sea region

• Main Author: Yiu, Yu Yeung Scott
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Churchill College 2018
• Subjects: El Niño; Teleconnections; Amundsen Sea Low; Amundsen sea region; Tropical > extra tropical teleconnections; Pacific South America pattern; Southern Annular mode; Seasonality; ENSO > Amundsen sea region teleconnection; ENSO > Amundsen sea low teleconnection; Linearity; Amundsen Sea; Austral; Pacific; Antarc*; Antarctica
• Online Access: https://doi.org/10.17863/CAM.23516; https://www.repository.cam.ac.uk/handle/1810/276236

El Niño Southern Oscillation events have global implications both climatologically and socio-economically. One such climatological teleconnection is manifested in the Amundsen Sea region (ASR). The Amundsen sea low (ASL) is the dominant low pressure system located around the ASR and is important to the climate of Western Antarctica. Therefore, it is important to understand the ASL and any phenomena that may affect it. This thesis focuses on the ENSO--ASR teleconnection under El Niño conditions and the mechanism behind it. The ENSO--ASR teleconnection was explored using the UM version 8.4 (HadGEM3) model. Time--slice experiments with various magnitudes of idealised perpetual ENSO events are imposed. Two sets of `switch on' experiments in which tropical Pacific SSTs were ramped up were also carried out to investigate the transient nature of the teleconnection. The seasonality of the ENSO--ASR teleconnection is known from previous studies to be stronger in winter compared to summer. The mechanism behind the seasonality was explored using the time--slice experiments. The seasonality is found to originate from the seasonal differences in the Southern Hemispheric jets. As the subtropical jet is only present in austral winter, Rossby wave source anomalies can only be generated in the mid--latitudes in winter. Furthermore, the propagation of the Rossby waves is not possible in summer due to the strong polar front jet. The lack of the source and propagation in summer explains the weaker ENSO--ASR teleconnection. A flowchart summarising the mechanism was created and then verified by the transient runs. The linearity of the ENSO--ASR teleconnection within El Niño has not been previously investigated. This is mainly due to insufficient reanalysis data available to overcome the high internal variability in the ASR. In this thesis, the linearity of the teleconnection under El Niño is studied using the time--slice runs. The results indicate linearity (within errorbars) for both the summer and winter seasons up to historically ...